Acute and early life-stage toxicity of atrazine in sheepshead minnow (Cyprinodon variegatus).

Given the limited data available for estuarine/marine fish species and potential risk of being exposed to the herbicide atrazine, additional toxicity data regarding sensitive life-stages are needed. As such, this work sought to characterize: 1) the acute larval toxicity, and 2) early life-stage toxicity of technical atrazine in the model marine species sheepshead minnow (Cyprinodon variegatus). Atrazine was observed to be slightly to moderately toxic towards C. variegatus under acute conditions (as per U.S. EPA 2017 criteria). After 96 h exposure, mortality rates of 5%, 15%, 35%, and 90% were observed among fish exposed to atrazine at 4.6, 7.6, 13, and 22 mg a.i./L, respectively. Sub-lethal effects were observed among surviving fish exposed to > 3.2 mg a.i/L. The 96 h LC50 was 13 mg a.i./L and the NOEC was 3.2 mg a.i./L. In the 33 d early-life stage test, mean embryo survival rates in 0.15, 0.30, 0.57, 1.1, and 2.2 mg a.i./L treatments ranged from 71% to 79% and were not different from survival in the control (78%). Following 28 d post-hatch exposure (Day 33), mean larval survival ranged from 98% to 100% in all treatments and the control. Larval length and wet weight were the most sensitive indicators of the toxicity of atrazine to early life-stage sheepshead minnow. The NOEC for growth was 1.1 mg a.i./L and the LOEC was 2.2 mg a.i./L. Based on these, the MATC for atrazine to sheepshead minnow embryos and larvae was estimated to be 1.6 mg a.i./L. These results were consistent with previous investigations in sheepshead minnow and other marine fish species. Based on the results, atrazine would not be expected to pose unacceptable risks for sheepshead minnow early life-stages at environmentally relevant concentrations.