Butachlor contamination in surface water and sediment: Assessing human health, ecological risks, and environmental implications of the Bontanga irrigation scheme in the Northern region of Ghana

• Butachlor levels exceed the EFSA threshold (0.5 μg/L) in surface water. • All physicochemical parameters were within WHO limits. • Butachlor posed a medium acute risk to algae and fish. • Butachlor posed a high chronic risk to aquatic biota. • Urgent need for farmer education and alternative pest control methods. The Bontanga Irrigation Scheme in Ghana’s Kumbungu District, vital for local agriculture, faces significant ecological and health risks from Butachlor, an herbicide used in rice plantations. This study aimed to evaluate the physicochemical parameters of surface water, measure Butachlor concentrations in surface water and sediment, assess ecological risks, and estimate human health effects. A total of 100 water samples, 50 sediment samples were collected, and 50 farmers were interviewed about pesticide use. Physicochemical parameters such as pH, total dissolved solids, electrical conductivity, temperature, and turbidity were measured using standard analytical methods. Butachlor levels in surface water and sediment were determined using gas chromatography-mass spectrometry (GC–MS) and liquid chromatography-mass spectrometry (LC-MS). Results indicated that all physicochemical parameters in the water samples were within WHO limits. However, Butachlor concentrations ranged from 4.74 µg/L to 118.85 µg/L, exceeding the EFSA threshold of 0.5 µg/L, while sediment samples were below the detection limit of 0.01 mg/L. The toxic unit (TU) method revealed a medium acute risk to algae (0.28) and fish (0.13) and a low acute risk to aquatic invertebrates (0.02). The risk quotient (RQ) method indicated a high chronic risk to aquatic biota in surface water, though the non-carcinogenic health risk (HQ) to humans was minimal (HQ < 1). Butachlor residues may pose significant health risks, including neurological, respiratory, and reproductive disorders. This study recommends implementing Integrated Pesticide Management policies, developing pest-resistant plant species, proper disposal of pesticide containers, and educating farmers on pesticide usage. Future research should focus on Butachlor’s long-term effects on aquatic biota, alternative pest control strategies, and measures to reduce residues, protecting both wildlife and human health.