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whether the risk under consideration is one related to developmental toxicity, reproductive toxicity, or another type of toxicity (e.g., pulmonary, neurological, renal).

The toxicity produced by a particular exposure depends on a variety of factors, including the following:

  • The chemical and toxicological nature of the agent itself.

  • The agent's physical properties (e.g., solubility, volatility).

  • The conditions of exposure (e.g., dose, duration, frequency, timing, route).

  • The use of safety measures that reduce actual exposure (e.g., gloves, masks, and ventilation).

  • The agent's pharmacokinetics of absorption, metabolism, distribution, and excretion, all of which are subject to individual variability.

  • The pharmacodynamics (target organ, site of action, receptor interactions) that determine the agent's mechanism of action.

  • Concomitant exposures to other chemical or physical agents that affect the factors listed above or the agent's toxic activity.

  • Biological characteristics of the exposed individual (e.g., pregnancy, age, nutritional status, genetic susceptibility).

The only way to eliminate completely the possibility of toxic effects associated with exposure to an agent is to eliminate all exposures. When use of the agent is necessary, minimizing the exposure will minimize risk.

The guidelines below are for exposures that have not been adequately characterized with respect to reproductive and developmental toxicity, but for which there may be other data on toxicity, as listed above.

  • Use expert judgment to evaluate the available toxicity data.

  • Assume that susceptibility to reproductive or developmental toxicity may be greater than susceptibility to any known toxicity of the agent, and apply additional uncertainty factors to reflect the lack of data.

  • Substitute exposure to an agent that is known not to be associated with substantial risk for causing reproductive and developmental toxicity for an agent associated with unknown risk.

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