Chemical risk assessment: a review.

People are exposed to a staggering assortment of chemicals and foreign substances. Potential health risks accompany these exposures. Intelligent, informed decisions are needed on which risks can and should be reduced, eliminated, or simply ignored. Therefore, a method of determining the attendant human health risks involved in chemical exposure is necessary. This need has resulted in the evolution of the risk assessment process which was developed to aid in identifying, characterizing and quantifying risks. Risk assessment today is an essential component of regulatory decision-making. In the context of chemical exposure, risk assessment is an evaluation of the risk in human exposure to chemicals in the environment. Quantitative risk assessment (QRA) is the use of experimental laboratory data and/or human epidemiological data in a process to derive a quantitative value for the estimate of the probability of harm occurring to exposed human populations. It is a sophisticated process involving an array of techniques that can be used to identify potential risks to human health. There are 4 components involved in the formalized risk assessment process--hazard identification, toxicity assessment, exposure assessment and risk characterization. These 4 steps collectively address each of 6 key areas identified as essential in characterizing a risk situation involving a chemical exposure. The process of risk estimation involves uncertainties because there are always gaps in knowledge or a lack in understanding mechanisms. These crucial gaps in knowledge are filled when extrapolations, models or assumptions are used. The uncertainties inherent in the risk assessment process are the basis of arguments against the use of the process. Many of these sources of uncertainty inherent in the risk assessment process are examined herein. These include, but are not limited to, modeling methods, understanding mechanisms and pharmacodynamics, exposure data, assumptions and extrapolations. Some new techniques and approaches being applied to the risk assessment process are examined. These include improved models for extrapolating data and quantifying risks, improved laboratory techniques for investigating pharmacodynamic and mechanistic pathways and advancements in quality and application of epidemiological data. The actual concept of uncertainty is being examined and attempts are being made to directly address, quantify and manage uncertainty.