1 figure, 1 table omitted
Public health officials weigh the risk for mosquito-borne diseases against
the risk for human exposure to pesticides sprayed to control mosquitoes.1 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 spraying ultra-low volume (ULV) (<3
fluid ounces per acre [oz/acre]) mosquito-control (MC) pesticides, such as
naled, permethrin, and d-phenothrin. These ULV applications generate aerosols
of fine droplets of pesticides that stay aloft and kill mosquitoes on contact
while minimizing the risk for exposure to persons, wildlife, and the environment.2 This report summarizes the results of studies in Mississippi,
North Carolina, and Virginia that assessed human exposure to ULV naled, permethrin,
and d-phenothrin used in emergency, large-scale MC activities. The findings
indicated ULV application in MC activities did not result in substantial pesticide
exposure to humans; however, public health interventions should focus on the
reduction of home and workplace exposure to pesticides.
The 2002 West Nile virus (WNV) epidemic in Mississippi prompted an increase
in MC activities, including application of ULV permethrin by truck-mounted
foggers. Because of concerns about potential health effects from pesticides,
the Mississippi Department of Health and CDC assessed whether MC activities
increased individual urine pesticide metabolite concentrations. During September
8-19, 2002, investigators selected a geographically-random sample of 125 persons
by using maps of two regions where public health officials applied MC pesticides
and 67 persons from two control regions. Each participant completed a questionnaire
describing home and occupational use of pesticides and provided a spot urine
sample for analysis of pesticide metabolites 1-4 days after MC (i.e., within
5 half-lives). By using a cross-sectional design, investigators compared urine
pesticide metabolite concentrations of exposed and unexposed study participants.
Exposure to permethrin was verified by cross-referencing the global positioning
systems location of participants with local MC spray routes. Permethrin was
applied in MC regions at a concentration of 0.032 oz/acre.
Urine samples were analyzed at CDC by using tandem mass spectrometry.3 Urinary metabolite concentrations of 3-phenoxybenzoic
acid (3pba), a metabolite of synthetic pyrethroid pesticides such as permethrin,
did not differ significantly between MC and non-MC regions (geometric mean
[GM] = 1.25 μg/L versus 1.13 μg/L, respectively). Although 3pba 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 (n = 17) had
significantly higher (p = 0.02) mean 3pba concentrations than those who did
not (n = 174) (4.27 μg/L versus 1.07 μg/L, respectively). These findings
indicated that local MC activities did not lead to increased pesticide metabolite
concentrations in the urine of participants.
Hurricane Isabel made landfall in North Carolina on September 18, 2003.
Because of ensuing rains and flooding, mosquito populations were expected
to surge. To control mosquitoes and prevent transmission of WNV and other
arboviruses, 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.
Urine samples were analyzed at CDC by using tandem mass spectrometry.3
Of the 90 persons recruited to participate in this exposure assessment,
75 (83%) 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 (DMP), a metabolite
of organophosphate pesticides such as naled, was detected in 46% of pre-spray
and 49% of post-spray urine samples (limit of detection [LOD] = 0.5 μg/L).
The GM 3pba concentration from post-spray urine sampled was 0.2 μg/L.
Generalized estimating equations (GEE) indicated no statistically significant
differences in the urine concentrations of naled and permethrin metabolites
before and after spraying. Participants who ate fresh fruits or vegetables
≤3 days before completing the pre-spray (n = 58) or post-spray (n = 37)
questionnaires had significantly higher urine concentrations of dimethylthiophosphate
than participants who did not pre-spray (n = 16) or post-spray (n = 37) (pre-spray:
3.2 μg/L versus 1.4 μg/L; GEE p = 0.02) (post-spray: 3.3 μg/L
versus 1.2 μg/L; GEE p = 0.01). Two participants who worked on farms and/or
handled pesticides had significantly higher urine concentrations of nonspecific
organophosphorus pesticide metabolites (e.g., dimethyldithiophosphate, diethylthiophosphate,
and diethylphosphate) than participants who did not work on farms (n = 73)
or handle pesticides (n = 72).
To control mosquitoes and prevent transmission of arboviruses after
Hurricane Isabel, the Virginia Department of Health (VDH) decided to spray
ULV naled and d-phenothrin. 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 of d-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. Urine samples were analyzed at CDC by
using tandem mass spectrometry.3
Of the 95 persons recruited for the assessment, 83 (87%) provided pre-spray
and post-spray exposure questionnaires and urine samples. The concentrations
of all pesticide metabolites measured in participants’ urine samples
were low. DMP was detected in 42% of pre-spray and 48% of post-spray urine
samples (LOD = 0.5 μg/L). The geometric mean 3pba concentration from post-spray
urine samples was 0.6 μg/L. GEEs indicated no overall difference in the
urine concentrations of naled and d-phenothrin metabolites before and after
M Currier, MD, Univ of Mississippi Medical Center; M McNeill, MD, Mississippi
Dept of Health. D Campbell, MD, North Carolina Dept of Health and Human Svcs;
N Newton, PhD, North Carolina Dept of Environment and Natural Resources. JS
Marr, MD, E Perry, MD, SW Berg, MD, Virginia Dept of Health. DB Barr, PhD,
Div of Laboratory Sciences, GE Luber, PhD, SM Kieszak, MA, HS Rogers, PhD,
LC Backer, PhD, MG Belson, MD, C Rubin, DVM, Div of Environmental Hazards
and Health Effects, National Center for Environmental Health; E Azziz-Baumgartner,
MD, ZH Duprey, DVM, EIS officers, CDC.
Although ULV applications of naled and synthetic pyrethroids have a
low toxicity to humans, occupational studies suggest that excessive exposure
to these pesticides can cause serious health effects.4 Prolonged
exposure to high concentrations of naled and synthetic pyrethroids can cause
dermatitis, reactive airway disease, gastrointestinal distress, central nervous
system depression, paralysis, and death.5 Exposure
often results from use of these pesticides in food production, treatment of
wool, wood products, and pest-control efforts; however, few studies have quantitated
the level of human exposure to MC pesticides in nonoccupational settings.6
The studies described in this report represent the first efforts to
quantitate human exposure to MC pesticides during large-scale MC activities.
Two of these studies used a prospective crossover design that compared urine
metabolite concentrations after ULV spraying of pesticides with baseline concentrations.
Use of sensitive analytic methods in these studies indicated that the urine
pesticide metabolite concentrations measured were low (parts per billion).
The concentration of urine metabolites in these studies are comparable with
those measured in the general population.6,7 In
addition, these three studies did not indicate an overall increase of pesticide
metabolite concentrations in the urine of participants after spraying during
MC activities. The concentrations of naled, permethrin, and d-phenothrin during
emergency ULV applications might be too low to cause important human exposure.
In certain participants, investigators found an association between
home and/or work application of pesticides and pesticide metabolite concentrations.
The concentrations in participants who had histories of exposure were within
the range of the general U.S. population.8 These
findings are consistent with occupational studies in which prolonged exposure
to pesticides through several hours of work in plant nurseries and greenhouses
was associated with low but measurable concentrations of urine pesticide metabolites.9 These findings also are compatible with a prospective
study that quantitated higher 3pba concentrations in the urine of pest-control
operators 1 day after spraying pyrethroids.10
The findings in this report are subject to at least three limitations.
First, although naled, permethrin, and d-phenothrin remain in the environment
for a short period (e.g., naled has a 1-day half-life), CDC did not conduct
environmental sampling to confirm the presence of pesticide on the ground
after spraying. Second, the study did not quantify the effects of synergists
such as piperonyl butoxide in Anvil 10+10®, which help increase the efficacy
of synthetic pyrethroids. Finally, the use of self-reported questionnaire
data limits the ability to quantify actual home or occupational pesticide
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 these rural, suburban, and urban communities. These findings
suggest that ULV application of naled, permethrin, and d-phenothrin is safe
to humans as part of integrated vector control. The findings are noteworthy
because ULV applications of pesticides that kill adult mosquitoes are an important
tool in the public health response to WNV. Future studies should address the
long-term safety of low-concentration exposure to naled and synthetic pyrethroid
applications. In addition, public health interventions might be needed to
reduce home and workplace exposure to pesticides.
The findings in this report are based, in part, on contributions by
W Rayburn, Albemarle Regional Health Svcs, Elizabeth City; J Engel, North
Carolina Dept of Health and Human Svcs; M Tolliver, North Carolina Dept of
Environment and Natural Resources. Z Kazzi, Office of Director, Agency for
Toxic Substances and Disease Registry. K Johnson, C Sanchez, A Holmes, R Sabogal,
M Patel, A Funk, C Bell, S Young, A Greiling, D Burmeister, Div of Environmental
Hazards and Health Effects, C Dodson, Div of Laboratory Sciences, J Mason,
E Hansen, J Shughart, Div of Emergency and Environmental Health Svcs, National
Center for Environmental Health; A Hedley, Div of Health Examination Statistics,
National Center for Health Statistics; G Shaughnessy, G Han, A Terranella,
Epidemiology Program Office, CDC.
Human Exposure to Mosquito-Control Pesticides—Mississippi, North Carolina, and Virginia, 2002 and 2003. JAMA. 2005;294(4):419-421. doi:10.1001/jama.294.4.419