Agricultural Health Study Participants Research Articles

Drinking Water Sources and Water Quality in the Agricultural Health Study

BACKGROUND AND AIM: Drinking water contaminants have been associated with adverse health effects. However, little is known about exposures in agricultural communities where farm practices and well use may enhance exposures to specific contaminants. We describe the exposure assessment and exposure distributions for common drinking water contaminants by water source in an agricultural population. METHODS: We used questionnaire data from the Agricultural Health Study (AHS), a cohort of licensed pesticide applicators (mostly farmers) and their spouses in Iowa (IA) and North Carolina (NC) to ascertain drinking water source at enrollment (1993-1997). For users of public water supplies (PWS), we linked participants’ geocoded addresses to monitoring data for regulated contaminants, including five haloacetic acids (HAA5), total trihalomethanes (TTHM), and nitrate-nitrogen (NO₃-N). For private well users, we estimated nitrate levels using previously developed random forest models based on well depth, land use, soil characteristics, nitrogen inputs, and other relevant factors. RESULTS:We assigned drinking water source for 84% (N=74,919) of AHS participants; approximately 70% in IA and 75% in NC used private wells. Median nitrate concentrations (mg/L NO₃-N) in PWS were higher in IA (0.8, interquartile range (IQR): 0.2-3.1) than NC (0.5, IQR: 0.5-0.6), while median concentrations of HAA5 (µg/L) and TTHM (µg/L) were higher in NC (HAA5: 12.1, IQR: 3.8-33.4; TTHM: 35.4, IQR: 8.8-54.7) than IA (HAA5: 4.3, IQR: 3.0-10.5; TTHM: 13.0, IQR: 3.7-32.3). Private well nitrate concentrations in IA (1.5, IQR: 0.8-4.9) and NC (1.9, IQR: 1.4-2.5) were higher than in PWS. A larger proportion of private wells exceeded the 10mg/L regulatory limit in IA (12%) than NC (1%). CONCLUSIONS:Drinking water nitrate levels were higher for private well users and in IA PWS, while TTHM and HAA5 levels were higher in NC PWS. This work will facilitate future analyses of the health effects of drinking water contaminants in the AHS. KEYWORDS: Water quality, Exposure assessment, Environmental epidemiology

Overall and cause-specific mortality in a cohort of farmers and their spouses

ObjectivesLower mortality rates compared with the general population have been reported for Agricultural Health Study (AHS) participants (enrolled 1993–1997) followed through 2007. We extended analysis of mortality among AHS participants...

Industrial hog farming is associated with altered circulating immunological markers

ObjectivesThe previously observed inverse association between hog farming and risk of lung cancer in the Agricultural Health Study (AHS) has been attributed to endotoxin exposure, the levels of which are...

Pesticide Use and Relative Leukocyte Telomere Length in the Agricultural Health Study.

Some studies suggest that telomere length (TL) may be influenced by environmental exposures, including pesticides. We examined associations between occupational pesticide use reported at three time points and relative telomere length (RTL) in the Agricultural Health Study (AHS), a prospective cohort study of pesticide applicators in Iowa and North Carolina. RTL was measured by qPCR using leukocyte DNA from 568 cancer-free male AHS participants aged 31-94 years with blood samples collected between 2006 and 2008. Self-reported information, including pesticide use, was collected at three time points: enrollment (1993-1997) and two follow-up questionnaires (1998-2003, 2005-2008). For each pesticide, we evaluated cumulative use (using data from all three questionnaires), and more recent use (using data from the last follow-up questionnaire). Multivariable linear regression was used to examine the associations between pesticide use (ever, lifetime days, intensity-weighted lifetime days (lifetime days*intensity score)) and RTL, adjusting for age at blood draw and use of other pesticides. Of the 57 pesticides evaluated with cumulative use, increasing lifetime days of 2,4-D (p-trend=0.001), diazinon (p-trend=0.002), and butylate (p-trend=0.01) were significantly associated with shorter RTL, while increasing lifetime days of alachlor was significantly associated with longer RTL (p-trend=0.03). Only the association with 2,4-D was significant after adjustment for multiple comparisons. Of the 40 pesticides evaluated for recent use, malathion was associated with shorter RTL (p=0.03), and alachlor with longer RTL (p=0.03). Our findings suggest that leukocyte TL may be impacted by cumulative use and recent use of certain pesticides.

Pesticide exposure and amyotrophic lateral sclerosis

Our objectives were to summarize literature on the association of amyotrophic lateral sclerosis (ALS) with pesticides as a group and to evaluate associations of ALS with specific pesticides. We conducted a meta-analysis of published studies of ALS and pesticides as a group and investigated the association of ALS with specific pesticides, using data from the Agricultural Health Study (AHS), a cohort including 84,739 private pesticide applicators and spouses. AHS participants provided information on pesticide use at enrollment in 1993–1997. In mortality data collected through February 2010, ALS was recorded on death certificates of 41 individuals whom we compared to the remaining cohort (controls), using unconditional logistic regression adjusted for age and gender to calculate odds ratios (ORs) and 95% confidence intervals. In the meta-analysis, ALS was associated with use of pesticides as a group (1.9, 1.1–3.1). In the AHS, ALS was not associated with pesticides as a group, but was associated with use of organochlorine insecticides (OCs) (1.6, 0.8–3.5), pyrethroids (1.4, 0.6–3.4), herbicides (1.6, 0.7–3.7), and fumigants (1.8, 0.8–3.9). ORs were elevated forever use of the specific OCs aldrin (2.1, 0.8–5.1), dieldrin (2.6, 0.9–7.3), DDT (2.1, 0.9–5.0), and toxaphene (2.0, 0.8–4.9). None of these associations was statistically significant. Similar results were observed in an analysis restricted to men. In conclusion, the meta-analysis suggests that ALS risk is associated with use of pesticides as a group, and our analysis of AHS data points to OC use in particular. The latter results are novel but based on a small number of cases and require replication in other populations.

Suicide and Pesticide Use among Pesticide Applicators and Their Spouses in the Agricultural Health Study

Background: An association may exist between pesticide exposure and suicide.Objective: We sought to evaluate the existence of an association between pesticide use and suicide using data from the Agricultural Health Study (AHS), a prospective cohort study of licensed pesticide applicators and their spouses in Iowa and North Carolina.Methods: Via linkage to state mortality files and the National Death Index, we identified 110 suicides occurring between enrollment in the AHS (from 1993 to 1997) and 31 May 2009, among 81,998 cohort members contributing 1,092,943 person-years of follow-up. The average length of follow-up was 13.3 years. AHS participants provided data on pesticide use and potential confounders via self-administered questionnaires at enrollment. We evaluated several measures of pesticide use: use of any pesticide, ever use of 50 specific pesticides, cumulative lifetime days of use and intensity-adjusted cumulative lifetime days of use of 22 specific pesticides, and ever use of 10 functional and chemical classes of pesticides. We used Cox proportional hazards regression models to estimate adjusted hazard ratios and 95% confidence intervals.Results: After adjusting for age at enrollment, sex, number of children in family, frequency of alcohol consumption during the past 12 months, and smoking status, we found no association between prior pesticide use and suicide in applicators and their spouses. Results were the same for applicators and spouses together or for applicators alone and were consistent across several measures of pesticide use.Conclusions: Our findings do not support an association between moderate pesticide use and suicide.

Rotenone, Paraquat, and Parkinson’s Disease

BackgroundMitochondrial dysfunction and oxidative stress are pathophysiologic mechanisms implicated in experimental models and genetic forms of Parkinson’s disease (PD). Certain pesticides may affect these mechanisms, but no pesticide has been definitively associated with PD in humans.ObjectivesOur goal was to determine whether pesticides that cause mitochondrial dysfunction or oxidative stress are associated with PD or clinical features of parkinsonism in humans.MethodsWe assessed lifetime use of pesticides selected by mechanism in a case–control study nested in the Agricultural Health Study (AHS). PD was diagnosed by movement disorders specialists. Controls were a stratified random sample of all AHS participants frequency-matched to cases by age, sex, and state at approximately three controls: one case.ResultsIn 110 PD cases and 358 controls, PD was associated with use of a group of pesticides that inhibit mitochondrial complex I [odds ratio (OR) = 1.7; 95% confidence interval (CI), 1.0–2.8] including rotenone (OR = 2.5; 95% CI, 1.3–4.7) and with use of a group of pesticides that cause oxidative stress (OR = 2.0; 95% CI, 1.2–3.6), including paraquat (OR = 2.5; 95% CI, 1.4–4.7).ConclusionsPD was positively associated with two groups of pesticides defined by mechanisms implicated experimentally—those that impair mitochondrial function and those that increase oxidative stress—supporting a role for these mechanisms in PD pathophysiology.

An update of cancer incidence in the Agricultural Health Study.

Our objective is to reevaluate cancer incidence among Agricultural Health Study participants. Standardized incidence ratios (SIRs) and relative standardized ratios were calculated. A significant excess of prostate cancer was seen for private and commercial applicators (SIR = 1.19, 95% CI 1.14, 1.25 and SIR = 1.28, 95% CI = 1.00, 1.61, respectively). Excesses were observed for lip cancer (SIR = 1.97, 95% CI = 1.02, 3.44) and multiple myeloma (SIR = 1.42, 95% CI = 1.00, 1.95) among private applicators from North Carolina and for marginal zone lymphoma among Iowa spouses (SIR = 2.34, 95% CI = 1.21, 4.09). Although lower rates of smoking and increased physical activity probably contribute to the lower overall cancer incidence, agricultural exposures including pesticides, viruses, bacteria, sunlight, and other chemicals may increase risks for specific cancer sites.