Para-occupational quantitative risk assessment: Addressing exposure pathways, populations of interest and slope factors for carcinogenic pesticides

Introduction
Risk Assessments for pesticide exposures are primarily done for exposures incurred by farmers or farmworkers. Missing from this general approach is the para-occupational or ‘take-home’ exposures that exist for farm family members. Para-occupational exposures include pesticide residues in the home and on field vehicles, work clothes, footwear and hands. Pathways for exposure are direct (e.g. unpaid labour or proximity to spraying) and indirect (e.g. ingestion from residue on carpet). This research is part of CAREX Canada, an occupational and environmental carcinogen surveillance project.

Methods
We reviewed exposure literature to assess pathways and populations of interest for para-occupational pesticide exposure. Five pesticides identified were possible or probable carcinogens of interest to CAREX Canada: 2,4-D, atrazine, chlorothalonil, MCPA and MCPP. Slope factors and threshold values were obtained from the USEPA, Health Canada and IARC. For pesticides without slope factors, we reviewed animal studies for data to develop custom slopes for this project.

Results
We identified three populations of interest: farm spouses (low exposure, predominantly women), farm children in the home (medium exposure) and ‘young unpaid workers’ (high exposure, farm children who are present spraying). Slope factors were identified for chlorothalonil and atrazine and threshold values were identified for all five pesticides. Data from animal studies were used to develop slope factors for 2,4-D, MCPP and MCPA. Risk estimates for these chemicals and populations were generated using the US EPA Risk Assessment protocol.

Discussion
The evidence from this research shows that farm family members’ exposures are distinctly above what is considered “background,” highlighting the importance of including these populations when modeling the risks of pesticide use, and when undertaking health based studies. Additionally, given that most Canadian farmers live and work in the same place, formal risk assessments need to consider the contribution of para-occupational pathways when calculating farmers’ exposures as well.