7.4 Risk assessment methodology for conventional and alternative  (Page 2/17)

The four steps of risk assessment are i) hazard identification ; ii) toxicity (or dose-response) assessment; iii) exposure assessment ; and iv) risk characterization , which are described below in detail. The emphasis is given in documenting the resources necessary to successfully perform each step.

Hazard identification

In the hazard identification step, a scientific weight of evidence analysis is performed to determine whether a particular substance or chemical is or is not causally linked to any particular health effect at environmentally relevant concentrations. Hazard identification is performed to determine whether, and to what degree, toxic effects in one setting will occur in other settings. For example, is a chemical that is shown to cause carcinogenicity    in animal test species (e.g. rat, mouse) likely to be a carcinogen in exposed humans? In order to assess the weight of evidence for adverse health effects, risk analysts follow the following steps ( EPA, 1993 ): (1) Compile and analyze all the available toxicology data on the substance of interest; (2) Weigh the evidence that the substance causes a toxic effect (cancer of non-cancer health end-points); and (3) Assess whether adverse health effect (or toxicity) could occur from human exposure in a real-life setting.

In the first task of hazard identification, risk analyst examines the toxicity literature using the following analytical tools in the order of importance:

• Epidemiological studies
• Controlled human exposure chamber experiments
• In-vivo animal bioassays
• In-vitro cell and tissue culture bioassays
• Quantitative Structure –Activity Relationship Analysis (QSAR)

Among these, in-vivo animal bioassays are, by far, the most utilized source of information for hazard identification for chemicals and, on rare instances, for chemical mixtures (e.g. diesel). When available, well-conducted epidemiological studies are regarded as the most valuable source of human health hazard identification information since they provide direct human evidence for potential health effects. Epidemiology is the study of the occurrence and distribution of a disease or physiological condition in human populations and of the factors that influence this distribution ( Lilienfeld and Lilienfeld, 1980 ). The advantages of epidemiological studies for hazard identification are ( EPA, 1989 ; EPA, 1993 ): animal-to-human extrapolation is not necessary, real exposure conditions, and a wide range of subjects with different genetic and life-style patterns. However, epidemiological studies have a number of shortcomings, which limit their usefulness in hazard identification. Some of these disadvantages include difficulty in recruiting and maintaining a control group; having no control over some of the non-statistical variables related to exposures, lifestyles, co-exposure to other chemicals, etc.; absence of actual exposure measurements along with memory bias for retrospective studies; lengthy latency periods for chronic health effects such as cancer; and poor sensitivity and inability to determine cause-effect relationships conclusively.