Determinants of respirable quartz exposure in farming

The objectives of this article are to quantify personal respirable quartz exposure on sandy, sandy loam, and clay soil farms and to identify exposure determinants. The methods applied included observing and examining the variables soil type, commodity farmed, activity, process, quartz % in respirable dust, and weather variables. Multiple linear regression was used to identify determinants of respirable quartz concentration and logistic regression was applied to identify determinants of respirable quartz concentration > 50 µg.m^-3 (a commonly used reference value of over-exposure). The highest quartz concentration was 626 µg.m^-3 and 30%, 22%, and 31% of measurements were > 50 µg.m^-3 for sandy, sandy loam, and clay soil farms, respectively. In general, the commodities livestock farming and cereal grains as well as the activity cereal planter operator, decreased humidity on the day of measurement, the mechanical processes, and quartz % in respirable dust (in a confounding way) were associated with higher respirable quartz concentrations (p ≤ 0.10) as well as season (p = 0.14). Variables associated with quartz levels above 50 µg.m^-3 were cereal planter operator, increased quartz % in respirable dust, decreased humidity on day of measurement, and increased respirable dust concentration. Cereal planter operator (Multivariate Odds Ratio (OR) 4.56, 95% CI: 1.79-8.89) and levels of quartz % > 10 µg.m^-3 (Multivariate OR 6.01, 95% CI: 3.52-9.71 if quartz % > 10 but ≤ 20 µg.m^-3, and Multivariate OR 5.32, 95% CI: 2.56-8.34 if quartz % > 20 µg.m^-3) were clear determinants of quartz over-exposure. It can therefore be concluded that over-exposure to quartz in farming is possible. Joint influences of more farming characteristics and weather variables should be included, together with soil type in future farming exposure assessments.