Precautionary Principle

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Precautionary Principle

• The Role of Risk in Public Health
• December 6-7, 2007
• Holiday Inn Toronto Yorkdale
• Toronto, ON

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Lesbia F. Smith

• Assistant Professor
• Faculty of Medicine
• Department of Public Health Sciences
• University of Toronto

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Precaution basic principles

• Latin praecavere, to guard against prae-, pre-
  cavere, 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

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The exercise of good judgment or common sense in
practical matters

• Can you measure good judgment? Common sense?

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(No Transcript)
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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

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Risk Equations

• Risk hazard probability severity
• Public Health Risk probability severity
  number of people affected
• Benefit/cost lt risk/cost do it

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Measures of Risk

• Vaccine programs (recent HPV vaccine)
• Exclusion criteria for blood donations
• Introduction of new drugs / new treatments

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Lead in Drinking WaterThe numbers

• Allowable Daily intake
• Amount in water
• Childs water intake /lead
• Portion of daily allowance
• Margin of safety
• Precaution margin of safety

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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).

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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.

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Margin of Safety

• Acceptable if one assumes that there is a
  threshold
• Debate as to whether a threshold exists
• If not, then precaution.

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Transforming ?IQ to ?Incidence of Mild Mental
Retardation (I)

• See
• 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.

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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.

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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

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Making Choices

• Risk Assessment as a support
• Risk Management
• Costs
• Context
• Values

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Conclusion

• THE POLICY - Precautionary Principle
• The exercise of good judgment or common sense in
  practical matters ??
• Values
• Context
• Costs
• Risk Assessment as a support

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Thank you.