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Workplace Exposure Standards by ewghwehws

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									DEPARTMENT OF LABOUR HEALTH & SAFETY




    Workplace Exposure
    Standards
    Consideration PaPer on Lowering the workPLaCe
    exPosure standard for MethyL BroMide
Workplace exposure standards
consideration paper on loWering the
Workplace exposure standard for
Methyl BroMide
Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 2 of 33
TABLE OF CONTENTS

TABLE OF CONTENTS............................................................................................... 3
EXECUTIVE SUMMARY............................................................................................. 4

SECTION 1 - WORKPLACE EXPOSURE STANDARDS ................................................. 5

SECTION 2– WORKPLACE EXPOSURE STANDARDS UNDER HSNO ............................ 7
  2.1  Setting WES under HSNO ...............................................................................7
  2.2  WES as Controls under HSNO..........................................................................8

SECTION 3– TOXICOLOGICAL BASIS FOR SETTING METHYL BROMIDE WES ........... 9
  3.1  Basis for proposing an 8 hour TWA of 1ppm......................................................9
  3.2  Basis for proposing a short term exposure limit .................................................9
  3.3  Deriving a WES from animal data ....................................................................9
  3.4  Assessment factors ...................................................................................... 10
  3.5  Assessing the quality of animal studies........................................................... 11
  3.6  Using the nasal epithelium as an end point ..................................................... 13
SECTION 4– SAMPLING METHODS .........................................................................15
  4.1  Photo Ionisation Detector (PID) ..................................................................... 15
  4.2  Colorimetric (detector) tubes ........................................................................ 17
  4.3  Sampling pump and sorbent tube (active sampling)......................................... 17
  4.4  Other sampling methods .............................................................................. 18
  4.5  Discussion on lowering the WES and implications for sampling .......................... 19
  4.6  Calculating an 8 hour TWA............................................................................ 19
  4.7  Adjusting for shifts longer than 8 hours .......................................................... 21

SECTION 5– METHYL BROMIDE OCCUPATIONAL EXPOSURE LIMITS FROM OTHER
COUNTRIES............................................................................................................24

REFERENCES ..........................................................................................................25

APPENDIX A – CORRESPONDENCE ADVISING OF A REVIEW OF THE WES..............27

APPENDIX B - POSITION PAPER: PROPOSAL TO REDUCE WES-TWA FOR METHYL
BROMIDE FROM 5PPM TO 1PPM .............................................................................27
 Setting WES .......................................................................................................... 27
 ERMA reassessment of methyl bromide .................................................................... 28
 Respiratory protection and WES............................................................................... 28




Department of Labour Methyl Bromide WES Consideration Paper April 2010                        Page 3 of 33
EXECUTIVE SUMMARY

This paper discusses the proposed lowering of the Workplace Exposure Standard (WES) for
methyl bromide and the basis for that proposal. The paper also discusses setting WES under
the HSNO Act, discusses air sampling methods and lists methyl bromide exposure standards
from other countries.

The Department of Labour is proposing the following WES for methyl bromide:

    1. An 8 hour WES-TWA (Time Weighted Average) of 1ppm; and
    2. A WES-GEL (General Excursion Limit) of 3ppm.

The proposed WES are derived from a study on rats which showed degeneration and
hyperplastic lesions of the nasal epithelium at concentrations of 3.1ppm methyl bromide
administered for 30 hours per week for a period of 29 months (Reuzel, 1991). An
assessment factor (uncertainty factor) of three was applied to this Lowest Observed Adverse
Effects Level (LOAEL) to derive a WES-TWA.

A reduction in the WES-TWA or WES-GEL is not considered to have a negative impact on the
sampling methodology commonly used for methyl bromide. The methods have adequate
quantification limits and accuracy for determining time weighted averages at concentrations
below the proposed WES.

The methyl bromide occupational exposure limits from 18 other countries or standard setting
organisations are listed in this paper. The proposed 8-hour WES-TWA of 1ppm is equivalent
to nine of the 18 listed, more stringent than eight of the 18, and less stringent than one of
the 18.

The paper does not discuss the chemistry, use, controls for or wider toxicology of methyl
bromide as this information is provided in depth in other publications such as the ERMA
Methyl Bromide Application for Reassessment document (2009).

SUBMISSIONS ON THE REPORT

In order to assist the Department of Labour make their final decision on the Workplace
Exposure Standards for methyl bromide, submissions on this report are invited. For further
details, please refer to: http://www.dol.govt.nz/consultation/index.asp.




Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 4 of 33
SECTION 1 - WORKPLACE EXPOSURE STANDARDS

The Workplace Exposure Standards (WES) are health-based guidelines for airborne
contaminants and are endorsed by the Department of Labour. The current WES publication
(Workplace Exposure Standards and Biological Exposure Indices from 2002) is available at:
http://www.osh.dol.govt.nz/order/catalogue/329.shtml.

WES are intended to be used as guidelines for those involved in occupational health practice.
In assigning the standards, defining a level that will achieve freedom from adverse health
effects is the major consideration. Compliance with the designated value does not, however,
guarantee protection from discomfort or possible ill-health outcomes for all workers. The
range of individual susceptibility is wide and it is possible that workers will experience
discomfort or develop occupational illness from exposure to substances at levels below the
exposure standards.

In all instances the Workplace Exposure Standards relate to exposure that has been
measured by personal monitoring using methods that gather air samples in the worker’s
breathing zone.

The WES publication defines the following categories of WES:

    •   Time Weighted Average (WES-TWA) - The time-weighted average exposure
        standard designed to protect the worker from the effects of long-term exposure. This
        is based on an 8 hour working day and a 40 hour working week.
    •   Ceiling (WES-Ceiling) - A concentration that should not be exceeded during any part
        of the working day.
    •   Short-Term Exposure Limit (WES-STEL) - The 15-minute average exposure
        standard. Applies to any 15-minute period in the working day and is designed to
        protect the worker against adverse effects of irritation, chronic or irreversible tissue
        change, or narcosis that may increase the likelihood of accidents. The WES-STEL is
        not an alternative to the WES-TWA; both the short-term and time-weighted average
        exposures apply.
    •   General Excursion Limit (WES-GEL) - Often there is insufficient toxicological data
        available for the establishment of a Short Term Exposure Limit. Peak exposure should
        however still be controlled even in situations where the Time-Weighted Average level
        is not exceeded. A 15-minute exposure limit of three times the TWA is recommended.
        Where a STEL has been assigned, the STEL value takes precedence over the general
        excursion regardless of whether or not it is a stricter standard.

There is some confusion as to whether WES apply to air inside or outside respiratory
protective equipment. The intention of the WES is to establish a concentration that can be
inhaled without causing adverse health effects. If a respirator is worn the WES applies to the
concentration inside the respirator as this is the air that the worker will be breathing. As
inward leakage of air occurs with respiratory protection (due to poor face seals and valve
leakage etc), an important consideration when selecting a respirator is the reduction in
exposure the respirator can be expected to provide. This reduction, termed ‘protection
factor’, is defined as the ratio between the concentration of the contaminant outside the
respirator to the concentration inside the respirator i.e. breathed by the wearer. The
protection factor can also be expressed by the following equation (AS/NZS 1715:2009):




Department of Labour Methyl Bromide WES Consideration Paper April 2010    Page 5 of 33
Protection factor =     Ambient air concentration
                        Concentration inside respirator

The protection factor required of a respirator to reduce exposure to an accepted level is
called the ‘required minimum protection factor’. It can be expressed by the following
equation:

Required minimum protection factor =             Ambient air concentration
                                                 Exposure Standard

For example, if the air concentration (in the worker’s breathing zone) is 10ppm and the
exposure standard is 1ppm, the required minimum protection factor of a mask is (at least)
10.




Department of Labour Methyl Bromide WES Consideration Paper April 2010       Page 6 of 33
SECTION 2– WORKPLACE EXPOSURE STANDARDS UNDER HSNO

2.1     Setting WES under HSNO
Methyl bromide and certain formulations containing methyl bromide are approved
substances under the Hazardous Substance and New Organisms Act (1996) (the “HSNO
Act”) and as such are subject to controls established by that legislation.

Section 77B(1)(b) of the HSNO Act allows the Environmental Risk Management Authority
(ERMA New Zealand) to provide for the setting of exposure limits for approved substances.
Such exposure limits may comprise workplace exposure standards. Section 77B(3)(b)
requires the setting of the exposure limits to be according to a methodology.

On this basis, the Authority has provided for the setting of a methyl bromide WES by the
Department of Labour (DoL). The methodology by which the exposure limit (WES in this
case) is set, is defined in an operational agreement between DoL and ERMA.

(Extracted from Section 77B(5)): Before setting exposure limits, the Authority must:
   a) consider the best international practices and standards for the safe management of
       substances with toxic or ecotoxic properties; and
   b) be satisfied that, against other specified exposure limits that apply to the
              substance,—
              (i) the proposed exposure limit is more effective in terms of its effect on the
                       management, use, and risks of the substance; or
              (iii) the proposed exposure limit is more likely to achieve its purpose; and
   c) do everything reasonably practicable on its part to advise all people who in its opinion
       may be affected by the proposed exposure limit; and
   d) give those people a reasonable opportunity to make submissions and comments to
       the Authority on the proposed exposure limit; and
   e) consider all submissions and comments received.

In considering a lowering of the methyl bromide WES, the DoL considered:

    •   The best international practices and standards for the safe management of methyl
        bromide (S77B(5)(a)); and,
    •   Is satisfied that, against other specified exposure limits that apply to methyl bromide,
        that the proposed exposure limit is more effective in terms of its effect on the
        management, use, and risks (S77B(5)(b)(i)); and ,
    •   Is satisfied the proposed exposure limit is more likely to achieve its purpose
        (S77B(5)(b)(iii)).

In complying with sections 77B(5)(c), the DoL has done everything reasonably practicable to
advise all people who in its opinion may be affected by the proposed exposure limit, and to
give those people a reasonable opportunity to make submissions and comments on the
proposed exposure limit. This has been achieved by:

    •   a mail out on 29th November 2008 alerting affected people to the proposed change
        and requesting submissions by 31st January 2009 (Appendix A); and
    •   a web posting on the DoL Health and Safety site on 1st December 2008 alerting to the
        proposed change and requesting submissions by 31st January 2009; and



Department of Labour Methyl Bromide WES Consideration Paper April 2010    Page 7 of 33
    •   a mail out on the 19th December 2008 informing of an extension to the submission
        period (Appendix A) to 31st March 2009; and,
    •   a review of the submissions received, prompting a decision to hold a public meeting
        to discuss the issues raised in the submission process; and,
    •   a mail out on the 5th August 2009, to people affected by the proposed exposure limit
        to inform them of a public meeting to discuss the proposed change to the WES
        (Appendix A). This meeting was held on 23rd October 2009; and
    •   a web posting on the DoL Health and Safety site on 6th August 2009 alerting to the
        public meeting on 23rd October 2009; and
    •   an email sent on 14th October 2009 to the confirmed attendees to the public meeting
        with a DoL position paper on the proposed WES reduction (Appendix B); and
    •   a web posting on DoL Health and Safety site on 9th October 2009 of the position
        paper.

2.2     WES as Controls under HSNO
Regulation 29(4) of the Hazardous Substances (Classes 6, 8 and 9 Controls) Regulations
2001 requires that “The person in charge of a place of work must ensure that a person is not
exposed to a concentration of the substance that exceeds the workplace exposure standard
for that substance”. As such, workers exposure to methyl bromide must be controlled to
levels below the WES. HSNO legislation does not provide guidance on achieving control,
however the Health and Safety in Employment Act (1992) requires that where a significant
hazard exists, employers must take all practicable steps to eliminate it. If not practicable to
eliminate the significant hazard, it must be isolated, and if not practicable to isolate, it must
be minimised. The steps of elimination, isolation and minimisation (called the ‘hierarchy of
controls’) should be applied to methyl bromide exposures that exceed the WES.




Department of Labour Methyl Bromide WES Consideration Paper April 2010     Page 8 of 33
SECTION 3– TOXICOLOGICAL BASIS FOR SETTING METHYL
BROMIDE WES

3.1     Basis for proposing an 8 hour TWA of 1ppm
The DoL is proposing an 8 hour TWA of 1ppm based on the results of an animal study which
found a methyl bromide Lowest Observed Adverse Effects Level (LOAEL) of 3.1ppm (+/-0.4)
via inhalation. In the study (Reuzel, 1991), male and female Wistar rats were exposed by
inhalation 6 hours per day, 5 days per week for 29 months. A statistically significant
difference (p=<0.05) was found between controls and the group exposed at 3.1ppm at the
end of the 29 months in terms of degeneration and hyperplastic lesions of the basal cells of
the nasal epithelium*. It is noted that the frequency of this lesion also increased in controls
with age. The hyperplasia was described as very slight (17 out of 19 animals) or slight (2
out of 19 animals).

* Basal cell hyperplasia = A proliferation of basal cells beyond that which is ordinarily seen.
Hyperplasia may result in gross enlargement of an organ, the formation of a benign tumor or
may be visible under a microscope. The olfactory epithelium is specialized epithelial tissue
inside the nasal cavity.

3.2     Basis for proposing a short term exposure limit
The DoL WES book says that where there is insufficient toxicological data available for the
establishment of a Short Term Exposure Limit (WES-STEL), a 15 minute exposure limit of
three times the 8-hour TWA is recommended. This value is called a WES-GEL (General
Excursion Limit). In this review of the methyl bromide WES, it is considered that the detailed
toxicological data was insufficient to readily determine a WES-STEL. Thus a WES-GEL of 3
times the 8-hour TWA is proposed i.e. a WES-GEL of 3ppm.

3.3     Deriving a WES from animal data
In the absence of sound human exposure data, the common basis for deriving occupational
exposure standards is a No Observed Adverse Effect Level (NOAEL) or a Lowest Observed
Adverse Effect Level (LOAEL) for the most critical effect from repeated dose animal studies
(Ecetoc, 2006). The critical effect is the first (most sensitive) adverse effect that occurs as a
dose or concentration increases.

This animal studies approach to standard setting is becoming more common. In 1968,
approximately 50% of the ACGIH TLVs were derived from human data and about 30% from
animal data. By 1998, about 50% of the 700 or so ACGIH TLVs were derived primarily from
animal data (Perkins, 2003)

The OECD (2009) states: “The most sensitive [animal] species should normally be used,
except in those cases where evidence is available that the given effect(s) are species specific
and are not relevant for human health evaluation”.




Department of Labour Methyl Bromide WES Consideration Paper April 2010     Page 9 of 33
3.4     Assessment factors
Various assessment factors (also called safety or uncertainty factors) are applied to the
NOAEL/LOAEL to extrapolate from animal data to humans. These assessment factors are
used to account for uncertainties in experimental data and the application of animal data to
human health risk. Paustenbach states that “the uncertainty factor approach has been and
continues to be used by FDA, EPA OSHA and virtually all agencies and scientific bodies who
set acceptable levels of exposure to toxic substances” (Perkins, 2000).

The assessment factor for each specific uncertainty is determined, then an overall
assessment factor is calculated by multiplying the individual factors together. This overall
assessment factor is then applied to the NOAEL as follows:

                         Limit value = NOAEL/(overall assessment factor)

Assessment factors for specific uncertainties vary depending on the methodology applied.
The following sections describe the assessment factors used by various agencies. The
assessment factor used by the DoL in the setting of the proposed methyl bromide TWA is
discussed in Section 3.4.4.

3.4.1 Default assessment factors
In the absence of chemical specific assessment factors (i.e. biologically based predictors of
uncertainty specific to a particular substance), default assessment factors are commonly
used. Default assessment factors have been used for over 40 years to determine health
based guidance values based on NOAELs or LOAELs from animal studies (IPCS, 2005).
The following are common default assessment factors (Perkins, 2003):

    •   Factor of </=10 (but often 3) when extrapolating from animal data to humans;
    •   Factor of </=10 for inter-human variability (to protect sensitive individuals);
    •   Factor of </=10 (but generally 3) for adjusting from a LOAEL to an NOAEL;
    •   Factor of </=10 (but generally 3) when adjusting from acute or sub-chronic studies
        to chronic risk;
    •   Factor of </=10 to adjust for insufficiencies in the amount of information provided by
        toxicity studies e.g. only few studies for a critical effect.

The more conservative assessment factors are used for determining ambient air exposure
limits for the wider population including the very young, the very old, those with illnesses
and based on continuous lifetime exposure. As such they are unnecessarily conservative for
establishing occupational exposure limits (OELs). OELs are intended to protect a much
smaller and less diverse population that would not be continuously exposed for a lifetime
and a factor of 3 (for each uncertainty) is commonly used for determining an OEL (Pattys,
2000).

Organisations such as ATSDR (Agency for Toxic Substances and Disease Registry) in the
United States, Health Canada, The World Health Organisation International Programme on
Chemical Safety (IPCS) and RIVM (The National Institute for Public Health and the
Environment) in The Netherlands, apply the above default values when specific assessment
factors for specified substances have not been defined.




Department of Labour Methyl Bromide WES Consideration Paper April 2010     Page 10 of 33
3.4.2 REACH assessment factors
EU Regulation (EC) No 1907/2006 concerning the Registration, Evaluation, Authorisation and
Restriction of Chemicals (REACH), places an obligation on registrants to develop Derived No
Effects Levels (DNELs) for registered substances. A DNEL is defined as a level of exposure
above which humans should not be exposed. The purpose of the DNEL is to act as a
benchmark for determining adequate control of exposure for specified chemicals and
exposure scenarios.

In determining DNELs from animal data, assessment factors are used. The ECHA document
Guidance on information requirements and chemical safety assessment Chapter R.8:
Characterisation of dose [concentration]-response for human health – Guidance for the
Implementation of REACH (2008) describes in detail the rationale for the use of assessment
factors. It also provides default assessment factors to be used in the absence of relevant
substance specific information. Based on the ECHA guidance, the assessment factor applied
to the LOAEL of 3ppm from the Reuzel rat study (Reuzel, 1991) is (for local effects):

    •   (For interspecies variation) x 5 (for intra-species variation) x 1 (dose-response
        uncertainties including LOAEL/NOAEL extrapolation) x 1 (quality of whole database) =
        overall assessment factor of 5.

If this overall assessment factor is applied to the LOAEL, it would result in a WES-TWA of
0.6ppm.

3.4.3 ACGIH assessment factor for methyl bromide
In their 2001 review of the Threshold Limit Value for methyl bromide, the American
Conference of Governmental Industrial Hygienists (ACGIH) recommended an 8 hour TLV-
TWA (Threshold Limit Value Time Weighted Average) of 1ppm based on the Reuzel study
(Reuzel, 1991). This implies that in determining a TLV-TWA, the ACGIH applied an
assessment factor of three to convert the LOAEL in rats (3ppm) to a TLV-TWA. The ACGIH
consider the 1ppm value to minimise the potential for skin and respiratory tract irritation.
The ACGIH also stated that “This value also should offer additional protection against
pulmonary oedema and transient neurotoxicity observed following acute, high level
exposures”.

3.4.4 Assessment factor applied by the Department of Labour
The overall assessment factor applied by the DoL to the Reuzel study LOAEL is three i.e.
3ppm/3 = 1ppm TWA. This is the factor used by the ACGIH (2001).

In applying an assessment factor of three, the DoL has chosen a less conservative approach
than would otherwise be applied by using the default assessment factors (Section 3.4.1),
and the REACH assessment factors. Thus the DoL does not consider the assessment factor
of three to be overly conservative.

3.5     Assessing the quality of animal studies
Assessing the quality of the information provided by animal studies is an important
consideration when using the data to derive a WES. One common method used to assess
quality is that of Klimisch et. al. (1997) as described in the paper A Systematic Approach for
Evaluating the Quality of Experimental Toxicological and Ecotoxicological Data. Klimisch
uses three terms to describe the overall quality of animal studies data: reliability, relevance
and adequacy. The OECD (2009) summarises Klimisch’s terms as follows:



Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 11 of 33
    •   Reliability - evaluating the inherent quality of a test report or publication relating to
        preferably standardised methodology and the way the experimental procedure and
        results are described to give evidence of the clarity and plausibility of the findings;
    •   Relevance - covering the extent to which data and tests are appropriate for a
        particular hazard identification or risk characterisation; and
    •   Adequacy - defining the usefulness of data for hazard/risk assessment purposes.
        When there is more than one study for each SIDS* element, the greatest weight is
        attached to the study that is the most reliable and relevant. Robust study summaries
        are prepared for the highest quality or “key”studies.

(*SIDS = the OECD Screening Information Data Set that provides information needed for
health and environmental risk assessment of chemicals. The OECD SIDS for Methyl Bromide
is available through http://www.chem.unep.ch/irptc/sids/oecdsids/sidspub.html).

Using these criteria, Klimisch developed a scoring system to categorise the reliability of
studies. The ‘scores’ are as follows (Klimisch et.al. 1997):

        1 = reliable without restrictions: “studies or data...generated according to
        generally valid and/or internationally accepted testing guidelines (preferably
        performed according to good laboratory practice) or in which the test parameters
        documented are based on a specific (national) testing guideline...or in which all
        parameters described are closely related/comparable to a guideline method.”

        2 = reliable with restrictions: “studies or data...(mostly not performed according
        to good laboratory practice), in which the test parameters documented do not totally
        comply with the specific testing guideline, but are sufficient to accept the data or in
        which investigations are described which cannot be subsumed under a testing
        guideline, but which are nevertheless well documented and scientifically acceptable.”

        3 = not reliable: “studies or data...in which there were interferences between the
        measuring system and the test substance or in which organisms/test systems were
        used which are not relevant in relation to the exposure (e.g., unphysiologic pathways
        of application) or which were carried out or generated according to a method which is
        not acceptable, the documentation of which is not sufficient for assessment and
        which is not convincing for an expert judgment.”

        4 = not assignable: “studies or data....which do not give sufficient experimental
        details and which are only listed in short abstracts or secondary literature (books,
        reviews, etc.).”

The reliability criteria and categories provide a practical systematic approach for quality
evaluation of experimental toxicological data, considering such factors as the use of a
standardised test method, the availability of a description of the relevant details of the study
design (Ecetoc, 2009).

3.5.1 Quality of the Reuzel study using the Klimisch score
The following four parties have independently assessed the quality of the Reuzel study
(1991) using the Klimisch score:




Department of Labour Methyl Bromide WES Consideration Paper April 2010    Page 12 of 33
1.      Dr Martin Edwards’ (Toxicology Consulting Limited) Report on Toxicological Hazard
        Profile and Related Classifications of Methyl Bromide (Appendix D of the ERMA
        Application for Reassessment document) gives a Klimisch Score of 2 (reliable with
        restrictions). No comments on the derivation of the score are given in the document.

2.      Dr Kathy Parton (Massey University Institute of Veterinary, Animal and Biomedical
        Sciences) gives a Klimisch Score of 2 (reliable with restrictions). Comments from Dr
        Parton: “Acceptable study with a robust investigation of toxic effects. No evidence or
        mention of Good Laboratory Practice. Steps were taken to verify the concentration of
        methyl bromide exposure”.

3.      Dr Bernard Gadagbui (TERA (Toxicology Excellence for Risk Assessment)) gives a
        Klimisch Score of 2 (reliable with restrictions). Comments from Dr Gadagbui: “Based
        on our review of the published paper, the study appears to have been conducted
        under a recognized guideline (USEPA OPPTS 870.4300 – Combined Chronic
        Toxicity/Carcinogenicity) and was well documented. The only deviation noted is that
        there is no reference to the study being conducted under Good Laboratory Practice
        Standards (GLP). Based on this, TERA assigns a Klimisch Score of K2 (Reliable with
        restrictions) for the published study. However, a K1 (Reliable without restrictions)
        can be assigned if the unpublished report is available and is reported to be conducted
        under GLP. The study can be used for human health risk assessment purposes”.

4.      The OECD methyl bromide SIDS (2001) gives a Klimisch Score of 1 (reliable without
        restrictions). The document states: “The data quality from this study is considered
        high. The report included comprehensive documentation for method and analysis.
        The conducting laboratory is reputable.

3.6     Using the nasal epithelium as an end point
The Reuzel study (1991) reported an LOAEL for the rat nasal epithelium. The
appropriateness of the nasal epithelium effects as an end point was assessed by the
California Department of Pesticide Registration in their methyl bromide risk characterisation
document (CPDR, 2002), and they concluded:

        “Another important toxicity endpoint is the methyl bromide-induced damage to the
        olfactory epithelium of rats and mice after inhalation exposure (Reuzel et al., 1987
        and 1991; NTP, 1992). This endpoint is used by the U.S. EPA in the determination of
        the chronic reference inhalation concentration (RfC) (U.S. EPA 1992a) and by the
        Office of Environmental Health and Hazards Assessment (OEHHA) for chronic toxicity
        reference exposure levels (RELs) (OEHHA, 1996).” “In the chronic inhalation toxicity
        study, basal cell hyperplasia and degeneration in the olfactory epithelium were
        observed in the rat (Reuzel et al., 1987 and 1991). While the effect on the nasal
        cavity may generally be considered a finding limited to the rat due to anatomical
        considerations, it is not the case with methyl bromide. Dogs exposed to 156 ppm
        methyl bromide for only 6 days showed moderate to moderately severe olfactory
        degeneration (Newton, 1994b). Epithelial hyperplasia of the basal cell layer observed
        in rats and mice may be a regenerative response or an early indication of neoplasia
        (Boorman et al., 1990). The olfactory epithelium has remarkable regenerative
        capacity with a turnover time of 28 days. The basal cells are the stem cells for
        olfactory neurons. If the basal cells are destroyed, then olfactory epithelium cannot
        be reconstituted and olfactory function is impaired or lost. The regenerative ability of
        the basal cells does decline with age (Hastings, 1990). As part of the reparative


Department of Labour Methyl Bromide WES Consideration Paper April 2010    Page 13 of 33
        process, prolonged injury may result in squamous metaplasia and respiratory
        metaplasia. Squamous metaplasia is characterized by multiple layers of epithelial
        cells with eosinophilic cytoplasm (Boorman et al., 1990; Haschek and Witschi, 1991).
        Squamous cell neoplasms have been shown to develop from areas of squamous
        metaplasia in the olfactory epithelium (Boorman et al., 1990). Respiratory
        metaplasia, the conversion of olfactory epithelium to a ciliated respiratory type, after
        exposure to methyl bromide indicates a permanent change in the cell type (Hurtt et
        al., 1988; NTP, 1992; Eustis, 1992). Olfactory epithelial reconstitution after methyl
        bromide exposure has been used as the model to study the mechanism of recovery of
        the olfactory system (Schwob et al., 1995 and 1999). The nasal effects represented
        the most sensitive endpoint for chronic exposure”.




Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 14 of 33
SECTION 4– SAMPLING METHODS

A number of sampling methods are available for airborne methyl bromide. The method used
will depend on factors such as:

    •   Specificity - whether the method/instrument measures methyl bromide specifically or
        not;
    •   Accuracy of measurement (how close the reported value is to the true value);
    •   Quantification limit (lowest quantifiable concentration) - particularly in relation to the
        WES
    •   Interferences from other airborne substances;
    •   Instantaneous (direct reading) versus delayed monitoring results (those requiring
        analysis);
    •   Cost.

The most common sampling methods used in New Zealand include Photo Ionisation
Detectors, colorimetric tubes and active sampling with a sorbent tube. These are discussed
in some detail in Sections 4.1, 4.2 and 4.3. Other methods are discussed in section 4.4.

4.1     Photo Ionisation Detector (PID)

4.1.1 Method

The PID measures volatile organic compounds (VOC) using ultraviolet light to ionize the
sample into positive and negative ions, which are then counted by the detector. The charged
particles produce a current that is amplified and displayed on the meter in parts per billion
(ppb) or parts per million (ppm).

The meters are fitted with lamps of differing ionization potential (measured in electron volts
or eV). The most common lamp used in New Zealand is 10.6eV. As long as the ionisation
energy of the substance is less than that of the lamp, the substance can be detected and
measured. The ionisation energy of methyl bromide is 10.54eV. PIDs require regular
calibration and maintenance by a servicing agent.

4.1.2 Calibration and correction factor
The meter is usually calibrated against a known concentration of isobutylene. When
measuring a single gas, a specific correction factor is applied to the reading to give an
approximate reading of the atmospheric concentration. For example, methyl bromide
requires a correction factor of 1.7 to be applied to the displayed reading (isobutylene
equivalent in ppm) to give the methyl bromide concentration in air.

4.1.3 Accuracy and quantification limits
PIDs generally have a quantification threshold of 0.17ppm for methyl bromide (Technical
note TN-102 for the/ Rae Systems PID meter states that the instrument sensitivity can be
estimated by multiplying the correction factor by 0.1).

If isobutylene is used as the calibration gas, the accuracy of the meter is +/-2ppm or 10%
of the reading, whichever is greater. However, this specified accuracy only applies to
isobutylene. When measuring another gas, the accuracy can only be specifically determined
if the meter is calibrated with that gas. This, however is usually not done as isobutylene is




Department of Labour Methyl Bromide WES Consideration Paper April 2010     Page 15 of 33
the standard calibration gas. For substances other than isobutylene, the accuracy is given as
‘‘around 20%” (by one manufacturer).

Thus if using an isobutylene calibrated meter and a reading of 5ppm is shown, the methyl
bromide result will be 5ppm x correction factor (1.7) = 8.5ppm, with an error of 20%. Thus
the final concentration would be between 6.8 and 10.2ppm.

If using an isobutylene calibrated meter and a reading of 1ppm is shown, the methyl
bromide result will be 1ppm x correction factor (1.7) = 1.7ppm, with an error of 20%. Thus
the final concentration would be between 1.4 and 2ppm.

4.1.4 Interferences
A problem arises with the PID when other gases that can be ionised at less than 10.6eV are
present in the air. The meter will not distinguish between the methyl bromide and other
gases and the resultant concentration represents methyl bromide plus the other gases. This
can be a particular problem for measuring methyl bromide near timber treated with Light
Organic Solvent Preservative (LOSP). The LOSP solvent (usually white spirit) can off-gas
from the timber and will be detected by the PID meter along with methyl bromide, thus the
actual concentration of methyl bromide cannot be determined. Measurement of the solvent
levels before the timber is fumigated should be carried out to determine if it is going to
impact on the methyl bromide results. If so, results from PID monitoring will not be
conclusive in terms of methyl bromide concentration.

4.1.5 Applicability to a TWA

Most PIDs have a data logging function and also a time weighted averaging (TWA) function.
These can be used to determine an 8 hour TWA concentration that can be compared to the
WES-TWA. If the PID is used for one-off or occasional readings, the 8 hour TWA can only be
estimated by determining an average exposure level over a specified exposure period, using
the following equation:



                             (c1 x t1) + (c2 x t2) …(cn x tn)
                                         8 hours

                        based on a work shift of up to 8 hours
                                  c= concentration
                                 t = time (in hours)



For example, if one-off readings over a period of 30 minutes indicate an average exposure
level of 10ppm and for the rest of the 8 hour shift there is no exposure (as the worker is off
site), the 8 hour TWA would be calculated as:

                     (10ppm x 0.5 hours) + (0ppm x 7.5 hours)            = 0.63ppm
                                      8 hours

0.63ppm is the value that is compared to the 8 hour WES-TWA.




Department of Labour Methyl Bromide WES Consideration Paper April 2010        Page 16 of 33
4.2     Colorimetric (detector) tubes

4.2.1 Method
These tubes are simple to use, although require thorough understanding of the principles.
Glass tubes are attached to a hand/electric drawn sampling pump and air is drawn through
the tubes over a specified time period (equating to a specified volume of air).

The tubes contain a reagent that reacts in the presence of methyl bromide causing a colour
change. The length of the colour ‘stain’ up the tube is measured against a graduated scale.
Methyl bromide detection usually uses two tubes in line, the first (pre-treatment tube)
converts methyl bromide to bromine (Br2) and in the second tube, bromine is complexed
with another chemical causing the colour change.

4.2.2 Correction factor

The final concentration will depend on the number of pump ‘strokes’, as a correction factor
needs to be applied. The correction factors and sampling times vary with different brands of
tube.

4.2.3 Interferences

Other substances, especially other halogenated hydrocarbons can cause a colour change in
the tube, thus the user has to be aware of possible interferences giving a false or incorrect
result.

4.2.4 Quantification limits and accuracy
The quantification limits for methyl bromide detector tubes vary but are reported as 0.2 to
600ppm. The accuracy of detector tubes is generally considered to be +/-25% of the reading
(based on NIOSH criteria for accuracy of detector tubes). Thus a result of 5ppm should be
treated as between 3.75 to 6.25ppm.

4.2.5 Applicability to a TWA
Colourimetric tubes sample over very short periods of time (usually around 5 to 12 minutes)
thus a result from a 5 minute sample cannot be directly compared to the 8 hour TWA. The 8
hour TWA can be estimated by using the equation given in Section 4.1.5. As with a non-
datalogging PID, or PID readings taken non-continuously, a number of samples over the
exposure period should be taken to determine average exposure level for that period.

4.3     Sampling pump and sorbent tube (active sampling)

4.3.1 Method
A battery powered sampling pump and sorbent tube can be used to take both personal and
area samples for methyl bromide. Air is drawn by the pump through the tube where the gas
is trapped. The tube is then desorbed in a laboratory and the mass of methyl bromide on the
tube is reported. The final concentration is calculated from the mass and the volume of air
sampled. Methods specific to methyl bromide are available and include: NIOSH method
2520, ISO method 16017-2:2003, USEPA method TO-17.

4.3.2 Quantification limits and accuracy
Quantification limits of the methods vary. For NIOSH method 2520 it is around 0.23ppm and
for EPA method TO-17 it is around 0.008ppm.The accuracy (sampling and analytical error) is




Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 17 of 33
also dependant on the method used. For NIOSH method 2520 the standard deviation is
around 19%, for EPA method TO-17 it is around 20%.

4.3.3 Applicability to a TWA
As the samples are taken over a period of time, and can be taken as personal samples on
the operator, the results can be easily compared to the WES-TWA.

4.4     Other sampling methods

4.4.1 Passive sampling badge
Passive sampling badges work in a similar way to sampling pumps/sorbent tubes, however
they work on passive diffusion of air across the face of the badge rather than active air
movement (by a pump). The badge is ‘opened’ at the start of sampling, usually worn by a
worker and then sealed at the end of the sampling period. Analysis is carried out at a
specialised lab and a final TWA concentration is reported, based on the air volume and mass
of sample. One manufacturer reports a quantification level of 0.1ppm for an 8 hour sample,
with 25% accuracy at the 95% confidence interval.

One disadvantage of the method is that it requires air movement across the face of the
badge therefore can’t be used for static sampling in still air. As the air flow across the face
of the badge is low (an equivalent air sampling rate of about 10 to 40 mls/minute) the
badges need to be exposed for a long period to obtain a sufficient amount of gas to identify
air levels of around 0.1ppm. This period is at least 5 hours.

4.4.2 Electrochemical sensor
A meter utilising a specific electrochemical sensor for methyl bromide is available. The
quantification level is reported as 0.3ppm with accuracy of 10%. The meter is specific to
methyl bromide (thus interference from other substances not a problem) and it gives
instantaneous readings.

To calculate an 8 hour TWA from the results, either datalogging capability would be
necessary or a program of regular sampling throughout the exposure period would be
required.

4.4.3 Other real time analysers
Portable Flame Ionisation Detectors (FID), Fourier Transform Infrared Spectroscopy (FTIR),
portable Gas Chromatograph – Mass Spectrometry (GCMS) and Selected Ion Flow Tube Mass
Spectrometry (SIFT-MS) are more expensive methods. Although providing good
quantification levels and the specific measurement of methyl bromide, none are understood
to be in common use in New Zealand at present. They are not practical for personal
monitoring and require intensive calibration.

4.4.4 Halide lamps

Halide lamps burn a butane flame that changes colour from blue to green in the presence of
halides such as methyl bromide. The colour change occurs at around 20 to 30ppm therefore
is not sensitive or accurate enough for measurements against the WES. Other limitations of
the meter are that they do not distinguish between methyl bromide and other organic
halogen gases, cannot be used in the presence of flammable gases (e.g. LOSP vapour),
cannot be used in dusty atmospheres, and cannot be used by colour blind people.




Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 18 of 33
4.5     Discussion on lowering the WES and implications for sampling
An important consideration in choosing a sampling method and sampling strategy is the
level of quantification (detection) of the meter in regards to the exposure standard. Ideally
in occupational hygiene sampling a quantification limit of at least 10% of the WES is
desirable (taking into account sampling and analytical error).

For all methods listed above, with the exception of the halide lamp, a lower WES value
should not pose a significant problem as the quantification limits of the methods are below
the proposed 1ppm WES-TWA level. It must also be remembered that one-off readings
should not be compared directly to the WES-TWA but an 8 hour average* should be
calculated. Average exposures should be determined for specified time periods, then the 8
hour TWA should be calculated using the following equation:



                             (c1 x t1) + (c2 x t2) …(cn x tn)
                                         8 hours

                       *based on a work shift of up to 8 hours
                                 c= concentration
                                t = time (in hours)



Section 4.6 gives examples of calculating an 8 hour TWA.

For work shifts greater than 8 hours, commonly a time weighted average for the total shift is
calculated as follows, then an adjustment made to the WES-TWA for extended work shifts
(see Section 4.7).



                             (c1 x t1) + (c2 x t2) …(cn x tn)
                                           ttotal

                                      c= concentration
                                     t = time (in hours)
                                 ttotal = total time period


4.6     Calculating an 8 hour TWA
The air concentration of methyl bromide may at times allowably exceed the TWA
concentration, as long as 8 hour average falls below the WES-TWA.

Example 1:
A worker carried a PID meter with him while venting was carried out over a 30 minute
period. The average reading during venting was 6ppm and for the rest of the shift, no
methyl bromide was detected by the PID meter. The worker remained on the site for the full
8 hour work shift. Assuming a sampling error of 20%, the worker’s exposure during the shift
is:

    •   6ppm x 1.7 correction factor = 10.2ppm
    •   Sampling error means the actual result was between 8.2 and 12.2ppm


Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 19 of 33
    •   Using the worst case scenario, the average exposure during venting is 12.2ppm
    •   For the rest of the shift, no methyl bromide was detected. As the lowest detectable
        concentration using this sampling method is 0.17ppm, for a conservative estimate,
        this value should be used as the ‘no-exposure’ level (rather than 0ppm). Applying
        the sampling error, the minimum detection level is between 0.14 and 0.20ppm, thus
    •   For 7.5 hours, the average exposure was 0.2ppm.

To calculate the worker’s 8 hour exposure, use the following calculation:



                          (concentration x time) + (concentration x time) …
                                               8 hours



i.e. for the above example, the result (using the worst case exposure) is:



                               (12.2 x 0.5 hours) + (0.2ppm x 7.5 hours)
                                                8 hours



Thus the 8 hour exposure for the worker is 0.95ppm. This is the value that is compared to
the WES-TWA.

In managing this exposure, good practice would consider:
1.    Whether the result exceeds the WES-TWA,
2.    How close that result is to the TWA (note 1).
3.    Whether the result exceeds the WES-GEL, and
4.    How close that result is to the GEL.

In the above example, although the exposure that day is below a 1ppm WES-TWA, the
result is 95% of the WES-TWA. As a 15 minute sample was not taken, it cannot be
ascertained whether the WES-GEL was exceeded. However, as the 30 minute average was
6ppm, it is likely the exposure exceeds the proposed WES-GEL of 3ppm.

Based on these results, all practicable steps must to be taken to eliminate, isolate or
minimise exposure. If respiratory protection is used to minimise exposure, a respirator with
an appropriate protection factor should be worn. A protection factor of 10 (note 2) should
(assuming it is worn correctly and is working effectively) reduce the persons exposure to an
8 hour average of 0.095ppm, and 1.2ppm over the 30 minute exposure period.

(Note 1: The WES value should never be seen as a target to aim for. Good occupational
hygiene practice is to ensure exposures are less than 25% of the WES value).

(Note 2: Australian/New Zealand Standard AS/NZS 1715:2009 Selection, Use and
Maintenance of Respiratory Protective Equipment defines protection factors as “A measure of
the degree of protection afforded by the respirator, defined as the ratio of the concentration
of contaminant outside the respirator to that inside the respirator i.e. breathed by the
worker”. The Standard lists the protection factors of various respiratory protection used in
New Zealand.)



Department of Labour Methyl Bromide WES Consideration Paper April 2010     Page 20 of 33
Example 2:
Average methyl bromide exposure for a worker is 30ppm over 30 minutes (accounting for
error, result will be 24-36ppm). Average exposure over the highest 15 minutes during the
exposure period is 42ppm (34 – 50ppm). For the rest of the 8 hour shift there is no
exposure as the worker is not at the worksite for the rest of the day.

The worker’s 8 hour exposure = (36x0.5) + (0x7.5)             = 2.3ppm
                                        8

Based on a WES-TWA of 1ppm and a WES-GEL of 3ppm, all practicable steps must to be
taken to eliminate, isolate or minimise exposure. If respiratory protection is used, a
respirator with a protection factor of 10 would only reduce the concentration inside the mask
to 5ppm during the highest 15 minute period. As this level exceeds the WES-GEL, a
respirator with a protection factor greater than 10 would be required.

4.7     Adjusting for shifts longer than 8 hours

4.7.1 Brief and Scala model
Currently the DoL Workplace Exposure Standards publication requires that where the
workday is greater than 8 hours, an adjustment is made to the WES by applying the Brief
and Scala model as follows:

                      Adjusted WES-TWA = 8 x (24-h) x (8-hour-WES-TWA)
                                       16 x h

                                   (where h = length of work day)

The DoL WES publication states that: “It is noted that in some circumstances the Brief and
Scala model may be excessively protective. While in these cases the use of other models is
not ruled out, they should only be applied when all of the relevant data is available. In
particular if a pharmacokinetic model is to be used, then an understanding of the toxicology
and pharmacokinetics of the substance is required”. It further states “The adjustment
process is a complex issue and no single model provides a universal solution. The Brief and
Scala Model is relatively easy to apply and takes into account both the increased work hours
and the decrease in the recovery period between shifts.”

As a comparison to the adjusted TWA from the Brief and Scala model, two other models are
outlined in the following sections. The adjustments these models make to the methyl
bromide WES-TWA are given in section 4.7.5.

4.7.2 The Québec Model
The Québec Institut de Recherche Robert-Sauvé en Santé et en Sécurité du Travail (IRSST)
has developed a computer-based tool to calculate an adjusted TWA based on unusual work
schedules. The model makes adjustments of the Québec permissible exposure values (PEVs)
as defined in the Québec Regulation Respecting Occupational Health and Safety Health
(RROHS). Although some of the Québec TWA’s differ from New Zealand ones, the
adjustment factor is provided in the model, thus can be applied to New Zealand WES. The
model is downloadable at: http://www.irsst.qc.ca/en/_outil_100011.html.




Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 21 of 33
4.7.3 The McMaster Model
McMaster University, Ontario, Canada have developed a modified version of a
pharmacokinetic model that can be applied to substances with a known or unknown half life.
The model is available at: http://oehl.mcmaster.ca/downloads.html.

4.7.4 Other Models
A number of other models are used for adjusting for extended work shifts. These include the
OSHA model and pharmacokinetic models. The models are discussed briefly below, however
have not been used in the following comparison as 1) the OSHA model is not freely
available, and 2) pharmacokinetic models tend to be complex and variable.

The United States Occupational Safety and Health Administration (OSHA) model is referred
to in the OSHA Field Manual (for OSHA staff). The model is based on the assumption that
the magnitude of the toxic response of an agent is a function of the concentration that
reaches the site of action for that agent. The model was designed for systemic toxins but
not sensitisers and carcinogens. Each agent is categorised based on its toxic effect. The
assigned category is then used to determine if any adjustment is required and if so, what
equation is to be used. The model is not available to the public.

There are a number of pharmacokinetic models in use. These models are based on the
concept of body burden and how the biological half life of a substance can have a significant
impact on the maximum body burden for a given work schedule. They are based on ensuring
that the maximum body burden for an extended work shift doesn’t exceed that for an 8 hour
shift. These models are generally considered more accurate than other models however can
be very complicated and as half-lives can vary substantially between different individuals,
there are limitations.

4.7.5 Comparison of Brief and Scala, Québec and McMaster models

Table 1 compares various TWAs derived by adjustments applied to an 8 hour TWA of 1ppm
using the Brief and Scala, Québec and McMaster models respectively.

  Table 1: Comparison of adjusted methyl bromide TWAs for 10, 12 and 14 hour work days

                                Brief and Scala              Québec       McMaster*
       10 hour work day
                                       0.70                    0.80           0.82
         adjusted TWA
       12 hour work day
                                       0.50                    0.67           0.69
         adjusted TWA
       14 hour work day
                                       0.36                    0.57           0.61
         adjusted TWA

* The tissue elimination half-life of methyl bromide is 0.5 to 8 hours with the exception of
the liver which is 33 hours (UNEP SIDS, 2001). The adjustments in Table 1 are based on the
elimination half-life of the liver.

Using Brief and Scala, the 8 hour TWA is halved for a 12 hour shift.
For the Quebec model, the 8 hour TWA is halved for a 16 hour shift.
For the McMaster model, the 8 hour TWA is halved for an 18 hour shift.




Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 22 of 33
As can be seen, Brief and Scala is the most conservative of these models. The DoL is
currently reviewing its protocol for adjusting for extended work shifts.




Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 23 of 33
SECTION 5– METHYL BROMIDE OCCUPATIONAL EXPOSURE
LIMITS FROM OTHER COUNTRIES

The following table lists current methyl bromide occupational exposure limits for other
countries.


           Country                    8 hour exposure limit              Short term limit (ppm)
                                             (ppm)

          Argentina                                1                                 -

           Australia                               5                            15 (STEL)

      Canada – Alberta                             1                                 -

 Canada – British Columbia                         1                        3 (excursion limit)

     Canada – Manitoba                             1                        3 (excursion limit)

      Canada – Ontario                             1                        3 (excursion limit)

      Canada - Quebec                              5                                 -

           Denmark                                 5                                 -

            Finland                                5                            10 (STEL)

            France                                 5                                 -

             Japan                                 1                                 -

             Spain                                 1                                 -

         South Africa                              5                            15 (STEL)

            Sweden                                 5                            10 (STEL)

         Switzerland                               1                                 -

       The Netherlands                           0.25                                -

       United Kingdom                              5                            15 (STEL)
   United States - ACGIH                           1                        3 (excursion limit)

    United States - OSHA                           -                           20 (ceiling)




Department of Labour Methyl Bromide WES Consideration Paper April 2010          Page 24 of 33
REFERENCES

1.      ACGIH (American Conference of Governmental Industrial Hygienists). 7th Edition of
        Documentation of the Threshold Limit Values and Biological Exposure Indices - Methyl
        Bromide. Signature Publications (2001)

2.      ACGIH (American Conference of Governmental Industrial Hygienists). Threshold Limit
        Values for Chemical Substances and Physical Agents and Biological Exposure Indices.
        Signature Publications (2009)

3.      Australian/New Zealand Standard AS/NZS 1715:2009 Selection, Use and
        Maintenance of Respiratory Protection Equipment. Standards New Zealand (2009)

4.      CDPR (California Department of Pesticide Registration). Methyl Bromide Risk
        Characterization Document Volume 1 - Inhalation Exposure (2002)

5.      Department of Labour Workplace Exposure Standards and Biological Indices, 4th
        Edition (2010)

6.      Dourson, M.L; Felter, S.P; and Robinson, D. Evolution of Science-Based Uncertainty
        Factors in Noncancer Risk Assessment. Regulatory Toxicology and Pharmacology
        24:108-120 (1996)

7.      ECETOC (European Centre for Ecotoxicology and Toxicology of Chemicals). Report
        No. 101 Guidance for Setting Occupational Exposure Limits: Emphasis on Data-Poor
        Substances (2006)

8.      ECETOC (European Centre for Ecotoxicology and Toxicology of Chemicals). Report
        No. 104 Framework for the Integration of Human and Animal Data in Chemical Risk
        Assessment (2009)

9.      ECHA (European Chemicals Agency) Guidance on Information Requirements and
        Chemical Safety Assessment – chapter R.8: Characterisation of Dose
        [Concentration]- Response for Human health (2008)

10.     ERMA (Environmental Risk Management Authority of New Zealand). Application for
        the Reassessment of a Hazardous Substance under Section 63 of the Hazardous
        Substances and New Organisms Act 1996: Methyl Bromide. Application number HRC
        08002 (2009)

11.     ERMA (Environmental Risk Management Authority of New Zealand). Application for
        the Reassessment of a Hazardous Substance under Section 63 of the Hazardous
        Substances and New Organisms Act 1996: Methyl Bromide. Application number HRC
        08002. Appendix D: Dr Martin Edwards report on toxicological hazard profile and
        related classifications of methyl bromide (2009)

12.     EU Regulation (EC) No 907/2006 concerning the Registration, Evaluation,
        Authorisation and Restriction of Chemicals REACH), establishing a European
        Chemicals Agency, amending Directive 1999/45/EC and repealing Council Regulation
        (EEC) No 793/93 and Commission Regulation (EC) No 1488/94 as well as Council


Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 25 of 33
        Directive 76/769/EEC and             Commission       Directives   91/155/EEC,     93/67/EEC,
        93/105/EC and 2000/21/EC

13.     IPCS Harmonization Project Document No.2 Chemical-Specific Adjustment Factors for
        Interspecies Differences and Human Variability: Guidance document for Use of Data
        in Dose/Concentration-Response Assessment. World Health Organization, Geneva
        (2005)

14.     Klimisch, H. J; Andreae, M; Tillman U. A Systematic Approach for Evaluating the
        Quality of Experimental Toxicological and Ecotoxicological data. Regulatory Toxicology
        and Pharmacology 25, 1–5 (1997)

15.     New Zealand Department of Labour Workplace Exposure Standards effective from
        2002. Occupational Health and Safety Service, Wellington (2002)

16.     OECD (Organisation for Economic Co-operation and Development) Manual for
        Investigation of HPV Chemicals: Chapter 3 – Data Evaluation. UNEP Publications
        (2009)

17.     OECD (Organisation for Economic Co-operation and Development) SIDS Methyl
        Bromide. UNEP Publications (2001)

18.     Patty’s Industrial Hygiene. 5th Edition, Volume 3. Chapter 40 Pharmacokinetics and
        Unusual Work Schedules by D.J. Paustenbach. John Wiley and Sons (2000)

19.     Patty’s Industrial Hygiene. 5th Edition, Volume 3. Chapter 41 History and Biological
        Basis of Occupational Exposure Limits by D.J. Paustenbach. John Wiley and Sons
        (2000)

20.     Perkins J.L. Modern Industrial Hygiene Volume II Biological Aspects. American
        Conference of Governmental Industrial Hygienists (2003)

21.     Reuzel, P.G.J.; Dreef-van der Meulen, H.C.; Hollanders, V.M.H.; Kuper, C.F.; Feron,
        V.J. and van der Heijden, C.A. Chronic Inhalation Toxicity and Carcinogenicity study
        of Methyl Bromide in Wistar Rats. Food. Chem. Toxicol. 29:31-39 (1991)

22.     UNEP SIDS Initial Assessment Report: Methyl Bromide UNEP Publications (2001)




Department of Labour Methyl Bromide WES Consideration Paper April 2010         Page 26 of 33
APPENDIX A – CORRESPONDENCE ADVISING OF A REVIEW OF
THE WES


29th November 2008



x
x

Dear x,



NOTICE OF INTENDED CHANGES TO WORKPLACE EXPOSURE STANDARDS

Prior to the publication of the third edition of the New Zealand Workplace Exposure
Standards (WES), stakeholder consultation is sought in regard to proposed changes for
some substances. This document summarises the objectives behind the proposed changes,
refers to the status of the WES under the Hazardous Substances and New Organisms Act
1996 (HSNO), and explains the process for making submissions.

1.      The proposed changes are listed in Table 1 overleaf.

2.      Some of the WES have been revised in order to bring them more into line with
        current international best practice, notably, USA and the United Kingdom. As New
        Zealand does not have prevalent epidemiological studies of the working population,
        New Zealand’s standards reflect international experience. The standards chosen for
        review are currently inconsistent with international comparators and require
        moderation.

3.      Regardless of the WES, it is expected that employee exposure to hazardous
        substances will be controlled to a level as far below the WES as practicable by
        applying the hierarchy of control required by the Health and Safety in Employment
        Act 1992 (HSE).

4.      Some WES set by the Department of Labour are now enforceable controls under
        HSNO legislation via the Hazardous Substances (Chemicals) Transfer Notice 2006.
        Therefore, all places of work that use approved hazardous substances must also
        comply with the HSNO Act as well as the HSE Act. The Department of Labour (DOL)
        enforces both laws and their associated regulations in the place of work.

5.      DOL now seeks your views on the proposed changes. Submissions close at 5pm on
        31st January 2009. No specific format for submissions is provided, however a letter
        or email outlining your submission is requested please.

Submissions can be sent to:
Department of Labour
Workplace Services
PO Box 105 146
Auckland
New Zealand
Attention: Philippa Gibson

Or emailed to:
philippa.gibson@dol.govt.nz



Department of Labour Methyl Bromide WES Consideration Paper April 2010   Page 27 of 33
Table 1: Proposed changes to WES


          Substance                                          Current WES                                   Proposed change

                                                                                                         0.5 ppm (8 hour TWA)
           Benzene                                      5 ppm (8 hour TWA)
                                                                                                            2.5 ppm (STEL)

                                               Suspension level of ≥ 3.2 µmol/L,                           BEI of 1.5 µmol/L
              Lead
                                         or 3 consecutive monthly estimations of ≥                   Suspension level of 2.4 µmol/L
     (in whole blood)
                                                                2.6 µmol/L                        Return to work level of 1.93 µmol/L

                                                                                                         0.3 ppm (8 hour TWA)
       Formaldehyde                                         1 ppm (Ceiling)
                                                                                                            0.6 ppm (STEL)

      Methyl bromide                                     5 ppm (8 hour TWA)                               1 ppm (8 hour TWA)

                                                 0.2 mg/m3 for respirable quartz                    0.1 mg/m3 for respirable quartz
     Crystalline silica
                                             0.1 mg/m3 for respirable cristobalite                0.1 mg/m3 for respirable cristobalite

    Synthetic vitreous
                                                         1 respirable fibre/mL           0.2 respirable fibre/mL (for refractory ceramic fibres)
  fibres (currently listed                                        3
                                                      5 mg/m inspirable dust         1 respirable fibre/mL (for special purpose glass (micro) fibres)
 under synthetic mineral
                                                             (8 hour TWA’s)                      1 respirable fibre/mL (all other SVF’s)
              fibres)

                                             1 mg/m3 for certain hard wood dusts                     1 mg/m3 for hard wood dusts
          Wood dust
                                                   5 mg/m3 for soft wood dusts                        1 mg/m3 for soft wood dusts




Department of Labour – Methyl Bromide WES consideration paper April 2010                                                                    page 25 of 30
19th December 2008

xx

Att:

Dear X,

          NOTICE OF INTENDED CHANGES TO WORKPLACE EXPOSURE STANDARDS

                                           Change of date for submissions

Due to overwhelming interest, the closing date for submissions on proposed changes to the
New Zealand Workplace Exposure Standards (WES) has been changed to 31st March 2009.
The proposed changes are listed in Table 1 overleaf.

     PLEASE NOTE:

     1. The purpose of the consultation process is to provide interested parties with the
        opportunity to provide evidence to further assist in the decision making process
        surrounding a particular WES level.

     2. These WES have been revised in order to bring them more into line with current
        international best practice. As New Zealand does not have prevalent epidemiological
        studies of the working population, New Zealand’s standards reflect international
        experience. The standards chosen for review are currently inconsistent with
        international comparators and require moderation.

     3. In the absence of opposing evidence the department has no option but to accept
        international best practice as the standard for New Zealand.

     4. Some WES set by the Department of Labour are now enforceable controls under HSNO
        legislation via the Hazardous Substances (Chemicals) Transfer Notice 2006. Therefore,
        all places of work that use approved hazardous substances must also comply with the
        HSNO Act as well as the HSE Act. The department enforces both laws and their
        associated regulations in the place of work.

     5. We welcome any input you may have that would inform the decision making process.



          Send submissions to:                                             or email:
          Department of Labour                                             philippa.gibson@dol.govt.nz
          Workplace Services
          PO Box 105 146
          Auckland
          New Zealand
          Attention: Philippa Gibson




Department of Labour – Methyl Bromide WES consideration paper April 2010                                 page 26 of 30
Table 1: Proposed changes to WES


          Substance                                          Current WES                                   Proposed change

                                                                                                         0.5 ppm (8 hour TWA)
           Benzene                                      5 ppm (8 hour TWA)
                                                                                                            2.5 ppm (STEL)

                                               Suspension level of ≥ 3.2 µmol/L,                           BEI of 1.5 µmol/L
              Lead
                                         or 3 consecutive monthly estimations of ≥                   Suspension level of 2.4 µmol/L
     (in whole blood)
                                                                2.6 µmol/L                        Return to work level of 1.93 µmol/L

                                                                                                         0.3 ppm (8 hour TWA)
       Formaldehyde                                         1 ppm (Ceiling)
                                                                                                            0.6 ppm (STEL)

      Methyl bromide                                     5 ppm (8 hour TWA)                               1 ppm (8 hour TWA)

                                                 0.2 mg/m3 for respirable quartz                    0.1 mg/m3 for respirable quartz
     Crystalline silica
                                             0.1 mg/m3 for respirable cristobalite                0.1 mg/m3 for respirable cristobalite

    Synthetic vitreous
                                                         1 respirable fibre/mL           0.2 respirable fibre/mL (for refractory ceramic fibres)
  fibres (currently listed                                        3
                                                      5 mg/m inspirable dust         1 respirable fibre/mL (for special purpose glass (micro) fibres)
 under synthetic mineral
                                                             (8 hour TWA’s)                      1 respirable fibre/mL (all other SVF’s)
              fibres)

                                             1 mg/m3 for certain hard wood dusts                     1 mg/m3 for hard wood dusts
          Wood dust
                                                   5 mg/m3 for soft wood dusts                        1 mg/m3 for soft wood dusts




Department of Labour – Methyl Bromide WES consideration paper April 2010                                                                    page 27 of 30
  5th August 2009

  x

  x



  Att: x

  Dear x,

  Consultation meeting - proposed changes to Workplace Exposure
  Standards for Methyl Bromide

  Prior to the publication of the third edition of the New Zealand Workplace
  Exposure Standards (WES), stakeholder consultation was sought in regard to
  proposed changes for some substances. Some of the WES are in need of revision
  in order to bring them more into line with current international best practice,
  notably, USA and the United Kingdom. As New Zealand does not have prevalent
  epidemiological studies of the working population, New Zealand’s standards
  reflect international experience. The standards chosen for review are currently
  inconsistent with international comparators and require moderation.

  The proposed change to the Methyl Bromide standard is given below.



  Substance                    Current WES                      Proposed change
Methyl bromide             5 ppm (8 hour TWA)                  1 ppm (8 hour TWA)

  The technical committee has reviewed the feedback received so far for the Methyl
  Bromide Workplace Exposure Standard (WES), and is of the opinion further
  consultation is required.

  This letter is to invite you as an interested party to attend a meeting on Friday
  23rd October 2009 in Wellington to discuss submissions received on the proposed
  changes to the Workplace Exposure Standard for methyl bromide and to produce
  an agreed timetable for the drafting of this exposure standard. The Department of
  Labour’s perspectives on the proposed changes will also be discussed.

  The meeting is to be held in the Sonja Davies Room, Level 3 Greenock House, 39
  The Terrace, Wellington from 10am to 1pm. Please note that due to constraints of
  available venues we are only able to welcome one representative from each
  organization.

  Yours sincerely



  Richard Steel
  Manager Technical Services




                 26
APPENDIX B - POSITION PAPER: PROPOSAL TO REDUCE
WES-TWA FOR METHYL BROMIDE FROM 5PPM TO 1PPM

The Department of Labour Workplace Exposure Standards
The Department of Labour is the primary agency responsible for setting
Workplace Exposure Standards (WES) as part of the administration of the Health
and Safety in Employment Act (HSE), 1992.

WES relate to worker exposure to airborne substances in workplaces.

WES are health-based values. In assigning the WES value, defining a level that
will achieve freedom from adverse health effects is the major consideration.
Employee exposure to hazardous substances should be controlled to a level as far
below the relevant WES as practicable by applying the hierarchy of control
required by the HSE Act. Section 10(2)(c) of the Act requires that where
significant hazards are minimised, the employer must monitor the employees
exposure to the hazard. WES can be used by those involved in occupational
health practice as guidelines for evaluating exposure to airborne hazards.
Compliance with the designated value does not, however, guarantee protection
from discomfort or possible ill-health outcomes for all workers.

As New Zealand does not have prevalent epidemiological studies of the working
population, New Zealand’s standards reflect international experience. The methyl
bromide WES was chosen for review as it is inconsistent with some international
workplace exposure guidelines.

Setting WES
Animal studies of the health effects from chronic inhalation of methyl bromide gas
suggest that the (maximum) no-observed-adverse-effect-level (NOAEL) for at
least one species may be less than the current WES-TWA level of 5ppm. In a
study in rats, a concentration of 3ppm was the lowest-observed-adverse-effect-
level (LOAEL), but the NOAEL was not identified, as no concentration lower than
3ppm was tested. However in such situations it is conventional to regard the
NOAEL as likely being around three-fold lower than the observed LOAEL.
Accordingly, one agency (ACGIH) have established a WES-TWA of 1ppm, and this
level is also being considered in New Zealand.

It can be noted that this level is not derived directly from data on the human
experience, but rather that the animal data cannot reasonably exclude the
possibility of adverse human effects at these levels. The level does not represent
an extremely conservative interpretation of the animal data, as it does not
incorporate additional uncertainty or safety factors, such as to allow for the
possibility of greater susceptibility of humans than the test species to the
observed adverse effect.




                                                                                 27
ERMA reassessment of methyl bromide
In July 2008, the Environmental Risk Management Authority (ERMA) decided
there were grounds for the reassessment of fumigant methyl bromide. The
reassessment process and final decision are expected to be completed mid-late
2010.

The outcome of the Department of Labour review of the methyl bromide WES
should be viewed as an input into the ERMA reassessment process.

Respiratory protection and WES
When minimising airborne exposure by using respiratory protection, the type of
respirator used must be selected on the basis of the airborne concentration and
the protection factor of the respirator. If the airborne concentration (outside the
mask) is 10ppm and the protection factor of the respirator is 10, then the
concentration of the substance inside the mask could be up to 1ppm. The WES
apply to the concentration of the substance that the worker is inhaling therefore
knowledge of airborne concentration as well as respirator protection factor is vital
in determining the level of protection required.




                                                                                  28
FOR MORE INFORMATION ON HEALTH AND SAFETY
VISIT WWW.DOL.GOVT.NZ




                                            PLa 11199 noV 09

								
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