Traditionally, chronic toxicity tests have utilized life-cycle tests or early-life-stage tests. The U.S. Environmental Protection Agency's national “Policy for the Development of Water Quality-Based Permit Limitations for Toxic Pollutants” and the associated “Technical Support Document for Water Quality-Based Toxics Control” emphasized development of less-expensive chronic estimation testing alternatives for National Pollution Discharge Elimination System (NPDES) effluent testing requirements.

Mysid seven-day short-term chronic estimation tests, developed in accordance with EPA water quality-based effluent testing, were conducted with the reference toxicants potassium dichromate (hexavalent chromium) and sodium pentachlorophenate (pentachlorophenol). The seven-day estimated chronic values (MATCs) of the three tests ranged between 0.49 and 0.69 mg/L Cr⁺⁶ for hexavalent chromium and from 298 to 702 μg/L PCP for pentachlorophenol tests. The mean (± SD) MATC values for hexavalent chromium was 0.62 (±0.12) mg/L with a coefficient of variation of 19.4%, while the mean MATC (±SD) for pentachlorophenol was 498 (±202) μg/L with a coefficient of variation of 40.5%.