Occurrence and risk assessment of organic micropollutants in freshwater systems within the Lake Victoria South Basin, Kenya
Graphical abstract
Introduction
The widespread and intensive use of chemicals such as pesticides, pharmaceuticals and personal care products (PPCPs) has given rise to concern on their occurrence in and impact on aquatic ecosystems (Posthuma et al., 2019). There has been an increase in the use of pesticides and PPCPs due to the increasing population and diseases especially in developing countries (Bernhardt et al., 2017; Peng et al., 2018). In this context, Kenya being a developing country, faces great challenges to cater for food, clean water and health needs of its growing population. Agriculture is a main economic branch contributing >70% of Kenya's foreign trade which increases 10% on average annually (Moya et al., 2019). This has led to an increased demand for plant protection products. Between 2006 and 2010, the Ministry of Environment, Water and Natural resources reported approximately 36 thousand tons of pesticide importation into Kenya which increased to 54 thousand tons by 2013 (Loha et al., 2018). In addition, (re)emergence of diseases and epidemics (Berger et al., 2010) has led to increased use of pharmaceutical products in the country and to an increased release of these compounds into the environment. Many organic micropollutants (OMPs) are persistent in the environment including carbendazim, clothianidin, diuron and atrazine with several studies showing that exposure to these compounds results in acute and chronic effects to aquatic organisms (Ccanccapa et al., 2016; Liess and Von Der Ohe, 2005; Shahid et al., 2018; Velki et al., 2019).
Monitoring of emerging OMPs has been increasingly done in the western world; however, there is still a big lack of data for Africa (Aus der Beek et al., 2016; Fekadu et al., 2019; Madikizela et al., 2017). Most studies on water quality monitoring in Africa are based on environmental or drinking water guidelines which cover only few OMPs (Gwenzi and Chaukura, 2018). The lack of state-of-the-art analytical equipment to detect concentrations in the ng L−1 range is a major obstacle to monitoring of hazardous environmental contamination in many developing countries. Although the occurrence of some pesticides in environmental matrices in Kenya has been monitored since 1987 (Kahunyo et al., 1988), the compounds analyzed were generally low in number. Only very few studies have been performed in Kenyan water systems characterizing pharmaceutical pollution patterns in surface waters. These studies focused on a few pharmaceuticals (Bagnis et al., 2020; K'oreje et al., 2012, K’oreje et al., 2016, K'oreje et al., 2018; Kimosop et al., 2016; Ngumba et al., 2016) and only three studies (Bagnis et al., 2020; K'oreje et al., 2018; Ngumba et al., 2016) reported potential risks on aquatic organisms based on the measured environmental concentrations.
To reduce this knowledge gap, the present study focused on the assessment of surface waters including rivers, drainage channels and dams to obtain information on the extent of pesticides, PPCPs and industrial compound pollution within the Lake Victoria South Basin (LVSB) in Kenya. The aim of this study was to (1) determine the level of OMPs pollution in various surface water systems within LVSB (2), to perform suspect screening for a comprehensive characterization of multi-residue pollution, (3) to undertake risk assessment on aquatic organisms based on toxic units (TU) and (4) for the first time, to prioritize compounds for regulation and monitoring in Kenya.
Section snippets
Chemicals
LC-MS grade methanol, formic acid and ammonium formate were obtained from Honeywell, while LC-MS grade water was purchased from Thermo-Fisher. Analytical standards were obtained from various suppliers and at least of 97% purity. More information on the compounds analyzed is presented in supplementary information (Table SI-1).
Study area and sampling
The study was performed within the LVSB, Kenya (Fig. 1) covering Kericho, Kisumu, Kisii, Nyamira, Migori, Narok and Homabay counties. LVSB has an estimated area of 21,720 km
Results and discussion
The results from the analysis of general water quality parameters are given in the supplementary information (Table SI-9).
Conclusions
The present study has provided a comprehensive identification and risk assessment of emerging OMPs in freshwater systems in rural areas within the Lake Victoria South Basin for three representative organism groups including crustaceans, algae and fish. Particularly high concentrations (> 1 μg L −1) were detected for some pharmaceuticals and pesticides with A-SMX being reported at 24 μg L −1. Suspect screening supported the detection of two common antiretroviral drugs used in the first line of
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Deutsche Forschungsgemeinschaft (DFG), Germany under project SENTINEL [grant number LI 1708/4-1, BR 2931/3-1, HO 3330/12-1]. We are grateful to Paul Ouma for the support during sampling and Hubert Schupke for LC-HRMS analysis. A free academic license of JChem for Office (Excel) was used for structure based property calculation and Marvin was used for drawing, displaying and characterizing chemical structures, Marvin/Jchem 17.21.0, 2019 ChemAxon (//www.chemaxon.com
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