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An assessment was performed to asses the aquatic toxicity of the submission substance.

Short-term Toxicity to fish: The objective of the study was to establish of acute toxicity of N-(n-Butyl)thiophosphoric triamide (NBPT) to the bluegill,Lepomis macrochirus, a freshwater fish. This study was conducted according to EnviroSystems Test Protocol 8967-BR (Acute Static Toxicity of Test Substance to the Bluegill (Lepomis macrochirus) and basedon theproceduresof theU.S. Environmental Protection Agency (1986, 1987). The method used basically follows the EPA OPPTS 850.1075 (Freshwater and Saltwater Fish Acute Toxicity Test) which is similar to OECD Guideline 203 (Fish, Acute Toxicity Test).

The acute toxicity of the test material to the freshwater fish bluegill (Lepomis macrochirus) has been investigated and resulted in a 96 hour LC50of 1,140 mg/L NBPT, with a 95 % confidence interval of 905 mg/L - 1,360 mg/L.

Short-term Toxicity to Daphnia: The objective of the study was to establish acute toxicity levels of N-(n-Butyl) thiophosphoric triamide (NBPT) to the daphnid, Daphnia magna, a freshwater invertebrate.The definitive toxicity test was performed according to EnviroSystems Test Protocol 8968-BR (Acute Static Toxicity of Test Substance to the DaphnidDaphnia magna),which is based on procedures of the U.S. Environmental Protection Agency (1986, 1987).

Exposure of daphnids to the test substance resulted in a 48 hour LC50 of 350 mg/L NBPT, with a 95 percent confidence interval of 300 - 410 mg/L, and a 48 hour EC50 (based on immobilization) of 290 mg/L NBPT, with a 95 percent confidence interval of 250 - 400 mg/L. The no observed effect concentration is estimated to be 150 mg/L NBPT.

Toxicity to aquatic algae and cyanobacteria: The acute toxicity of N-(n-Butyl)thiophosphoric triamide (NBPT) to the freshwater alga, Selenastrum capricornutum, is described in this final report. The test was conducted for Enimont Americas, Inc. for 96 hours during March 9 to 13, 1990, at the EnviroSystems Division of Resource Analysts, Inc. in Hampton, New Hampshire. It was conducted by Jeanne Hagazu, Peter Kowalski, Robert Boeri, and Timothy Ward according to the protocol developed for EnviroSystems Study Number 8966-BR.

Exposure of algae to the test substance for 96 hours resulted in a median effective concentration (EC50) of 280 mg/L NBPT, with a 95 percent confidence interval of 200 - 400 mg/L. The 96 hour no observed effect concentration is 75 mg/L.

Toxicity to Microorganisms: A study was performed to assess the effect of the test material on the respiration of activated sewage sludge. The method followed that described in the OECD Guidelines for Testing of Chemicals (1984) No 209 "Activated Sludge, Respiration Inhibition Test", Method C.11 of EEC Commission Directive 88/302/EEC and US EPA Draft Ecological Effects Test Guidelines OPPTS 850.6800.

The effect of the test material on the respiration of activated sewage sludge micro-organisms gave a 3-Hour EC50 of 880 mg/l. The No Observed Effect Concentration (NOEC) after 3 hours exposure was 10 mg/I.