Trophic transfer patterns of arsenic in freshwater ecosystem layers in arsenic-endemic Ganges Delta and its potential human health risk.

Abstract

Arsenic (As) is a toxic environmental contaminant with global public health concern. In aquatic ecosystems, the quantification of total As is restricted chiefly to the individual organisms. The present study has quantified the total As in different trophic layers (sediment-water-phytoplankton-periphyton-zooplankton-fish-gastropod-hydrophytes) of lentic freshwater ecosystems. As transfer pathways quantifying the transmission rate across trophic-level compartmental route were delineated using a novel model-based approach along with its potential contamination risk to humans. Lentic water bodies from Indo-Gangetic region, acore area of groundwater As, were selected for the present investigation. The study revealed that among the lower biota, zooplankton were the highest accumulator of total As (5554-11,564µgkg-1) with magnification (rate = 1.129) of the metalloid, followed by phytoplankton (2579-6865µgkg-1) and periphytic biofilm (1075 to 4382µgkg -1). Muscle tissue of zooplanktivore Labeo catla is found to store higher As (80-115µgkg-1 w.w.) compared to bottom-dwelling omnivore Cirrhinus mrigala (58-92µgkg-1 w.w.). Whereas, Amblypharyngodon mola has accumulated higher As (203-319µgkg-1 w.w.) than Puntius sophore (30-98µgkg-1 w.w.) that raised further concern. The hepatic concentration indicated arsenic-mediated stress based on As stress index (threshold value = 1). Mrigal and Mola showed significant biomagnification among fishes while biodiminution was observed in Catla, Bata, Rohu and Punti. All the studied fishes were under the arsenic mediated stress. In the 'sediment-water-periphytic biofilm-gastropod' compartment, the direct grazing accumulation was higher (rate = 0.618) than the indirect path (rate = 0.587). Stems of edible freshwater macrophytes accumulated lesser As (32-190µgkg-1 d.w.) than roots (292-946µgkg-1 d.w.) and leaves (62-231µgkg-1 d.w.). The target cancer risk (TCR) revealed a greater concern for adults consuming edible macrophyte regularly. Similarly, the varied level of target hazard quotient and TCR for adults consuming fishes from these waterbodies further speculated significant health concerns. The trophic transfer rate of environmental As in soil-water-biota level at an increasing trophic guild and consumer risk analysis have been unravelled for the first time in the Indo-Gangetic plains, which will be helpful for the strategic mitigation of As contamination.