Hazard assessment of temephos applied to a southwest Florida, USA, salt marsh community

This investigation was undertaken to determine whether the mosquito larvici de temephos (applied as Abate 4-E(R)) created an environmental hazard for n ontarget organisms in a southwest Florida salt marsh community. Field toxic ity tests were performed during routine larvicide applications using larvae of salt marsh crabs (Aratus pesonii and Uca rapax) and adult Mysidopsis ba hia. 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 mu g/L temephos. First-molt LOEC ranged from 7 to 12 mu g/L. No effect on M. bahia survival, growth, or fecundity was observed up to 40 mu g/L temephos. Field studies of routine temephos application rates produced an expected environmental concentration (EEC) of 12 +/- 10 mu g/L in marsh water, causing an environmental hazard to crab larvae. Reduction of the ap plication rate effectively reduced the EEC to 4 +/- 3 mu g/L, indicating no hazard for 48 and 96 h toxicity; however, a hazard was observed for surviv al 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.