Hazard/Risk Assessment HAZARD ASSESSMENT OF TEMEPHOS APPLIED TO A SOUTHWEST FLORIDA, USA, SALT MARSH COMMUNITY

This investigation was undertaken to determine whether the mosquito larvicide temephos (applied as Abate 4-Et) created an environmental hazard for nontarget organisms in a southwest Florida salt marsh community. Field toxicity tests were performed during routine larvicide applications using larvae of salt marsh crabs (Aratus pesonii and Uca rapax) and adult Mysidopsis bahia. Laboratory toxicity tests were performed using survival through 48 and 96 h and through first molt as toxicity endpoints. Larvae of both species exhibited 96 h lowest observable effects concentration (LOEC) in the range of 15 to 20 mg/L temephos. First-molt LOEC ranged from 7 to 12 mg/L. No effect on M. bahia survival, growth, or fecundity was observed up to 40 mg/L temephos. Field studies of routine temephos application rates produced an expected environmental concentration (EEC) of 12 6 10 mg/L in marsh water, causing an environmental hazard to crab larvae. Reduction of the application rate effectively reduced the EEC to 4 6 3 mg/L, indicating no hazard for 48 and 96 h toxicity; however, a hazard was observed for survival through the first molt. This information was used to modify larviciding applications to effect a reduction of the environmental hazard to nontarget organisms in the salt marsh. Keywords—Temephos Hazard Nontarget Toxicity Larvicide