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Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment
Thesis (PhD)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613990331351040 |
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| access_status_str | Open Access |
| author | Tiya, Luthando Lukhanyo |
| author2 | Kellermann, Tracy |
| author_browse | Kellermann, Tracy Tiya, Luthando Lukhanyo |
| author_facet | Kellermann, Tracy Tiya, Luthando Lukhanyo |
| author_sort | Tiya, Luthando Lukhanyo |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134840 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:44:55.028Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134840 Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment Tiya, Luthando Lukhanyo Kellermann, Tracy Verdoorn, Gerhard Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine. Division of Clinical Pharmacology. Pesticides -- Toxicology Serum -- Analysis Zebra danio -- Effect of chemicals on Biological monitoring Agricultural laborers -- Health and hygiene Thesis (PhD)--Stellenbosch University, 2025. Tiya, L. L. 2025. Biomonitoring of Pesticide Exposure in Farming-Intensive Communities of the Western Cape: A Study Using Human Serum Analysis and Zebrafish Toxicity assays for more comprehensive Risk Assessment. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/a6f21561-2c41-441d-976d-3ec584274a1a ENGLISH ABSTRACT: South Africa is the largest consumer of pesticide active ingredients in Sub-Saharan Africa. Consequently, both agricultural workers and the general population face increased risk of pesticide exposure through occupational contact and contaminated food and water. Existing regulatory frameworks are inadequate for chronic, low-dose exposures. There is a notable lack of comprehensive data on pesticide metabolism and metabolite toxicity in humans, impeding effective risk assessment. Cholinesterase (ChE) activity remains the principal biomarker currently used to monitor pesticide exposure but exhibits limited specificity and sensitivity, especially for many modern pesticides. In this study, we evaluate acute and chronic toxicological effects of low-level pesticide exposures and their metabolites using a zebrafish (Danio rerio) model. These findings are correlated with quantitative measurements of pesticide concentrations in human serum from high-exposure regions, using liquid chromatography–tandem mass spectrometry (LC–MS/MS). The diagnostic utility of ChE activity as a biomarker was also evaluated. To evaluate risk posed by pesticides and metabolites, this study implemented a dual-model approach that combined high-resolution human biomonitoring with zebrafish (Danio rerio) embryo toxicity assays. Human biomonitoring was performed using 258 serum samples collected from individuals residing in agriculturally intensive regions of the Western Cape, South Africa: Ceres, Op die Berg, Prince Alfred Hamlet, Worcester, and Wolseley. Four liquid chromatography–tandem mass spectrometry (LC–MS/MS) methods were developed and validated for the quantitative analysis of common pesticides (glyphosate, imidacloprid, mancozeb, chlorpyrifos, emamectin benzoate and abamectin) and their metabolites in human serum. This study represents the first investigation in Sub-Saharan Africa to analyze human serum for multiple classes of pesticides and their metabolites that are widely applied in South Africa, thereby offering a comprehensive, population-level assessment of pesticide exposure. Concurrently, zebrafish embryos were exposed to parent pesticides and their principal metabolites at concentrations extrapolated from internationally recognized human exposure thresholds. Morphological endpoints, including survival, spinal curvature, and pericardial edema, were assessed at 118 hours post-fertilization (hpf), alongside behavioural outcomes evaluated using light–dark transition testing (LDTT) to measure locomotor activity. Human biomonitoring detected glyphosate and metabolites in 30 of 258 serum samples, trace imidacloprid olefin in five, and emamectin benzoate in one. Pesticide metabolites generally showed greater toxicity to zebrafish larvae than parent compounds. Imidacloprid and chlorpyrifos metabolites caused severe teratogenic and neurotoxic effects, with chlorpyrifos oxon inducing total mortality. Glyphosate’s metabolite, methylphosphonic acid, and mancozeb’s metabolite, ethylenethiourea, also caused significant developmental toxicity and mortality. The correlation between zebrafish toxicity and human serum data suggests that chronic, low-level pesticide exposures may cause significant developmental and neurological harm, highlighting deficiencies in existing risk assessment methods. ChE activity was evaluated in three suspected poisoning cases at Tygerberg Hospital. Despite one patient showing organophosphate symptoms, pseudocholinesterase levels were normal. Our analytical methods detected glyphosate, highlighting ChE’s limitation for detecting pesticides with different modes of action. These findings underscore the need for an integrated, multi-modal risk assessment paradigm that incorporates advanced metabolomics, in vivo toxicity data, and high-resolution analytical chemistry. Adoption of such a framework is crucial for safeguarding vulnerable populations in regions with intensive pesticide use, where traditional biomonitoring approaches may substantially underestimate the extent and severity of toxicological risks. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Doctoral 2026-01-12T09:41:36Z 2026-01-12T09:41:36Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134840 Stellenbosch University 207 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Pesticides -- Toxicology Serum -- Analysis Zebra danio -- Effect of chemicals on Biological monitoring Agricultural laborers -- Health and hygiene Tiya, Luthando Lukhanyo Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment |
| title | Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment |
| title_full | Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment |
| title_fullStr | Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment |
| title_full_unstemmed | Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment |
| title_short | Biomonitoring of pesticide exposure in farming-intensive communities of the Western Cape: a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment |
| title_sort | biomonitoring of pesticide exposure in farming intensive communities of the western cape a study using human serum analysis and zebrafish toxicity assays for more comprehensive risk assessment |
| topic | Pesticides -- Toxicology Serum -- Analysis Zebra danio -- Effect of chemicals on Biological monitoring Agricultural laborers -- Health and hygiene |
| url | https://scholar.sun.ac.za/handle/10019.1/134840 |
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