Abstract
Lake Ziway, a freshwater lake located in Ethiopia, is under the pressure of pesticide and nutrient pollution due to agricultural activity and urbanization. This study has analysed concentrations of insecticides, fungicides and nutrients in water and sediment samples of Lake Ziway taken in the wet and dry season at 13 sites expected to be under different environmental stress and assessed their expected ecological impacts. Malathion, dimethoate, metalaxyl, diazinon, chlorpyrifos, fenitrothion and endosulfan were detected in more than half of the water samples, while diazinon, α-cypermethrin and endosulfan were frequently detected (>25%) in sediment samples. Higher levels of physicochemical parameters were observed at sample locations proximate to agricultural and urban activities. Risk quotients (RQ) and multi-substance Potentially Affected Fraction (msPAFRA) were calculated to assess the ecological risk of individual and mixture of pesticides, respectively. The majority of the pesticides detected in the water of the lake showed a potential acute risk (RQ > 1), specifically the insecticides chlorpyrifos, λ-cyhalothrin and α-cypermethrin for which high potential acute risks were calculated using a 2nd tier risk assessment. Levels of pesticides in sediment showed low ecological risks. Arthropods and fishes are expected to be highly affected by mixtures of pesticides (msPAFRA = < 1–80%) detected at locations that are proximate to smallholders’ farms, and receive largescale farms’ wastewater and at sites where inflow rivers join the lake. Macroinvertebrates based redundancy analysis showed the effectiveness of EPT richness to assess ecological status of the lake. Training for smallholder farmers on pesticides safety and usage, and implementation of improved effluent management mechanisms by floriculture farms are urgently needed intervention measures to reduce the pollution.
Highlights
Lands and the intensification of the use of agrochemicals (Bachewe et al, 2018; Pretty, 2011)
In line with Merga et al (2020) and Teklu et al (2018), our result indicates that physicochemical properties of Lake Ziway may be affected by floriculture, agricultural and urban activities in the catchment area of the lake ecosystem
Our results indicate that evaluating mixtures of pesticides instead of individual pesticides in the ecological risk assessment using the msPAF model is important to avoid underestimation of overall risks as it reported by Ra€mo€ et al (2018)
Summary
Lands and the intensification of the use of agrochemicals (Bachewe et al, 2018; Pretty, 2011). The levels of pesticides have never been evaluated in sediments, nor in combination with biological sampling, despite their high importance for environmental risk assessment as biological communities disclose historical anthropogenic disturbances that further strengthen the risk assessment of the present pollution (Aazami et al, 2015; Abbasi and Abbasi, 2011; Ccanccapa et al, 2016; Kebede et al, 2020) To address these issues, the objectives of the present study were to 1) assess the concentrations of insecticides and fungicides in water and sediment samples, and the levels of physicochemical parameters in water samples of Lake Ziway, 2) perform a risk assessment for the insecticide and fungicide concentrations measured in both matrixes 3) correlate the abundance of biological organisms (macroinvertebrates and fish) to monitored pesticide concentrations and levels of physicochemical parameters and 4) evaluate the correlation between macroinvertebrate based biotic indices and the monitored pesticide concentrations and levels of physicochemical parameters. This with the aim to assess the risks posed by pesticides to aquatic, non-target (macroinvertebrates and fish) organisms in Lake Ziway and to select appropriate biological indices to assess future changes in biological water quality
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