ENVIRONMENTAL AND TOXICOLOGICAL EFFECTS OF PARAQUAT USED IN FARMING ACTIVITIES ON SOIL, CROP, AND WATER IN SELECTED COMMUNITIES OF ONDO STATE, NIGERIA

Abstract

ABSTRACT Paraquat (PQ) is a toxic quaternary ammonium herbicide commonly used in Nigeria but has been banned and restricted in many countries because of its high toxicity. This study assessed the environmental and toxicological effects of paraquat residues in soil, water, and crops from (Awo, Bolo, Epe, and Roti) farms across four Local Government Areas (LGAs) of Ondo State, Nigeria. Descriptive survey using copies of structured questionnaires were administered to 240 farmers to elicit information on the management and risk awareness of herbicide usage in the study areas. Soil samples (top and sub soil), water samples and two crop samples (during harvesting) were collected from each farm from May 2023 to March 2024. The physical and chemical parameters of soil and water samples were determined using standard procedures while PQ residues were extracted through standard methods and quantified using High Performance Liquid Chromatograph (HPLC). The resultant PQ residues in crops and water were administered to 24 Wistar rats that were divided into four groups (control, 0.01 mg/kg PQ, 3.09 mg/kg PQ and 8.14 mg/kg PQ) and toxicological effects were assessed using biochemical assays and histological examination. Data obtained were analysed using descriptive and inferential statistics while means were separated with the Duncan Multiple Range Test at p ≤ 0.05 using Statistical Package for Social Sciences (version 20.0). The results revealed that 76.3% of the farmers had no training on herbicide usage, 76.7% used knapsack sprayer, 62.5% used gloves or mask, and 25.8% dressed in normal clothes without any protective equipment during herbicide application. Soil pH ranged from 5.98±0.14 to 7.73±0.10 and pH in water samples ranged from 5.40±1.04 to 7.47±0.83. Low concentrations of exchangeable cations were recorded in the soil samples for all farms with values ranging from 0.12±0.01 to 0.39±0.01 (K+), 1.09±0.05 to 1.29±0.13 (Ca2+), 0.30±0.01 to 0.38±0.01 (Na+), and 0.27±0.02 to 1.04±0.02 cmol/kg (Mg2+). PQ residues were detected in the soils of Awo and Roti farms throughout the year at concentration ranging from 0.001±0.000 to 0.547±0.009 and 0.006±0.000 to 2.174±0.115 respectively but only in July at Bolo farm at 0.039±0.006 mg/kg. In Epe farm, PQ was not detected in subsoil from September to March but residues detected ranged from 0.001±0.000 to 0.157±0.006 mg/kg. Higher levels of PQ were found in surface water less than 200 m away from the farms with concentration ranging from 0.001±0.000 to 0.068±0.001mg/L while PQ residues were found in all crop samples at concentration ranging from 0.006±0.00 to 8.09±0.04 mg/kg. The biochemical assays done on the serum, liver, and kidney tissues of Wistar rats, especially at the highest concentration detected in crops and water, revealed tissue damage, electrolyte imbalance, signs of tissue inflammation, and low antioxidant activities. The histological examination showed multiple protein casts on the tubular lumen of the kidney and inflammatory cell infiltration in the hepatic parenchyma of the liver. In conclusion, soil, water, and crop samples from the studied farms contained paraquat residues, which could lead to deleterious health issues in humans and animals when consumed.