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Health Risk Science
- Hazard identification

Hazard identification is the determination of a cause-effect relationship between a particular chemical and a decline in health status using epidemiological studies of human populations, animal bioassay data, mutagenicity tests, and examination of molecular structure. Evidence of causation must be evaluated in terms of its nature and amount. Since very few chemicals assessed are definite substances causing particular health effects on which we have human data to confirm this relationship, results from laboratory studies with animals or other test systems are, in general, enough to be considered as evidence that this agent is potentially a health risk for humans. In-vitro test and structural similarity to well-known chemical hazards can also be considered as evidence.

Epidemiological studies of human populations
One method of hazard identification is well-designed epidemiologic studies. A positive result of an association between a substance and a health problem is considered as strong evidence of human health risk. But, this type of study is not easily conducted for reasons such as low risk and number of exposed individuals, long latency periods between first exposure and clinical diagnosis of disease and a multitude of potential confounders and bias. Therefore, results always need to be carefully interpreted and it’s only when several positive studies are available can we be confident a true association between an agent and disease does exist.  

Animal bioassay data
This method provides most of the data available in hazard identification. Results from animal studies are applicable to humans and consistent positive results are a strong indication of adverse health effects in human. Again, since the data is not always sufficient and not necessarily of the same magnitude and direction to confirm health effects, interpretation of animal tests may sometimes be difficult. Although some uncertainties will continue to exist, animal bioassay data will be of importance in identifying health hazard.
Mutagenicity tests
Positive result of a mutagenicity assay indicates that the substance is likely to be carcinogenic. These short-term tests are used to determine if a chemical is potentially carcinogenic and provide additional evidence to animal and epidemiologic studies but are hardly ever enough by itself to conclude a chemical is carcinogenic.

Molecular structure
This method examines the molecular structure including the chemical and physical properties of the agent investigated compared with those of know carcinogens. Comparison of molecular structure of an agent is usually done to find potential carcinogens which will be studies further with animal bioassay and possibly human epidemiological studies.



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