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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The bioaccumulation potential of ashes (residues) is 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 m3coal 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.

In 2009 and 2010 benthic (bottom-dwelling) and pelagic (mid-water column) fish communities were collected from the spill site by the Tennessee Valley Authority in order to examine among others the bioaccumulation potential of ash related constituents (Riggs et al. 2014). Following fish species were chosen for investigation: bluegill (Lepomis macrochirus), channel catfish (Ictalurus punctatus), gizzard shad (Dorosoma cepedianum), largemouth bass (Micropterus salmoides), redear sunfish (Lepomis microlophus), and white crappie (Pomoxis annularus). 26 trace metals and metalloids were measured in order to evaluate if uptake poses a risk for fish health. Fish tissue concentrations were compared with literature-based critical body residues. Concentrations of ash-related contaminants in water were additionally compared to US Environmental Protection Agency's Ambient Water Quality Standards for Fish and Aquatic Life and finally Hazard Quotients were calculated. The outcome of this study revealed little evidence of elevated uptake of ash related metals of potential ecological concern in fish. As and Se were an exception for which tissue concentrations were significantly higher in ash than in reference sites and exceeded consistently critical body burdens, such as NOAEL (NOAEL Se: 0.018 – 0.524 mg/kg ww; NOAEL As: 0.04 – 8.4 mg/kg ww for liver, muscle, ovary and whole body). The authors express a reservation toward the results due to uncertainties in retrieving the critical body residues (US Army Corps of Engineers/USEPA Environmental Residue-Effects Database) considering these values as very conservative. 

Stanley et al. (2013) conducted laboratory studies with juvenile fish in order to study among others the potential bioaccumulation effects of dredging activities and potential metal mobilization to fish health. The experiments were designed in such way to represent extreme conditions of exposure to oxidized and mobilized metal species. Juvenile Pimephales promelas were exposed for 10 d to elutriates prepared by bubbling river water with two different fly ash types for 10 days. Then elutriates were diluted to create different exposure concentrations (0, 10, 50 and 100%). Emory river water and dechlorinated tap water were used as controls. Concerning the study of bioaccumulation potential, a juvenile fish elutriate bioassay and the analysis of metal contents in the gut were performed. 24 metals (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 measured in fish tissues with a special focus on 4 selected metals of higher concern: As, Cr, Hg and Se. No mortality was observed in the study. A dose-response (increased concentrations) relationship was observed between mean concentrations of the four metals in fish (whole body) and elutriates (not significant for Cr). Nevertheless, all mean measured body burdens of As, Cr, Hg and Se in fish were below critical body residues (CBRs) based on literature search by the authors. Only in one case measured As was slightly higher (2.95 (±0.76) mg/kg wet weight) compared to literature critical body residue values. The analysis of gut metal content suggests that above mentioned metals were mostly associated to gut content and not fish tissue. The study results demonstrate a low potential of toxic bioaccumulation from ash occurring at extreme conditions.

Se bioaccumulation and potential health concerns in fish were investigated over time from 2009 through 2013 after the Kingston ash spill (Mathews et al., 2014). A monitoring was performed in two affected rivers i.e. Emory and Clinch as well as downstream of the spill. Reference sites were additionally monitored for comparison. Three fish species (Bluegill sunfish, Redear sunfish, Largemouth bass) with different trophic habits were examined. Water and sediment samples, fish fillets as well as whole body fish were analyzed for Se. Se concentrations in water were low within the 5 year investigation period and in most cases below the detection limit. Detectable Se was mostly found in samples collected close to the spill source. In only one case the Se concentration in water was higher (1.34 µg/L) than the USEPA aqueous criterion for Se of 1.3 µg/L in lentic systems. Concentrations in sediments were between 1.15 µg/g to 8.25 µg/g at ash-affected sites and between 1.01 and 6.17 µg/g in not affected sites, without statistic significant difference. Se concentrations in fish fillet were higher in contaminated (1.2 - 8 µg/g) compared to non-contaminated sites (1.2 - 5.5 µg/g). Similar trends were observed for whole body fish. However, this depends on fish species while the USEPA proposed whole body Se threshold in fish (8.1 µg/g) was not exceeded in any case, the study does not indicate high risks for aquatic life from Se at this spill site. 

Fish health and reproductive metrics were linked to contaminant bioaccumulation at the Tennessee Valley Authority Kingston coal ash spill by Pracheil et al. (2016). Fish monitoring was performed in the affected Emory and Clinch rivers. Three of the affected sites and three reference sites were analyzed. Species with different diet preferences were chosen to capture bioaccumulation and biomagnification of metals. Fish were monitored for 5 years. Multiple parameters like body burdens, blood parameters, metrics of fish health and reproduction were examined, while As, Hg, and Se were investigated intensively. Bioaccumulation was related through MANCOVA correlation to fish metrics and reproductive health. The MANCOVA analysis showed in most cases that there was no difference between the reference site and the affected site for most parameters. Ash spill sites had generally higher Se concentrations in all fish species compared to Se burdens in reference sites and was verified by Tukey’s test. For Hg and As, the trends were different. Hg was significantly elevated only in one of the reference sites compared to the other sites. Elevation of As was observed in bluegill and largemouth bass from spill sites the years directly after the spill (2010-2011). The study did no show consistent patterns in blood chemistry functional response groups over years for any species. A short-term reproductive disability following the spill was observed which however needs to be treated with caution due to the small sample size of the results. In conclusion although some ash associated contaminants were elevated at ash affected sites, there was no clear evidence to affect fish health. Long-term health effects due to the ash spill are considered to be low.

Se and As bioaccumulation were examined by Otter et al. (2012). The bioaccumulation of As and Se in the liver, ovary and muscle tissues of multiple fish species and the potential reasons of the differences after the coal ash spill in Kingston were investigated in this study. Fish were collected from two affected sites of the Emory River and two reference sites upstreams of the spill of the same river for comparison. Concentrations of As and Se in liver, ovary and muscle tissues, differences in species stomach and intestine pH as well as different trophic dynamics (that could affect different bioaccumulation patterns) were explored. As concentrations were elevated in ash contaminated sites in multiple fish species while Se was higher concentrated only in sunfish and bluegill fish in the ash affected sites. However As and Se concentrations in fish were generally low. The trophic dynamic study indicated some significant differences between ash affected and non ash affected sites. The pH in stomach and intestine was not found to have an impact to Se or As bioaccumulation.

Greeley et al. investigated the bioaccumulation and maternal transfer of the often ash-related metals As, Se and Hg in redear sunfish (Lepomis macrolophus), two years after the Kingston spill. Ash affected and non ash affected sites from the Emory and Clinch Rivers were compared. In this study, similar to other studies, it was shown that although whole body (4.9–5.3 mg/kg d.w.) and ovary (6.7–9.0 mg/kg d.w.) concentrations of Se were significantly higher compared to concentrations in fish from reference sites (2.2–3.2 mg/kg d.w.for whole bodies and 3.6–4.8 mg/kg d.w. for ovaries), Se concentrations remained below the proposed U.S. Environmental Protection Agency (USEPA) criteria for the protection of aquatic life.

Further two publications related to the Kingston ash spill are available for the bioaccumulation of ash related metals to two sediment organisms. Sediment organisms had slightly different patterns concerning accumulation of metals that fish.

The first available publication intended to in situ investigate the bioaccumulation of metals in three different mussel species (black sandshell, elephant ear, purple wartyback) during and after dredging activities in the ash affected sites (Otter et al. 2015). Mussels were caged for 1 year in ash affected and unaffected river sites for both the dredging period and the post-dredging period. Additionally mussels of each species were kept under laboratory conditions as a control. Mussel health (mussel condition index) and concentrations of 23 metals (As, Cd, Cr, Pb, Ni, Se, Hg, U, Fe, Mg, Al, Sb, Ba, Be, Co, Cu, Mn, Mo, Ag, Sr, Tl, V, and Zn) in soft tissues were measured. Potential differences based on location, dredging activities and species were investigated. Metal mussel concentrations were compared with contaminant advisory levels given mainly by the Food and Drug Administration in order to identify potential threats. From all metals measured, only the mean of lead concentrations were observed in two cases to exceed the respective contaminant advisory level given by the Food and Drug Administration (1.7 mg/kg). This was observed in the post-dredging period for purple wartyback, (3.2 mg/kg, Lower Clinch) and elephant ear (1.9 mg/kg, Upper Clinch). Dredging activities had in some cases effects on mussel health but were not linked to increased accumulation of specific metals.

In a further study with sediment invertebrates mayfly nymphs (Hexagenia bilineata) were monitored for 17 ash-associated metals in the tree ash spill affected rivers Emory, Little Emory, Clinch and Tennessee from 2009 to 2012 (Smith, 2016). Hexagenia nymphs from sediment samples were collected from affected and reference sites for metal analysis. Spatial and temporal trends for concentrations of metals in nymphs of affected and reference sites were observed and analyzed. Principal analysis support that concentrations of As, Ba, Be, Mo, Sb, Se, Sr, and V were higher in nymphs at ash-affected sites than at reference site and concentrations in animals decreased with increasing distance from the spill. Se concentrations in nymphs were even higher than in pond ash samples. The results of the study strongly suggested that the ash-associated metals in nymphs started to decline after 2010, and this was increasingly observed in 2012 with As, Se, Sr, Sb, Mo, and V bearing the lowest levels in this study. However, the overall values were still elevated compared to the reference sites. The authors conclude that the concentrations found are not high enough to cause adverse effects.

Finally, 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.

The available studies 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. 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. However, individual metals of concern such as As and Se seem to be longer in flux and therefore of higher concern especially for adult fish. Bioaccumulation was, not surprisingly, found to be species dependent considering diet preferences. Mussels and hexagenia nymphs were representative organisms for the sediment compartment investigated for ash-related metal bioaccumulation. Bioaccumulation of several metals was observed in representative sediment organisms. However, concentrations were in both cases not high enough to cause concerns and were not related to toxicity. Transfer of the ash related metals from the aquatic to the terrestrial compartment as studied for tetragnathid spiders was found to be low except in case of Se, which was found to be elevated in the organisms. However, 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.

Reference:

Greeley Jr. M.S., Adams S. M., Elmore L.R., McCracken M.K. (2016) Influence of metal(loid) bioaccumulation and maternal transfer onembryo-larval development in fish exposed to a major coal ash spill. Aquatic Toxicology 173, 165–177.