ABSTRACT
The disciplines of human toxicology and the environmental and occupational (E & O) health sciences are rapidly converging. It is generally perceived that for the E & O health sciences to be on a firm footing, toxicological principles must be adopted. Human toxicologists and epidemiologists perform essentially two types of studies: mortality and morbidity. A threshold is the minimal amount of energy, either physical or chemical, just sufficient to produce an observable effect. Phys-icochemists, pharmacologists, and neuro-physiologists determine at what concentration a given chemical substance appears to produce a physical, chemical, physiological, or behavioral change. Both the stimulus and the effects are intertwined. The concept of dose-response relationship is fundamental in experimental pharmacology, human toxicology, and E & O health sciences. Toxicologists view the dose and response as causally related, whereas epidemiologists tend to be more cautious, speaking of statistical associations between exposure levels and neurological signs and symptoms or the results of electrophysiological and psychometric tests.
