Longitudinal associations and interactions of heat and metal(loid) exposure with kidney outcomes in Mexican agricultural workers

Background: Agricultural workers perform physically demanding labor in extreme heat, increasing their risk for kidney injury. Agricultural workers are also exposed to nephrotoxic metal(loid)s, yet little research examines the combined effects of heat and metal(loid) exposure on kidney health. Objective: This study assessed how simultaneous exposure to metal(loid)s and heat impacts acute kidney injury (AKI) and kidney function over time. Methods: As part of a longitudinal study, we followed a cohort of male grape farmworkers near the Arizona-Sonora border (n = 77), collecting biological samples and questionnaires at two timepoints: at the beginning (i.e., baseline) and again at the end of the work season (i.e., follow-up). Physiological strain index (PSI) was estimated using inner ear temperature and heart rate. Urine samples were analyzed for metal(loid)s, specific gravity, and neutrophil gelatinase-associated lipocalin (uNGAL), while blood serum was used to calculate estimated glomerular filtration rate (eGFR). Linear mixed effect and linear regression models evaluated the impact of metal(loid)s and PSI on kidney health, incorporating interaction terms for chronic (seasonal) and acute (PSI) heat exposure. Results: Participants averaged 29 years old, with 35 % primarily speaking an Indigenous language. Urinary arsenic (β = 0.35, 95 %CI: 0.15, 0.55), cadmium (β = 0.27, 95 %CI: 0.14, 0.40), and chromium (β = 0.54, 95 %CI: 0.20, 0.88) were associated with increased uNGAL, while increased uranium was associated with reduced eGFR (β = −2.45, 95 %CI: 4.81, −0.08). Effects were attenuated in stratified models. Interactions showed chronic heat exposure exacerbated arsenic and cadmium's effects (arsenic-uNGAL, p < 0.01; cadmium-uNGAL, p = 0.02). No significant interactions were observed for acute heat stress. Discussion: Heat may modify the impact of toxic metal(loid)s on kidney health, emphasizing the need for workplace policies that mitigate heat stress among agricultural workers.