Evaluating organochlorine pesticide residues in the aquatic environment of the Lake Naivasha River basin using passive sampling techniques

Agricultural intensification in Lake Naivasha Catchment in Kenya and associated nutrients and pesticides pollution

Investments in agricultural intensification in sub-Saharan Africa aim to fulfill food and economic demands. However, the increased use of fertilizers and pesticides poses ecological risks to water bodies in agricultural catchments. This study focused on assessing the impact of agricultural intensification on nutrient and pesticide pollution in the L. Naivasha catchment in Kenya. The research revealed significant changes in the catchment's agricultural landscape between 1989 and 2019, driven by intensified agricultural expansion. As a result, nutrient and pesticide emissions have worsened the lake's trophic status, shifting it towards hypereutrophic conditions. The study found a weak relationship between total nitrogen (TN) and sum dichlorodiphenyltrichloroethane (∑DDT), indicating that an increase in TN slightly predicted a reduction in ∑DDT. Analysis also showed potential phosphorus (P) limitation in the lake. Additionally, the observed ratio between dichlorodiphenyldichloroethane and dichlorodiphenyldichloroethylene (DDD:DDE) and (DDE + DDD):DDT ratios suggest recent use of banned DDT in the catchment. The study concludes that the transformation of L. Naivasha landscape shows unsustainable agricultural expansion with reduced forest cover, increased croplands, and increased pesticide contamination. This reflects a common issue in sub-Saharan Africa, that sustainable catchment management must address, specifically for combined pollutants, to support water quality and achieve the SDGs in agriculture.

Toxic mechanisms of imazalil, azoxystrobin and their mixture to hook snout carp (Opsariichthys bidens)

While combinations of pesticides better represent actual conditions within aquatic ecosystems, the specific toxic effects of these combinations have not been determined yet. The objective of this research was to assess the combined impact of imazalil and azoxystrobin on the hook snout carp (Opsariichthys bidens) and delve into the underlying causes. Our findings indicated that the 4-day LC50 value for imazalil (1.85 mg L-1) was greater than that for azoxystrobin (0.90 mg L-1). When imazalil and azoxystrobin were combined, they presented a heightened effect on the species. Enzyme activities like SOD, CAT, GST, and CarE, along with androgen and estrogen levels, displayed marked differences in most single and combined treatments in comparison to the baseline group. Moreover, four genes (mn-sod, cu-sod, il-1, and esr) related to oxidative stress, immunity, and the endocrine system exhibited more pronounced expression changes when exposed to combined pesticides rather than individual ones. Our tests revealed that the combined use of imazalil and azoxystrobin had more detrimental effect on aquatic vertebrates than when evaluated individually. This finding suggested that future ecological hazard analyses based only on individual tests might not sufficiently safeguard our aquatic ecosystems.

Organochlorine, organophosphorus, and carbamate pesticide residues in an Ethiopian Rift Valley Lake Hawassa: occurrences and possible ecological risks

Currently, pesticide production and use are on the rise globally. This trend is certain to continue in the coming decades with residues posing risks to the environment and human health even at low levels. Although various aspects of pesticides and their possible implications have widely been studied, such studies have mostly been carried out in developed countries leaving the rest of the world with little scientific information. We present here the results of a study on the occurrences, concentrations, and ecological risks of 30 pesticide residues (PRs) in water and sediment samples from a tropical freshwater Lake Hawassa in the Ethiopian Rift Valley. A total of 54 composite samples of water and sediment were collected from three sampling sites on three occasions. The samples were prepared by quick, easy, cheap, effective, rugged, and safe (QuEChERS) technique, and analyzed using GC-MS at Bless Agri Food Laboratory Service located in Addis Ababa, Ethiopia. The study applied the risk quotient (RQ) method to scrutinize the risks posed to aquatic biota by the detected PRs. The results showed occurrences of 18 and 20 PRs in the water and sediment samples, respectively. The majority, 78 and 75% of the detected PRs in water and sediment samples, respectively represent the organochlorine chemical class. Concentrations of heptachlor epoxide were significantly (p ≤ 0.001) higher than those of the remaining pesticides in both matrices. Of the pesticides detected, 77% were present in water and 83% in sediment samples and pose a serious risk (RQ ≥ 1) to the Lake Hawassa biota. This calls for further research to investigate the risks to human health posed by the PRs. The findings of this study can contribute to the development of global protocols, as they support the concerns raised about the ecological and public health impacts of PRs on a global level.

Toxicity effects of pesticides based on zebrafish (Danio rerio) models: Advances and perspectives

Pesticides inevitably enter aquatic environments, posing potential risks to organisms. The common aquatic model organism, zebrafish (Danio rerio), are widely used to evaluate the toxicity of pesticides. In this review, we searched the Web of Science database for articles published between 2012 and 2022, using the keywords "pesticide", "zebrafish", and "toxicity", retrieving 618 publications. Furthermore, we described the main pathways by which pesticides enter aquatic environments and the fate of their residues in these environments. We systematically reviewed the toxicity effects of pesticides on zebrafish, including developmental toxicity, endocrine-disrupting effects, reproductive toxicity, neurotoxicity, immunotoxicity, and genotoxicity. Importantly, we summarized the latest research progress on the toxicity mechanism of pesticides to zebrafish based on omics technologies, including transcriptomics, metabolomics, and microbiomics. Finally, we discussed future research prospects, focusing on the combined exposure of multiple pollutants including pesticides, the risk of multigenerational exposure to pesticides, and the chronic toxicity of aquatic nanopesticides. This review provides essential data support for ecological risk assessments of pesticides in aquatic environments, and has implications for water management in the context of pesticide pollution.

Decadal Assessment of Microplastics, Pharmaceuticals, and Pesticides as Contaminants of Emerging Concern in Kenya's Surface Waters: A Review

Studies investigating microplastics, pharmaceuticals, and pesticides as contaminants of emerging concern (CECs) in surface water sources in Kenya are reviewed. Contaminants of emerging concern are chemicals that have recently been discovered that may pose a threat to the environment, aquatic life, and human life. Microplastics in surface waters range from 1.56 to as high as 4520 particles/m3 , with high concentrations recorded in coastal waters. The dominant microplastics are fibers, fragments, and films, with foams, granules, and pellets making up only a small percentage. The main source of pharmaceuticals in water sources is not wastewater-treatment plants but rather raw untreated sewage because high concentrations are found near informal settlements with poor sewage connectivity. Antibiotics are detected in the range of the limit of quantification to 320 μg/L, with sulfamethoxazole, trimethoprim, and ciprofloxacin being the most abundant antibiotics. The high frequency of detection is attributed to the general misuse of antibiotics in the country. A health risk assessment indicated that only ciprofloxacin and acetaminophen posed noncarcinogenic health risks in the Ndarugo River and Mombasa periurban creeks, respectively. Similarly, the detection of antiretroviral drugs, mainly lamivudine, nevirapine, and zidovudine, is associated with human immunodeficiency virus prevalence in Kenya. In the Lake Naivasha, Nairobi River, and Lake Victoria basins, frequently detected organochloride pesticides (OCPs) are methoxychlor, alachlor, endrin, dieldrin, endosulfan, endosulfan sulfate, α-hexachlorocyclohexane (α-HCH), γ-HCH, and dichlorodiphenyltrichloroethane (DDT), some of which occur above permissible concentrations. The presence of DDT in some sites translates to illegal use or historical application. The majority of individual OCPs posed no noncarcinogenic health risk, except dieldrin and aldrin which had a hazard quotient >1 in two sites. Therefore, more surveying and regular monitoring in different regions in Kenya concerning CECs is essential to determine the spatial variability and effective measures to be taken to reduce pollution. Environ Toxicol Chem 2023;42:2105-2118. © 2023 SETAC.

Overview of African water resources contamination by contaminants of emerging concern

This review look at several classes of contaminants of emerging concern (CECs) in conventional and non-conventional water resources across the African continent's five regions. According to the review, pharmaceuticals, endocrine-disrupting chemicals, personal care products, pesticides, per- and polyfluoroalkyl compounds, and microplastics were found in conventional and non-conventional water resources. Most conventional water resources, such as rivers, streams, lakes, wells, and boreholes, are used as drinking water sources. Non-conventional water sources, such as treated wastewater (effluents), are used for domestic and agricultural purposes. However, CECs remain part of the treated wastewater, which is being discharged to surface water or used for agriculture. Thus, wastewater (effluent) is the main contributor to the pollution of other water resources. For African countries, the prevalence of rising emerging pollutants in water poses a severe environmental threat. There are different adverse effects of CECs, including the development of antibiotic-resistant bacteria, ecotoxicological effects, and several endocrine disorders. Therefore, this needs the urgent attention of the African Union, policymakers, Non-Governmental Organizations, and researchers to come together and tackle the problem.

Seasonal Changes in Pesticide Residues in Water and Sediments from River Tano, Ghana

Pollution due to pesticide residues has been reported in the downstream of the Tano Basin in the rainy season and has been attributed to the anthropogenic activities upstream. However, data on the seasonal variations in pesticide residues in the upstream of Tano Basin are limited. Seasonal variations in 13 organochlorine pesticide residues, 8 organophosphorus pesticide residues, and 5 synthetic pesticide residues in water and sediment samples of River Tano upstream were assessed through extraction and Varian CP-3800 gas chromatography equipped with a CombiPAL Auto sampler set at ionization mode electron impact methods. Significantly higher pesticide residues were detected in water and sediment samples in the rainy season than the dry season. Permethrin (rainy: 0.007 ± 0.01 mg/kg; dry: 0.008 ± 0.02 mg/kg) and profenofos (rainy: 0.021 ± 0.02 mg/kg; dry: 0.026 ± 0.01 mg/kg) showed higher dry season concentrations in the sediment samples. Two isomers of lindane (δ-HCH = 0.059 ± 0.24 μg/L; γ-HCH = 0.002 ± 0.01 μg/L) were detected in the water in the rainy season, but 3 were detected in the sediment samples (δ-HCH = 0.004 ± 0.12 mg/kg; γ-HCH = 0.003 ± 0.01 mg/kg; aldrin = 0.001 ± 0.01 mg/kg) suggesting possible illegal use. The detected pesticide residual levels in both water and sediment samples were lower than the maximum residual levels in water and sediment. The Chemical Control and Management Centre of the Environmental Protection Agency should check possible faking and adulteration of banned organochlorine pesticides.

Exploring the Environmental Exposure to Methoxychlor, α-HCH and Endosulfan-sulfate Residues in Lake Naivasha (Kenya) Using a Multimedia Fate Modeling Approach

Distribution of pesticide residues in the environment and their transport to surface water bodies is one of the most important environmental challenges. Fate of pesticides in the complex environments, especially in aquatic phases such as lakes and rivers, is governed by the main properties of the contaminants and the environmental properties. In this study, a multimedia mass modeling approach using the Quantitative Water Air Sediment Interaction (QWASI) model was applied to explore the fate of organochlorine pesticide residues of methoxychlor, α-HCH and endosulfan-sulfate in the lake Naivasha (Kenya). The required physicochemical data of the pesticides such as molar mass, vapor pressure, air-water partitioning coefficient (K_AW), solubility, and the Henry's law constant were provided as the inputs of the model. The environment data also were collected using field measurements and taken from the literature. The sensitivity analysis of the model was applied using One At a Time (OAT) approach and calibrated using measured pesticide residues by passive sampling method. Finally, the calibrated model was used to estimate the fate and distribution of the pesticide residues in different media of the lake. The result of sensitivity analysis showed that the five most sensitive parameters were K_OC, logKow, half-life of the pollutants in water, half-life of the pollutants in sediment, and K_AW. The variations of outputs for the three studied pesticide residues against inputs were noticeably different. For example, the range of changes in the concentration of α-HCH residue was between 96% to 102%, while for methoxychlor and endosulfan-sulfate it was between 65% to 125%. The results of calibration demonstrated that the model was calibrated reasonably with the R² of 0.65 and RMSE of 16.4. It was found that methoxychlor had a mass fraction of almost 70% in water column and almost 30% of mass fraction in the sediment. In contrast, endosulfan-sulfate had highest most fraction in the water column (>99%) and just a negligible percentage in the sediment compartment. α-HCH also had the same situation like endosulfan-sulfate (e.g., 99% and 1% in water and sediment, respectively). Finally, it was concluded that the application of QWASI in combination with passive sampling technique allowed an insight to the fate process of the studied OCPs and helped actual concentration predictions. Therefore, the results of this study can also be used to perform risk assessment and investigate the environmental exposure of pesticide residues.

Heavy metals in surface sediments of Lake Naivasha, Kenya: spatial distribution, source identification and ecological risk assessment

Heavy metals retained in sediments pose a threat to aquatic ecosystem and society. Knowledge of the status and sustainability of lake sediment in areas undergoing rapid economic development is scarce, and yet it is required in order to achieve the United Nations Sustainable Development goals. We investigated heavy metal concentration in Lake Naivasha sediments using enrichment factor, geoaccumulation index, pollution load index (PLI), risk index (RI) and multivariate statistics to determine metal accumulation, distribution and the lake’s pollution status. Sediments sampling followed a grid approach, and seven heavy metals: Co, Cr, Cu, Mn, Pb, Zn and Fe, were analyzed in total; concentrations were determined using portable X-ray fluorescence. The distribution maps were interpolated in a GIS platform, and the toxicity risk of sediments was determined. The concentrations of elements in the sediments are in the following decreasing order: Fe > Mn > Zn > Cu > Cr > Co > Pb. High concentration of heavy metals is found in the southern shoreline and east of the lake due to shoreline discharge and agricultural effluents drained into the lake and shoreline transgression. Pb and Zn are of anthropogenic origin, while Cu and Mn originate from both natural and anthropogenic sources and Fe and Co are from natural sources. In addition, the mean toxicity decreases in the order: Cu > Fe > Co > Pb > Zn > Mn > Cr. The PLI values were above one (> 1), indicating progressive deterioration of the sediment quality. Though the overall ecological risk of the lake is low to moderate (RI 36.73–60.51), hotspots of pollution should be marked for intervention. This assessment also helps to fill the knowledge gap required to formulate the right policies in implementing sustainable development goals in similar lakes.

Methods for Sample Collection, Storage, and Analysis of Freshwater Phosphorus

Although phosphorus (P) is an essential nutrient for biological productivity, it can cause freshwater degradation when present at fairly low concentrations. Monitoring studies using continuous sampling is crucial for documenting P dynamics in freshwater ecosystems and to reduce the risk of eutrophication. Despite literature updates of developments of the analytical methods for measurement of P species in natural waters, there has been no comprehensive review addressing freshwater sample collection, sample preparation, and sample treatment to fractionate and characterize different forms of P. Therefore, this paper aims to elaborate the different techniques for freshwater sampling and to introduce alternative laboratory methods for sample preservation and P fractionation. The advantages and disadvantages of various sampling techniques, including the traditional manual and the recently developed automatic and passive methods, are presented to highlight the importance of collecting representative freshwater samples. Furthermore, we provide suggestions for sample pretreatment, including filtration, transportation, and storage steps to minimize microbial activity and to maximize the accuracy of measurement of various P fractions. Finally, the most common laboratory methods to measure dissolved and particulate as well as the organic and inorganic freshwater P fractions are efficiently provided. Using this guide, a comprehensive monitoring program of P dynamics in freshwater ecosystems can be developed and applied to improve water quality, particularly of P-rich freshwaters.

Modeling Pesticide and Sediment Transport in the Malewa River Basin (Kenya) Using SWAT

Understanding the dynamics of pesticide transport in the Malewa River and Lake Naivasha, a major fresh water resource, is critical to safeguard water quality in the basin. In this study, the soil and water assessment tool (SWAT) model was used to simulate the discharge of sediment and pesticides (notably the organochlorine residues of lindane, methoxychlor and endosulfan) into the Malewa River Basin. Model sensitivity analysis, calibration and validation were performed for both daily and monthly time steps using the sequential uncertainty fitting version 2 (SUFI-2) algorithm of the SWAT-CUP tool. Water level gauge data as well as a digital turbidity sensor (DTS-12) for suspended sediment transport were used for the SWAT calibration. Pesticide residues were measured at Upper and Down Malewa locations using a passive sampling technique and their quantity was determined using laboratory gas chromatography. The sensitivity analysis results showed that curve number (CN2), universal soil loss equation erodibility factor (USLE-K) and pesticide application efficiency (AP_EF) formed the most sensitive parameters for discharge, sediment and pesticide simulations, respectively. In addition, SWAT model calibration and validation showed better results for monthly discharge simulations than for daily discharge simulations. Similarly, the results obtained for the monthly sediment calibration demonstrated more match between measured and simulated data as compared to the simulation at daily steps. Comparison between the simulated and measured pesticide concentrations at upper Malewa and down Malewa locations demonstrated that although the model mostly overestimated pesticide loadings, there was a positive association between the pesticide measurements and the simulations. Higher concentrations of pesticides were found between May and mid-July. The similarity between measured and simulated pesticides shows the potential of the SWAT model as initial evaluation modelling tool for upstream to downstream suspended sediment and pesticide transport in catchments.