Evaluating trends and risks of aquatic pesticide pollution in the Western Cape, South Africa
- 1Department of Earth Sciences, Stellenbosch University, Stellenbosch, South Africa (email@example.com)
- 2Swiss Tropical and Public Health Institute, Switzerland
- 3Swiss Federal Institute of Aquatic Research, Switzerland
South Africa is the leading user of pesticides in Sub-Saharan Africa. Consequently, there is an urgent need to improve our understanding of which pesticides persist in the environment and how they are being transported to non-target environments. The presence of pesticides in non-target environments, such as surface water or groundwater, could be detrimental to aquatic ecosystems and human health.
Our research focuses on monitoring for pesticides in the rivers of three agricultural catchments (Grabouw, Hex River Valley, and Piketberg) within the Western Cape, South Africa. Passive samplers are being deployed from March 2022 to March 2023, adding to a pre-existing dataset of analytical and pesticide application data from 2017 to 2019. Laboratory methods are being developed and validated at Stellenbosch University (SU) to analyze for pesticides using Liquid Chromatography-Mass Spectrometry. Duplicate samples were analyzed at the Swiss Federal Institute of Aquatic Research (Eawag), as a quality control step. Limits of Quantification were lower at Eawag and measured concentrations were typically higher compared to SU. These differences are likely due to variations in the instrument used and sample extraction procedure.
Results from 2017-2019 indicate that 83% of samples contained five or more pesticides. In every year of sampling, total pesticide concentrations were typically attributable to a single/few compounds per catchment. Six pesticides exceeded Environmental Quality Standard (EQS) values in at least one of the sampling periods. Imidacloprid was highlighted as a pesticide of concern since it consistently exceeded EQS values over all sampling periods. Detection/exceedances of pesticides generally coincided with their application and rainfall events, except for imidacloprid and terbuthylazine. This suggests that alternate transport pathways, such as storage and input from groundwater, may be relevant. Recent results from 2022 sampling indicate that the concentrations of imidacloprid are decreasing; however, they are still exceeding EQS values. Lastly, expansion of the analytes in 2022 led to the detection of two new pesticides, dimethomorph and diphenylamine.
Our results suggest that establishing a long-term data set regarding aquatic pesticide pollution in the Western Cape will lead to a better understanding of the trends and risks of pesticide use. This improved knowledge will lead to the development of targeted mitigation measures for more sustainable agricultural practices in South Africa and beyond.
How to cite: Chow, R., Davies, E., Fuhrimann, S., and Stamm, C.: Evaluating trends and risks of aquatic pesticide pollution in the Western Cape, South Africa, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9553, https://doi.org/10.5194/egusphere-egu23-9553, 2023.
Utafiti wa Uharibifu wa Wanyama wa Bahari ya Magharibi (Swiss Tropical and Public Health Institute) - Taasisi ya Utafiti wa Wanyama wa Bahari ya Magharibi (Swiss Federal Institute of Aquatic Research) Kwa hivyo, kuna haja ya haraka ya kuboresha uelewa wetu wa dawa za kuua wadudu ambazo zinaendelea katika mazingira na jinsi zinavyosafirishwa kwa mazingira yasiyo ya lengo. Uwepo wa dawa za kuua wadudu katika mazingira yasiyo ya lengo, kama vile maji ya uso au maji ya chini ya ardhi, inaweza kuwa na madhara kwa mifumo ya ikolojia ya majini na afya ya binadamu. Utafiti wetu unazingatia ufuatiliaji wa dawa za kuua wadudu katika mito ya mifereji mitatu ya kilimo (Grabouw, Hex River Valley, na Piketberg) ndani ya Western Cape, Afrika Kusini. Vipimo vya Passive sampler vitatumika kuanzia Machi 2022 hadi Machi 2023 na kuongeza data zilizopo za uchambuzi na matumizi ya dawa za kuua wadudu kutoka 2017 hadi 2019. Njia za maabara zinaendelezwa na kuthibitishwa katika Chuo Kikuu cha Stellenbosch (SU) kuchambua kwa dawa za kuua wadudu kwa kutumia Chromatography ya Kioevu-Mass Spectrometry. Sampuli duplicate walikuwa kuchambuliwa katika Uswisi Shirikisho Taasisi ya Utafiti Aquatic (Eawag), kama hatua ya kudhibiti ubora. Mipaka ya Quantification walikuwa chini katika Eawag na viwango vilivyopimwa walikuwa kawaida juu ikilinganishwa na SU. Tofauti hizi ni uwezekano kutokana na tofauti katika chombo kutumika na utaratibu wa uchimbaji sampuli. Matokeo ya uchunguzi wa mwaka 2017-2019 yanaonyesha kuwa asilimia 83 ya sampuli hizo zilikuwa na dawa tano au zaidi za kuua wadudu. Katika kila mwaka wa sampuli, jumla ya viwango vya dawa za kuua wadudu kwa kawaida zilitokana na misombo moja au chache kwa kila mkusanyiko. Dawa sita za kuua wadudu zilizidi viwango vya kiwango cha ubora wa mazingira (EQS) katika angalau kipindi kimoja cha sampuli. Imidacloprid ilionyeshwa kama dawa ya kuua wadudu ya wasiwasi kwani ilizidi viwango vya EQS kwa muda wote wa kuchukua sampuli. Ugunduzi wa dawa za kuua wadudu au kuzidi kwa dawa za kuua wadudu kwa ujumla kulifanana na matumizi yao na matukio ya mvua, isipokuwa imidacloprid na terbuthylazine. Hii inaonyesha kwamba njia mbadala za usafirishaji, kama vile kuhifadhi na pembejeo kutoka maji ya chini ya ardhi, inaweza kuwa muhimu. Matokeo ya hivi karibuni kutoka kwa sampuli ya 2022 yanaonyesha kuwa viwango vya imidacloprid vinapungua, hata hivyo, bado vinazidi maadili ya EQS. Kwa mujibu wa ripoti ya utafiti wa mwaka huu, kemikali mbili mpya za kuua wadudu zimegunduliwa, dimethoprim na diphenylamine. Matokeo yetu yanaonyesha kwamba kuanzisha seti ya data ya muda mrefu kuhusu uchafuzi wa wadudu wa majini katika Western Cape itasababisha uelewa bora wa mwenendo na hatari za matumizi ya wadudu. Ujuzi huu ulioboreshwa utaongoza kwenye maendeleo ya hatua za kupunguza lengo kwa mazoea ya kilimo endelevu zaidi nchini Afrika Kusini na zaidi. "Kama ilivyoelezwa katika makala ya kwanza ya jarida la ""Chough, R. Davies, E. Fuhrmann, S. Stamm, C. Tathmini ya mwenendo na hatari za uchafuzi wa wadudu wa majini katika Western Cape, Afrika Kusini,"" Mkutano Mkuu wa EGU 2023, Vienna, Austria, Aprili 24, 2023, EGU 2023, EGU 2023, EGU 2023, EGU 2023, EGU 2023, EGU 2023, EGU 2023, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU 2024, EGU."