Characterizing Occupational Risk Factors and Kidney Function in Migrant Farm Workers

Abstract

As the number of hot days and heat waves are expected to rise globally within the next decades due to climate change, heat-related injuries and illnesses such as kidney disease, are also expected to increase. An important epidemic that has been associated with heat stress is chronic kidney disease of unknown etiology (CKDu). This epidemic is disproportionally affecting young agricultural workers with no traditional risk factor such as diabetes, hypertension, high lipoprotein levels, and tobacco usage. Although the risk factors are not yet fully understood, some have been proposed to explain the pattern of this disease, including exposure to pesticides, dehydration, and heat stress. However, there is a paucity of studies that have comprehensively examined the potential combined effect of kidney function in relation to several occupational factors though time. Therefore, in this dissertation we longitudinally evaluate the kidney function in migrant and seasonal farm workers (MSFWs) in relation to pesticide exposure, heat stress and dehydration. The first goal was to determine throughout the working season, the heat stress levels in workers followed by a complete evaluation of the physiological responses to heat stress during their work. The second goal was to investigate whether exposure to pesticides and/or heat stress coupled with dehydration can affect kidney dysfunction in migrant farm workers. We recruited 101 MSFWs, of which 50 were randomly selected to work in the organic certified area and 51 were randomly selected to work in the conventional area of a grape farm. We also enrolled 50 office workers as a reference group. Samples were collected at two times during the harvest season, early in the harvest and late in the harvest. We administered questionnaires to collect information on demographic, behavioral, and occupational characteristics. In addition to several anthropometric measurements, urine and blood samples were collected from all workers in the morning before their work shift. The samples were analyzed for kidney function and dehydration biomarkers. Heat stress was assessed using several environmental heat stress parameters throughout the study. The physiological response towards heat stress was calculated from participants’ core body temperature and heart rate, which were collected several times in the workday from all participants at every sampling period. Descriptive statistics were calculated for demographic and baseline characteristics. Differences at baseline between worker groups were assessed using a t-test for continuous variables and a chi-square test for categorical variables. One-way repeated measures ANOVA was used to evaluate changes over time within the same variable. To test associations with other variables over time, linear mixed models were built based on the main exposures of interests (heat strain, dehydration, and job category, as a proxy to pesticide exposure).We determined that all migrant farm workers in our study exceeded recommended heat stress levels during the late harvest. Also, we found that climate change could considerably worsen the conditions of MSFWs who are already working over the recommended heat exposure limits in this region. We determined that heat stress was significantly associated with the physiological response during the harvest season even after controlling for several covariates. Additionally, we found a significant declined in kidney function in MSFWs during the harvest season. Finally, we found an interaction between heat strain and job categories, which was used as a proxy for pesticide exposure. Thus, an increase in heat strain among MSFWs who worked in the conventional field had a significant decrease in kidney function when compared to office workers. To our knowledge, this is the first longitudinal study that evaluates several occupational risk factors and kidney function in migrant farm workers. It is also the first study of its kind collecting longitudinal data from workers in an organic certified field, a conventional field and a control group to better understand differences in exposures.