ABSTRACT
The analysis of effects for risk and other predictive assessments has two components: hazard identification and exposure–response analysis. The hazard of an agent is its intrinsic capacity to cause an effect. The clearest hazard is death, particularly acute mortality. The conventional ecological chronic hazards are reduced survival, growth, and reproduction, all of which may contribute to reduced population size or growth. Acute and chronic are important terms in environmental toxicity, but you may find them confusing because they are used ambiguously. In toxicology and assessments, they refer to temporal durations of exposures and associated effects. An acute exposure is brief, as in applications of pesticides, spills of chemicals, failures of wastewater treatment plants, or passage through hydroelectric turbines. Chronic effects are those occurring for a long time either because the causal exposure is chronic or because there is no recovery from an acute exposure. The standard chronic ecotoxicological effects are mortality, fecundity, and growth. For humans, a chronic effect is variously defined as continuing for anywhere from three months to a year or more.
