Pesticide-Induced Diseases: Parkinson’s Disease

The second most common neurodegenerative disease, Parkinson’s disease (PD) occurs when nerve cells in the substantia nigra region of the brain are damaged or destroyed and can no longer produce dopamine, a nerve-signaling molecule that helps control muscle movement. People with PD have a variety of symptoms including loss of muscle control, trembling and lack of coordination. They may also experience anxiety, constipation, dementia, depression, urinary difficulties, and sleep disturbances. Over time, symptoms intensify. At least one million Americans have PD and about 50,000 new cases are diagnosed each year. With less than one percent of cases caused by genetics, researchers have been looking for the potential risk factors for developing Parkinson’s disease (PD). The epidemiological and toxicological evidence is repeatedly identifying exposure to pesticides, as well as specific gene-pesticide interactions, as significant adverse risk factors that contribute to PD. See Beyond Pesticides' Parkinson's Disease article from the Spring 2008 issue of Pesticides and You.

• Occupational pesticide exposure and screening tests for neurodegenerative disease among an elderly population in Costa Rica
  Researchers conducted screening tests for neurologic disease and occupational pesticide use in a population-based sample of 400 elderly subjects at two government-run clinics in Costa Rica.Past occupational pesticide exposure was reported by 18% of subjects. Exposed subjects performed worse on the MMSE than the non-exposed. The exposed had significantly elevated risks of abnormal scores on two UPDRS items, tremor-at-rest, and finger-tapping. Thirty-three (23%) of those examined by the neurologist were diagnosed with possible/probable PD, 3–4 times the expected based on international data; 85% of these cases had not been previously diagnosed. Researchers report that elderly subjects with past occupational pesticide exposure performed significantly worse on screening tests for dementia and PD, and had an increased risk of an eventual PD diagnosis.
  [Steenland, K, Wesseling, C, Roman, N, Quiros, I and Juncos, JL. 2013. Environmental Research. 120:96-101]
• Genetic modification of the association of paraquat and Parkinson's disease
  Authors investigated PD risk associated with paraquat use in individuals with homozygous deletions of the genes encoding glutathione S-transferase M1 (GSTM1) or T1 (GSTT1). Eighty-seven PD subjects and 343 matched controls were recruited from the Agricultural Health Study, a study of licensed pesticide applicators and spouses in Iowa and North Carolina. Two hundred and twenty-three (52%) subjects had GSTM1*0, 95 (22%) had GSTT1*0, and 73 (17%; all men) used paraquat. GSTT1 genotype significantly modified the association between paraquat and PD. In men with functional GSTT1, the odds ratio (OR) for association of PD with paraquat use was 1.5; in men with GSTT1*0, the OR was 11.1. Although replication is needed, our results suggest that PD risk from paraquat exposure might be particularly high in individuals lacking GSTT1. GSTT1*0 is common and could potentially identify a large subpopulation at high risk of PD from oxidative stressors such as paraquat.
  [Goldman, S, Kamel, F, Webster Ross, G, et al. 2012. Movement Disorders. 27(13):1652-1658]
• Is Pesticide Use Related to Parkinson Disease? Some Clues to Heterogeneity in Study Results
  This study is updates the literature published on PD and exposure to pesticides by performing a systematic review and meta-analysis.Summary estimates for subclasses of pesticides indicated a positive association with herbicides and insecticides, but not with fungicides. This review affirms the evidence that exposure to herbicides and insecticides increase the risk of PD. Future studies should focus on more objective and improved methods of pesticide exposure assessment.
  [van der Mark, M, Brouwer, M et al. 2012. Environ Health Perspect. 120(3):340-347]
• Occupational exposure to pesticides and Parkinson's disease: A systematic review and meta-analysis of cohort studies
  The aim of this study was to systematically review available cohort studies and estimate quantitatively the association between occupational exposure to pesticides and Parkinson's disease (PD). Relative risk (RR) estimates were extracted from 12 studies published between 1985 and 2011. Meta-analyses were performed on the whole set of data and separate analyses were conducted after stratification for gender, exposure characterisation, PD cases identification, geographic location, reported risk estimator and cohort study design.A statistically significant increased risk of PD was observed when all studies were combined. A significant increased risk was also seen for banana, sugarcane and pineapple plantation workers. Study concludes that there is some support for the hypothesis that occupational exposure to pesticides increases the risk of PD.
  [Van Maele-Fabry, G, Hoet, P, Vilain, F and Lison, D. 2012. Envrionment International. 46:30-43]
• Parkinson’s disease risk from ambient exposure to pesticides
  A study has found that people whose workplaces were close to fields sprayed with chemicals — not just those who live nearby — are at higher risk of developing Parkinson’s disease (PD). From 2001 to 2007, researchers enrolled 362 incident PD cases and 341 controls living in the Central Valley of California and estimated ambient exposures to the pesticides ziram, maneb, and paraquat at work places and residences from 1974 to 1999. Risk estimates for ambient workplace exposure were greater than for exposures at residences and were especially high for younger onset PD patients and when exposed in both locations. Study is the first to implicate ziram in PD etiology. Combined ambient exposure to ziram and paraquat as well as combined ambient exposure to maneb and paraquat at both workplaces and residences increased PD risk substantially. Those exposed to ziram, maneb, and paraquat together experienced the greatest increase in PD risk. Results suggest that pesticides affecting different mechanisms that contribute to dopaminergic neuron death may act together to increase the risk of PD considerably. Daily News
  [Wang A, et al. 2011. Eur J Epidemiol. DOI: 10.1007/s10654-011-9574-5]
• Rotenone, Paraquat and Parkinson's Disease
  Study investigated whether pesticides that cause mitochondrial dysfunction or oxidative stress are associated with PD or clinical features of parkinsonism in humans. Reserachers assessed lifetime use of pesticides selected by mechanism in a casecontrol study nested in the Agricultural Health Study (AHS). PD was diagnosed by movement disorders specialists.n 110 PD cases and 358 controls, PD was associated with use of a group of pesticides that inhibit mitochondrial Complex I including rotenone and with use of a group of pesticides that cause oxidative stress including paraquat.PD was positively associated with two groups of pesticides defined by mechanisms implicated experimentally: those which impair mitochondrial function and those which increase oxidative stress, supporting a role for these mechanisms in PD pathophysiology.
  [Tanner, CM. et al. 2011. Environ Health Perspect.doi:10.1289/ehp.1002839]
• Interaction Between ABCB1 and Professional Exposure to Organochlorine Insecticides in Parkinson Disease
  Study examined the association between Parkinson disease (PD) and 2 polymorphisms in ABCB1 among subjects enrolled in the French health system for agricultural workers, as well as the interaction between ABCB1 and organochlorine insecticides. Among 101 male cases and 234 matched controls, the odds ratio for organochlorines was 3.5 times higher among homozygous carriers of variant G2677(A,T) alleles than noncarriers. Among cases only, study found an association between carrying 2 variant G2677(A,T) alleles and organochlorines as well as with the number of cumulative lifetime number of hours of exposure. Findings suggest that the ABCB1 gene and exposure to organochlorine insecticides interact to increase PD risk: in subjects professionally exposed to organochlorines, polymorphisms associated with a decreased ability of ABCB1 to clear xenobiotics from the brain increased the risk of PD. These findings support the hypothesis of gene x pesticides interactions in PD.
  [Dutheil. F. et al. 2010. Arch Neurol;67(6):739-745]
• Paraoxonase 1, agricultural organophosphate exposure, and Parkinson disease
  Study found that participants with two copies of a common gene variant showed an increased risk of Parkinson's disease (PD) when exposed to pesticides used in agriculture. In the study group, 14 percent of the pesticide-exposed subjects and 10 percent of the control subjects had the genotype with two copies of the methionine PON1 variant - the MM PON1-55 genotype. Individuals with the variant genotype have an increased risk of Parkinson's disease with exposure to specific insecticides. Participants with the MM PON1-55 genotype and exposed to diazinon or chlorpyrifos showed a twofold increased risk of Parkinson's disease (PD) compared to exposed subjects with wildtype genotype or only one variant copy or non-pesticide exposed subjects. The authors found no increased risk of PD with parathion exposure regardless of genotype.
  [Manthripragada AD, et al. 2010. Epidemiology 21(1):87-94]
• Dopamine Transporter Genetic Variants and Pesticides in Parkinson’s Disease
  324 incident PD patients and 334 population controls from this rural California case–control study were genotyped; rs2652510, rs2550956 (for the DAT 5' clades), and 3' variable number of tandem repeats (VNTR). Using geographic information system methods, authors determined residential exposure to agricultural maneb and paraquat applications. Occupational pesticide use data was also collected. PD risk was increased separately in DAT A clade diplotype carriers and 3' VNTR 9/9 carriers, and data suggest a gene dosing effect. Importantly, high exposure to paraquat and maneb in carriers of one susceptibility allele increased PD risk 3-fold, and in carriers of two or more alleles more than 4-fold. Similar results for occupational pesticide measures were obtained.
  [Ritz BR, et al. 2009. Environ Health Perspect 117(6)]
• Well-Water Consumption and Parkinson’s Disease in Rural California
  Study investigated whether consuming water from private wells located in areas with documented historical pesticide use was associated with an increased risk of PD.Cases were more likely to have consumed private well water and to have consumed it on average 4.3 years longer than controls. High levels of possible well-water contamination with methomyl, chlorpyrifos, and propargite resulted in approximately 70–90% increases in relative risk of PD. Exposure to a higher number of water-soluble pesticides and organophosphate pesticides also increased the relative risk of PD.
  [Gatto NM, et al. 2009. Environ Health Perspect 117:1912-1918]
• Parkinson's Disease and Residential Exposure to Maneb and Paraquat From Agricultural Applications in the Central Valley of California
  In 1998–2007, the authors enrolled 368 incident PD cases and 341 population controls from the Central Valley of California in a case-control study. They generated estimates for maneb and paraquat exposures incurred between 1974 and 1999. Exposure to both pesticides within 500 m of the home increased PD risk by 75% (95% confidence interval (CI): 1.13, 2.73). Persons aged =60 years at the time of diagnosis were at much higher risk when exposed to either maneb or paraquat alone (odds ratio = 2.27, 95% CI: 0.91, 5.70) or to both pesticides in combination (odds ratio = 4.17, 95% CI: 1.15, 15.16) in 1974–1989. This study provides evidence that exposure to a combination of maneb and paraquat increases PD risk, particularly in younger subjects and/or when exposure occurs at younger ages.
  [Costello, S. et al. 2009. American Journal of Epidemiology, doi:10.1093/aje/kwp006]
• Occupation and Risk of Parkinsonism: A Multicenter Case-Control Study
  This multicenter case-control study compared lifelong occupational and job task histories to determine associations with parkinsonism and certain clinical subtypes (postural instability and gait difficulty and age at diagnosis). Risk of parkinsonism increased with pesticide use (odds ratio, 1.90; 95% confidence interval, 1.12-3.21), use of any of 8 pesticides mechanistically associated with experimental parkinsonism (2.20; 1.02-4.75), and use of 2,4-dichlorophenoxyacetic acid (2.59; 1.03-6.48).
  [Tanner, C.M. 2009. Arch Neurol ;66(9):1106-1113]
• Professional exposure to pesticides and Parkinson disease
  Study found a positive association between PD and overall professional pesticide use (odds ratio [OR] = 1.8, 95% confidence interval [CI] = 1.1-3.1), with a dose-effect relation for the number of years of use (p = 0.01). In men, insecticides were associated with PD (OR = 2.2, 95% CI = 1.1-4.3), in particular organochlorine insecticides (OR = 2.4, 95% CI = 1.2-5.0). These associations were stronger in men with older onset PD than in those with younger onset PD, and were characterized by a dose-effect relation in the former group. Results support an association between PD and professional pesticide exposure, and show that some pesticides (ie, organochlorine insecticides) may be more particularly involved.
  [Elbaz, A.et al. 2009. Ann Neurol;66:494-504]
• Ziram Causes Dopaminergic Cell Damage by Inhibiting E1 Ligase of the Proteasome
  Study measured the relative toxicity of ziram (a UPS inhibitor) and analogs to dopaminergic neurons and examined the mechanism of cell death. Results demonstrate that ziram causes selective dopaminergic cell damage in vitro by inhibiting an important degradative pathway implicated in the etiology of PD. Chronic exposure to widely used dithiocarbamate fungicides may contribute to the development of PD.
  [Chou, A. et al. 2008. Journal of Biological Chemistry; 283 pp.34696-34703]
• Pesticide exposure and risk of Parkinson's disease: A family-based case-control study
  Associations of direct pesticide application did not vary by sex but were modified by family history of PD, as significant associations were restricted to individuals with no family history. When classifying pesticides by functional type, both insecticides and herbicides were found to significantly increase risk of PD. Two specific insecticide classes, organochlorines and organophosphorus compounds, were significantly associated with PD. Consuming well-water and living/working on a farm were not associated with PD. Data corroborate positive associations of broadly defined pesticide exposure with PD in families, particularly for sporadic PD.
  [Hancock, D.B., et al. 2008. BMC Neurology 8(6):1471-2377]
• Pesticide exposure and risk of Parkinson's disease: A family-based case-control study
  Using 319 cases and 296 relative and other controls, associations of direct pesticide application, well-water consumption, and farming residences/occupations with PD were examined using generalized estimating equations while controlling for age-at-examination, sex, cigarette smoking, and caffeine consumption. Overall, individuals with PD were significantly more likely to report direct pesticide application than their unaffected relatives (odds ratio = 1.61; 95% confidence interval, 1.13–2.29). Frequency, duration, and cumulative exposure were also significantly associated with PD in a dose-response pattern (p = 0.013). Associations of direct pesticide application did not vary by sex but were modified by family history of PD, as significant associations were restricted to individuals with no family history. When classifying pesticides by functional type, both insecticides and herbicides were found to significantly increase risk of PD. Two specific insecticide classes, organochlorines and organophosphorus compounds, were significantly associated with PD.
  [Hancock, D,B. et al. 2008. BMC Neurology 8(6)]
• Environmental risk factors for Parkinson’s disease and parkinsonism: the Geoparkinson study
  A case–control study of 959 prevalent cases of parkinsonism (767 with Parkinson’s disease) and 1989 controls in Scotland, Italy, Sweden, Romania and Malta was carried out. Adjusted logistic regression analyses showed significantly increased odds ratios for Parkinson’s disease/parkinsonism with an exposure–response relationship for pesticides. Hypnotic, anxiolytic or antidepressant drug use for more than 1 year and a family history of Parkinson’s disease showed significantly increased odds ratios. The association of pesticide exposure with Parkinson’s disease suggests a causative role. Repeated traumatic loss of consciousness is associated with increased risk.
  [Dich, F.D. et al. 2007. Occup Environ Med;64:666-672]
• Pesticide exposure on southwestern Taiwanese with MnSOD and NQO1 polymorphisms is associated with increased risk of Parkinson's disease.
  From southwestern region of Taiwan, 153 patients with idiopathic PD and 155 healthy control subjects matched for age, sex and origin were studied. Exposure to pesticides associated with PD was significant among patients with an increased odds ratio (OR) of 1.69 (95%CI, 1.07-2.65), and this association remained significant after adjustment for age, sex, and cigarette smoking (aOR=1.68, 95%CI, 1.03-2.76, P=0.023). Considering genetic factors, there were no significant differences in frequencies of both genotypes of manganese-containing superoxide dismutase (MnSOD) and quinone oxidoreductase 1 (NQO1) polymorphisms between PD patients and the control subjects (P>0.05). However, this difference in genotype distribution was significant among subjects who had been exposed to pesticide, for MnSOD C allele and for NQO1 T allele, respectively. Moreover, among subjects exposed to pesticide, the combined MnSOD/NQO1 variant genotype was significantly associated with a 4.09-fold increased risk of PD (95%CI, 1.34-10.64, P=0.0052).
  [Fong, C., et al. 2007. Clinica Chimica Acta 378(1-2):136-141]
• Developmental exposure to pesticides zineb and/or endosulfan renders the nigrostriatal dopamine system more susceptible to these environmental chemicals later in life.
  The purpose of this study was to test the hypothesis that exposure to pesticides such as endosulfan and/or zineb during critical periods of postnatal development could result in neuronal dysfunction and enhance the impact of these pesticides during exposure as adults. Mice exposed to these pesticides as juveniles and re-exposed at 8 months of age had significantly altered striatum and brain cortex neurotransmitter levels. Thus, mice re-exposed during adulthood to zineb, endosulfan and their mixtures showed a significantly depleted striatal dopamine levels, to 22, 16 and 35% of control, respectively. Acetylcholinesterase activity in the cerebral cortex was significantly increased in all pesticide treated groups (rho< or =0.05) upon repeated exposure, and pesticide mixture treatment also significantly increased levels of normal and aggregated alpha-synuclein. Collectively, these findings support our hypothesis that exposure to pesticides such as endosulfan and zineb during critical periods of postnatal development contributes to neurotransmitter changes upon re-challenge in adulthood.
  [Jia, Z., et al. 2007. Neurotoxicology 28(4):727-735]
• Microglial activation as a priming event leading to paraquat-induced dopaminergic cell degeneration
  Authors found that a single paraquat exposure was followed by an increase in the number of cells with immunohistochemical, morphological and biochemical characteristics of activated microglia, including induction of NADPH-oxidase. If this microglial response was inhibited by the anti-inflammatory drug minocycline, subsequent exposures to the herbicide failed to cause oxidative stress and neurodegeneration. On the other hand, if microglial activation was induced by pre-treatment with lipopolysaccharide, a single paraquat exposure became capable of triggering a loss of dopaminergic neurons. Finally, mutant mice lacking functional NADPH-oxidase were spared from neurodegeneration caused by repeated paraquat exposures. Data indicate that microglial activation and consequent induction of NADPH-oxidase may act as risk factors for Parkinson’s disease by increasing the vulnerability of dopaminergic cells to toxic injury.
  [Purisai, M.G., et al. 2007. Neurobiology of Disease 25(2):392-400]
• Dopaminergic system modulation, behavioral changes, and oxidative stress after neonatal administration of pyrethroids.
  Pyrethroids are a class of insecticides involved in different neurological disorders. They cross the blood-brain barrier and exert their effect on dopaminergic system, contributing to the burden of oxidative stress in Parkinson's disease through several pathways. The aim of this study was to evaluate the effect of neonatal exposition to permethrin and cypermethrin (1/10 of DL(50)) in rats from the eighth to the fifteenth day of life. Open-field studies showed increased spontaneous locomotor activity in the groups treated with permethrin and the one treated with cypermethrin, while a higher number of center entries and time spent in the center was observed for the cypermethrin-treated group. Lower dopamine and higher homovanillic acid levels were measured in the striatum from both treated groups. A reduction of blood glutathione peroxidase content was measured, while no change in blood superoxide dismutase was observed. Carbonyl group formation increased in striatum, but not in erythrocytes. Lipid peroxidation occurred in erythrocytes, but not in striatum. No changes in fluidity at different depths of plasma membrane were measured in striatum or erythrocytes. The activation of monocyte NADPH oxidase by phorbol esters (PMA) shows that superoxide anion production was reduced in the pyrethroid-treated groups compared to the control group. Study suggests that neonatal exposition to permethrin or cypermethrin induces long-lasting effects after developmental exposure giving changes in open-field behaviors, striatal monoamine level, and increased oxidative stress. Although the action of pyrethroids on various target cells is different, a preferential interaction with the extracellular side of plasma membrane proteins can be observed.
  [Nasuti C, Gabbianelli R, Falcioni ML, et al.2007. Toxicology. 229(3):194-205.]
• Pesticide exposure and self-reported Parkinson's disease in the agricultural health study.
  The authors used data obtained from licensed private pesticide applicators and spouses participating in the Agricultural Health Study to evaluate the relation of self-reported PD to pesticide exposure. Cohort members, who were enrolled in 1993-1997, provided detailed information on lifetime pesticide use. Incident PD was associated with cumulative days of pesticide use at enrollment (for highest quartile vs. lowest, odds ratio (OR) = 2.3, 95% confidence interval: 1.2, 4.5; p-trend = 0.009), with personally applying pesticides more than half the time (OR = 1.9, 95% confidence interval: 0.7, 4.7), and with some specific pesticides (ORs > or = 1.4). Prevalent PD was not associated with overall pesticide use. This study suggests that exposure to certain pesticides may increase PD risk.
  [Kamel, F., et al. 2007. American Journal of Epidemiology 165(4):364-74]
• GSTpi expression mediates dopaminergic neuron sensitivity in experimental parkinsonism.
  Study uses a MPTP model of parkinsonism to examine the role of a dual function protein, GSTpi, in dopaminergic neuron death. GSTpi is the only GST family member expressed in substantia nigra neurons. GSTpi reduction by pharmacological blockade, RNA inhibition, and gene targeting increases sensitivity to the pesticide MPTP, suggesting that differential expression of GSTpi contributes to the sensitivity to xenobiotics in the substantia nigra and may influence the pathogenesis of reactive oxygen species-induced neurological disorders including PD.
  [Smeyne, M., et al. 2007. Proceedings of the National Academy of Sciences 104(6)1977-1982]
• Interaction between genes and environment in neurodegenerative diseases.
  Study found that the inverse association between smoking and the risk of PD depended on a polymorphism of the iNOS (inducible NO synthase) gene. We also found that the cytochrome P450 2D6 gene could have a modifying effect on the risk of PD among persons exposed to pesticides. Both interactions have biological plausibility supported by laboratory studies and could contribute to better understand the aetiology of PD.
  [Elbaz, A. et al. 2007. Comptes Rendus Biologies 330(4):318-328]
• Pesticides and Parkinson’s Disease—Is There a Link?
  A comprehensive review of the published epidemiologic and toxicologic literature and critical evaluation of whether a relationship exists between pesticide exposure and PD. From the epidemiologic literature, there does appear to be a relatively consistent relationship between pesticide exposure and PD. This relationship appears strongest for exposure to herbicides and insecticides, and after long durations of exposure. Toxicologic data suggest that paraquat and rotenone may have neurotoxic actions that potentially play a role in the development of PD, with limited data for other pesticides. At present, the weight of evidence is sufficient to conclude that a generic association between pesticide exposure and PD exists but is insufficient for concluding that this is a causal relationship or that such a relationship exists for any particular pesticide compound or combined pesticide and other exogenous toxicant exposure.
  [Brown, T.P., et al. 2006. Environmental Health Perspectives 114(2):156-164]
• Pyrethroid pesticide-induced alterations in dopamine transporter function.
  Parkinson's disease (PD) is a progressive neurodegenerative disease affecting the nigrostriatal dopaminergic pathway. Several epidemiological studies have demonstrated an association between pesticide exposure and the incidence of PD. Studies have demonstrated that certain pesticides increase levels of the dopamine transporter (DAT), an integral component of dopaminergic neurotransmission and a gateway for dopaminergic neurotoxins. Study reports that repeated exposure of mice to two commonly used pyrethroid pesticides, deltamethrin and permethrin, increases DAT-mediated dopamine uptake by 31 and 28%, respectively. Using cells stably expressing DAT, study determined that exposure (10 min) to deltamethrin and permethrin (1 nM-100 microM) had no effect on DAT-mediated dopamine uptake. Extending exposures to both pesticides for 30 min (10 microM) or 24 h (1, 5, and 10 microM) resulted in significant decrease in dopamine uptake. This reduction was not the result of competitive inhibition, loss of DAT protein, or cytotoxicity. However, there was an increase in DNA fragmentation, an index of apoptosis, in cells exhibiting reduced uptake at 30 min and 24 h. These data suggest that up-regulation of DAT by in vivo pyrethroid exposure is an indirect effect and that longer-term exposure of cells results in apoptosis. Since DAT can greatly affect the vulnerability of dopamine neurons to neurotoxicants, up-regulation of DAT by deltamethrin and permethrin may increase the susceptibility of dopamine neurons to toxic insult, which may provide insight into the association between pesticide exposure and PD.
  [Elwan MA, Richardson JR, Guillot TS, et al. 2006. Toxicol Appl Pharmacol.211(3):188-97]
• Pesticide exposure and risk for Parkinson's disease
  Exposure to pesticides was reported by 7,864 participants (5.7%), including 1,956 farmers, ranchers, or fishermen. Individuals exposed to pesticides had a 70% higher incidence of PD than those not exposed (adjusted relative risk, 1.7; 95% confidence interval, 1.2-2.3; p = 0.002). The relative risk for pesticide exposure was similar in farmers and nonfarmers. No relation was found between risk for PD and exposure to asbestos, chemical/acids/solvents, coal or stone dust, or eight other occupational exposures. These data support the hypothesis that exposure to pesticides may increase risk for PD.
  [Ascherio, Al, et al. 2006. Annals of Neurology 60(2): 197-203.]
• Principles for evaluating health risks in children associated with exposure to chemicals
  The United Nation’s World Health Organization report on children’s heightened vulnerability to chemical exposures at different periods of their growth and development states, “neurotoxic insults during development that result in no observable phenotype at birth or during childhood could manifest later in life as earlier onset of neurodegenerative diseases such as [PD].”
  [Louis, G.B., et al. 2006. Environmental health criteria: 237. World Health Organization. Geneva, Switzerland]
• Chemical exposures and Parkinson's disease: a population-based case-control study.
  Study identified all subjects who developed PD in Olmsted County, Minnesota, from 1976 through 1995, and matched them by age (+/- 1 year) and sex to general population controls. Authors assessed exposures to chemical products by means of telephone interview with cases, controls, or their proxies (149 cases; 129 controls). Exposure to pesticides related or unrelated to farming was associated with PD in men (odds ratio, 2.4; 95% confidence interval, 1.1-5.4; P = 0.04). The association remained significant after adjustment for education or smoking. This population-based study suggests a link between pesticides use and PD that is restricted to men. Pesticides may interact with other genetic or nongenetic factors that are different in men and women.
  [Frigerio, R., et al. 2006. Movement Disorders 21(10): 1688-1692]
• Developmental exposure to the pesticide dieldrin alters the dopamine system and increases neurotoxicity in an animal model of Parkinson’s disease
  Study reports that perinatal exposure of mice during gestation and lactation to low levels of dieldrin (0.3, 1, or 3 mg/kg every 3 days) alters dopaminergic neurochemistry in their offspring and exacerbates MPTP toxicity. Results suggest that developmental exposure to dieldrin leads to persistent alterations of the developing dopaminergic system and that these alterations induce a "silent" state of dopamine dysfunction, thereby rendering dopamine neurons more vulnerable later in life. In all cases there were greater effects observed in the male offspring than the female, similar to that observed in human cases of PD.
  [Richardson, J.R., et al. 2006. The FASEB Journal 20(10):1695-1697]
• Parkinson Disease: PD Gene and Oxidative Stress
  Drosophila flies lacking the DJ-1 gene showed selective sensitivity to widely used agricultural toxicants that kill neurons mainly through oxidative stress. DJ-1 mutant flies exposed to the herbicide paraquat died much sooner than normal flies. The mutants also showed marked sensitivity to the insecticide rotenone and to hydrogen peroxide-both agents that promote oxidative stress. These results suggest that DJ-1 normally protects against oxidative stress and that its inactivation may leave neurons susceptible to oxidative damage. The study also found that exposure to paraquat led to biochemical modification of the DJ-1ß protein, a change which may influence the ability of DJ-1 to protect neurons from oxidative damage. Studies of DJ-1 in Drosophila will provide greater understanding of fundamental activities of the gene, helping to elucidate how its function may be critical in PD.
  [Phillips, M.L. 2006. Environmental Health Perspectives 114(2)]
• Perinatal heptachlor exposure increases expression of presynaptic dopaminergic markers in mouse striatum.
  In this study, authors examined the effects of developmental exposure to heptachlor on the dopamine transporter (DAT), and other key components of the dopaminergic system, including the vesicular monoamine transporter 2 (VMAT2), tyrosine hydroxylase (TH), and aromatic amino acid decarboxylase (AADC). On postnatal day 28, DAT, VMAT2, and TH levels were increased by 100, 70, and 30%, respectively, with no change in AADC levels or total dopamine levels. The ratio of DAT:VMAT2 was increased 29%. Since an increase in the DAT:VMAT2 ratio appears to predict susceptibility of brain regions to Parkinson's disease (PD) and results in increased toxicity of MPTP, these results suggest that alterations of the dopaminergic system by developmental heptachlor exposure may increase the susceptibility of dopamine neurons to toxic insult.
  [Caudle, W.M., et al. 2005. NeuroToxicology 26(4):721-728]
• Drosophila DJ-1 mutants are selectively sensitive to environmental toxins associated with Parkinson's disease.
  Study involoving Drosophila flies to develop an animal model that would allow integrative study of genetic and environmental influences. Study demonstrates that fly DJ-1 activity is selectively involved in protection from environmental oxidative insult in vivo and that the inherited PD gene, DJ-1beta protein, is biochemically responsive to oxidative stress. Study of these flies will provide insight into the critical interplay of genetics and environment in PD.
  [Meulener, M., et. al. 2005. Current Biology 15(17): 1572-1577]
• Developmental pesticide exposures and the Parkinson's disease phenotype.
  Study found that postnatal exposures of mice to pesticides, paraquat + maneb, led not only to a permanent and selective loss of dopaminergic neurons in the substantia nigra pars compacta but also enhanced the impact of these pesticides administered during adulthood relative to developmental only or adult only treatment. Exposure to maneb alone during gestation resulted in a dramatic response to paraquat in adulthood, including notable reductions in levels of dopamine and metabolites and a loss of nigral dopamine (DA) neurons, despite the fact that paraquat does not share structural similarity to or mechanisms of action with maneb. Collectively, these studies provide developmental environmental models of the PD phenotype.
  [Cory-Slechta D.A., et al. 2005. Birth Defects Res A Clin Mol Teratol 73:136–139]
• Pesticides and risk of Parkinson disease: a population-based case-control study.
  Study investigated associations between pesticide exposures and idiopathic PD and found significantly increased ORs from lifelong well water consumption (OR, 1.81; 95% CI, 1.02-3.21). Study also found elevated ORs from herbicides (OR, 1.41; 95% CI, 0.51-3.88) and paraquat (OR, 1.67; 95% CI, 0.22-12.76).
  [ J.A., et al. 2005. Archives of Neurology 62(1):91-95]
• Modulation of antioxidant defense systems by the environmental pesticide maneb in dopaminergic cells.
  Authors believe environmental contaminants such as pesticides make dopamine cells more vulnerable to damage from normal aging, infection, or subsequent exposure to pollutants. Study primarily utilized the PC12 cell line, which displays a catecholaminergic phenotype. Low concentrations of maneb (50-1000 ng/ml) had little effect on cell viability, as measured by LDH release. hese same concentrations, however, led to increases in glutathione (GSH) and its oxidized form, GSSG. Results suggest that following an insult to the GSH antioxidant system, maneb can act as an additional insult to the system and prevent the normal recovery of those defenses. Dopaminergic neurons, as a population, are inherently vulnerable to oxidative stress, and the disruption of antioxidant systems by the fungicide maneb may contribute to the neurodegeneration of these cells, especially with concurrent exposures to other environmentally relevant oxidative stressors.
  [Barlow, B.K., et al. 2005. Neurotoxicology 26(1):63-75]
• A fetal risk factor for Parkinson's disease.
  This study hypothesized that prenatal exposure to pesticides would disrupt the development of the nigrostriatal dopamine (DA) system and enhance its vulnerability to dopaminergic neurotoxicant exposures later in life. One week after the last exposure to maneb or paraquat, only male mice exposed to prenatal maneb and adulthood paraquat showed significant reductions in locomotor activity (95%) and changes in striatal neurochemistry. Stereological assessment of the substantia nigra pars compacta (SNpc) and ventral tegmental area correspondingly confirmed selective dopaminergic-neuron loss in SNpc. The lack of changes in other exposure groups suggests a specificity to the sequence of exposures as well as gender specificity. These results suggest that prenatal exposure to maneb produces selective, permanent alterations of the nigrostriatal dopaminergic system and enhances adult susceptibility to paraquat exposure.
  [Barlow, B.K., et al. 2004. Dev Neurosci 26(1):11-23]
• No evidence for heritability of Parkinson disease in Swedish twins
  The aim of the study was to evaluate heritability of PD in same-sexed and opposite-sexed twin pairs in the Swedish Twin Registry (STR). For possible PD, there were only two concordant pairs, both female dizygotic. Similarly, concordances were low in all zygosity groups when the definition of affected was expanded to include twins with suspected parkinsonism or movement disorder in addition to possible PD. Sex differences in the relative importance of genetic and environmental effects were indicated with a marginally larger familial component in women. Results suggest that environmental factors are most important in the etiology of PD. Compared with other complex diseases, the importance of genetic effects in PD is notably low. The preponderance of discordant twin pairs provides an ideal material for studying environmental risk factors and potential genotype-by-environment interaction.
  [Wirdefeldt, K., et al. 2004. Neurology 63(2):305-311]
• A case-control study of Parkinson's disease in a horticultural region of British Columbia
  Study compared personal histories of 127 cases and 245 controls to identify possible environmental risk factors for idiopathic parkinsonism (IP). Data found a significant association between IP and having had an occupation in which exposure through handling or directly contacting pesticides was probable, but no specific chemicals were associated with IP. Study concluded that although occupations involving the use of agricultural chemicals may predispose to the development of IP, it seems likely that the pathogenesis is multifactorial rather than related to a specific agent.
  [Hertzman, C., et al. 2004. Movement Disorders 9(1):69-75]
• Association between Parkinson’s disease and exposure to pesticides in southwestern France.
  A case-control study was performed in southwestern France in order to assess the relationship between pesticide exposure and Parkinson's disease (PD) in the elderly. During the period from 1997 to 1999, 84 cases were recruited together with 252 population-based controls. A positive association was found with occupational pesticide exposure (odds ratio = 2.2, 95% confidence interval 1.1-4.3) in conditional logistic multiple regression analysis taking into account age, sex, educational level and smoking; however, no clear dose relationship was found.
  [Baldi, I., et al. 2003. Neuroepidemiology 22(5):305-310]
• Neurodegenerative Diseases and Exposure to Pesticides in the Elderly
  The authors investigated the hypothesis that exposure to pesticides could be related to central nervous system disorders in a prospective cohort study of 1,507 French elderly (1992–1998). Lower cognitive performance was observed in subjects who had been occupationally exposed to pesticides. In men, the relative risks of developing Parkinson’s disease and Alzheimer’s disease for occupational exposure assessed by a job exposure matrix were 5.63 (95% confidence interval: 1.47, 21.58) and 2.39 (95% confidence interval: 1.02, 5.63), respectively, after confounding factors were taken into account. These results suggest the presence of neurologic impairments in elderly persons who were exposed occupationally to pesticides.
  [Baldi, I., et al. 2003. American Journal of Epidemiology 157(5):409-414]
• Age-related irreversible progressive nigrostriatal dopaminergic neurotoxicity in the paraquat and maneb model of the Parkinson's disease phenotype.
  Study tested exposed C57BL/6 mice that were 6 weeks, 5 months or 18 months old to the herbicide paraquat, the fungicide maneb or paraquat + maneb, a combination that produces a Parkinson's disease phenotype in young adult mice. Paraquat + maneb-induced reductions in locomotor activity and motor coordination were age dependent, with 18-month-old mice most affected and exhibiting failure to recover 24 h post-treatment. Three months post-treatment, reductions in locomotor activity and deficits in motor coordination were sustained in 5-month-old and further reduced in 18-month-old paraquat + maneb groups. Progressive reductions in dopamine metabolites and dopamine turnover were greatest in 18-month-old paraquat + maneb and paraquat groups 3 months post-treatment. Collectively, these data demonstrate enhanced sensitivity of the ageing nigrostriatal dopamine pathway to these pesticides, particularly paraquat + maneb, resulting in irreversible and progressive neurotoxicity.
  [Thiruchelvam, M., et al. 2003. Eur J Neurosci 18(3):589-600]
• Familial and environmental risk factors in Parkinson's disease: a case-control study in north-east Italy.
  Study of136 patients with neurologist confirmed PD and 272 age- and sex-matched controls, affected by neurological diseases not related to PD. The risk of developing idiopathic PD associated with the following familial and environmental factors: positive family history of PD, positive family history of essential tremor (ET), age of mother at subject's birth, rural birth, rural living, well water use, farming as an occupation, exposure to pesticides, head tremor, exposure to general anaesthesia and to ionizing radiations, food restriction, concentration camp imprisonment and smoking has been assessed by using univariate and multivariate statistical techniques.
  [Zorzon, M., et al. 2002. Acta Neurol Scand 105(2):77-82]
• Plantation work and risk of Parkinson disease in a population-based longitudinal study.
  Objective of this study was to determine whether working on a plantation in Hawaii and exposure to pesticides are associated with an increased risk of PD decades later. During follow-up, 116 men developed PD. Age-adjusted incidence increased significantly among men who worked more than 10 years on a plantation. The relative risk of PD was 1.0 (95% confidence interval, 0.6-1.6), 1.7 (95% confidence interval, 0.8-3.7), and 1.9 (95% confidence interval, 1.0-3.5) for men who worked on a plantation 1 to 10 years, 11 to 20 years, and more than 20 years compared with men who never did plantation work (P =.006, test for trend). These longitudinal observations regarding plantation work in Hawaii support case-control studies suggesting that exposure to pesticides increases the risk of PD.
  [Petrovitch, H., et al. 2002. Archives of Neurology 59(11):1787-1792]
• Developmental exposure to the pesticides paraquat and maneb and the Parkinson's disease phenotype.
  This study hypothesized that paraquat (PQ) and maneb (MB) exposure during critical periods of development could permanently change the nigrostriatal dopamine (DA) system and enhance its vulnerability to subsequent neurotoxicant challenges. Mice exposed developmentally to PQ + MB and rechallenged as adults were the most affected, showing a 70% reduction in motor activity 2 weeks following the last rechallenge dose. Striatal DA levels were reduced by 37% following developmental exposure to PQ + MB only, butfollowing adult re-challenge levels were reduced by 62%. A similar pattern of nigral dopaminergic cell loss was observed, with the PQ + MB treated group exhibiting the greatest reduction, with this loss being amplified by adult re-challenge. Following adult re-challenge, significant decreases in DA and nigral cell counts were observed, suggesting that exposure to either neurotoxicant alone produced a state of silent toxicity that was unmasked following adult re-exposure. Taken together, these findings indicate that exposure to pesticides during the PN period can produce permanent and progressive lesions of the nigrostriatal DA system, and enhanced adult susceptibility to these pesticides, suggesting that developmental exposure to neurotoxicants may be involved in the induction of neurodegenerative disorders and/or alter the normal aging process.
  [Thiruchelvam, M., et al. 2002. Neurotoxicology 23(4-5):621-633]
• Environmental Risk Factors and Parkinson's Disease: A Metaanalysis
  A series of metaanalyses of peer-reviewed studies were performed, using 16 studies for living in rural area, 18 studies for well water drinking, 11 studies for farming, and 14 studies for pesticides.The majority of the studies reported consistent elevation in the risk of PD with exposure to environmental factors such as rural living and farming. Findings suggest that living in a rural area, drinking well water, farming, and exposure to pesticides may be a risk factor for developing PD.
  [Priyadarshi, A., et al. 2001.Environ Res 86(2):122-127]
• Parkinsonism and occupational exposure to pesticides
  Parkinsonism may be associated with long term occupational exposure to pesticides, although no associations with specific pesticides could be detected. This finding is consistent with most of the publications on this topic.
  [Engel, L.S., et al. 2001.Occupational and Environmental Medicine 58(9):582-589]
• Parkinson's disease mortality and pesticide exposure in California 1984-1994.
  A California mortality study of individuals whose death certificates mention PD as an underlying cause of death and cross-referenced with agricultural and pesticide use data finds that the counties using restricted use pesticides (RUP) for agricultural purposes have about a 40 percent increase in PD mortality when compared to those counties reporting no RUP.
  [Ritz B, and Yu F. 2000. International Journal of Epidemiology 29(2):323-329]
• Agricultural work and the risk of Parkinson's disease in Denmark, 1981-1993
  This study examined the possible association between agricultural and horticultural work and the subsequent morbidity of Parkinson's disease. A high risk of Parkinson's disease was found for the men and women in agriculture and horticulture (134 cases, SHR 132, 95% CI 111-156). Statistically significantly high risks were found for farmers (79 cases, SHR 130, 95% CI 103-163) and for all men in agriculture and horticulture (109 cases, SHR 134, 95% CI 109-162).
  [Tuchsen, F., et al. 2000. Scand J Work Environ Health 26(4):359-362]
• Exposure to home pesticides linked to Parkinson disease.
  This study raises concerns for residential pesticide exposure. Stanford University researchers find a 70 percent increased risk of developing PD for individuals that use pesticides in their home. Exposure to garden insecticides carries a 50 percent increased risk of developing the disease. Among herbicide users, the risk of developing PD increases as the number of days in contact with herbicides grows. Respondents who reported handling or applying herbicides for up to 30 days are 40 percent more likely to develop the disease, whereas respondents that reported 160 days exposure, have a 70 percent increase.
  [Stephenson, J. 2000. JAMA 283:3055-3056]
• A meta-analysis of Parkinson's disease and exposure to pesticides.
  A series of meta-analysis of peer-reviewed studies were performed, using 19 studies published between 1989 and 1999. The majority of the studies reported consistent elevation in the risk of PD with exposure to pesticides. The combined OR studies was 1.94 [95% confidence interval (95% CI) 1.49-2.53] for all the studies, and 2.15 (95% CI 1.14-4.05) for studies performed in United States. Although the risk of PD increased with increased duration of exposure to pesticides, no significant dose-response relation was established, and no specific type of pesticide was identified. Findings suggest that exposure to pesticides may be a significant risk factor for developing PD.
  [Priyadarshi, A., et al. 2000. Neurotoxicology 21(4):435-440.]
• Nutritional and occupational factors influencing the risk of Parkinson's disease: a case-control study in southeastern Sweden.
  Study investigates the possible impact of nutritional and environmental risk factors for idiopathic Parkinson's disease (IP), a case-control study was performed in the county of Ostergötland in southeastern Sweden. The study involved 113 cases of IP and 263 control subjects. A reduced risk was found for coffee, wine, and liquor at various consumption levels but also for fried or broiled meat, smoked ham or meat, eggs, French loaf or white bread, and tomatoes. All these food and drink items contain niacin. As in many studies, the frequency of preceding and present smoking was reduced in IP patients. Various occupational groups and exposures were analyzed and increased risks of IP in men were found for agricultural work along with pesticide exposure; this was also the case for male carpenters and female cleaners.
  [Fall, P., et al. 1999. Movement Disorders 14(1):28-37]
• Genetic and environmental risk factors for Parkinson’s disease in a Chinese population
  An epidemiological study of the environmental and genetic factors as well as the possible interplay between them was conducted among 215 patients with Parkinson’s disease and 313 controls in a Chinese population in Hong Kong. In multivariate analysis, current smoking reached borderline significance at the 5% level and the variables, years exposed to pesticides and family history were significant at the 10% level.
  [Chan, D.K. 1998. Journal of Neurology, Neurosurgery and Psychiatry 65:781-784]
• Parkinson's disease, pesticides, and glutathione transferase polymorphisms.
  Study investigated the role of GST polymorphisms in the pathogenesis of idiopathic Parkinson's disease. Authors genotyped by PCR polymorphisms in four glutathione transferases (GST) classes (GSTM1, GSTT1, GSTP1, and GSTZ1) in 95 Parkinson's disease patients and 95 controls. The distribution of the GSTP1 genotypes differed significantly between patients and controls who had been exposed to pesticides No association was found with any of the other GST polymorphisms. Pesticide exposure and a positive family history were risk factors for Parkinson's disease. GSTP1-1, which is expressed in the blood-brain barrier, may influence response to neurotoxins and explain the susceptibility of some people to the parkinsonism-inducing effects of pesticides.
  [Menegon, A., et al. 1998. The Lancet 352(9137):1344-1346]
• The Epidemiology of Parkinson’s Disease in an Australian Population
  A prevalence study of Parkinson’s disease (PD) was conducted in the rural town of Nambour, Australia. A positive family history of PD was the strongest risk factor for the development of the disease (odds ratio = 3.4; p < 0.001). In addition, rural residency was a significant risk factor for PD (odds ratio = 1.8, p < 0.001).
  [McCann, S.J., et al. 1998. Neuroepidemiology 17(6):310-317]
• The risk of Parkinson's disease with exposure to pesticides, farming, well water, and rural living.
  Study assessed exposure to pesticides, farming, well water use, and rural living as risk factors for Parkinson's disease (PD) in a population-based case-control study consisting of men and women > or = 50 years of age. Farming as an occupation was significantly associated with PD (OR, 2.79; 95% CI, 1.03, 7.55). The association of occupational exposure to herbicides or insecticides with PD remained after adjustment for farming. The association of farming with PD was maintained after adjustment for occupational herbicide exposure and was of borderline significance after adjustment for occupational insecticide exposure. These results suggest that PD is associated with occupational exposure to herbicides and insecticides and to farming and that the risk of farming cannot be accounted for by pesticide exposure alone.
  [Gorell, J.M., et al. 1998. Neurology 50:1346-1350]
• Gene-toxin interaction as a putative risk factor for Parkinson's disease with dementia.
  Study explores the hypothesis that genetic traits coupled with nongenetic factors may raise the risk of development of Parkinson's disease with dementia (PD + D). The study cohort of 43 PD + D and 51 PD-D subjects was analyzed examining environmental, sociodemographic and clinical variables along with 3 candidate gene markers. Subjects who had pesticide exposure and at least 1 copy of the CYP 2D6 29B+ allele had 83% predicted probability of PD + D (stepwise logistic regression model: p = 0.0491). This case-control study provides preliminary evidence that a gene-toxin interaction may play an etiological role in PD + D.
  [Hubble, J.P., et al. 1998. Neuroepidemiology 17(2):96-104]
• Possible environmental, occupational, and other etiologic factors for Parkinson's disease: A case-control study in Germany
  A case-control study investigated the possible etiologic relevance to Parkinson's disease (PD) of rural factors such as farming activity, pesticide exposures, well-water drinking, and animal contacts; toxicologic exposures such as wood preservatives, heavy metals, and solvents; general anesthesia; head trauma; and differences in the intrauterine environment. There were significantly elevated odds ratios (OR) for pesticide use, in particular, for organochlorines and alkylated phosphates, but no association was present between PD and other rural factors. A significantly elevated OR was present for exposure to wood preservatives.
  [Seidler, A. et al. 1996.Nuerology; 46:1275]
• The Role of the Environment in Parkinson's Disease
  Thirty leading scientists in the field of Parkinson's disease research attended a conference, "The Role of the Environment in Parkinson's Disease," 17-19 September 1995, sponsored and hosted by the National Institute of Environmental Health Sciences. The role of the environment was highlighted, but considerable attention was given to pathological neurochemistry and genetic issues in the etiopathogenesis of Parkinson's disease.
  [Gorrell, J.M. et al. 1996. Meeting Report. National Institute of Environmental Health Sciences. Environmental Health Perspectives;104(6)]
• Neurodegenerative diseases: occupational occurrence and potential risk factors, 1982 through 1991.
  To identify potential occupational risk factors, this study examined the occupational occurrence of various neurodegenerative diseases:presenile dementia, Alzheimer's disease, Parkinson's disease, and motor neuron disease. Excess mortality was observed for all four categories in the following occupational categories: teachers; medical personnel; machinists and machine operators; scientists; writers/designers/entertainers; and support and clerical workers. Clusters of three neurodegenerative diseases were also found in occupations involving pesticides, solvents, and electromagnetic fields and in legal, library, social, and religious work.
  [Schulte, P.A., et al. 1996. American Journal of Public Health 86(9):1281-1288]
• Environmental antecedents of young-onset Parkinson's disease
  An exploratory study of young-onset Parkinson's disease (YOPD) to examine occupational and environmental factors associated with disease risk.PD was positively associated with insecticide exposure (OR = 5.75, p < 0.001), past residency in a fumigated house (OR = 5.25, p = 0.046), herbicide exposure (OR = 3.22, p = 0.033), rural residency at time of diagnosis (OR = 2.72, p = 0.027), and nuts and seed eating 10 years before diagnosis (OR = 1.49, p = 0.021). These findings are consistent with hypotheses linking PD to exposure to pesticide agents.
  [Butterfield, P.G., et al. 1993. Neurology 43(6):1150-1158.]
• Risk factors for Parkinson's disease
  Study examined social and medical histories of predominantly rural populations to determine relative risk factors for PD. Significant predictors of PD emerged (in order of strength): pesticide use, family history of neurologic disease, and history of depression. The predicted probability of PD was 92.3% (odds ratio = 12.0) with all three predictors positive. Pesticide use (distinguishable from rural living) can be considered a risk factor for the development of PD, with family history of neurologic disease and history of depression serving as weaker predictors of PD.
  [Hubble, J.P., et al. 1993. Neurology 43:1693-97]
• Parkinson's disease and exposure to agricultural work and pesticide chemicals.
  A population-based case-control study of 130 Calgary residents with neurologist-confirmed idiopathic Parkinson's disease (PD) and 260 randomly selected age- and sex-matched community controls to determine whether agricultural work or the occupational use of pesticide chemicals is associated with an increased risk for PD. In the multivariate analysis, which controlled for potential confounding or interaction between the exposure variables, previous occupational herbicide use was consistently the only significant predictor of PD risk.
  [Semchuk, K.M., et al. 1992. Neurology 42:1328-1335]
• Parkinson's disease in Ferrara, Italy, 1967 through 1987.
  Authors studied the frequency of Parkinson's disease in the Local Health Service of Ferrara, northeastern Italy. The study revealed a significantly higher incidence rate among agricultural workers (20.6/100,000). These results would seem to give further support to the hypothesis of a possible causal role of environmental factors that are mainly linked to agriculture, most likely due to the continual exposure to toxic agents in this area.
  [Granieri, E., et al. 1991. Archives of Neurology 48(8):854-857]
• Environmental risk factors in Parkinson's disease
  Study investigated possible risk factors for Parkinson's disease (PD) and conducted a case-control study of 150 PD patients and 150 age- and sex-matched controls. Rural living and drinking well water were significantly increased in the PD patients. This was observed regardless of age at disease onset. Drinking well water was dependent on rural living. There were no significant differences between cases and controls for farming or any measure of exposure to herbicides or pesticides. These data provide further evidence that an environmental toxin could be involved in the etiology of PD.
  [Koller, W. et al. 1990. Neurology. 40(8):1218-1221]
• Ecogenetics of Parkinson's disease: prevalence and environmental aspects in rural areas.
  Study demonstrates that the prevalence of Parkinson's disease is of uneven distribution within rural areas of Quebec, Canada. Study further investigates the characteristics of the regions of high prevalence. These regions which are predominantly agricultural and areas of intensive market gardening were also the areas with the highest use of pesticides.
  [Barbeau, A., et al. 1987. Can J Neurol Sci 14(1) 36-41]