Implementation of a Laboratory Toxicity Study Design for Assessing Effects on Aquatic and Sediment Biota Exposed to Fly Ash in a River System

摘要

Background/Objectives. An integral part of the Tennessee Valley Authority’s response to the 2008 release of fly ash to the Emory and Clinch Rivers is to assess the potential for toxicity to aquatic and sediment-dwelling biota. Early laboratory toxicity studies conducted the following year were aimed at discerning effects to water-column species from dredging activities and answering the question “is ash toxic” to benthic species. These studies included several sentinel species and laboratory results indicated that no acute or short-term chronic toxicity to water-column species would occur from dredging and only one benthic species tested (Hyalella azteca) responded in mortality upon exposures to samples containing primarily ash. More in-depth studies with this species utilizing toxicity identification procedures led to the conclusion that physical attributes of fly ash (grain size or morphology) were responsible for survival effects while metals and metalloids contributed to sublethal effects. Approach/Activities. This presentation describes the laboratory toxicity study design that was formulated and implemented to study the long-term effects of ash remaining in the rivers on benthic species. Emphasis was placed on epibenthic (H. azteca and Ceriodaphnia dubia) and infaunal (Chironomus dilutus) species that earlier studies indicated risks might exist. H. azteca typically inhabits submerged rooted vegetation and often forages in the upper layers of sediment. C. dubia is known to scour sediments during periods of diel migration, and thus serves as a good sentinel species for determining if the sediment/water interface might incur risks from contaminants that leach to the overlying water column. C.dilutus burrows into sediment and is ideal for studying exposures to toxicants in sediment and porewaters. The study design described here included 28-day H. azteca, 3-brood chronic C. dubia, and C. dilutus partial life-cycle (until 3 days no emergence) laboratory toxicity exposures to whole-sediment samples collected from the Emory and Clinch Rivers after the dredging activities ceased. Results/Lessons Learned. This laboratory study indicated that effects observed for H. azteca and C. dilutus exposures to ash-containing river sediments were positively correlated with ash content, but no effects were noted for C. dubia. These findings were integral to risk assessments identifying the ecological receptors that are the focus of remedial actions addressing the residual ash in the river system. Consequently, they play an important role both in evaluation of possible alternatives for remediation of the residual ash, and in the monitoring strategy to evaluate long-term effectiveness of the selected remediation alternatives.