Mosquito management and risk
Robert K. D. Peterson
Peterson, R.K.D. 2010. Mosquito management and risk. Wing Beats 21: 28-31. (PDF)
A human-health risk assessment for West Nile virus and
insecticides used in mosquito management
Robert K. D. Peterson, Paula A. Macedo, and
Ryan S. Davis
West Nile Virus (WNV) has become a major public health
concern in North America since 1999 when the first outbreak in the Western
Hemisphere occurred in New York City. As a result of this ongoing disease outbreak,
management of mosquitoes which vector WNV throughout the U.S. and Canada has
necessitated using insecticides in areas where they traditionally have not
been used, or have been used less. This has resulted in concerns by the
public about the risks from insecticide use. The objective of this study was
to use reasonable worst-case risk assessment methodologies to evaluate
human-health risks for WNV and the insecticides most commonly used to control
We evaluated documented health effects from WNV infection and determined
potential population risks based on reported frequencies. We determined
potential acute (1 day) and subchronic (90 day) multi-route residential
exposures from each insecticide for several human subgroups. We then compared
potential insecticide exposures to toxicological and regulatory effect
levels. Risk quotients (RQ’s, the ratio of exposure to toxicological effect)
were less than 1.0 for all subgroups. Acute RQ’s ranged from 0.0004 to
0.4726. Subchronic RQ’s ranged from 0.00014 to 0.2074. Results from our risk
assessment and the current weight of scientific evidence suggest that
human-health risks from residential exposure to mosquito insecticides are low
and are not likely to exceed levels of concern. Further, our results suggest
that, based on human-health criteria, the risks from WNV exceed the risks
from exposure to mosquito insecticides.
Peterson, R.K.D., Macedo, P.A., and Davis, R.S.
2006. A human health risk assessment of West Nile Virus and insecticides used
in mosquito management. Environmental Health Perspectives 114 (3): 366-372. (PDF)
Risk assessments for exposure of
deployed military personnel to insecticides and personal protective measures
used for disease-vector management
Paula A. Macedo, Robert K. D. Peterson, and Ryan S.
Infectious diseases are problematic for deployed military forces throughout
the world, and, historically, more military service days have been lost to
insect-vectored diseases than to combat. Because of the limitations in
efficacy and availability of both vaccines and therapeutic drugs, vector
management often is the best tool that military personnel have against most
vector-borne pathogens. However, the use of insecticides may raise concerns
about the safety of their effects on the health of the military personnel
exposed to them. Therefore, our objective was to use risk assessment
methodologies to evaluate health risks to deployed U.S. military personnel
from vector management tactics. Our conservative tier-1, quantitative risk
assessment focused on acute, subchronic, and chronic exposures and cancer
risks to military personnel after insecticide application and use of personal
protective measures in different scenarios. Exposures were estimated for
every scenario, chemical, and pathway. Acute, subchronic, and chronic risks
were assessed using a margin of exposure (MOE) approach. Our MOE was the
ratio of a no-observed-adverse-effect-level (NOAEL) to an estimated exposure.
MOEs were greater than the levels of concern (LOCs) for all surface residual
and indoor space spraying exposures, except acute dermal exposure to
lambda-cyhalothrin. MOEs were greater than the LOCs for all chemicals in the
truck-mounted ultra-low-volume (ULV) exposure scenario. The aggregate cancer
risk for permethrin exceeded 1 x 10-6, but more realistic exposure
refinements would reduce the cancer risk below that value. Overall, results
indicate that health risks from exposures to insecticides and personal
protective measures used by military personnel are low.
Macedo, P.A., R.K.D. Peterson, and
R.S. Davis. 2007. Risk assessments for exposure of deployed military
personnel to insecticides and personal protective measures used for
disease-vector management. Journal of Toxicology and Environmental Health,
Part A 70: 1758–1771. (PDF)
Risk assessments for
the insect repellents DEET and picaridin
Frank B. Antwi, Leslie M. Shama, and Robert K. D.
For the use of topical insect repellents, DEET and picaridin, human health
risk assessments were conducted for various population subgroups.
Acute, subchronic, and chronic dermal exposures were examined.
No-observed-effect-levels (NOELs) of 200, 300, and 100 mg/kg body weight (BW)
were used as endpoints for DEET for acute, subchronic, and chronic exposures,
respectively. For picaridin, a NOEL of 2000 mg/kg BW/day for acute exposure
and a NOEL of 200 mg/kg BW/day for subchronic and chronic exposures were
used. Daily exposures to several population subgroups were estimated. Risks
were characterized using the Margin of Exposure (MOE) method (NOEL divided by
the estimated exposure), whereby estimated MOEs were compared to an MOE of
100. Estimates of daily exposures ranged from 2 to 59 mg/kg BW/day for DEET
and 2 to 22 mg/kg BW/day for picaridin. Children had the lowest MOEs.
However, none of the estimated exposures exceeded NOELs for either repellent.
At 40% DEET for acute exposure, children 612 years had MOEs below 100. For
subchronic and chronic exposures children at 25% DEET and at 15% picaridin
had MOEs below 100. Therefore, we found no significant toxicological risks
from typical usage of these topical insect repellents.
Antwi, F., L.M. Shama, and R.K.D. Peterson. 2008. Risk
assessments for the insect repellents DEET and picaridin. Regulatory
Toxicology and Pharmacology 51: 31-36. (PDF)
A two-dimensional probabilistic acute
human-health risk assessment of insecticide exposure after adult mosquito
Schleier III, Paula A. Macedo, Ryan S. Davis, Leslie M. Shama, and
Robert K. D. Peterson
(ULV) aerosol applications of insecticides are used to manage high densities
of adult mosquitoes. We used two-dimensional probabilistic risk assessment
methodologies to evaluate three pyrethroid insecticides (phenothrin,
resmethrin, and permethrin), pyrethrins, and two organophosphate insecticides
(malathion and naled), applied by truck-mounted ULV sprayer. Piperonyl
butoxide, a synergist commonly used in pyrethroid and pyrethrins
formulations, was also assessed. The objective of our study was to evaluate
probabilistically if a deterministic human-health risk assessment of mosquito
insecticides was sufficiently conservative to protect human-health. Toddlers
and infants were the highest risk groups while adult males were the lowest
risk group assessed in this study. Total acute exposure ranged from 0.00003
to 0.0003 mg/kg day-1 for the chemicals and subgroups assessed examining
inhalation, dermal, oral, and hand-to-mouth exposure. We used the risk
quotient (RQ) method for our risk assessment, which is calculated by dividing
the total potential exposure for each subgroup and chemical by its ingestion
toxic endpoint value (RfD). Mean RQs ranged from 0.000004 to 0.034 for all
subgroups and chemicals, with none exceeding the RQ level of concern. Naled
had the highest RQs of any chemical assessed while PBO had the lowest.
Sensitivity analysis demonstrated that the exposure from inhalation and
deposition contributed the largest variance to the model output. Results
support the findings of previous studies that the risks from adult mosquito
management are most likely negligible, and that the human-health
deterministic risk assessment is most likely sufficiently conservative.
Schleier III, J.J., P.A. Macedo, R.S. Davis, L.M. Shama, and R.K.D. Peterson. 2009. A two-dimensional probabilistic acute human-health risk assessment of insecticide exposure after adult mosquito management. Stochastic Environmental Research and Risk Assessment 23: 555-563. (PDF)
A probabilistic risk assessment for deployed military personnel after the implementation of the “Leishmaniasis Control Program” at Tallil Air Base, Iraq.
Schleier III, Ryan S. Davis, Loren M. Barber, Paula A. Macedo, and
Robert K. D. Peterson
Leishmaniasis has been of concern to the U.S. military and has re-emerged in importance because of recent deployments to the Middle East. We conducted a retrospective probabilistic risk assessment for military personnel potentially exposed to insecticides during, the "Leishmaniasis Control Plan" (LCP) undertaken in 2003 in Tallil Air Base, Iraq. We estimated acute and subchronic risks from resmethrin, malathion, piperonyl butoxide (PBO), and pyrethrins applied using a truck-mounted ultra-low-volume (ULV) sprayer and cyfluthrin, bifenthrin, chlorpyrifos, and cypermethrin used for residual sprays. We used the risk quotient (RQ) method for our risk assessment (estimated environmental exposure/toxic endpoints) and set file RQ level of concern (LOC) at 1.0. Acute RQs for truck-mounted ULV and residual sprays ranged from 0.00007 to 33.3 at the 95th percentile. Acute exposure to lambda-cyhalothrin, bifenthrin, and chlorpyrifos exceeded the RQ LOC Subchronic RQs for truck-mounted ULV and residual sprays ranged from 0.00008 to 32.8 at the, 951:11 percentile. Subchronic exposures to lambda-cyhalothrin and chlorpyrifos the LOC. However, estimated exposures to lambda-cyhalothrin, bifenthrin, and chlorpyrifos did not exceed their respective no observed adverse effect levels.
Schleier III, J.J., R.S. Davis, L.M. Barber, P.A. Macedo, and R.K.D. Peterson. 2009. A probabilistic risk assessment for deployed military personnel after the implementation of the “Leishmaniasis Control Program” at Tallil Air Base, Iraq. Journal of Medical Entomology 46: 693-702. (PDF)
Deposition and air concentrations of permethrin and naled used for adult mosquito management
Schleier III and
Robert K. D. Peterson
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. Because of the lack of environmental fate studies and concerns about the safety of the insecticides used for the management of adult mosquitoes, we conducted an environmental fate study after truck-mounted applications of permethrin and naled. One hour after application, concentrations of permethrin on cotton dosimeters placed at ground level 25, 50, and 75 m from the spray source were 2, 4, and 1 ng/cm(2) in 2007 and 5, 2, and 0.9 ng/cm(2) in 2008, respectively. One hour after application, concentrations of naled 25, 50, and 75 m were 47, 66, and 67 ng/cm(2) in 2007 and 15, 6.1, and 0 (nondetectable) ng/cm(2) in 2008, respectively. Deposition concentrations 12 h after application were not significantly different than 1 h after application for permethrin and naled either year. During 2007 and 2008 permethrin applications, two quantifiable air concentrations of 375 and 397 ng/m(3) were observed 1 h after application. In 2007 and 2008, naled air concentrations ranged from 2300 to 4000 ng/m(3) 1 h after application. There were no quantifiable air concentrations between 1 and 12 h after application in either 2007 or 2008 for both naled and permethrin. Environmental concentrations observed in this study demonstrate that models used in previous risk assessments were sufficiently conservative (i.e., the models overestimated environmental concentrations). However, we also demonstrate inadequacies of models such as AgDrift(A (R)) and AGDISP, which currently are used by the US Environmental Protection Agency to estimate environmental concentrations of ULV insecticides.
Schleier III, J.J., and R.K.D. Peterson. 2010. Deposition and air concentrations of permethrin and naled used for adult mosquito management. Archives of Environmental Contamination and Toxicology 58: 105-111. (PDF)
Economic cost analysis of West Nile virus outbreak, Sacramento County, California, USA, 2005
Loren M. Barber, Jerome J.
Schleier III, and
Robert K. D. Peterson
In 2005, an outbreak of West Nile virus (WNV) disease occurred in Sacramento County, California; 163 human cases were reported. In response to WNV surveillance indicating increased WNV activity, the Sacramento-Yolo Mosquito and Vector Control District conducted an emergency aerial spray. We determined theeconomic impact of the outbreak, including the vector control event and the medical cost to treat WNV disease. WNV disease in Sacramento County cost $42.28 million for medical treatment and patients' productivity loss for both West Nile fever and West Nile neuroinvasive disease. Vector control cost $701,790, including spray procedures and overtime hours. The total economic impact of WNV was $2.98 million. A cost-benefit analysis indicated that only 15 cases of West Nile neuroinvasive disease would need to be prevented to make the emergency sorav cost-effective.
Barber, L.M., J.J. Schleier III, and R.K.D. Peterson. 2010. Economic cost analysis of West Nile virus outbreak, Sacramento County, California, USA, 2005. Emerging Infectious Diseases 16: 480-486. (PDF)
Evaluation of efficacy and human health risk of aerial ultra-low volume applications of pyrethrins and piperonyl butoxide for adult mosquito management in response to West Nile virus activity in Sacramento County, California
Paula A. Macedo, Jerome J. Schleier III, Marcia Reed, Kara Kelley, Gary W. Goodman, David A. Brown, and
Robert K.D. Peterson
The Sacramento and Yolo Mosquito and Vector Control District (SYMVCD, also referred to as "the District") conducts surveillance and management of mosquitoes in Sacramento and Yolo counties in California. Following an increase in numbers and West Nile virus (WNV) infection rates of Culex tarsalis and Culex pipiens, the District decided on July 26, 2007, to conduct aerial applications of Evergreen(R) EC 60-6 (60% pyrethrins: 6% piperonyl butoxide) over approximately 215 km(2) in the north area of Sacramento County on the nights of July 30, July 31, and August 1, 2007. At the same time, the District received notification of the firsthuman WNV case in the area. To evaluate the efficacy of the applications in decreasing mosquito abundance and infection rates, we conducted pre- and post-trapping inside and outside the spray zone and assessed human health risks from exposure to the insecticide applications. Results showed a significant decrease in abundance of both Cx. tarsalis and Cx. pipiens, and in the minimum infection rate of Cx. tarsalis. Human-health risks from exposure to the insecticide were below thresholds set by the US Environmental Protection Agency.
Macedo, P.A., J.J. Schleier III, M. Reed, K. Kelley, G.W. Goodman, D.A. Brown, and R.K.D. Peterson. 2010. Evaluation of efficacy and human health risk of aerial ultra-low volume applications of pyrethrins and piperonyl butoxide for adult mosquito management in response to West Nile virus activity in Sacramento County, California. Journal of the American Mosquito Control Association 26: 57-66. (PDF)