Levels of pesticide residues in sediment and soils of Fogera district, Northwestern Ethiopia: indications of some risks to local biota.

This study aimed to analyze pesticide residues in the sediments and soils of Fogera District, Ethiopia, to evaluate the risks posed to organisms that dwell in these environments. A total of 7 sediments from rivers, canals and ponds, and 13 soil samples from irrigated farmlands were collected from April to June 2023 using a cross-sectional study design. The samples were collected from 0-8 cm depth in both sediments and soils using scoops and spoons. Analytes were prepared following the buffered procedures, extracted following the Quick, Effective, Cheap, Rugged, and Safe (QuEChERS) method and extracts were analyzed using the triple quad gas chromatography-mass spectrometry technique. Twenty-seven pesticides were identified and quantified both in the sediment and soil samples. More than 85% of the pesticide residues in the sediment and soil samples were organochlorines and organophosphates. The concentrations of the organochlorine and organophosphate pesticides in sediments ranged from ND to 9.94 µg/kg and ND to 12.12 µg/kg, respectively. Similarly, the concentration of the organochlorine and organophosphate pesticides in the soil samples ranged from ND to 13.69 µg/kg and ND to 10.70 µg/kg, respectively. Though the mean concentration difference between the pesticide residues in the sediment and soil samples was insignificant (t (18) = -0.871, p = 0.395), the risks of pesticide residues in sediments to aquatic biota were much higher than those in the soil biota. Of the 27 pesticides detected in sediments, 24 of them pose a higher risk and 1 moderate risk to aquatic biota. The risk quotients of Endrin aldehyde and Endrin ketone in sediments were not calculated due to the lack of endpoint concentrations. In a general case scenario, the risk quotients of the pesticides ranged from 0.80 (Para-methyl) to 21086.43 (Deltamethrin) in sediments and from 0.001 (Malathion) to 17.689 (Profenofos) in soils. The pesticide residues in sediments and soils might pose adverse effects on the biota of aquatic and terrestrial ecosystems. Therefore, a transparent pesticide supply chain and deploying qualified experts to monitor and inspect the types of pesticides in use and the pesticide application practices, detail studies on the level of toxicities of the commonly applied pesticides to the biota of aquatic and terrestrial ecosystems, and enforcing the pesticide laws are required to reduce the adverse effects of pesticides.