Assessing Biota Accumulation Due to Contamination of Sediments by Stormwater Heavy Metals.

Evaluating sediment recontamination due to stormwater discharges is important when evaluating the long-term effectiveness of sediment remedial efforts in reducing biological impacts. The bioaccumulation of the heavy metals, Zn, Ni, Cu, Cd, Hg and Pb, and the metalloid As in a clam Macoma nasuta was studied in surficial sediments before and after stormwater inputs from Paleta Creek, CA during wet seasons in 2015-2016 and 2016-2017. The bioaccumulation was compared to bulk sediment concentrations and porewater concentrations measured by diffusion gradient in thin film devices. Significant reductions in biota accumulation and porewater concentrations were observed in samples collected after storm seasons compared to before storm seasons despite bulk sediment concentrations remaining the same or increasing. This was apparently the result of the deposition of stormwater contaminants in low bioavailable forms. The bioaccumulation of all the measured contaminants showed a positive significant correlation with porewater concentrations (p<0.1, α=0.1) and weak or no correlations with bulk sediment concentration. In conclusion, observed bulk sediment recontamination due to stormwater should not be assumed to lead directly to greater biota accumulation without bioavailability assessment. This article is protected by copyright. All rights reserved.