Teresa J. Mathews

Monitoring Fish Contaminant Responses to Abatement Actions: Factors that Affect Recovery

Monitoring of contaminant accumulation in fish has been conducted in East Fork Poplar Creek (EFPC) in Oak Ridge, Tennessee since 1985. Bioaccumulation trends are examined over a twenty year period coinciding with major pollution abatement actions by a Department of Energy facility at the stream’s headwaters. Although EFPC is enriched in many contaminants relative to other local streams, only polychlorinated biphenyls (PCBs) and mercury (Hg) were found to accumulate in the edible portions of fish to levels of human health concern. Mercury concentrations in redbreast sunfish were found to vary with season of collection, sex and size of individual fish. Over the course of the monitoring, waterborne Hg concentrations were reduced >80%; however, this did not translate into a comparable decrease in Hg bioaccumulation at most sites. Mercury bioaccumulation in fish did respond to decreased inputs in the industrialized headwater reach, but paradoxically increased in the lowermost reach of EFPC. As a result, the downstream pattern of Hg concentration in fish changed from one resembling dilution of a headwater point source in the 1980s to a uniform distribution in the 2000s. The reason for this remains unknown, but is hypothesized to involve changes in the chemical form and reactivity of waterborne Hg associated with the removal of residual chlorine and the addition of suspended particulates to the streamflow. PCB concentrations in fish varied greatly from year-to-year, but always exhibited a pronounced downstream decrease, and appeared to respond to management practices that limited episodic inputs from legacy sources within the facility.

Selenium bioaccumulation in fish exposed to coal ash at the Tennessee Valley Authority Kingston spill site

In December 2008, 4.1 million cubic meters of coal ash were released into the Emory and Clinch Rivers by the Tennessee Valley Authority Kingston Fossil Plant. Coal ash contains several contaminants, including the bioaccumulative metalloid selenium (Se). Because Se is predominantly accumulated in aquatic organisms through dietary rather than aqueous exposure, tissue-based toxicity thresholds for Se are currently being considered. The proposed threshold concentrations range between 4 μg/g and 9 μg/g Se (dry wt.) in whole body fish, with a proposed fillet threshold of 11.8 μg/g. In the present study, the authors examined the spatial and temporal trends in Se bioaccumulation and examined the relationship between the Se content in fillets and in whole bodies of fish collected around the Kingston spill site to determine whether Se bioaccumulation was a significant concern at the ash spill site. Whereas Se concentrations in fish (whole bodies and fillets) were elevated at sampling locations affected by the Kingston ash spill relative to reference locations, concentrations do not appear to be above risk thresholds and have not been increasing over the 5-yr period since the spill. These findings are not only relevant to guiding the human health and ecological risk assessments at the Kingston ash spill site, but because of current national discussions on appropriate guidelines for Se in fish as well for the disposal of coal combustion wastes, the results are also relevant to the general understanding of Se bioaccumulation in contaminated water bodies.

Decreasing aqueous mercury concentrations to meet the water quality criterion in fish: examining the water-fish relationship in two point-source contaminated streams.

East Fork Poplar Creek (EF) and White Oak Creek (WC) are two mercury-contaminated streams located on the United States (U.S.) Department of Energy Oak Ridge Reservation in East Tennessee. East Fork Poplar Creek is the larger and more contaminated of the two, with average aqueous mercury (Hg) concentrations exceeding those in reference streams by several hundred-fold. Remedial actions over the past 20 years have decreased aqueous Hg concentrations in EF by 85% (from >1600 ng/L to <400 ng/L). Fish fillet concentrations, however, have not responded to this decrease in aqueous Hg and remain above the U.S. Environmental Protection Agency National Recommended Water Quality Criteria (NRWQC) of 0.3 mg/kg. The lack of correlation between aqueous and fish tissue Hg concentrations in this creek has led to questions regarding the usefulness of target aqueous Hg concentrations and strategies for future remediation efforts. White Oak Creek has a similar contamination history but aqueous Hg concentrations in WC are an order of magnitude lower than in EF. Despite the lower aqueous Hg concentrations (<100 ng/L), fish fillet concentrations in WC have also been above the NRWQC, making the aqueous Hg remediation goal of 200 ng/L in EF seem unlikely to result in an effective decrease in fillet Hg concentrations. Recent monitoring efforts in WC, however, suggest an aqueous total Hg threshold above which Hg bioaccumulation in fish may not respond. This new information could be useful in guiding remedial actions in EF and in other point-source contaminated streams.

Sources of mercury in a contaminated stream—implications for the timescale of recovery

Mercury contamination in East Fork Poplar Creek in Tennessee arises from dissolved mercury exiting a headwater industrial complex and residual mercury in the streambed and soil throughout the watershed downstream. The headwater inputs generate chronic base flow concentrations of total mercury of about 1,000 ng/L, but most of the annual export of mercury from the system appears to originate farther downstream. Effective targeting of remedial efforts requires determining how long downstream sources might continue to contaminate the system following elimination of the headwater mercury inputs. The authors calculations suggest that (1) contaminated soils and sediments account for >80% of the annual mercury export from the entire watershed, with most export occurring during wet weather events; (2) bank erosion and resuspension of streambed particulates are the major mercury sources maintaining high annual mercury export rates; and (3) the inventory of particle-associated mercury in the streambed was not large enough to sustain the estimated export rates for more than a few years. The authors findings imply that to prevent waterborne mercury contamination in this system from continuing for decades, remedial actions will have to control the headwater mercury source that sustains day-to-day base flow mercury concentrations and the riparian stream-bank sources that generate most of the mercury export from the system.

The effects of a stannous chloride-based water treatment system in a mercury contaminated stream

We assessed the impacts of an innovative Hg water treatment system on a small, industrially-contaminated stream in the southeastern United States. The treatment system, installed in 2007, removes Hg from wastewater using tin (Sn) (II) chloride followed by air stripping. Mercury concentrations in the receiving stream, Tims Branch, decreased from >100 to ∼10 ng/L in the four years following treatment, and Hg body burdens in redfin pickerel (Esox americanus) decreased by 70% at the most contaminated site. Tin concentrations in water and fish increased significantly in the tributary leading to Tims Branch, but concentrations remain below levels of concern for human health or ecological risks. While other studies have shown that Sn may be environmentally methylated and methyltin can transfer its methyl group to Hg, results from our field studies and sediment incubation experiments suggest that the added Sn to the Tims Branch watershed is not contributing to methylmercury (MeHg) production or bioaccumulation in this system. The stannous chloride treatment system installed at Tims Branch was effective at removing Hg inputs and reducing Hg bioaccumulation in the stream, but future studies are needed to assess longer term impacts of Sn on the environment.

Linking Adverse Outcome Pathways to Dynamic Energy Budgets: A Conceptual Model

Ecological risk assessment quantifies the likelihood of undesirable impacts of stressors, primarily at high levels of biological organization. Data used to inform ecological risk assessments come primarily from tests on individual organisms or from suborganismal studies, indicating a disconnect between primary data and protection goals. We know how to relate individual responses to population dynamics using individual-based models, and there are emerging ideas on how to make connections to ecosystem services. However, there is no established methodology to connect effects seen at higher levels of biological organization with suborganismal dynamics, despite progress made in identifying Adverse Outcome Pathways (AOPs) that link molecular initiating events to ecologically relevant key events. This chapter is a product of a working group at the National Center for Mathematical and Biological Synthesis (NIMBioS) that assessed the feasibility of using dynamic energy budget (DEB) models of individual organisms as a “pivot” connecting suborganismal processes to higher level ecological processes. AOP models quantify explicit molecular, cellular or organ-level processes, but do not offer a route to linking sub-organismal damage to adverse effects on individual growth, reproduction, and survival, which can be propagated to the population level through individual-based models. DEB models describe these processes, but use abstract variables with undetermined connections to suborganismal biology. We propose linking DEB and quantitative AOP models by interpreting AOP key events as measures of damage-inducing processes in a DEB model. Here, we present a conceptual model for linking AOPs to DEB models and review existing modeling tools available for both AOP and DEB.

Heterogeneity in Nitrogen Sources Enhances Productivity and Nutrient Use Efficiency in Algal Polycultures

Algae hold much promise as a potential feedstock for biofuels and other products, but scaling up biomass production remains challenging. We hypothesized that multispecies assemblages, or polycultures, could improve crop yield when grown in media with mixed nitrogen sources, as found in wastewater. We grew mono- and poly- cultures of algae in four distinct growth media that differed in the form (i.e., nitrate, ammonium, urea, plus a mixture of all three) but not the concentration of nitrogen. We found that mean biomass productivity was positively correlated with algal species richness, and that this relationship was strongest in mixed nitrogen media (on average 88% greater biomass production in 5-species polycultures than in monocultures in mixed nitrogen treatment). We also found that the relationship between nutrient use efficiency and species richness was positive across nitrogen treatments, but greatest in mixed nitrogen media. While polycultures outperformed the most productive monoculture only 0-14% of the time in this experiment, they outperformed the average monoculture 26-52% of the time. Our results suggest that algal polycultures have the potential to be highly productive, and can be effective in recycling nutrients and treating wastewater, offering a sustainable and cost-effective solution for biofuel production.

Identifying non-reference sites to guide stream restoration and long-term monitoring

The reference condition paradigm has served as the standard for assessing the outcomes of restoration projects, particularly their success in meeting project objectives. One limitation of relying solely on the reference condition in designing and monitoring restoration projects is that reference conditions do not necessarily elucidate impairments to effective restoration, especially diagnosing the causal mechanisms behind unsuccessful outcomes. We provide a spatial framework to select both reference and non-reference streams to guide restoration planning and long-term monitoring through reliance on anthropogenically altered ecosystems to understand processes that govern ecosystem biophysical properties and ecosystem responses to restoration practices. We then applied the spatial framework to East Fork Poplar Creek (EFPC), Tennessee (USA), a system receiving 30years of remediation and pollution abatement actions from industrialization, pollution, and urbanization. Out of >13,000 stream reaches, we identified anywhere from 4 to 48 reaches, depending on the scenario, that could be used in restoration planning and monitoring for specific sites. Preliminary comparison of fish species composition at these sites compared to EFPC sites were used to identify potential mechanisms limiting the ecological recovery following remediation. We suggest that understanding the relative role of anthropogenic pressures in governing ecosystem responses is required to successful, process-driven restoration.