Sex and Hormonal Status

Some chemicals differ in their toxicity between males and females. Both the nature and location of toxic effects could be different in each sex. The critical factor that determines if a chemical might have different toxicity across sexes is a link between the metabolism of the chemical and sex hormones. Males often metabolize chemicals more quickly than females. In most cases, this leads to more resistance in the male because metabolism usually detoxifies a chemical. In those few ceises where metabolism actually increases the toxicity of a chemical (e.g., cancer effects of PAHs), males may be more sensitive to the chemical than females. 

Changes to hormone status other than sex hormones (e.g., hyperthyroidism) could increase sensitivity to a chemical. Too much thyroid activity can interfere with the male sex hormone actions on metabolism of chemicals. As a result, the benefit of faster metabolism is offset by the action of the thyroid. 

Chemicals that affect hormone status are referred to as endocrine disrupters. This recent area of study has revealed new ways of evaluating the toxic potential of chemicals. These types of effects may be the underlying mechanism behind much of the toxicity seen for a wide range of chemicals (e.g., DDT. This concept will be further discussed in chapter 11. 

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