These criteria protect against long term adverse effects on crops and livestock as a result of crop irrigation and livestock watering. A bioassay or toxicity test measures the degree of response of an exposed test organism to a specific chemical or effluent. WET can only be measured using living organisms, not by an instrument. WET consists of acute and chronic toxicity tests. Acute toxicity tests measure the responses of organisms that occur soon after exposure to a test substance.
Chronic tests measure the long-term response to test substances.
WET measures the accumulative effects of chemicals present in an effluent that cannot be assessed using chemical-specific criteria. Biological Criteria Biological criteria are based on aquatic community characteristics that are measured both structurally and functionally. These criteria are used to evaluate the attainment of aquatic life uses. The data collected in these assessments are used to characterize aquatic life impairment and to help diagnose the cause of this impairment. These three indices are based on species richness, trophic composition, diversity, presence of pollution-tolerant individuals or species, abundance of biomass, and the presence of diseased or abnormal organisms.