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Arsenic in seaweed—Forms_ concentration and dietary exposure

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Seaweed rich in vitamin A, vitamin B1 and vitamin B2, is more important is its ability to help the body rid their bodies of waste and excess water.

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									      Arsenic in seaweed—Forms, concentration and dietary exposure
                        a,*
   Martin Rose                , John Lewis a, Nicola Langford a, Malcolm Baxter a, Simona Origgi b,
                                Matthew Barber b, Helen MacBain b, Kara Thomas b
                                     a
                                         Defra Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK
                                          b
                                            Food Standards Agency, 125 Kingsway, London WC2 6NH, UK




Abstract

    This study has measured the content of total and inorganic forms of arsenic in seaweed available on retail sale for consumption, to
provide data for dietary exposure estimates and to support advice to consumers. A total of 31 samples covering five varieties of seaweed
were collected from various retail outlets across London and the internet. All of the samples were purchased as dried product. For four of
the five varieties, soaking was advised prior to consumption. The recommended method of preparation for each individual sample was
followed, and total and inorganic arsenic were analysed both before and after preparation. The arsenic remaining in the water used for
soaking was also measured. Arsenic was detected in all samples with total arsenic at concentrations ranging from 18 to 124 mg/kg. Inor-
ganic arsenic, which can cause liver cancer, was only found in the nine samples of hijiki seaweed that were analysed, at concentrations in
the range 67–96 mg/kg. Other types of seaweed were all found to contain less than 0.3 mg/kg inorganic arsenic, which was the limit of
detection for the method used.
    Since consumption of hijiki seaweed could significantly increase dietary exposure to inorganic arsenic, the UK Food Standards
Agency (FSA) issued advice to consumers to avoid eating it.
Crown Copyright

Keywords: Arsenic; Seaweed; Hijiki; Dietary intake; Consumer exposure




1. Introduction                                                           trial food chain and these higher levels result in the poten-
                                                                          tial for elevated dietary exposure through diets rich in fish
   Arsenic is an environmental contaminant and can arise                  and other food harvested or farmed at sea. Consumption
from natural sources such as rocks and sediments and also                 of fish and seafood is known to have beneficial health
as a result of anthropogenic activities such as coal burning,             effects and it is recommended that the general population
copper smelting and the processing of mineral ores. Levels                in some countries, especially where fish consumption is
of arsenic are higher in the aquatic environment than in                  lower than average, should increase the amount of fish
most areas of land as it is fairly water-soluble and may                  (especially fish rich in oils) in the diet (Food Standards
be washed out of arsenic-bearing rocks. In particular, sea-               Agency, 2006; COT, 2004a). Arsenic exists in different
weed is known to contain high concentrations of arsenic in                chemical forms, or ‘species’. These are either as ‘free’ inor-
comparison to terrestrial plants owing to the ability of mar-             ganic arsenic species such as As(III) or As(V), or as arsenic
ine plants to concentrate the arsenic they derive from sea                present in organic molecules such as arsenobetaine and
water (Norman et al., 1987). Higher levels of arsenic are                 arseno-sugars (Francesconi and Kuehnelt, 2004). Inorganic
thus expected in the aquatic food chain than in the terres-               arsenic has no known beneficial effect, and long-term expo-
                                                                          sure may be harmful to health. Arsenic is genotoxic and is a
                                                                          known human carcinogen associated especially with liver,
                                                                          bladder, lung and skin cancer. As(III) is generally recogni-
                                                                          sed as being more toxic than As(V). Human exposure to
inorganic arsenic compounds should thus be kept as low as         the Environment (COT) noted the evidence produced since
reasonably practicable (COT, 2003).                               the JECFA evaluation and the IARC opinion and con-
   The 1997 UK Total Diet Study showed a concentration of         cluded that dietary exposure to inorganic arsenic should
4.4 mg/kg of total arsenic in the fish group, which accounts       be as low as reasonably practicable (ALARP). JECFA
for 94% of the average population exposure to arsenic (Ysart      are scheduled to review the PTWI for arsenic.
et al., 2000). Most of this arsenic was present in the less          The aim of this study was to assess dietary exposure of
toxic organic forms such as arsenobetaine, with inorganic         inorganic and organic forms of arsenic arising due to the
arsenic only accounting for ca. 1–3% of the total arsenic.        consumption of seaweed in order to form the basis of
Seaweed was not included in these total diet samples.             advice to consumers.
   The reason that the fraction of inorganic arsenic is so
low in fish is because most aquatic organisms have the             2. Materials and methods
ability to metabolise the toxic inorganic forms of arsenic
to the less toxic forms, such as dimethylarsinate (DMA)           2.1. Samples
and arsenobetaine. Certain seaweeds do not use this meta-
                                                                      A total of 31 samples comprising five different varieties of seaweed on
bolic conversion process, and deposit the arsenic in a range      retail sale within the UK were collected from London and the surrounding
of chemical forms, including significant proportions as the        area between October and December 2003. Samples were collected at
toxic inorganic forms, As(III) and As(V). There are several       random from a variety of retail outlets ranging from specialist retailers to
suggestions for the reasons for this, including (i) lack of the   major supermarket chains, according to availability. It was ensured that
genetic capability, (ii) it is energetically too expensive to     all major imported varieties were included in the sampling exercise.
                                                                  Because all of the purchased samples were imported, there is no reason to
perform the metabolic transformation, and (iii) the stores        believe that there would be any regional variation in quality within the
of inorganic arsenic within the cellular structure act as a       UK. The instructions for preparation and cooking were translated from
form of protection against predation (Castlehouse et al.,         the product package labels. All samples were analysed for total arsenic
2003; Devalla and Feldmann, 2003).                                and inorganic arsenic as sold. Where package instructions directed further
   Seaweed is rich in some nutrients such as iodine (Lin          preparation prior to consumption, the directions were followed. This
                                                                  applied for 24 of the samples (four out of the five different varieties) and
et al., 2003) and Eastern varieties are increasingly consumed     for these products the samples were analysed after preparation as well as
in Western countries including the United Kingdom as              the water that was used for soaking the product (see below).
oriental dishes become more popular. Following a report
that the Canadian Food Inspection Agency was advising             2.2. Sub-sampling and preparation of samples
consumers to avoid the consumption of hijiki seaweed
owing to its high inorganic arsenic content (CFIA, 2001),             Nori was the only seaweed type purchased as ready-to-eat. The other
the UK Food Standards Agency (FSA) conducted a survey             types required either soaking in cold or boiling water prior to consump-
                                                                  tion. In order to assess the impact of cooking/preparation on the levels of
of seaweed available on the UK market with the Central
                                                                  total and inorganic arsenic in the seaweed, these samples were analysed
Science Laboratory (CSL) performing the analyses.                 both ‘as bought’ (without preparation) and ‘as consumed’ (following
   There are no Europe-wide regulations for arsenic in            preparation). The water remaining after preparation was also analysed,
food. In the UK, the Arsenic in Food Regulations (SI              because it was claimed by some producers that the preparation steps
1959 no. 831), as amended, lay down a general limit of            significantly reduced the levels of inorganic arsenic in their products due to
                                                                  the greater water solubility. All stages of sample preparation were there-
1 mg/kg for total arsenic in food. However, this limit does
                                                                  fore performed gravimetrically, allowing a mass balance calculation to be
not apply to fish and edible seaweed where it is naturally         performed.
present. There is a lack of standard validated methods                Homogenisation of the ‘as-bought’ samples was carried out using
for the determination of arsenic species. There are no fully      sharp stainless steel knives, on plastic chopping boards. For the kelp-like
characterised certified reference materials (CRMs) for             seaweeds, which are sold as dry sheets of material, the samples were split
                                                                  vertically to give two equivalent halves. One half was homogenised, ready
arsenic species, although there are some materials which
                                                                  for analysis ‘as-bought’. The other half was prepared, homogenised using
are partially characterised e.g., DORM 2 dogfish muscle            a Buchi Mixer B-400 and taken for immediate analysis. A representative
                                                                      ¨
with a value for total As of 18 mg/kg dry weight and arsen-       sub-sample of the water remaining after preparation of each seaweed was
obetaine at 16.4 mg/kg and BCR 627 tuna fish with an               transferred to an acid-washed Nunc vial and stored at 4 °C until required
arsenobetaine content of 52 lmol/kg, dimethyl arsinic acid        for analysis.
                                                                      For those samples of seaweed supplied in other forms (typically
(DMAA) at 2 lmol/kg and total As at 4.8 mg/kg (NRCC,
                                                                  resembling grass), every effort was made to mix the individual strands so
1993; EC BCR, 1997).                                              as produce a representative sub-sample of each packet. When sub-sam-
   In 1989, JECFA established a provisional tolerable             pling these varieties, the samples were cut horizontally so as to give a
weekly intake (PTWI) for arsenic of 15 lg/kg bodyweight.          representative sub-sample of the many individual plants making up each
In 2002, the International Agency for Cancer Research             sample.
(IARC) concluded that arsenic in drinking water (primarily
inorganic arsenic as arsenate and to a lesser extent arsenite)    2.3. Analytical method (i) total arsenic
was carcinogenic to humans on the basis of sufficient evi-
                                                                     Samples (0.5 g dry weight or equivalent wet weight, typically 4 g) were
dence for an increased risk for cancer of the urinary blad-       quantitatively digested in quartz high pressure closed vessels using con-
der, lung and skin. In May 2003, the UK Committee on              centrated nitric acid (5 ml) and a microwave-assisted digestion system
Toxicity of Chemicals in Food, Consumer Products and              (Multiwave, Perkin–Elmer Ltd, Beaconsfield, Buckinghamshire, UK). The
digest liquor was quantitatively transferred to a graduated test tube and       to calculate that, even using the upper bound value of
made up to volume (10 ml) with water. An aliquot (1 ml) of the resulting        0.3 mg/kg inorganic arsenic, the percentage of the speci-
solution was quantitatively transferred to a test tube, and an aliquot (4 ml)
of diluent (an aqueous solution containing rhodium, as internal standard)
                                                                                ated form could not have been greater than 2%. Levels that
was added. Total arsenic was measured using inductively coupled plasma-         were not detected were at the limit of detection. This was
mass spectrometry (ICP-MS). The method used was that published pre-             indicated in the table as <2 and agrees with other values
viously (Ysart et al., 2000).                                                   reported, i.e., about 3% (Devalla and Feldmann, 2003).
                                                                                   For those seaweeds where the levels of inorganic arsenic
2.4. Analytical method (ii) inorganic arsenic                                   are above the LOD, i.e., the hijiki samples, values for the
                                                                                percentage of inorganic arsenic have been calculated and
    The non-chromatographic methodology used was based on that
developed by Munoz et al. (2000). Following dissolution of samples in           are quoted in Table 1.
concentrated hydrochloric acid, and conversion of inorganic arsenic into           In hijiki, the mean percentage of inorganic arsenic is
As(III), the As(III) was converted into a covalent halide and extracted into    highest in seaweed as sold (73%), less in prepared seaweed
chloroform. The arsenic was back extracted into dilute hydrochloric acid        (67%) and is further reduced when it is soaked (55%). In
and was measured using ICP-MS operating at a resolution of 10 000. The
                                                                                the other two varieties of seaweed the percentage of inor-
back extraction step also extracts the toxic mono-methylated forms of
arsenic (MMA) but the procedure will not extract the relatively non-toxic       ganic arsenic was higher in the prepared seaweed than in
compounds such as arsenobetaine and arseno-sugars.                              the seaweed as sold.
                                                                                   All of the hijiki samples, both before and after pre-
2.5. Analytical quality assurance                                               paration, had significantly high levels of inorganic arsenic
                                                                                (68–73% and 61–73%, respectively). These data seem to
    CRMs for total arsenic, reagent blanks and reagent blanks spiked with       contradict the claims made by some producers, that the
a known amount of analyte (for recovery purposes) were analysed                 preparation steps can significantly reduce the fraction of
alongside samples. The method used for total arsenic is accredited to the
ISO 17025 (UKAS) standard and the method for inorganic arsenic was
                                                                                water soluble inorganic arsenic. This variety of seaweed
carried out with similar rigorous quality control criteria i.e., in an envi-    also had significantly higher levels of total arsenic than
ronment with controlled record keeping and using in-house reference             the four other varieties tested.
materials where CRMs were not available. Proficiency testing exercises              The levels of both total and inorganic arsenic were mea-
carried out around the time of this study for arsenic in food, gave satis-      sured in the preparation water and were also found to be
factory results for both total and inorganic arsenic. There are no CRMs
for inorganic arsenic. QC was monitored by recovery from fortified tissue.
                                                                                higher in the samples from hijiki than from any of the other
    The criteria used for the survey were those routinely applied in the        varieties.
laboratory and were always met:
                                                                                4. Risk assessment
 • Results for duplicate analysis were acceptable if the relative standard
   deviation was less than 25%, or if the difference was no more than               In order to conduct an effective risk assessment and
   two times the limit of detection, whichever was greater.                     establish a safe level of seaweed consumption, it is neces-
 • Procedural blanks and fortified procedural blanks analysed to estimate
   recovery were accepted if recovery was 80–120%.
                                                                                sary to know the typical seaweed portion size. No compre-
 • Analysis of the CRM gave results within the certified range, or within        hensive data are available for seaweed consumption in the
   25% of the quoted value, whichever was greater.                              UK: seaweed is not a regular part of the UK diet and con-
                                                                                sumption patterns have not been captured during routine
                                                                                dietary surveys (Henderson et al., 2002). The packaging
3. Results and discussion                                                       labels on the samples purchased did not state a recom-
                                                                                mended quantity of seaweed consumption per person, but
   Results for the survey are shown in Table 1.                                 in some instances did include recipe suggestions. In order
   All data are corrected for reagent blank and spike recov-                    to calculate an average portion size for each of the five dif-
ery. The limit of detection (LOD) was calculated as three                       ferent types of seaweed tested in this study, a range of rec-
times the standard deviation of reagent blank values                            ipes were obtained and an average amount of each type of
adjusted for dilution and sample weight. Table 1 presents                       seaweed used calculated (see Table 2).
both the totals and the inorganic arsenic data obtained for                        Hijiki seaweed was the only type of seaweed for which
the seaweed samples ‘as sold’ and ‘after preparation’, and                      levels of inorganic arsenic were above the LOD. Consump-
also the water remaining after preparation of the samples.                      tion of the maximum suggested amount of hijiki seaweed
   Where possible, the percentage of inorganic arsenic was                      (25 g) with the maximum concentration of inorganic
calculated for all three sample types, i.e., ‘as sold’, ‘pre-                   arsenic (22.7 mg/kg) would lead to an inorganic arsenic
pared’ and ‘water’. As nori seaweed is eaten without further                    intake of 0.57 mg. Results from the survey of total and
preparation, there were no ‘water’ data to accompany the                        inorganic arsenic in the 1999 Total Diet Study (FSA,
seven samples of this species.                                                  2004a) showed upper-bound daily intakes ranged from
   Where calculation of the inorganic arsenic used results                      0.1 lg/kg bw for a normal-consuming adult to 0.3 lg/kg
below the LOD for the method, this was represented in                           bw for a high consuming toddler (1.5–4.5 years). The addi-
the table by ‘–’ (not measured). For those samples where                        tional exposure from a 25 g portion of hijiki seaweed would
the levels of total arsenic were very high, it was possible                     represent a 30–50-fold increase in these arsenic intakes. In
Table 1
Total and inorganic arsenic in seaweeds
Total arsenic – as     Seaweed (as sold)                                                        Prepared seaweed                                                    Soaking water
sold (mg/kg)
                       Inorganic arsenic – as    Percentage            Total arsenic (mg/kg)    Inorganic arsenic           Percentage            Total arsenic     Inorganic arsenic   Percentage
                       sold (mg/kg)              inorganic arsenic     (wet weight)             (mg/kg) (wet weight)        inorganic arsenic     (mg/kg)           (mg/kg)             inorganic arsenic
Hijiki
107                     73                       69%                   19                       13                          71%                   14.0                  7.8             55%
112                     80                       72%                   7.9                      5.1                         64%                    1.5                  0.9             60%
116                     83                       71%                   12                       7.9                         69%                    4.6                  2.9             64%
100                     69                       69%                   16                       10                          66%                    3.4                  2.1             64%
95                      67                       71%                   14                       8.3                         60%                    3.5                  2.3             64%
110                     81                       73%                   11                       7.9                         70%                    6.0                  3.6             59%
112                     76                       68%                   31                       23                          73%                    3.0                  0.4             15%
102                     72                       71%                   8.9                      5.5                         61%                    4.7                  4.0             86%
124                     96                       72%                   26                       19                          71%                    8.2              –
Mean: 109               77                       71%                   16                       11                          67%                    5.4                  3               55%
Arame
32                     <0.3                      <0.9%                 2.6                      <0.3                        <11%                   1.0              <0.01
31                     <0.3                      <1.0%                 2.7                      <0.3                        <11%                   1.1              –
28                     <0.3                      <1.1%                 3.4                      <0.3                        <8.8%                  –                –
Mean: 30                                                               2.9                                                                         1.1
Wakame
35                     <0.3                      <0.9%                 5.2                      <0.3                        <5.8%                  0.2              <0.01
42                     <0.3                      <0.7%                 6.1                      <0.3                        <4.9%                  –                –
34                     <0.3                      <0.9%                 4.6                      <0.3                        <6.5%                  0.1              <0.01
29                     <0.3                      <1.0%                 2.6                      <0.3                        <12%                   0.09             <0.00
36                     <0.3                      <0.8%                 3.4                      <0.3                        <8.9%                  1.3              <0.01
Mean: 35                                                               4.4                                                                         0.4
Kombu
51                     <0.3                      <0.6%                 2.3                      <0.3                        <13%                   0.28             <0.01
32                     <0.3                      <0.9%                 0.9                      <0.3                        <34%                   0.08             <0.01
69                     <0.3                      <0.4%                 6.5                      <0.3                        <4.6%                  –                –
75                     <0.3                      <0.4%                 5.2                      <0.3                        <5.7%                  0.64             <0.01
75                     <0.3                      <0.4%                 5.8                      <0.3                        <5%                    0.69             <0.01
19                     [0.3]                     [1.6%]                1.4                      <0.3                        <21%                   0.07             <0.01
28                     <0.3                      <1.1%                 2.3                      <0.3                        <13%                   0.05             <0.01
Mean: 50                                                               3.5                                                                         0.3
Nori
23                     <0.3                      <1.3%
22                     <0.3                      <1.4%
18                     <0.3                      <1.6%
26                     <0.3                      <1.1%
32                     <0.3                      <0.9%                 LOD for total arsenic = 0.02 mg/kg for solids and 0.003 mg/kg for water
18                     <0.3                      <1.6%                 LOD for inorganic arsenic = 0.3 mg/kg for solids and 0.01 mg/kg for water
29                     <0.3                      <1.0%
Mean: 24
Square brackets indicate concentration above the limit of detection but below the limit of quantification and these values may therefore have greater uncertainty.
– Indicates not measured.
Table 2                                                                    Castlehouse, H., Smith, C., Raab, A., Meharg, A.A., Feldmann, J., 2003.
Estimated average portion sizes for different seaweed varietiesa               Biotransformation of arsenic in soil amended with seaweed. Environ.
                                                                              Sci. Technol. 37, 951–957.
Type       Amount      No. of     Quantity          Average portion size
                       servings   per portion (g)   per person (g)         Committee on Toxicity of Chemicals in Food, Consumer Products and the
                                                                              Environment (COT), 2003. Statement on arsenic in food: results of the
Arame      1 cup       4          12.5              14                        1999 total diet survey, <http://www.food.gov.uk/multimedia/pdfs/
           0.34 cup    4          4.25                                        ArsenicStatement.PDF>.
           0.5 cup     1          25                                       Committee On Toxicity Of Chemicals In Food, Consumer Products And
Hijiki     1.5   oz    5          8.4               18                        The Environment (COT), 2004a. Advice on fish consumption: benefits
           0.5   cup   2          12.5                                        & risks. The Stationary Office, Norwich. ISBN 0 11 243083 X.
           0.5   cup   1          25                                          Available       from:      <http://www.food.gov.uk/multimedia/pdfs/
           1.4   oz    2          19.6                                        fishreport2004full.pdf>.
           0.5   cup   1          25                                       Committee On Toxicity Of Chemicals In Food, Consumer Products And
                                                                              The Environment (COT), 2004b. Tox/2004/35. Urgent COT Opinion
Kombu      2 strips    2          n/a                7                        On Arsenic In Seaweed, <http://www.food.gov.uk/multimedia/pdfs/
           1 oz        4          7                                           TOx-2004-35.PDF>.
Nori       2.8 g       1          2.8                3                     Devalla, S., Feldmann, J., 2003. Determination of lipid-soluble arsenic
                                                                              species in seaweed-eating sheep from Orkney. Appl. Organmet. Chem.
Wakame     30 g        2          15                10                        17, 906–912.
           28.3 g      6          4.7                                      European Commission. Community Bureau of Reference (EC BCR),
 a
   Sourced from various internet recipes and instructions on seaweed          1997. Certified Reference Material BCR 627, <http://www.irmm.jrc.
packaging.                                                                    be/html/reference_materials_catalogue/catalogue/certificates_and_
                                                                              reports/BCR-627_cert.pdf>.
                                                                           Food Standards Agency (FSA), 2004a. Food Survey Information Sheet 51/
other words, the amount of inorganic arsenic in a single                      04. Total and Inorganic arsenic in the 1999 total diet study. <http://
                                                                              www.food.gov.uk/science/surveillance/fsis2004branch/fsis5104arsenic>.
portion of hijiki seaweed would be equal to the amount                     Food Standards Agency (FSA), 2004b, Food Survey Information Sheet
of inorganic arsenic to which a consumer would normally                       61/04: Arsenic in seaweed, <http://www.food.gov.uk/science/surveil-
be exposed in their diet over a period of 1–2 months.                         lance/fsis2004branch/fsis6104>.
   In 2003, the UK independent Committee on Toxicity of                    Food Standards Agency (FSA), 2006. Healthy diet: Fish and Shellfish,
Chemicals in Food, Consumer Products and the Environ-                         <http://www.eatwell.gov.uk/healthydiet/nutritionessentials/fishand-
                                                                              shellfish/>.
ment (COT) concluded that it would be more appropriate                     Francesconi, K.A., Kuehnelt, D., 2004. Determination of arsenic species:
not to set a PTWI value because arsenic is a genotoxic                        A critical review of methods and applications, 2000–2003. The Analyst
carcinogen, and instead, that exposure should be ‘as low                      129, 373–395.
as reasonably practicable (ALARP)’. Based on the results                   Henderson, L., Gregory, J., Swan, G., 2002. The National Diet and
from the 1999 UK Total Diet Study (TDS), the high level                       Nutrition Survey: Adults Aged 19 to 64. The Stationary Office,
                                                                              London.
(97.5&) consumer was estimated to be exposed to 0.05–                      Lin, F.-M., Wu, H.-L., Kou, H.-S., Lin, S.-J., 2003. Highly sensitive
0.1 lg/kg bodyweight/day (the range represents lower–                         analysis of iodine anion in seaweed as pentafluorophenoxyethyl
upper bound exposure where lower-bound assumes                                derivative by capillary gas chromatography. Journal of Agricultural
non-detects are at zero concentration and upper-bound                         and Food Chemistry 51 (4), 867–870.
assumes that arsenic is present at the LOD for the method).                Munoz, O., Devesa, V., Suner, M.A., Velez, D., Montoro, R., Urieta, I.,
                                                                              Macho, M.L., Jalon, M., 2000. Total and inorganic arsenic in fresh
Consumption of a 25 g portion of hijiki would therefore                       and processed fish products. Journal of Agricultural and Food
increase intake of inorganic arsenic by around 30 times.                      Chemistry 48 (9), 4369–4376.
The ALARP approach indicated a need for risk manage-                       National Research Council, Canada (NRCC), 1993 DORM 2 dogfish
ment action to reduce this source of exposure and resulted                    muscle Certified reference material for trace metals, <http://inms-
in the COT and Food Standards Agency issuing advice to                        ienm.nrc-cnrc.gc.ca/en/calserv/crm_files_e/DORM-2_certificate.pdf>.
                                                                           Norman, J.A., Pickford, C.J., Sanders, T.W., Waller, M., 1987. Human
consumers not to eat hijiki seaweed (FSA, 2004b; COT,                         intake of arsenic and iodine from seaweed-based food supplements and
2004b).                                                                       health foods available in the UK. Food Additives and Contaminants 5
                                                                              (1), 103–109.
Acknowledgement                                                            SI 1959 no. 831, Arsenic in Food Regulations <http://www.opsi.gov.uk/
                                                                              si/si1992/Uksi_19921971_en_1.htm>.
                                                                           Ysart, G., Miller, P., Croasdale, M., Crews, H., Robb, P., Baxter, M., De
  This work was funded by the UK Food Standards                               L’Argy, C., Harrison, N., 2000. 1997 UK Total diet study – dietary
Agency.                                                                       exposures to aluminium, arsenic, cadmium, chromium, copper, lead,
                                                                              mercury, nickel, selenium, tin and zinc. Food Additives and Contam-
References                                                                    inants 17, 775–786.

Canadian Food Inspection Agency (CFIA), Consumer Advisory (Ottawa,
   October 2, 2001) Inorganic arsenic and hijiki seaweed consumption,
   <http://www.inspection.gc.ca/english/corpaffr/foodfacts/arsenice.pdf>.

								
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