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Report No . 465 COAL ASH CONSTITUENTS AT THE BASE OF AQUATIC FOOD WEBS : PROCESSES AFFECTING BIOACCUMULATION AND TROPHIC TRANSFER By

Project Title: Coal ash constituents at the base of aquatic food webs: Processes affecting bioaccumulation and trophic transfer. The goal of this research was to investigate arsenic bioaccumulation at the base of aquatic food webs, including uptake of arsenic from solution and depuration kinetics by benthic invertebrates, uptake and bioconcentration of arsenic by periphyton, and potential trophic transfer to primary consumers. To better understand arsenate bioaccumulation dynamics in lotic food webs we used a radiotracer approach to characterize accumulation in periphyton and subsequent trophic transfer to benthic grazers. Flux rates from solution for a variety of benthic invertebrates are also described. Our results show that over an 8 day period periphyton concentrated As from environmentally realistic exposures 3,200–9,700-fold on a dry weight basis without reaching steady state. These As-enriched diets resulted in negligible accumulation of As in Neocloeon triangulifer relative to the concentration in periphyton after a full lifecycle exposure. Other dietary studies with invertebrate grazers showed that the assimilation efficiency of As from periphyton is generally quite low, ranging from 22% in the mayfly N. triangulifer to 75% in the mayfly Isonychia sp., suggesting factors controlling bioavailability limit the amount of As that is transferred to grazers. We propose that two such mechanisms may be the role of As adsorption to iron oxides in periphyton, and biotransformation of As by periphyton. Data showing relatively low uptake rate constants (Ku) from solution in benthic invertebrates ranging from 0.063±0.04 L g-1d-1 in Psephenus herricki, to 0.001±0.003 L g-1d-1 in M. pudicum. Efflux (Ke) was generally high ranging from 0.15±0.03 d-1 in Maccafertium sp. to 0.03±0.03 d-1 in Pleurocera sp. Together these results have broad implications for monitoring programs by highlighting the role of periphyton as a sink for arsenate as well as interspecies differences in As bioaccumulation.