The behavioral toxicology of metals.

Many metals express their toxic actions through behavioral disturbances. Such disturbances most often reflect impairment of central nervous system function, but also may arise from deleterious effects in other systems. Numerous factors influence behavioral toxicity. Uptake into brain obviously is important; the chemical form of the metal (e.g., inorganic versus organic) and route of exposure are key determinants of brain penetration. Species differences in toxicity may arise from differences in kinetics (e.g., blood-brain ratio) and affinity to target brain structures. Developmental stage is still another crucial variable, but the young organism is not necessarily the most susceptible, and nutritional considerations confound the standard paradigms. Furthermore, parametric variations of behavioral functions can no more be ignored than dose-effect functions, a principle exemplified in research on methylmercury. Unwarranted loyalties to traditional psychological tests may be one source of the current dispute about safe levels of lead simply because parametric variations of clearly specified functions are beyond the scope of such instruments.