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| Reduction |
| | A change in a chemical characterized by the gain of electrons. |
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| Reference Dose (RfD) |
| | The EPA estimate of a lifetime daily exposure level for humans that is likely to be without risk of harmful effects. RfD's are acceptable safety levels for chronic non-carcinogenic and developmental effects. The process used to derive an RfD is a modification of that used to derive an ADI. |
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| Relative Risk (RR) |
| | A statistical calculation of the ratio of disease in an exposed population to that of an unexposed population. |
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| Reproductive Toxicity |
| | Toxicity of the male or female reproductive system. Toxic effects may include damage to the reproductive organs or offspring. |
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| Respiratory Toxicity |
| | Toxicity of the upper (nose, pharynx, larynx, and trachea) or lower (bronchi, bronchioles, and lung alveoli) respiratory system. |
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| Retrospective Cohort Study |
| | An
epidemiology study in which cohorts are identified according to past exposure conditions and follow-up proceeds forward in time |
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| RfD |
| | see Reference Dose |
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| Risk |
| | The probability that a hazard or effect will occur at a specific level of exposure. |
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| Risk Assessment |
| | The process by which the probability that an adverse effect will occur at a defined exposure level is determined. |
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| Risk Characterization |
| | The final stage in the risk assessment process which involves the prediction of the frequency and severity of effects in exposed populations. |
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| Risk Management |
| | The process of weighing policy alternatives and selecting the most appropriate regulatory action based on the results of risk assessment and social, economic, and political concerns. |
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