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Short-term toxicity to fish

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Description of key information

In a 96 -hour static acute toxicity freshwater study of the test substance (free acid of Diflufenzopyr sodium salt)  with rainbow trout (Oncorhynchus mykiss) the LC50 value was 106 mg a.i./L. 
In a marine water key static study, the 96-hour LC50 value for sheepshead minnows exposed to the test substance (free acid of Diflufenzopyr sodium salt) was > 138 mg a.i./L, the highest concentration tested.

Key value for chemical safety assessment

LC50 for freshwater fish:
106 mg/L
LC50 for marine water fish:
138 mg/L

Additional information

The short term toxicity to fish was assessed with several studies of marine and freshwater species.

Short-term toxicity to fish (freshwater)

A key study with the read across substance (free acid of Diflufenzopyr sodium salt) according to the Procedures outlined in Series 72 of Pesticide Assessment Guidelines. Subdivision E Hazard Evaluation: Wildlife and Aquatic Organisms and ASTM Standard E 729-88, Standard Practice for Conducting Acute Toxicity Tests with Fishes. Macroinvertebrates and Amphibians (guidelines equivalent or similar to OCDE guideline 203, EU-method C.1 and EPA OPPTS 850.1075) was performed to evaluate the short term toxicity to fish in a static test system. Oncorhynchus mykiss were exposed to a geometric series of five test concentrations and a negative (well water) control. Two replicate test chambers were used in each treatment and control group, with 10 bluegill in each test chamber. Nominal test concentrations of 15.6, 25.9, 43.2, 72.0, and 120 mg active ingredient (a.i.)/L were selected and were based on the results of range finding toxicity tests. Mean measured concentrations of the test substance were determined from analyses of water collected from each treatment and control group at the beginning and end of the test as 16, 26, 46, 74, and 135 mg a.i./L. In this study, the 96-hour LC50 value for rainbow trout exposed in a static system to a read across substance was 106 mg a.i./L (measured concentration). The 96-hour no mortality concentration and no observed effect concentration, determined by a visual examination of the mortality data, was 80 mg a.i./L (measured concentration)

In addition to these results a toxicity test to bluegill (Lepomis macrochirus) according to the Procedures outlined in Series 72 of Pesticide Assessment Guidelines was performed with a read across substance free acid of Diflufenzopyr sodium

The 96-hour LC50 value was >135 mg a.i./L. The 96-hour no mortality concentration and no observed effect concentration was 16 mg a.i./L.

Short-term toxicity to fish (marine water)

A key study according to the Procedures outlined in Series 72 of Pesticide Assessment Guidelines. Subdivision E Hazard Evaluation: Wildlife and Aquatic Organisms and ASTM Standard E 729-88, Standard Practice for Conducting Acute Toxicity Tests with Fish. Macroinvertebrates and Amphibians and Standard Evaluation Procedure, Acute Toxicity Test for Estuarine and Marine Organisms (guidelines equivalent or similar to OCDE guideline 203, EU-method C.1 and EPA OPPTS 850.1075) was performed to evaluate the short term toxicity of the read acoss substance (free acid of Diflufenzopyr sodium salt) to fish in a static test system.

Sheepshead minnows were exposed to a geometric series of five test concentrations and a negative (saltwater) control. Two replicate test chambers were maintained in each treatment and control group, with 10 sheepshead minnows in each test chamber. Nominal test concentrations were selected in consultation with the Sponsor, and were based upon the results of a rangefinding toxicity test. Nominal test concentrations selected were 16, 26, 43, 72 and 120 mg active ingredient (a.i.)/L. Mean measured test concentrations were determined from samples of test water collected from each test chamber at the beginning of the test and at test termination. The sheepshead minnows were impartially assigned to exposure chambers at test initiation. Observations of mortality and other clinical signs were made approximately 6, 24, 48, 72 and 96 hours after test initiation. Cumulative percent mortality observed in the treatment groups was used to estimate LC50 values at 24, 48, 72 and 96 hours. The no mortality concentration and no observed effect concentration (NOEC) were determined by examination of the mortality and clinical observation data.

The 96-hour LC50 value for sheepshead minnows exposed to a read across substance was > 138 mg a.i./L, the highest concentration tested. The 96-hour no mortality concentration and NOEC were 138 mg a.i./L.