Heavy metal contamination in soil and Indian mustard (Brassica juncea L. Czern.) irrigated with borewell water and paper mill effluent

Irrigation with paper mill effluent (PME) in peri-urban agricultural landscapes poses significant risks to soil integrity, crop quality, and public health. This field-based comparative study in Saharanpur district, Uttar Pradesh, India, evaluated physicochemical properties of irrigation water and soil, morpho-physiological responses of Indian mustard ( Brassica juncea L. Czern.), and heavy metal (Cd, Cr, Cu, Fe, Mn, Zn) accumulation in plant tissues under borewell water (control) and PME irrigation. Bioaccumulation Factor (BAF), Enrichment Factor (EF), and Translocation Factor (TF) were computed to characterize metal partitioning, while Target Hazard Quotient (THQ) and Health Risk Index (HRI) quantified non-carcinogenic dietary risk for adults and children. PME significantly elevated soil alkalinity (pH 8.79), electrical conductivity (4.73 dS/cm), organic matter (3.94%), and concentrations of all six heavy metals ( p < 0.001). Although PME promoted vegetative growth—including chlorophyll content (6.09 mg g −1 fwt.), leaf area (229.68 cm 2 ), and siliqua yield—it simultaneously induced pronounced heavy metal accumulation, predominantly in roots. BAF values for Fe and Mn exceeded the hyperaccumulation threshold; TF values were consistently < 1, confirming preferential root sequestration and limited acropetal translocation. EF values indicated substantial tissue enrichment, particularly for Cu (root EF = 226.50) and Cr (root EF = 40.51). Dietary risk modeling revealed that leaf Cr HRI exceeded the safety threshold in children (HRI = 1.05), while leaf Cd and Cr approached risk levels in adults. Baseline (borewell-irrigated control) soil metal concentrations were low and within agriculturally safe ranges, while PME-irrigated soils exhibited marked enrichment, with the highest tissue concentrations recorded in roots, followed by stem, leaves, and seeds. These findings emphasize the urgent need for regulatory monitoring, mandatory effluent pre-treatment, and risk-informed management of PME-irrigated agricultural systems.