Ecological Risk Assessments
©2004 RKD Peterson.
An Ecological Risk Assessment for Insecticides Used in Adult Mosquito Management
Ryan S. Davis, Robert K.D. Peterson, and Paula A. Macedo
West Nile virus (WNV) has been a concern for people across the United States since
the disease was initially observed in the summer of 1999. Since 1999, WNV has caused
the largest arboviral encephalitis epidemic in US history. Vector control management
programs have been intensively implemented to control mosquitoes that carry WNV. Our
deterministic ecological risk assessment focused on 6 common mosquito adulticides
used in vector control, including 3 pyrethroids (d-phenothrin, resmethrin, and permethrin),
pyrethrins, and 2 organophosphates (malathion and naled). Piperonyl butoxide, a synergist
for the pyrethroids, was also assessed. Both aquatic and terrestrial nontarget organisms
were considered for acute and chronic exposures to the adulticides. Tier I exposure
estimates were derived from ISCST3 and AERMOD for deposition and air concentrations
affecting terrestrial organisms and PRZM-EXAMS for standard pond concentrations affecting
aquatic organisms. Nontargets exposed to adulticides included small mammals, birds,
as well as aquatic vertebrates and invertebrates in a pond subject to receiving the
chemical via drift and runoff. Risk quotients were obtained by comparing exposures
to toxic endpoints. All risk quotients were low indicating that risks to ecological
receptors most likely were small.
Davis, R.S., R.K.D. Peterson, and P.A. Macedo. 2007. An ecological risk assessment for insecticides used in adult mosquito management. Integrated Environmental Assessment and Management 3: 373-382. (PDF)
Equine Risk Assessment for Insecticides Used in Adult Mosquito Management
Jerome J. Schleier III, Ryan S. Davis, Leslie M. Shama, Paula A. Macedo, and Robert K. D. Peterson
Since West Nile virus (WNV) was introduced to New York City in 1999, it has subsequently spread through the Americas, creating human and animal health risks. Our equine risk assessment focused on three pyrethroid insecticides (phenothrin, resmethrin, and permethrin), pyrethrins, and two organophosphate insecticides (malathion and naled). Piperonyl butoxide, a synergist commonly used in pyrethroids, was also assessed. The objective was to use deterministic and probabilistic risk assessment methodologies to evaluate health risks to horses from vector management tactics used for control of adult mosquitoes. Our exposure estimates were derived from the Kenaga nomogram for food deposition, AgDRIFT® for deposition onto soil and hair, AERMOD for ambient air concentrations, and PRZM-EXAMS for water concentrations. We used the risk quotient (RQ) method for our assessment with the RQ level of concern (LOC) set at 1.0. RQs were determined by comparing the exposure to no-observable-effect-levels. Acute deterministic RQs ranged from 0.0004 for phenothrin to 0.2 for naled. Subchronic deterministic RQs ranged from 0.001 for phenothrin to 0.6 for naled. The probabilistic assessment revealed estimates of deterministic acute and subchronic RQs were highly conservative. Our assessment revealed that risks to horses from adult mosquito insecticides are low and not likely to exceed the LOC.
Schleier III, J. J., R. S. Davis, L. M. Shama, P. A. Macedo, and R. K. D. Peterson. 2008. Equine risk assessment for insecticides used in adult mosquito management. Human and Ecological Risk Assessment 14: 392-407. (PDF)
Regional ecological risk assessment for the introduction of Gambusia affinis (western mosquitofish) into Montana watersheds
Jerome J. Schleier III, Sharlene E. Sing, and Robert K. D. Peterson
Qualitative risk assessment methodologies were used to assess the risk of establishment and consequent impacts on native minnows and species of concern (SOC) associated with the intentional or unintentional introduction of the mosquito biological control agent, Gambusia affinis, to various Montana watersheds. Gambusia affinisintroductions for mosquito control have been made throughout the world; some introductions have resulted in deleterious effects on native species. We used average January water temperatures, the presence of dams, and the presence of native minnows and SOC to define endpoints for our assessment. Our results suggest that a section of the Missouri River running between Wolf Creek and Landusky had the highest overall risk score, which corresponds to the highest likelihood of establishment and effects on native minnows and SOC. We also demonstrate how rivers with the highest temperatures are not necessarily at the highest risk of having deleterious effects on minnows and SOC; conversely, these rivers were found to be at highest risk of a population of G. affinisestablishing.
Schleier III, J. J., S. E. Sing, and R. K. D. Peterson. 2008. Regional ecological risk assessment for the introduction of Gambusia affinis (western mosquitofish) into Montana watersheds. Biological Invasions 10: 1277-1287. (PDF)
Environmental concentrations, fate, and risk assessment of pyrethrins and piperonyl butoxide after aerial ultralow-volume applications for adult mosquito management
Jerome J. Schleier III, Robert K. D. Peterson, Paula A. Macedo, and David A. Brown
One of the most effective ways of managing adult mosquitoes that vector human and animals diseases is the use of ultralow-volume insecticides. Because of concerns about the safety of the insecticides used for the management of adult mosquitoes, we conducted an environmental fate and efficacy study in Princeton and Colusa (both CA, USA) after aerial applications of pyrethrins and piperonyl butoxide (PBO). One hour before application, PBO concentrations in water were 0.008 and 0.2175 mg/L for Princeton and Colusa, respectively. One hour after the spray event in Princeton, the average PBO concentrations were 0.0125 mg/cm2 on ground-deposition pads and 0.1723 mg/L in water samples, with concentrations decreasing significantly over time. One hour after the spray event in Colusa, the average PBO concentrations were 0.0199 mg/cm2 on deposition pads and 1.274 mg/L in water samples, with concentrations decreasing significantly over time. A significant time and location effect for both deposition pads and water samples in Princeton and Colusa was observed (P < 0.001 and P = 0.014, respectively). Pyrethrins were not detected in nearly all ground and water samples. One hour after application, mortality of Culex tarsalis and Culex pipiens in sentinel cages was significantly higher than at the control site for both locations (P < 0.001). Risk quotients for aquatic surrogate species in Princeton and Colusa were 0.002 or less at 1 h after application, which did not exceed the U.S. Environmental Protection Agency risk quotient level of concern for endangered aquatic organisms of 0.05. Our results suggest that the amounts of pyrethrins and PBO deposited on the ground and in water after aerial ULV insecticide applications are lower than those estimated by previous exposure and risk assessments.
Schleier III, J.J., R.K.D. Peterson, P.A. Macedo, and D.A. Brown. 2008. Environmental concentrations, fate, and risk assessment of pyrethrins and piperonyl butoxide after aerial ultralow-volume applications for adult mosquito management. Environmental Toxicology and Chemistry 27: 1063-1068. (PDF)
Effects of single and multiple applications of mosquito insecticides on non-target arthropods
Ryan S. Davis and Robert K. D. Peterson
Mosquito management plans have been implemented in the U.S. and globally to manage mosquito vectors of West Nile Virus (WNV) and many other diseases. However, there is public concern about ecological risks from using insecticides to manage mosquitoes. Two studies were conducted during the late summers of 2004 through 2006 at Benton Lake National Wildlife Refuge near Great Falls, Montana. The first experiment was conducted in 2004 and 2005 to assess acute impacts of mosquito adulticides (permethrin and d-phenothrin) and larvicides (Bacillus thuringiensis israelensis and methoprene) on non-target aquatic and terrestrial arthropods after a single application. The second experiment was conducted in 2005 and 2006 to assess longer term impacts of permethrin on non-target terrestrial arthropods after multiple repeated applications. For aquatic samples, in the first study, no overall treatment effects were observed despite a potentially deleterious effect on amphipods on sample date 1 in 2004. During the same study, 1 of 54 responses had a significant overall treatment effect for sticky card samples. Many of the responses for sticky card samples suggested significant time effects and time-by-treatment effects. Three response variables were associated with fewer individuals present in the insecticide treated plots in a multivariate analysis. For the multiple spray study conducted in 2005 and 2006, 6 of the response variables collected via sticky cards exhibited significant overall treatment effects, but none was associated with fewer individuals in the insecticide treated plots. None of the responses collected using sweep net sampling suggested overall treatment effects. Time and time-by-treatment effects were prevalent in 2005, but no discernable pattern was evident. In general, nearly all of the responses evaluated for either study indicated few, if any, deleterious effects from insecticide application.
Davis, R.S., and R.K.D. Peterson. 2008. Effects of single and multiple applications of mosquito insecticides on non-target arthropods. Journal of the American Mosquito Control Association 24: 270-280. (PDF)
Toxicity to non-target insects after exposure to δ-phenothrin and resmethrin
Frank B. Antwi and Robert K. D. Peterson
BACKGROUND: The susceptibility of adult house cricket, Acheta domesticus (L.), adult convergent lady beetle,Hippodamia convergens (Guérin-Méneville), and larval fall armyworm, Spodoptera frugiperda (J. E. Smith), to resmethrin and δ-phenothrin (synergized with piperonyl butoxide (PBO)) was evaluated in a laboratory bioassayprocedure.
RESULTS: The 1-d LC50 values for resmethrin+PBO were 23.2, 32.08, and 307.18 ng/cm2 for house cricket, convergent lady beetle, and fall armyworm, respectively. The 1-d LC50 values for δ-phenothrin+PBO were 26.9, 74.91, and 228.57 ng/cm2 9 for house cricket, convergent lady beetle, and fall armyworm, respectively. The regression relationship between species mortality and concentration explained 51 to 81% of the variation for resmethrin+PBO and 72 to 97% of the variation for δ-phenothrin+PBO. The LC50 values decreased with time for these insecticides for all surrogate species. In terms of sensitivities among the insects to resmethrin+PBO and δ-phenothrin+PBO, house cricket was most sensitive, followed by convergent lady beetle, then fall armyworm.
CONCLUSION: Our results indicate that resmethrin+PBO was generally more toxic than δ-phenothrin+PBO.
Based on our results, the house cricket seems to be a good surrogate species for estimating
potential non-target terrestrial insect impacts from exposure to pyrethroids used
in public health applications.
Antwi, F.B., and R.K.D. Peterson. 2009. Toxicity to non-target insects after exposure to δ-phenothrin and resmethrin. Pest Management Science 65: 300-305. (PDF)
Toxicity and risk of permethrin and naled to non-target insects after adult mosquito management
Jerome J. Schleier III and Robert K. D. Peterson
We derived laboratory LC50 values, assessed non-target insect risks, and conducted
a field bioassay for ultra-low-volume (ULV) aerosol applications of insecticides used
to manage adult mosquitoes. The house cricket, Acheta domesticus (L.), was used as
an indicator species for medium- to large-bodied ground dwelling insects. The 24-h
LC50 values for Permanone(A (R)) (formulated product of permethrin), Permanone + piperonyl
butoxide (PBO), technical grade permethrin, and technical grade permethrin + PBO ranged
from 0.052 to 0.9 mu g/cm(2). The 24 h LC50 for technical grade naled and Trumpet(A
(R)) (formulated product of naled) were 0.038 and 0.44 mu g/cm(2), respectively. The
synergist ratio was 2.65 for Permanone + PBO and 1.57 for technical grade permethrin
+ PBO. The toxicity of technical grade permethrin was about 10-fold greater than Permanone.
A risk assessment using modeled estimated environmental concentrations resulted in
risk quotients (RQ) that exceeded regulatory levels of concern, but when compared
to field-derived actual environmental concentrations RQs did not exceed a regulatory
level of concern, except in the case of technical grade naled. These results were
expected because higher tiered risk assessments using field-verified data generally
lead to lower risk estimates. Field bioassays using caged crickets showed no significant
mortality for permethrin or naled after a single truck-mounted ULV application. The
results of the risk assessment using actual environmental concentrations are supported
by the field bioassays and suggest that a single ULV application of synergized or
unsynergized permethrin and naled most likely will not result in population impacts
on medium- to large-bodied insects.
Schleier III, J.J., and R.K.D. Peterson. 2010. Toxicity and risk of permethrin and naled to non-target insects after adult mosquito management. Ecotoxicology 16: 1140-1146. (PDF)
A Refined Aquatic Ecological Risk Assessment for a Pyrethroid Insecticide Used for Adult Mosquito Management
Jerome J. Schleier III and Robert K. D. Peterson
The use of pyrethroid insecticides has increased substantially throughout the world over the past few decades as the use of organophosphorous, carbamate, and organochlorine insecticides is being phased out. Pyrethroids are the most common class of insecticides for ultralow-volume (ULV) aerosol applications used to manage high densities of adult mosquitoes. Pyrethroids are highly toxic to nontarget organisms such as certain aquatic organisms, and there have been concerns about the effect of applications of ULV insecticides on these organisms. To address the uncertainties associated with the risks of ULV applications and the contradictory findings of other ecological risk assessments, the authors performed a probabilistic aquatic ecological risk assessment for permethrin using actual environmental deposition on surfaces to estimate permethrin concentrations in water. The present study is the first ecological risk assessment for pyrethroids to quantitatively integrate the reduction in bioavailability resulting from the presence of dissolved organic matter. As part of the risk assessment, the authors incorporated a species sensitivity distribution to take into account the differences in toxicity for different species. The 95th percentile estimated concentration would result in less than 0.0001% of the potentially affected fraction of species reaching the lethal concentration that kills 50% of a population. The results of the present study are supported by the weight of evidence that pyrethroids applied by ground-based ULV equipment will not result in deleterious effects on aquatic organisms.
Schleier III, J.J. and R.K.D. Peterson. 2013. A refined aquatic ecological risk assessment for a pyrethroid insecticide used for adult mosquito management. Environmental Toxicology and Chemistry 32: 948-953. (PDF)
Other Ecological Risk Assessments:
Maine Board of Pesticides Control - http://www.state.me.us/agriculture/pesticides/wnv/results3.htm
New York City Department of Health Adult Mosquito Control Programs -http://www.nyc.gov/html/doh/html/wnv/feis.shtml