POPs Toolkit Glossary


U.S. EPAUnited States Environmental Protection Agency.
UncertaintyA deficiency in knowledge concerning parameter values and the appropriate extrapolation of the significance of adverse health effects, to a situation involving different species and exposure conditions. Uncertainty can result from lack of knowledge, inherent variability (stochasticity), confounding effects, or imprecise measurements. Also see: Safety Factor.
Uncertainty FactorOne of several factors used in calculating the reference dose from experimental data. UFs are intended to account for (1) the variation in sensitivity among humans; (2) the uncertainty in extrapolating animal data to humans; (3) the uncertainty in extrapolating data obtained in a study that covers less than the full life of the exposed animal or human; and (4) the uncertainty in using LOAEL data rather than NOAEL data.
Unconfined AquiferAn aquifer containing water that is not under pressure; the water level in a well is the same as the water table outside the well.
Upper Detection LimitThe largest concentration that an instrument can reliably detect.
UXOUnexploded Ordinance.
Hatfield Consultants The World Bank funded by the Canadian POPs Trust Fund through the      
Canadian International Development Agency
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