Evaluation of metals, metalloids, and ash mixture toxicity using sediment toxicity testing

Abstract

In December 2008, a release of 4.1 million m3 of coal ash from the Tennessee Valley Authority Kingston Fossil Plant occurred. Ash washed into the Emory River and migrated downstream into the Clinch and Tennessee Rivers. A Baseline Ecological Risk Assessment evaluated risks to ecological receptors from ash in the river system post‐dredging. This article describes the approach used and results from sediment toxicity tests, discussing any causal relationships between ash, metals, and toxicity. Literature is limited in the realm of aquatic coal combustion residue (CCR) exposures and the potential magnitude of effects on benthic invertebrates. Sediment samples along a spectrum of ash content were used in a tiered toxicity testing approach and included a combination of 10 day sediment toxicity acute tests and longer‐term, partial life cycle “definitive” tests with 2 species (Hyalella azteca and Chironomus dilutus). Arsenic, and to a lesser extent Se, in the ash was the most likely toxicant causing observed effects in the laboratory toxicity tests. Sites in the Emory River with the greatest statistical and biologically significant effects had As concentrations in sediments twice the probable effects concentration of 33 mg/kg. These sites contained greater than 50% ash. Sites with less than approximately 50% ash in sediments exhibited fewer significant toxic responses relative to the reference sediment in the laboratory. The results discussed here present useful evidence of only limited effects occurring from a worst‐case exposure pathway. These results provided a valuable line of evidence for the overall assessment of risks to benthic invertebrates and to other ecological receptors, and were crucial to risk management and development of project remediation goals. Integr Environ Assess Manag 2015;11:21–31. © 2014 SETAC

Application of ecological risk assessment in managing residual fly ash in TVA's Watts Bar Reservoir, Tennessee

“…The 17 receptor groups evaluated included fish, benthic invertebrates, aquatic plants (periphyton and macrophytes), and wildlife that feed in and around the river system (see conceptual site model in Figure 2 in Walls, Jones et al 2015, this issue). BERA details are available in the project report (ARCADIS ), and details for several receptors are presented in 5 other articles in this series (Buys et al , Meyer et al , Rigg et al , Stojak et al , Walls, Meyer et al ).…”

Ecological risk assessment for residual coal fly ash at Watts Bar Reservoir, Tennessee: Limited alteration of riverine‐reservoir benthic invertebrate community following dredging of ash‐contaminated sediment

“…The colocated sediment data collected in 2011 found that while benthic community composition was mostly correlated with substrate types and water depth, 3 individual samples in the immediate area of the release appeared to have associated adverse benthic community effects potentially related to fly ash. Metals in sediment ash is of concern in other studies, as mentioned throughout this series (Stojak et al , this issue) especially when ash is present at greater than 40%. These 3 samples demonstrate the heterogeneous nature of these areas still containing pockets of ash.…”

“…Based on the colocated sediment samples collected with the benthic invertebrate community samples, approximately 5.5% of the samples had ash content exceeding 40%. The 40% threshold was derived from sediment toxicity tests (Stojak et al , this issue). The only samples which had a community response slightly correlated to ash and metals content ranged from 62‐65% ash, much greater than the 40% laboratory threshold.…”

Ecological risk assessment for residual coal fly ash at Watts Bar Reservoir, Tennessee: Site setting and problem formulation

“…These various types of samples were used to estimate bioavailability and bioaccumulation of COPECs from diet and other exposure pathways, as well as to model bioavailability to the respective predators. Subsequent articles focus on the evaluations for fish (Rigg et al , this issue), benthic invertebrates (Buys et al , this issue, and Stojak et al , this issue), aquatic‐ and riparian‐feeding wildlife (Meyer et al , this issue), and aerial‐feeding insectivores (i.e., tree swallows; Walls et al , this issue).…”