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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 matters 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 threshold • Debate as to whether a threshold exists • If not, then precaution. Transforming ∆IQ to ∆Incidence of Mild Mental Retardation (I) 120 % Cummulative Distribution 100 80 Reference Population 60 Exposed Population; 40 Mean IQ -5 20 0 50 70 90 110 130 150 IQ 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. 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 Costs Context Values Conclusion THE POLICY - Precautionary Principle The exercise of good judgment or common sense in practical matters ?? Values Context Costs Risk Assessment as a support Thank you.