Browsing by Author "Davies, Emma Jane"

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    Evaluating sources and environmental risk of pesticide pollution in Western Cape rivers
    (Stellenbosch : Stellenbosch University, 2023-12) Davies, Emma Jane; Chow, Reynold; Stamm, Christian; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: Agriculture is key to South Africa’s economy which has led to the country becoming a leading pesticide user in Sub-Saharan Africa. The Western Cape is a dominant agricultural region in South Africa, making it particularly vulnerable to pesticide pollution. After application, pesticides can be transported away from the designated site, potentially causing adverse health effects to non-target organisms. Therefore, the risk of pesticide pollution must be better understood. This research deployed passive samplers in rivers for two-week intervals every month from February 2022 - March 2023 in the agricultural catchments Grabouw, Hex River Valley, and Piketberg. This expands on a previous campaign from 2017-2019. 44 pesticides were measured using Liquid Chromatography Mass Spectrometry. The original aspects of this study include the expansion of the sampling list to include the fungicide dimethomorph and a suite of drugs. 22 (out of 44) pesticides and seven (out of 20) drugs were detected above the limit of quantification. Piketberg had high drug concentrations and detection frequencies which correlated with pesticide concentrations, whereas Grabouw and Hex River Valley did not. This suggests that pesticide pollution in Piketberg is likely sourced from both wastewater treatment plants and agriculture, whereas the absence of drugs in Grabouw and Hex River Valley suggests that pesticide contamination is more likely sourced from agriculture. This is particularly true for terbuthylazine and carbendazim because their concentrations correlated with cumulative drug concentrations (R²=0.47 and 0.77, respectively). Five pesticides were detected in control samples deployed in Jonkershoek Nature Reserve. While detections could be from neighbouring agricultural catchments via atmospheric transport, they also indicate non-agricultural sources of herbicides (e.g., atrazine and terbuthylazine from trail maintenance or invasive plant control). A few compounds typically contributed to majority of the detected concentrations, specifically, imidacloprid (54%) and dimethomorph (22%) in Hex River Valley, imidacloprid (46%) and chlorantraniliprole (38%) in Grabouw and imidacloprid (22%) and terbuthylazine (27%) in Piketberg. The newly measured fungicide, dimethomorph, had high concentrations up to 80 ng/L and detection frequencies in Hex River Valley (96%) and Piketberg (25%). Pesticides with high detection frequencies were not applied year-round but have high Groundwater Ubiquity Scores (GUS), suggesting a high leaching potential into groundwater. Environmental risk was evaluated by comparing concentrations to European Environmental Quality Standards (EQS). Four compounds exceeded EQS values, namely the insecticides imidacloprid and chlorpyrifos, the herbicide terbuthylazine, and the fungicide spiroxamine. Exceedances for chlorpyrifos, spiroxamine, and terbuthylazine coincide with application events and rainfall. All compounds that exceeded in 2022/2023 (except for spiroxamine) also exceeded during the 2017-2019 campaign, indicating high persistence and continual exposure risk to aquatic life. Assessment of pesticide mixtures suggests that certain combinations (e.g., imidacloprid and chlorantraniliprole) can have increased toxicity effects on organisms, and almost occur year-round. Hydrological and concentration patterns suggest that increased detections are mainly driven by rainfall in winter, pesticide application in summer and constant input from wastewater treatment plants or groundwater transport. Future research should prioritize sampling of groundwater, wastewater influent and effluent and soils to improve our understanding of pesticide transport pathways.