Occurrence, removal and risk assessment of chemicals of emerging concern in selected rivers and wastewater treatment plants in western Kenya.

Water resources play a crucial role in sustaining life on earth yet chemicals of emerging concern (CECs) arising from extensive human applications are an increasing threat towards their existence. In this study, we examined the occurrence, removal and potential risk of CECs found in rivers and wastewater treatment plants (WWTPs) in western Kenya. Samples were prepared by solid-phase extraction and analysed using high performance liquid chromatography-mass spectrometry with a target list of 785 compounds. Out of these, 333 and 352 (influent 322, effluent 265) compounds were quantified in rivers and wastewater respectively, with pharmaceuticals, industrial compounds, and pesticides being frequently detected in both rivers and WWTPs. Compounds with highest concentrations included saccharin (9.9 µg/L), metformin (7.5 µg/L), and oxypurinol (6.5 µg/L) in rivers whereas caffeine (280 µg/L), deoxycholic acid (179 µg/L), 2-oxindole (10.9 µg/L) and ibuprofen (8.1 µg/L) were found at high concentrations in WWTPs. Based on the types of crops grown, samples from maize growing regions recorded the highest number of pesticides (75) which coincided with the spraying season. The WWTP showed the capacity to eliminate some compounds although the removal efficiencies varied greatly with 204 compounds exhibiting an average removal efficiency exceeding 50 %. Based on the risk assessment, crustaceans had the highest potential risk for toxicity with toxic unit (TU) values up to 5.4 driven primarily by diazinon and dichlorvos followed by algae (TU up to 0.07) and fish (TU up to 0.01) in rivers. A similar trend was observed in WWTP with diazinon (TU up to 5.5), diuron (TU up to 0.07) and carbendazim (TU up to 0.006) driving the risk for crustaceans, algae and fish respectively. These findings highlight the significance of surface water and WWTPs as sources and sinks of CECs in the environment translating to potential risks on aquatic organisms and humans.

Seasonal hot spots of pollution and risks in Western Kenya: A spatial-temporal analysis of almost 800 organic micropollutants.

The release of chemicals into the environment presents a significant threat to aquatic ecosystems dependent on the proximity to emission sources and seasonal dynamics of emission and mobilization. While spatial-temporal information on water pollution in Europe is increasing, there are substantial knowledge gaps on seasonal pollution dynamics in tropical countries. Thus, we took Lake Victoria South Basin in western Kenya as a case study to identify spatial and seasonal hot spots of contamination, quantified toxic risks to different groups of organisms, and identified seasonal risk drivers. For this purpose, we analyzed grab water samples from five rivers with agricultural and wastewater treatment plants in their catchment in four different seasons. We used liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) with a target list of 785 organic micropollutants. A total of 307 compounds were detected with concentrations ranging from 0.3 ng/L to 6.6 µg/L. Using a Toxic Unit (TU) approach based on mixture toxicity to standard test organisms, crustaceans were identified as the most affected group followed by algae and fish. For crustaceans, chronic risk thresholds were exceeded in 96 % of all the samples, while 56 % of all samples are expected to be acutely toxic, with the highest risk in February during the dry season. High toxic unit values for algae and fish were recorded in July dry season and May wet season. Diazinon, imidacloprid, clothianidin and pirimiphos-methyl were the major drivers for crustacean toxicity while triclosan and different herbicide mixtures drive risks to algae in dry and wet seasons, respectively. A total of 18 chemicals were found to exceed acute and chronic environmental risk thresholds. With this study, strong spatial-temporal patterns of pollution, risks and risk drivers could be confirmed informing prioritization of monitoring and abatement to enhance water quality and reduce toxic risks.

One planet: one health. A call to support the initiative on a global science-policy body on chemicals and waste.

The chemical pollution crisis severely threatens human and environmental health globally. To tackle this challenge the establishment of an overarching international science-policy body has recently been suggested. We strongly support this initiative based on the awareness that humanity has already likely left the safe operating space within planetary boundaries for novel entities including chemical pollution. Immediate action is essential and needs to be informed by sound scientific knowledge and data compiled and critically evaluated by an overarching science-policy interface body. Major challenges for such a body are (i) to foster global knowledge production on exposure, impacts and governance going beyond data-rich regions (e.g., Europe and North America), (ii) to cover the entirety of hazardous chemicals, mixtures and wastes, (iii) to follow a one-health perspective considering the risks posed by chemicals and waste on ecosystem and human health, and (iv) to strive for solution-oriented assessments based on systems thinking. Based on multiple evidence on urgent action on a global scale, we call scientists and practitioners to mobilize their scientific networks and to intensify science-policy interaction with national governments to support the negotiations on the establishment of an intergovernmental body based on scientific knowledge explaining the anticipated benefit for human and environmental health.

Occurrence and risk assessment of organic micropollutants in freshwater systems within the Lake Victoria South Basin, Kenya.

The unintended release of chemicals to the environment has led to global concern on water quality prompting widespread research on the occurrence of these compounds in water. While increasing information on organic micropollutants (OMPs) in European water resources is available, there is still limited information on the occurrence of OMPs in African water systems. In this study, a multi-residue analysis covering 428 chemicals using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) was performed on water samples collected from 48 surface water sites within the Lake Victoria South Basin, Kenya. A total of 75 compounds including pharmaceuticals, personal care products (PPCPs), pesticides, and industrial chemicals were detected and an additional three compounds (nevirapine, lamivudine and adenosine) were identified through suspect screening. Four compounds including diphenhydramine, simazine, triethylphosphate and acetyl-sulfamethoxazole (A-SMX) were detected in >80% of the sites showing their ubiquitous nature in the study area. Individual compound concentrations were detected up to 24 µg L-1. Concentrations above 1 µg L-1 were also reported for triethylcitrate, N-ethyl-o-toluenesulfonamide, hexazinone, nevirapine, adenosine and carbendazim. While crustaceans were potentially the taxon at risk for acute toxicity (toxic unit (TU) up to 2) with diazinon driving this risk, lower but substantial acute risk (TU 0.5) was observed for algae. Chronic risks were observed in 11 sites for algae (TU > 0.02) and in 5 sites for fish (TU > 0.01). A total of 16 compounds were prioritized based on frequency and extent of the exceedance of thresholds for acute and chronic risks to algae, crustaceans and fish and another 7 compounds prioritized by applying lowest Predicted No-Effect Concentrations (PNEC). Based on these indicators, this study provides candidate priority compounds for monitoring, assessment and abatement in western Kenya.

Pesticide pollution in freshwater paves the way for schistosomiasis transmission.

Schistosomiasis is a severe neglected tropical disease caused by trematodes and transmitted by freshwater snails. Snails are known to be highly tolerant to agricultural pesticides. However, little attention has been paid to the ecological consequences of pesticide pollution in areas endemic for schistosomiasis, where people live in close contact with non-sanitized freshwaters. In complementary laboratory and field studies on Kenyan inland areas along Lake Victoria, we show that pesticide pollution is a major driver in increasing the occurrence of host snails and thus the risk of schistosomiasis transmission. In the laboratory, snails showed higher insecticide tolerance to commonly found pesticides than associated invertebrates, in particular to the neonicotinoid Imidacloprid and the organophosphate Diazinon. In the field, we demonstrated at 48 sites that snails were present exclusively in habitats characterized by pesticide pollution and eutrophication. Our analysis revealed that insensitive snails dominated over their less tolerant competitors. The study shows for the first time that in the field, pesticide concentrations considered "safe" in environmental risk assessment have indirect effects on human health. Thus we conclude there is a need for rethinking the environmental risk of low pesticide concentrations and of integrating agricultural mitigation measures in the control of schistosomiasis.

Author Correction: Pesticide pollution in freshwater paves the way for schistosomiasis transmission.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Occurrence, fate and removal of pharmaceuticals, personal care products and pesticides in wastewater stabilization ponds and receiving rivers in the Nzoia Basin, Kenya.

Although there is increased global environmental concern about emerging organic micropollutants (EOMPs) such as pharmaceuticals, personal care products (PPCPs) and polar pesticides, limited information is available on their occurrence in Africa. This study presents unique data on concentrations and loads of 31 PPCPs and 10 pesticides in four wastewater stabilization ponds (WSPs) and receiving rivers (flowing through urban centres) in Kenya. The WSPs indicate a high potential to remove pharmaceutically active compounds (PhACs) with removals by up to >4 orders of magnitude (>99.99% removal), mainly occurring at the facultative stage. However, there are large differences in removal among the different classes, and a shift in the relative PhACs occurrence is observed during wastewater treatment. Whereas the influent is dominated by high-consumption PhACs like anti-inflammatory drugs (e.g. paracetamol and ibuprofen, up to 1000 µg L-1), the most recalcitrant PhACs including mainly antibiotics (e.g. sulfadoxin and sulfamethoxazole) and antiretrovirals (e.g. lamivudine and nevirapine) are largely abundant (up to 100 µg L-1) in treated effluent. Overall, concentrations of EOMPs in the Nzoia Basin rivers are the highest in dry season (except pesticides) and in small tributaries. They are of the same order of magnitude as those measured in the western world, but clearly lower than what we recently measured in the Ngong River, Nairobi region. Based on the specific consumption patterns and recalcitrant behavior, high concentrations (>1000 ng L-1) are observed in the rivers for PPCPs like lamivudine, zidovudine, sulfamethoxazole and methylparaben. Concentration levels of pesticides are in general one order of magnitude lower (<250 ng L-1). Our data suggest a continuous input of EOMPs to the rivers from both point (WSPs) and diffuse (urban centres) sources. To better understand and manage the impact of both sources, EOMP removal mechanisms in WSPs and their attenuation in rivers merit further research.