1. Uses of Toxicity Tests
Toxicity tests are desirable in water-quality evaluations because chemical and physical tests alone are not sufficient to assess potential effects on aquatic biota.1–3 For example, the effects of chemical interactions and the influence of complex matrices on toxicity cannot be determined from chemical tests alone. Different species of aquatic organisms are not equally susceptible to the same toxic substances, nor are organisms equally susceptible throughout their life cycle. Even previous exposure to toxicants can alter susceptibility. In addition, organisms of the same species can respond differently to the same level of a toxicant from time to time, even when all other variables are held constant.
Toxicity tests are useful for a variety of purposes, which include determining:
• suitability of environmental conditions for aquatic life;
• favorable and unfavorable environmental factors, such as dissolved oxygen (DO), pH, temperature, salinity, or turbidity;
• effect of environmental factors on waste toxicity;
• toxicity of wastes to a test species;
• relative sensitivity of aquatic organisms to an effluent or toxicant;
• amount and type of waste treatment needed to meet water pollution control requirements;
• effectiveness of waste treatment methods;
• permissible effluent discharge rates; and
• compliance with water-quality standards, effluent requirements, and discharge permits.
In such regulatory assessments, use toxicity test data with receiving-water and site-specific discharge data on volumes, dilution rates, and exposure times and concentrations.