Human Exposure to Mosquito Control Pesticides in The South

Public health officials weigh the risk for mosquito-borne diseases against the risk for human exposure to pesticides sprayed to control mosquitoes. Response to outbreaks of mosquito-borne diseases has focused on vector control through habitat reduction and application of pesticides that kill mosquito larvae. However, in certain situations, public health officials control adult mosquito populations by making ultra-low volume (ULV) applications. The 2002 West Nile virus epidemic in Mississippi and the landing of hurricane Isabel in North Carolina and Virginia in 2003 prompted increases in mosquito control activities, including application of ULV permethrin, naled, and phenothrin by truck or air. Because of concerns about potential health effects from pesticides, state agencies and Centers for Disease Control (CDC) assessed whether mosquito control activities increased the pesticide metabolite concentrations in humans.

In Mississippi during the fall of 2002, investigators selected a geographically-random sample of 125 persons by using maps of two regions where public health officials applied ULV pesticide and 67 persons from two control regions. Each participant completed a questionnaire describing home and occupational use of pesticides and provided a urine sample for analysis of pesticide metabolites one to four days after ULV application. Permethrin was applied at a concentration of 0.032 oz/acre. Urinary metabolite concentrations of 3-phenoxybenzoic acid, a metabolite of synthetic pyrethroid pesticides such as permethrin, did not differ significantly between control and non-control regions (1.25 µg/L versus 1.13 µg/L, respectively). Although metabolite concentrations did not differ between participants who used pesticides at home or at work and those who did not, participants who used pesticides on pets had significantly higher metabolite concentrations than those who did not (4.27 µg/L versus 1.07 µg/L, respectively).

Hurricane Isabel made landfall in North Carolina and Virginia in September of 2003. To control adult mosquitoes and prevent transmission of viruses, the North Carolina Department of Environmental and Natural Resources (NCDENR) sprayed ULV naled and permethrin. The North Carolina Department of Health and Human Services, NCDENR, and CDC conducted a prospective exposure assessment of ULV spraying of pesticides. Investigators recruited 90 persons from a random sample of census blocks (that accounted for the population density) marked for spraying. Participants then completed a pre-spray questionnaire about household and occupational exposure to pesticides and provided urine samples to quantify concentrations of pesticide metabolites. On September 30, aircraft in North Carolina sprayed ULV naled at 0.7 oz/acre. In addition, trucks sprayed ULV permethrin (Biomist 30+30®) at 0.0014 lbs/acre. Eighteen hours after aerial spraying (approximately one half-life), each participant completed a post-spray questionnaire about household and occupational exposure to pesticides and provided a second urine sample. Of the 90 persons recruited to participate in this exposure assessment, 75 (83 percent) provided pre-spray and post-spray questionnaires and urine samples. The concentrations of all pre- and post-spray pesticide metabolites measured in participant urine samples were low. Dimethylphosphate, a metabolite of organophosphate pesticides such as naled, was detected in 46 percent of pre-spray and 49 percent of post-spray urine samples. Statistical analysis indicated no statistically significant differences in the urine concentrations of naled or permethrin metabolites before and after spraying.

In Virginia in 2003, the Virginia Department of Health (VDH) decided to spray ULV naled and d-phenothrin. The VDH and CDC assessed exposure to ULV spraying of pesticides by randomly selecting 95 residents of high population-density census blocks marked for spraying. Participants then completed pre-spray questionnaires about household and occupational exposure to pesticides and provided urine samples to quantify concentrations of pesticide metabolites. On September 30, aircraft sprayed ULV naled at 0.5 oz/acre while trucks sprayed ULV phenothrin (Anvil 10+10®) at 0.0036 lbs/acre. Eighteen hours after spraying (approximately one half-life), each participant completed a post-spray questionnaire about household and occupational exposure to pesticides and provided a second urine sample. Of the 95 persons recruited for the assessment, 83 (87 percent) provided pre-spray and post-spray exposure questionnaires and urine samples. The concentrations of all pesticide metabolites measured in participants' urine samples were low. Dimethylphosphate was detected in 42 percent of pre-spray and 48 percent of post-spray urine samples. Statistical analysis indicated no statistically significant differences in the urine concentrations of naled or phenothrin metabolites before and after spraying.

The authors concluded that aerial spraying with ULV naled and truck-mounted spraying with permethrin/d-phenothrin were not associated with an increase in urine pesticide metabolite concentrations among residents of rural, suburban, and urban communities. These findings also suggest that ULV application of naled, permethrin, and d-phenothrin is safe to humans as part of integrated vector control. (Morbidity and Mortality Update, Vol. 54, No. 21, 6/3/05).