Neurologic Symptoms in Licensed Private Pesticide Applicators
Neurologic Symptoms in Licensed Private Pesticide Applicators
Exposure to high levels of many pesticides has both acute and long-term neurologic consequences, but little is known about the neurotoxicity of chronic exposure to moderate levels of pesticides. We analyzed cross-sectional data from 18,782 white male licensed private pesticide applicators enrolled in the Agricultural Health Study in 1993-1997. Applicators provided information on lifetime pesticide use and 23 neurologic symptoms typically associated with pesticide intoxication. An indicator of more symptoms (≥ 10 vs. < 10) during the year before enrollment was associated with cumulative lifetime days of insecticide use: odds ratios (95% confidence intervals) were 1.64 (1.36-1.97) for 1-50 days, 1.89 (1.58-2.25) for 51-500 days, and 2.50 (2.00-3.13) for > 500 days, compared with never users. A modest association for fumigants [> 50 days, 1.50 (1.24-1.81)] and weaker relationships for herbicides [> 500 days, 1.32 (0.99-1.75)] and fungicides [> 50 days, 1.23 (1.00-1.50)] were observed. Pesticide use within the year before enrollment was not associated with symptom count. Only associations with insecticides and fumigants persisted when all four pesticide groups were examined simultaneously. Among chemical classes of insecticides, associations were strongest for organophosphates and organochlorines. Associations with cumulative exposure persisted after excluding individuals who had a history of pesticide poisoning or had experienced an event involving high personal pesticide exposure. These results suggest that self-reported neurologic symptoms are associated with cumulative exposure to moderate levels of fumigants and organophosphate and organochlorine insecticides, regardless of recent exposure or history of poisoning.
Pesticides are used extensively throughout the world. In the United States, > 18,000 products are licensed for use, and annual use of pesticides for crops, homes, schools, parks, and forests exceeds 2 billion pounds [U.S. Environmental Protection Agency (EPA) 2002]. Neurologic dysfunction is the best-documented health effect of pesticide exposure. High-level exposure has both acute and long-term neurologic effects, and adverse effects have been reported for most types of pesticides, including organophosphate, carbamate, organochlorine, and pyrethroid insecticides, herbicides, fungicides, and fumigants. Organophosphates have been studied in greatest detail. Acute organophosphate poisoning can involve a wide range of both central and peripheral neurologic symptoms (Ecobichon 1996; Keifer and Mahurin 1997). Effects of organophosphate poisoning may persist long after the acute response is resolved; sequelae include increased neurologic symptoms, deficits in neurobehavioral performance, decreased vibration sensitivity, and impaired nerve conduction (Kamel and Hoppin 2004). Effects continue up to 10 years after poisoning (Savage et al. 1988), suggesting permanent residual damage. Even less severe poisoning can have long-term consequences (Wesseling et al. 2002).
Questions remain concerning the neurologic effects of moderate pesticide exposure. Most studies show effects on cognitive and psychomotor neurobehavioral function in chronically exposed individuals without a history of poisoning, although clinical measures of peripheral nerve function like vibration sensitivity and nerve conduction are not generally affected (Kamel and Hoppin 2004). Increases in both central and peripheral neurologic symptoms are also found in many studies of moderate exposure (Kamel and Hoppin 2004). Increased symptom prevalence may provide early evidence of neurologic dysfunction, before clinically measurable signs are evident. Unresolved issues regarding the relationship of pesticide exposure to symptom prevalence include the relative importance of acute and chronic exposure, of pesticide poisoning or high-exposure events compared with chronic moderate exposure, and of pesticides other than organophosphates.
The Agricultural Health Study (AHS) is a large cohort study of licensed pesticide applicators and their spouses (Alavanja et al. 1996, 1999a). Questionnaires completed by applicators at enrollment provided information on neurologic symptoms during the prior year as well as detailed information on lifetime pesticide use and exposure. We used this information for a cross-sectional analysis of the relationship of symptoms to several measures of pesticide exposure.
Exposure to high levels of many pesticides has both acute and long-term neurologic consequences, but little is known about the neurotoxicity of chronic exposure to moderate levels of pesticides. We analyzed cross-sectional data from 18,782 white male licensed private pesticide applicators enrolled in the Agricultural Health Study in 1993-1997. Applicators provided information on lifetime pesticide use and 23 neurologic symptoms typically associated with pesticide intoxication. An indicator of more symptoms (≥ 10 vs. < 10) during the year before enrollment was associated with cumulative lifetime days of insecticide use: odds ratios (95% confidence intervals) were 1.64 (1.36-1.97) for 1-50 days, 1.89 (1.58-2.25) for 51-500 days, and 2.50 (2.00-3.13) for > 500 days, compared with never users. A modest association for fumigants [> 50 days, 1.50 (1.24-1.81)] and weaker relationships for herbicides [> 500 days, 1.32 (0.99-1.75)] and fungicides [> 50 days, 1.23 (1.00-1.50)] were observed. Pesticide use within the year before enrollment was not associated with symptom count. Only associations with insecticides and fumigants persisted when all four pesticide groups were examined simultaneously. Among chemical classes of insecticides, associations were strongest for organophosphates and organochlorines. Associations with cumulative exposure persisted after excluding individuals who had a history of pesticide poisoning or had experienced an event involving high personal pesticide exposure. These results suggest that self-reported neurologic symptoms are associated with cumulative exposure to moderate levels of fumigants and organophosphate and organochlorine insecticides, regardless of recent exposure or history of poisoning.
Pesticides are used extensively throughout the world. In the United States, > 18,000 products are licensed for use, and annual use of pesticides for crops, homes, schools, parks, and forests exceeds 2 billion pounds [U.S. Environmental Protection Agency (EPA) 2002]. Neurologic dysfunction is the best-documented health effect of pesticide exposure. High-level exposure has both acute and long-term neurologic effects, and adverse effects have been reported for most types of pesticides, including organophosphate, carbamate, organochlorine, and pyrethroid insecticides, herbicides, fungicides, and fumigants. Organophosphates have been studied in greatest detail. Acute organophosphate poisoning can involve a wide range of both central and peripheral neurologic symptoms (Ecobichon 1996; Keifer and Mahurin 1997). Effects of organophosphate poisoning may persist long after the acute response is resolved; sequelae include increased neurologic symptoms, deficits in neurobehavioral performance, decreased vibration sensitivity, and impaired nerve conduction (Kamel and Hoppin 2004). Effects continue up to 10 years after poisoning (Savage et al. 1988), suggesting permanent residual damage. Even less severe poisoning can have long-term consequences (Wesseling et al. 2002).
Questions remain concerning the neurologic effects of moderate pesticide exposure. Most studies show effects on cognitive and psychomotor neurobehavioral function in chronically exposed individuals without a history of poisoning, although clinical measures of peripheral nerve function like vibration sensitivity and nerve conduction are not generally affected (Kamel and Hoppin 2004). Increases in both central and peripheral neurologic symptoms are also found in many studies of moderate exposure (Kamel and Hoppin 2004). Increased symptom prevalence may provide early evidence of neurologic dysfunction, before clinically measurable signs are evident. Unresolved issues regarding the relationship of pesticide exposure to symptom prevalence include the relative importance of acute and chronic exposure, of pesticide poisoning or high-exposure events compared with chronic moderate exposure, and of pesticides other than organophosphates.
The Agricultural Health Study (AHS) is a large cohort study of licensed pesticide applicators and their spouses (Alavanja et al. 1996, 1999a). Questionnaires completed by applicators at enrollment provided information on neurologic symptoms during the prior year as well as detailed information on lifetime pesticide use and exposure. We used this information for a cross-sectional analysis of the relationship of symptoms to several measures of pesticide exposure.
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