Environmental concentrations, fate, and risk assessment of insecticides used for adult mosquito management

Abstract

One of the most effective ways of managing adult mosquitoes that vector human and animal pathogens is the use of ultra-low-volume (ULV) insecticides. Due to a lack of studies examining the environmental fate of ULV insecticides and because previous risk assessments have shown that environmental concentrations of insecticides contributed the largest amount of variance to the estimated total exposure, I measured deposition onto surfaces and air concentrations of permethrin and naled. I also conducted risk assessments for human and other non-target organisms using the values I measured. Deposition concentrations of permethrin and naled generally decreased as distance from the spray source increased. Overall, approximately 3.2% of the permethrin and 15% of the naled applied deposited on the ground within 75 m from the spray source 1 h after application. Concentrations of permethrin and naled 12 h after application were not significantly different than concentrations 1 h after application. The results of my probabilistic human-health risk assessment using actual environmental concentrations showed that previous risk assessments overestimated risks. Thus they were conservative in protecting human health. The non-target risk assessment and field bioassay using the house cricket, Acheta domesticus (L.), as a surrogate for medium- to large-bodied ground dwelling insects showed that ULV applications most likely would not result in impacts on populations. I also measured actual environmental concentrations of pyrethrins and piperonyl butoxide (PBO) after aerial ULV applications. Pyrethrins were not detected in the water or on deposition pads. However PBO was detected in the water and on deposition samples, but concentrations rapidly decreased to background levels by 36 h after application. The estimated risks of pyrethrins and PBO to aquatic surrogates were lower than those estimated by previous ecological risk assessments. My study is the first to relate actual environmental concentrations of ULV insecticides to estimates of human-health risks. Results of my environmental fate studies, human-health and non-target risk assessments, and the current weight of scientific evidence, demonstrate that the risks to humans and the environment after ULV applications of insecticides most likely are below regulatory levels of concern.