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Environmental fate & pathways

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Ashes, including cenospheres, are inorganic complex compounds consisting of multitude of unknown and variable constituents (UVCB), and it is therefore technically not possible to determine an overall bioaccumulation for this substance. However, most of metals contained in ashes, which are of concern have been reviewed in literature. 

End of 2008 4.1 million m^3 coal ash were released into the Emory, Tennessee and Clinch rivers due to an accident in the Tennessee Valley Authority (TVA) Kingston Fossil Plant. This unfortunate accidence provided an opportunity to directly study the impact of coal fly ash in a large lotic system since more than one rivers were affected. A variety of studies were initiated by multiple actors to assess ecological risks to different organisms. More than 24 metals (e.g. As, Cr, Hg, Se, Ag, Al, Ba, Be, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sb, Tl, V, Zn) were investigated. Among multiple toxicological and ecotoxicological studies, bioaccumulation potential of metals associated to fly ash was investigated either as an endpoint solely or in combination with toxicological effects.

Bioavailability and consequently bioaccumulation of ash-related metals is complex and dependent on multiple factors like pH, redox potential, geochemical interactions etc. The site monitoring and lab investigations of the presented publications and monitoring data for aquatic, sediment and terrestric compartments showed in a weight of evidence approach that bioaccumulation of ash associated metals is generally very low and not of concern for any compartment. In only very few cases (e.g. for As and Se) concentrations in organisms exceeded proposed thresholds (e.g. from US EPA, FDA) for the protection of the environment and humans but was observed for only very high ash concentration in the river and under the extreme conditions caused by the spill.

Furthermore, cenospheres are not bioavailable for aquatic organisms due to its physical chemicals properties as inert, hollow balls of sand-like material; therefore a bioaccumulation potential can be excluded.

Additionally, the Tennessee Valley Authority (TVA) initiated multi-phase laboratory toxicity studies in March 2009 to evaluate potential risks to biota from exposure to fly ash including cenospheres from the ash release to the river and subsequent dredging. Results from a „A Multi-phased Toxicity Study for Evaluating Potential Risks of Kingston Fossil Plant Fly Ash Exposure to Benthic and Aquatic Biota“ ash composite samples indicated no appreciable bioaccumulation of Ash including cenospheres (R. Sherrard; Poster, SETAC, 2009).