Trophic Transfer and Accumulation of Heavy Metal and Arsenic Speciation in Freshwater Aquatic Organisms in Huangshui Creek, Shimen Realgar Mine, China by Quantifying Diet Compositions

Abstract

Heavy metal pollution is a worldwide concern and understanding the sources of metal accumulation in aquatic organisms is essential for maintaining a healthy ecosystem. In this study, aquatic organisms and five potential food sources (leaf litter, coarse and fine particulate organic matter (CPOM and FPOM), epilithon and fish) were collected around the Shimen Realgar Mine and 8 heavy metal concentrations and arsenic (As) speciation were analysed. Stomach content analysis and stable nitrogen and carbon isotope analysis, combined with the new Bayesian mixing model (MixSIAR), were used to quantify diet composition of aquatic organisms. The δ13C and δ15N values varied among different fish size and sampling sites and were probably related to the diet shift of aquatic organisms. The MixSIAR modelling results showed that large proportion of the aquatic organisms’ food were composed of FPOM (9%-68%) and epilithon (15%-65%), with leaf litter, CPOM and fish accounting for lower proportions (2%-30%). Concentrations ranged from 0.91 to 1298 mg/kg for As, 0.01 to 1.30 mg/kg for Cd, 0.12 to 37.79 mg/kg for Pb, 0.63 to 1158 mg/kg for Cr, 1.22 to 411 mg/kg for Cu, 0.82 to 1772 mg/kg for Mn, 0.31 to 542 mg/kg for Ni and 21.84 to 1414 mg/kg for Zn in all collected samples, including the aquatic organisms and the relevant food sources. Heavy metal concentrations in CPOM, FPOM and epilithon were significantly higher than those in aquatic organisms and leaf litter. In addition, the biomagnification factors were all less than 1, indicating a biodilution from diet to freshwater organisms. The predominant As species were organic As in aquatic organisms, while inorganic As was common in their food sources, indicating that As biotransformation occurred within the freshwater food chain.

Keywords: Diet composition, stable isotopes, Heavy metal, MixSIAR model, Biomagnification factor