Abstract
Pesticides pose a serious risk to ecosystems. In this study, we used European Food Safety Authority methods, such as risk quotient (RQ) and toxicity exposure ratios (TER), to assess the potential ecological risks of 15 pesticide residues detected in agricultural soils in the Gaidahawa Rural Municipality of Nepal. The mean and maximum concentrations of the detected pesticide residues in the soil were used for risk characterization related to soil organisms. RQmean, TERmean and RQmaximum, TERmaximum were used to determine general and the worst-case scenarios, respectively. Of all the detected pesticides in soils, the no observed effect concentration (NOEC) for 27% of the pesticides was not available in literature for the tested soil organisms and their TER and RQ could not be calculated. RQ threshold value of ≥1 indicates high risk for organisms. Similarly, TER threshold value of ≥5, which is acceptable trigger point value for chronic exposure, indicates an acceptable risk. The results showed that the worst-case scenario (RQmaximum) indicated a high risk for soil organisms from chlorpyrifos [RQmaximum > 9 at depths (cm) of 0–5, 15–20 and 35–40 soil layer]; imidacloprid (1.78 in the 35–40 cm soil layer) and profenofos (3.37 in the 0–5 cm and 1.09 in the 35–40 cm soil layer). Likewise, for all the soil depths, the calculated TER for both the general and worst-case scenarios for chlorpyrifos ranged from 0.37 to 3.22, indicating chronic toxicity to F. candida. Furthermore, the risk of organophosphate pesticides for soil organisms in the sampling sites was mainly due to chlorpyrifos, except for two study sites where the risk was from profenofos. Ecological risk assessment (EcoRA) of the pesticide use in the study area indicated that the EFSA soil organisms were at risk at some of the localities where farmers practiced conventional farming.
Highlights
Over 4 million tons of pesticides are used annually worldwide (FAO, 2017)
This is the first case study that assessed the ecological risk of pesticide residues in 3 depths of soil from vegetable production areas of Nepal
For the worst-case scenarios, chlorpyrifos, profenofos and imidacloprid posed a potential risk to soil organisms, application of these pesticides in agriculture should be reduced
Summary
Over 4 million tons of pesticides are used annually worldwide (FAO, 2017). This number is only expected to increase due to the burgeoning world population demanding more food from shrinking agricultural lands that suffer from declining soil quality. Modern farming methods rely on chemical pesticides to control insects and diseases, thereby improving food quantity. Both the abundant use and in some cases, misuse of pesticides have contributed to soil pollution (Tsaboula et al, 2016). Research has discovered that pesticides can bioaccumulate and become biomagnified in soil, leading to even greater possible risks for the environment (Haj-Younes et al, 2015; Yuantari et al, 2015). There should be systematic monitoring of pesticide levels in soil that should include an evaluation of pesticide toxicity as well as an ecological risk assessment (EcoRA)
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