Ecological Risk Assessment
The methods of ecological risk assessment parallel those of human health risk assessment. The potential issues of concern, however, are both more numerous and open-ended due to the need to consider myriad plant and animal species and their interactions with the environment and each other. Furthermore, effects-based toxicity data are generally more sparse compared with human health endpoints. Problem definition and approach are thus key elements of ecological risk characterization. Cambridge Environmental typically follows a two-step process in assessing ecological risks, consistent with regulatory guidance. The first step typically involves a screening-level assessment in which contaminant concentrations measured in soil, sediment, and surface water are compared to both background and ecological benchmarks such as ECO-SSLs, sediment quality criteria, and water quality criteria designed generically to protect environmental receptors. Contaminant levels lower than background or consistent with local conditions generally indicate no discernible site impact. Contaminant concentrations greater than background also frequently exceed screening-level ecological benchmarks, which are designed to protect the most sensitive species. In this case, the second step of a refined ecological risk assessment considers risks to specific indicator species and environmental endpoints, and may involve elements of toxicity testing, studies of macroinvertebrate prevalence and diversity, analyses of biota to measure pollutant uptake, dietary food chain modeling for persistent bioaccumulative pollutants, and other measures.
Sample Projects
PCBs at an Air Force base and in a marsh habitat
Cambridge Environmental evaluated potential ecological risks associated with polychlorinated biphenyl (PCB) contamination in two different settings that demonstrate difficulties and uncertainties in ecological risk assessment. In the first example, an ecological risk assessment was performed for Andersen Air Force Base in Guam in support of a Remedial Investigation/Feasibility Study for the site and included the results of sampling and analysis of soil, seawater, and marine biota for PCBs. Potential ecological risks were evaluated for soil invertebrate and plant communities, terrestrial birds, the endangered Mariana fruit bat, and the marine community, including fish and piscivorous wildlife. The ecological risk assessment concluded that risks to ecological receptors at the site from exposure to PCBs were generally acceptable, but potential risks to the yellow bittern (a terrestrial carnivore) and to soil invertebrates could not be ruled out without additional data collection.
In the second example, Cambridge Environmental commented on behalf of a stakeholder group on the proposed remediation of a PCB-contaminated marsh at a Superfund site in southern Massachusetts. The U.S. EPA proposed extensive excavation of sediments due to excessive risks to mink. Cambridge Environmental supported a local citizens group concerned that habitat disruption caused by excavation could pose greater risk than the benefit of removing PCBs. Excessive risk demonstration was based on concentrations of PCBs in sediments higher than the level of a draft sediment quality criterion derived from an Ambient Water Quality Criterion, a model of the relationship between PCBs in water and sediment, bioaccumulation of PCBs in fish, and ingestion of fish by a mink (a species known to be sensitive to PCB toxicity). Detailed review found limited relevance of the sediment quality criterion to the marsh habitat, principally because of an incomplete exposure pathway due to a lack of fish in the marsh and uncertainties in the modeled water-sediment relationship.
Threatened and endangered species consultations
Section 7 of the Endangered Species Act requires federal agencies to consult with the U.S. Fish and Wildlife Service when approving actions that might affect threatened and endangered wildlife species. Cambridge Environmental has supported the proponents of proposed air pollution sources seeking permit approval from the U.S. EPA by developing relevant studies that have helped the federal agencies to reach determinations in their consultations. A variety of different issues have been examined, many requiring innovative evaluations outside of standard guidance documents. Studies have examined potential phytotoxicity of increased air pollutant concentrations, such as potential leaf damage from hydrogen fluoride and reduced levels of photosynthesis due to particle deposition and accumulation on vegetated surfaces. Pollutant air-to-ground deposition models have been used to estimate increased levels of metals and other persistent bioaccumulative organic compounds in soil, and to compare these projected concentrations to ecotoxicity-based benchmark concentrations. The question of whether an increase in deposition of nitrogenous compounds could endanger native prairie species emerged from the possibility that invasive species might be encouraged by increased nutrient availability. Deposition algorithms of air dispersion models were extended to estimate deposition rates of ammonia and nitrogen oxides due to facility emissions, and the projected increases in nitrogen deposition, added to background rates, were compared to levels found to encourage invasive species in nutrient limited soils. A different question of whether the acidity of precipitation could be increased to damaging levels from scavenging of sulfur dioxide and other acid gases spurned the development of an acid fog equilibrium model, which found that short-term increases in fog acidity due to source emissions of acid gases would not likely result in pH levels low enough to damage vegetation.