Tracing heavy metal pathways from soil to silkworm: Bioaccumulation, trophic transfer, and ecological risk in wasteland based Eri silkworm farming.

Abstract

Heavy metal contamination remains an enduring environmental challenge because of its persistence, bioaccumulative behavior and associated ecological risks, particularly within wasteland ecosystems shaped by industrial and urban pressures. In this study, we examined the bioaccumulation and translocation of Cu, Mn, Ni, and Pb in the soil-plant-insect pathway in wasteland based Eri culture. Eri silkworms were reared on Castor leaves grown in contaminated wastelands. Heavy metal concentrations were measured in soil, roots, leaves and silkworm tissues to elucidate trophic transfer dynamics. Pollution indices, including contamination factor (CF), degree of contamination (Cdeg), geo-accumulation index (Igeo), pollution load index (PLI), enrichment factor (EF) and potential ecological risk index (PERI), indicated contamination levels ranging from moderate to very high, with the refinery site emerging as the most polluted. Multivariate analysis, particularly Principal Component Analysis (PC1= 87.26%), clearly delineated a contamination gradient distinguishing the polluted sites, while Pearson correlation indicated strong positive associations among metals across soil, plant, and silkworm systems. Metal accumulation followed the order roots > leaves, suggesting predominant sequestration in roots. Bioaccumulation factors (BF > 1) confirmed effective uptake from soil, whereas translocation factors (TF < 1) indicated limited movement to aerial parts. Subsequent transfer to silkworms resulted in accumulation in the order faecal matter > larvae > pupae > silk, implying excretion as a major detoxification pathway. Although silk contained minimal metal levels, edible pre-pupae and pupae exceeded permissible limits, raising health concerns. Human health risk assessment indicated that all estimated daily intake (EDI) values were below the permissible limits; however, Pb exhibited the highest THQ, and HI values > 1 in contaminated silkworm samples, particularly from the refinery site and the dumpsite, indicated potential non-carcinogenic health risks to consumers. Overall, the study establishes a clear soil-plant-insect heavy metal transfer pathway driven by anthropogenic inputs and underscores the ecological and food safety implications of wasteland-based sericulture.