Reproductive and developmental effects of atrazine on the estuarine meiobenthic copepod Amphiascus tenuiremis

Atrazine is one of the most widely used herbicides in the United States. Atrazine concentrations in coastal environments chronically, range from 90 ng/L to 46 mug/L, with rare but measured concentrations near 60 Lg/L at edge-of-field conditions. Chronic atrazine effects on estuarine benthos exposed to environmentally relevant concentrations are unknown. The purpose of this research was to assess atrazine reproductive and developmental effects over multiple-generation exposures of the copepod Amphiascus tenuiremis. Copepods were chronically exposed to two environmentally relevant nominal atrazine concentrations (2.5 and 25 mug/ L. and to an environmentally unrealistic concentration (250 mug/L). Chronic exposures were performed using a 96-well microplate life cycle bioassay. Individual stage I copepodites (C-1 n = 60/treatment) were reared through two generations (F-0 and F-1) to sexual maturtity and individually mated in microwells containing 200 mu1 of atrazine solution. Copepod survival across all treatments and generations was >95%. Atrazine did not affect development to reproductive maturity, time to egg extrusion, or time to egg hatch p > 0.05). However. reproductive failures increased across generations with increasing atrazine concentrations. Reproductive failures in the 0-, 2.5- 25- and 250-mug/L atrazine treatments were 11, 11, 20, and 24% for the F-0 and 4, 9, 26, and 38% for the F, respectively. Compared to controls, total nauplii production per female was reduced by approximately 22% in F-0, females exposed to 250 mug/L atrazine (p < 0.05), and by approximately 23%, approximately 27%, and approximately 32% in F, females exposed to 2.5-. 25-, and 250-mug/L atrazine treatments, respectively (p < 0.05). The combined effect of reproductive failure and reduced offspring production sigificantly reduced total population growth in the F, generation (p < 0.05) even at atrazine concentrations lower than that considered safe for seawater chronic exposure (26 mug/L).