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Heath Risk Science - Use of risk assessment for exposure guidelines

Many goods and services on which the public relies either use or produce chemical substances. Under certain conditions, exposure to some of these substances could be harmful to human health.

In order to assess the risks posed to human health by chemical substances, scientists examine the types of health effects that a particular substance may cause and the likelihood and manner in which people could be exposed. Simply identifying a hazard does not imply that there are risks to the population; rather, characterization of risks requires that the relationship between different levels of exposure and the possible occurrence of adverse health effects is understood.

Characterizing exposure also permits understanding of by what routes, and the extent to which, the public is exposed to chemical substances (for example, through air, food, drinking water or household products).

Characterizing both the potential hazards to human health as well as human exposure, also enables identification of potential vulnerable subpopulations (eg., young children or infants) that might be either more highly exposed or more susceptible to the effects of certain chemical substances.

To characterize risk, estimated exposure of the population (or subgroups) is compared to the levels of a substance that may cause harmful effects.  This information is often derived from epidemiological studies of human populations exposed in the past or toxicological studies in experimental animals. Direct comparisons between levels which induce effects and estimated exposure result in Margins of Exposure (MOE). Alternatively, exposure is compared to a Tolerable or Acceptable Daily Intake which is the level to which it is believed that the public may be exposed daily without adverse effect. 

In interpreting Margins of Exposure or developing Tolerable or Acceptable Daily Intakes, potential variations between animals and humans and within the human population (e.g., susceptible populations) are taken into account. For tolerable daily intakes for example, levels which induce adverse effects are divided by uncertainty factors which protect for these differences between animals and humans and within the human population (e.g., for susceptible populations).

Guidelines or standards for chemicals in various media such as drinking water and air and products to which the public is exposed are often developed on the basis of these tolerable or acceptable daily intakes.  Media are then monitored to ensure that levels do not exceed these values and where they do, risk management action taken to reduce levels.

Estimates and margins of exposure and tolerable or acceptable daily intakes are generally based on a thorough review of the scientific literature involving input from highly qualified specialists through a formal process of engagement. Since there are sometimes gaps in knowledge, the relative uncertainty of and degree of confidence in the underlying databases on exposure and effects are characterized to provide information relevant to decision making on additional research and the management of risk.


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