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Precautionary Principle


									Precautionary Principle
 The Role of Risk in Public Health
      December 6-7, 2007
  Holiday Inn Toronto Yorkdale
          Toronto, ON
      Lesbia F. Smith
        Assistant Professor
        Faculty of Medicine
Department of Public Health Sciences
       University of Toronto
   Precaution – basic principles
• Latin praecavēre, to guard against : prae-, pre- +
  cavēre, to beware.] warding off impending
  danger or damage or injury (caveat emptor)
• practicing caution in advance
• judiciousness in avoiding harm or danger
• a safeguard
• forethought or circumspection
• The exercise of good judgment or common
  sense in practical matters
The exercise of good judgment or
   common sense in practical

        Can you measure good
     judgment? Common sense?
        Measures of Risk
Our discipline accepts quantitative
measures of risk to guide our decisions in
public health (“evidence based approach”)

– Cost benefit analysis – how much good at
  what cost (e.g., prevented adverse events)
– Cost risk analysis – how much harm at what
  cost (e.g., compensation)
– Consider severity of prevented event and of
  adverse consequence
        Risk Equations

  Risk = hazard * probability * severity
Public Health Risk = probability * severity *
         number of people affected

    Benefit/cost   <    risk/cost = do it
          Measures of Risk

• Vaccine programs (recent HPV vaccine)
• Exclusion criteria for blood donations
• Introduction of new drugs / new treatments
          Lead in Drinking Water
              The numbers
•   Allowable Daily intake
•   Amount in water
•   Child’s water intake /lead
•   Portion of daily allowance
•   Margin of safety

• Precaution = margin of safety
  Calculation for Implementation
• WHO PTWI lead for children = 25 ug/kg body weight
• ADI = 3.5 ug/kg bw per day
• For 2 year old: 3.5 ug/kg bw x 13.6 kg= 47.6 ug/day total

• The Guidelines on Canadian Drinking Water Quality identify the lead
  intake from all sources (air, water, food, dust and dirt) by a two year
  old child as 29.5 ug/day.

• The Guideline allocated the contribution of water to this daily intake
  as 2.9 ug based on the consumption of 0.6 litres.

• The difference between the WHO ADI and the HC daily intake is
  47.6 – 29.5 = 18.1 ug/day. If this difference is assigned to drinking
  water this allows a total of 21.0 ug/day (18.1+ 2.9 = 21.0) which is
  equivalent to drinking 0.6 L of water with 35 ug/L of lead (and still
  comply with the WHO PTWI).
             Ground Truth
• WHO (2000) PTWI of 25 ug/kg/week for
  lead has an associated blood lead level in
  the range of 1.8 -3.6 ug/dL.

• This is consistent with the blood lead
  concentration range currently observed in
  children living in perceived hot spots.
           Margin of Safety
• Acceptable if one assumes that there is a

• Debate as to whether a threshold exists

• If not, then precaution.
   Transforming ∆IQ to ∆Incidence
    of Mild Mental Retardation (I)
           % Cummulative Distribution


                                         80                                         Reference Population
                                                                                    Exposed Population;
                                         40                                         Mean IQ -5


                                              50   70   90        110   130   150
Gilbert, S. G. and B. Weiss (2006). "A rationale for lowering the blood lead action level from 10 to 2mug/dL."
     Neurotoxicology 27(5): 693-701.
Fewtrell, L. J., A. Pruss-Ustun, et al. (2004). "Estimating the global burden of disease of mild mental retardation and
     cardiovascular diseases from environmental lead exposure." Environ Res 94(2): 120-33.
                             Blood Pb Vs –IQ

Lanphear, B. P., R. Hornung,
et al. (2005). "Low-level
environmental lead exposure and
children's intellectual function: an
international pooled analysis. Environ
Health Perspect 113(7):894-9.
     Precaution without numbers
•   Cost of implementation       ????
•   Cost of adverse events       ????
•   Adverse Events numbers       Statistical
•   Severity of adverse events   Debated
•   Impact                       Population-wide
•   Benefits                     Theoretical

• Precaution                     YES
   Making Choices

Risk Assessment as a support
      Risk Management
  THE POLICY - Precautionary Principle
The exercise of good judgment or common
       sense in practical matters ??
     Risk Assessment as a support
Thank you.

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