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Environmental fate & pathways

Bioaccumulation: terrestrial

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Description of key information

Transfer of the ash related metals from the aquatic to the terrestrial compartment as studied for tetragnathid spiders is thus considered to be low.

Key value for chemical safety assessment

Additional information

Ashes 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. Since fly ash contains a diversity of metals such as As, Cr, Cu, Pb, Hg, Ni, Se, Tl, V, Zn, it is of a long-term ecological concern. 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.

 

Shortly after the spill, 90% of the ash was removed from the river by dredging. Studies concern both the period of dredging (March 2009 – May 2010) and the post-dredging period after the partial removal of the ash. 5 published studies related to the Kingston spill were taken into account as evidence for the bioaccumulation potential of ash related metals in fish. Publications cover both field monitoring data and laboratory experiments. In some studies special attention was given to specific metals or metalloids, such as Se, As and Hg.

 

One study provides information on the bioaccumulation of ash related metals to terrestrial organisms. Site-specific bioaccumulation of ash-associated metals in tetragnathid spiders in ash spill affected sites and the potential transfer from the aquatic to the terrestrial systems was investigated. Spiders and sediment were collected from ash affected and reference sites and analyzed for metal concentrations. Results showed that although concentrations of metals in sediments were higher at ash affect sites compared to reference sites in many cases, this was not reflected in spiders. Most of metals showed no significant site difference in the tested organisms indicating a lack of metal bioavailability for this organism. Se and Ni were found to be elevated in tetragnathid spiders. However, threshold values are scarce for this organisms and therefore it cannot be concluded that the concentrations could be hazardous. Transfer of the ash related metals from the aquatic to the terrestrial compartment as studied for tetragnathid spiders is based on the results of this study considered to be low.

Available studies for further trophic levels, which are more directly exposed to ashes (fish, sediment organisms) showed in a weight of evidence approach that bioaccumulation of ash associated metals is possible but did not indicate high concerns towards toxicity to any compartment. In only few cases concentrations in organisms exceeded proposed thresholds (e.g. from US EPA, FDA) for the protection of the environment and humans, even under the extreme conditions of the spill. These results are in line with the terrestrial study. Furthermore, it needs to be considered that the spill represents an extreme and worst case situation. 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 are highly representative for demonstrating the behavior of ash-associated metals in the water, sediment and soil, with indicating the impact of ash contamination on different fish species and potential of accumulations. However, the pool of these studies do not cover the completely possible spectrum on the bioaccumulation potential of ash related metals under the different environmental conditions.