Atmospheric transport of particulate matter and particulate-bound agrochemicals from beef cattle feedlots: human health implications for downwind agricultural communities

Background Beef cattle feedlot-derived particulate matter (PM) is a complex mixture of dust, animal waste, agrochemicals, and bioaerosols. No empirical data currently exists quantifying human exposure of PM-bound agrochemicals downwind of feedlots.

Objectives There were three objectives of the current study: 1) to determine spatial extent and magnitude of PM transport downwind of large beef cattle feedlot facilities, 2) to quantify occurrence of pyrethroid insecticides and anthelmintics in feedlot-derived PM, and 3) to assess cumulative human health risk of agrochemicals in agriculture-adjacent communities downwind of feedlots.

Methods Authors investigated downwind transport (<1 to >12 km) of total suspended particulates (TSP) from three feedlots in the Southern Great Plains (SGP) of North America. PM collected on TSP filters was analyzed via UHPLC-MS/MS for six pyrethroids (bifenthrin, λ-cyhalothrin, cypermethrin, esfenvalerate, fenvalerate, and permethrin) and five macrocyclic lactones (MLs; abamectin, doramectin, eprinomectin, ivermectin, and moxidectin). An empirical distance decay model was used to determine probabilistic PM concentrations in downwind ambient air.

Results Downwind TSP concentrations exhibited rapid decline from 0.01 - ≤1.6 km (Monte Carlo-simulated mean ± SEM; 5,049 ± 96.1 µg/m³) and subsequent stabilization >1.6 – 12.4 km (1,791 ± 9.9; µg/m³). TSP concentrations did not converge to background levels within the spatial extent of the study (12.4 km). Agrochemicals were detected downwind >LOQ at greater overall frequency (40.6%) than upwind locations (26.8%). Two pyrethroids were detected at the highest overall downwind concentrations (mean ± SEM; fenvalerate = 5.9 ± 0.8, permethrin = 1.1 ± 0.3 ng/m³), and screening-level cumulative exposure estimates indicate elevated pyrethroid risk (LOC = 1; RI = 0.173) in children (1-2 yrs) living near commercial agricultural operations in the SGP.

Discussion Results significantly expand the known distribution of feedlot-derived PM and agrochemicals, and consequently highlight exposure pathways unrecognized in residential human health assessments and feedlot risk evaluations.