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 responseto the 2008 release of fly ash to the Emory and Clinch Rivers is to assess the potential fortoxicity to aquatic and sediment-dwelling biota. Early laboratory toxicity studies conductedthe following year were aimed at discerning effects to water-column species fromdredging activities and answering the question “is ash toxic” to benthic species. Thesestudies included several sentinel species and laboratory results indicated that no acute orshort-term chronic toxicity to water-column species would occur from dredging and onlyone benthic species tested (Hyalella azteca) responded in mortality upon exposures tosamples containing primarily ash. More in-depth studies with this species utilizing toxicityidentification procedures led to the conclusion that physical attributes of fly ash(grain size or morphology) were responsible for survival effects while metals and metalloidscontributed to sublethal effects.Approach/Activities. This presentation describes the laboratory toxicity study designthat was formulated and implemented to study the long-term effects of ash remaining inthe rivers on benthic species. Emphasis was placed on epibenthic (H. azteca and Ceriodaphniadubia) and infaunal (Chironomus dilutus) species that earlier studies indicatedrisks might exist. H. azteca typically inhabits submerged rooted vegetation and often foragesin the upper layers of sediment. C. dubia is known to scour sediments during periodsof diel migration, and thus serves as a good sentinel species for determining if thesediment/water interface might incur risks from contaminants that leach to the overlyingwater column. C.dilutus burrows into sediment and is ideal for studying exposures to toxicantsin sediment and porewaters. The study design described here included 28-dayH. azteca, 3-brood chronic C. dubia, and C. dilutus partial life-cycle (until 3 days noemergence) laboratory toxicity exposures to whole-sediment samples collected from theEmory and Clinch Rivers after the dredging activities ceased.Results/Lessons Learned. This laboratory study indicated that effects observed forH. azteca and C. dilutus exposures to ash-containing river sediments were positively correlatedwith ash content, but no effects were noted for C. dubia. These findings wereintegral to risk assessments identifying the ecological receptors that are the focus of remedialactions addressing the residual ash in the river system. Consequently, they play animportant role both in evaluation of possible alternatives for remediation of the residualash, and in the monitoring strategy to evaluate long-term effectiveness of the selected remediationalternatives.