Chlorpyrifos-Ethyl Contamination in Agricultural Soils and Earthworms: Field Monitoring, Complementary QSAR-Based Prediction, Bioaccumulation, and Ecological Risk Assessment in Intensive Potato Agroecosystems of Larache Province, Northern Morocco

Abstract

Chlorpyrifos-ethyl remains one of the most extensively used organophosphate insecticides worldwide despite increasing concerns regarding its environmental persistence and ecological toxicity. However, information on its occurrence in agricultural soils, transfer to soil biota, and environmental behavior under field conditions remains limited for North African agroecosystems. This study investigated chlorpyrifos-ethyl contamination in intensive potato-growing systems of Larache Province through an integrated experimental and computational approach. Soil and earthworm samples collected from ten agricultural fields were analyzed by GC–ECD following QuEChERS extraction, while quantitative structure–activity relationship (QSAR) models implemented in the VEGA platform were used to obtain descriptive estimates of physicochemical properties, environmental fate, bioaccumulation potential, and earthworm toxicity. Chlorpyrifos-ethyl was detected in soils at concentrations ranging from not detected to 0.0965 mg kg⁻¹ and in earthworms from 0.0078 to 0.0440 mg kg⁻¹, indicating exposure of soil organisms at the sampled fields. Bioaccumulation factors ranged from 0.18 to 2.65, indicating variable field accumulation among sampling sites. Among the ten investigated fields, seven exhibited risk quotients (RQ) above 1, suggesting potential ecological concern under the specific conditions and dates sampled; given the single-composite sampling design and the limited number of fields, this observation should be regarded as a preliminary field-level indication rather than a regional risk characterization. QSAR predictions consistently characterized chlorpyrifos-ethyl as a highly hydrophobic compound (LogKow = 5.32) with strong soil sorption (logKOC = 3.62), low water solubility (1.26 mg L⁻¹), moderate soil persistence (half-life = 13 days), limited biodegradability, and considerable bioaccumulation potential (logBCF ≈ 3). This intrinsic bioconcentration potential contrasts with the generally low field-derived BAF values, a pattern that likely reflects the distinction between standardized, intrinsic bioconcentration (BCF) and realized, bioavailability-limited field accumulation (BAF), rather than a direct inconsistency between the two lines of evidence. Overall, integrating field monitoring with QSAR-based environmental prediction provides a comprehensive framework for evaluating pesticide behavior and ecological risk and supports the development of sustainable pesticide management strategies in intensive agricultural systems.