Estimating the risk of exposure to pesticides with carcinogenic potential in Canadian farmers and farm workers

Introduction
The CAREX surveillance project identified five pesticides with carcinogenic potential commonly used in Canadian agriculture (MCPP, MCPA, chlorothalonil, 2,4-D and atrazine). The objective of this project was to estimate the number of farmers/farmworkers exposed to these pesticides, their exposure levels and health risk estimates where data permitted.

Methods
Pesticide use was determined using crop-specific pesticide application guidelines from provincial Ministries of Agriculture. All crops in a geographical region (an ‘eco-district’) were summed to create regional estimates of exposure, which were mapped with ArcGIS. The Canadian Census and Labour Force Survey (LFS) were used to estimate the number of farmers and labourers exposed to carcinogenic pesticides.

Results
Pesticides with carcinogenic potential are used on a wide variety of crops in Canada. Pesticide use varied significantly by region, for example, high concentrations of 2,4-D were found in Saskatchewan whereas BC and Prince Edward Island had extremely high levels of chlorothalonil. These variations are due to crop-specific pesticide use and the distribution of arable land. A range of farm-related occupations from the Census and LFS were determined to be eligible for exposure and were grouped into two distinct exposure categories: farmers/farm managers and farm labourers. Population risk estimates were modeled using the US EPA Risk Assessment protocol.

Discussion
This project highlighted the importance of understanding pesticide exposure in terms of cumulative application. Many Canadian farms grow a variety of crops; “whole farm” application rates need to be considered when undertaking pesticide risk assessments. Additionally, GIS techniques are excellent aids for interpreting exposure data, for example, annual sales of chlorothalonil in BC are low compared to other provinces, however almost all of it is applied to a very small region, presenting a unique exposure scenario. There are serious problems with the way that farmworkers are tracked in Canada, making accurate estimates of their numbers very difficult.