Repeated Pesticide Exposure Among North Carolina Migrant and Seasonal Farmworkers

Published in the AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 53:802–813 (2010).

Thomas A. Arcury, PhD,
Joseph G. Grzywacz, Jennifer W. Talton, Haiying Chen, Quirina M. Vallejos, Leonardo Galván Dana B. Barr, and Sara A. Quandt

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Migrant and seasonal farmworker occupational exposure to pesticides is widely acknowledged [Quandt et al., 2006; Calvert et al., 2008; Arcury and Quandt, 2009; Arcury et al., 2009a], and this occupational pesticide exposure is considered an important health risk for farmworkers and their families [Villarejo, 2003; McCauley et al., 2006]. However, no published biomarker data document the number or percent of US farmworkers exposed to pesticides. Although Washington State now collects blood samples from pesticide applicators to measure cholinesterase depression resulting from pesticide exposure [Hofmann et al., 2009a,b], no other state or national surveillance system routinely collects urine or blood biomarkers to estimate the dose of pesticides farmworkers receive, the frequency with which they absorb pesticides, or their cumulative dose from multiple pesticides over extended time periods. Several factors have limited the collection of farmworker pesticide biomarker data. First, collecting biological samples from a large group of farmworkers is difficult, as they often live in dispersed and isolated locations, they migrate during the agricultural season, and their transportation and financial resources often limit their ability to appear at a central location for data location. Second, laboratory analysis for pesticide exposure biomarkers is expensive. Finally, the pesticides for which biomarkers are available are dependent on available laboratory techniques.

Existing studies of farmworker pesticide exposure that include biomarkers have been limited to a small number of metabolites, small numbers of participants, cross-sectional samples, or participants in intervention programs [Fenske et al., 2003; Salvatore et al., 2008; Thompson et al., 2008]. For example, Fenske et al. [2003] collected multiple urine samples from 20 apple thinners, and found high concentrations of the dialkylphosphate (DAP) organophosphorus (OP) pesticide urinary metabolite dimethyldithiophosphate (DMDTP). Other studies have documented the exposure of individuals living in farmworker communities [Quandt et al., 2004; Arcury et al., 2005, 2007; Bradman et al., 2005; Coronado et al., 2006; Eskenazi et al., 2007; Thompson et al., 2008]. For example, Thompson et al. [2008] report results based on their two cross-sectional surveys, 1999 and 2003, of approximately 210Washington State farmworker adults who had a co-resident child. For the 1999 survey, they found that the DAP urinary metabolites dimethylphosphate (DMP), dimethylthiophosphate (DMTP), andDMDTP were detected in 17.1%, 93.7%, and 54.6%, respectively, of the farmworker samples. For 2003, the frequencies of detection were 29.3% for DMP, 92.6% for DMTP, and 55.0% for DMDTP. Arcury et al. [2009a,b] have shown that the proportion of farmworkers with pesticide exposure biomarkers is large. For example, of 939 urine samples collected from 283 farmworkers in 2007, 3,5,6-trichloro-2-pyridinol, a urinary metabolite for the insecticides chlorpyrifos and chlorpyrifos methyl, was detected in 46.2% of samples; 3-phenoxybenzoic acid, a general pyrethroid insecticide urinary metabolite, was detected in 56.4% of samples; and 2,4- dichlorophenoxyacetic acid, the urinary metabolite for the herbicide 2,4-D, was detected in 68.1% of samples. These analyses have also shown that the percentage of farmworkers with pesticide exposure biomarkers varies across the agricultural season.

Analyses have not considered whether individual farmworkers have repeated exposures to specific pesticides in a single season based on biomarker data. Documenting the number of times individual farmworkers experience exposure to pesticides across an agricultural season is important. Repeated exposure increases risk for immediate and longterm health outcomes [Alavanja et al., 2004]. Knowing that farmworkers are exposed more than once will inform clinical care for farmworkers, factors needed to reduce exposure, and regulation to decrease exposure.

The analysis has two aims. The first aim is to document the number of times (0–4) that the urinary metabolite biomarkers for 12 pesticides commonly used in North Carolina agriculture are detected in individual farmworkers. These are all non-persistent pesticides that are metabolized and excreted from the body within 72 hr of exposure. Therefore, biomarkers that indicate that a pesticide urinary metabolite is present repeatedly at 1 month or greater intervals offer strong evidence of repeated exposure to that pesticide. The second aim is to determine factors associated with the number of times individual farmworkers had urinary metabolite biomarkers for the 12 pesticides.