Measurement and analyses of 25 CUPs in the atmosphere in three agricultural regions of the Western Cape, South Africa

Abstract

South Africa is the leading pesticide user in Africa, experiencing an increasing demand for currently used pesticides (CUPs). This raises concerns for public health along with a growing need to investigate their fate in the environment. This report aimed to study spatial and temporal differences of 25 CUPs in South Africa. In total, 36 passive air samplers were deployed between July 2017 and June 2018 at different sites (farm/village) within three study areas (Grabouw, Hex River Valley and Piketberg). Samples were extracted using methanol and CUPs were analysed using high-performance liquid chromatography and tandem mass spectrometry. Air concentrations (ng m-3) were derived from the results obtained with PUF-PAS disks (ng PUF-1). Meteorological data was provided by the closest weather stations. UpSet plots, line graphs and heatmaps were created to visualize pesticide mixtures and seasonal/spatial variations. Kruskal-Wallis tests were performed to assess differences in concentrations between areas and sites, while a linear mixed-effect model was built to understand how these vary according to several factors. 16 pesticides were quantified at least once. Only carbaryl and chlorpyrifos were quantified in all samples, with chlorpyrifos showing the highest concentrations across all sampling areas. 53% of the samples showed a mixture of carbaryl, chlorpyrifos, terbuthylazine, s-metolachlor, diazinon, tebuconazole, atrazine, simazine, malathion and metazachlor. In general, the highest concentrations of our pesticides in the atmosphere coincided with the most active spraying seasons in each area and warmer months, decreasing when rainfall peaked. Concentrations vary, therefore, according to the timing of pesticide application and meteorological factors.