A Probabilistic Ecological Risk Assessment of Tributyltin in Surface Waters of the Chesapeake Bay Watershed

The goal of this study was to conduct a probabilistic ecological risk assessment for tributyltin (TBT) in surface waters of the Chesapeake Bay watershed. Ecological risk was characterized by comparing the probability distributions of environmental exposure concentrations with the probability distributions of species response data determined from laboratory studies. The overlap of these distributions was a measure of risk to aquatic life. Tributyltin exposure data from the Chesapeake Bay watershed were available from over 3600 water column samples from 41 stations in nine basins from 1985 through 1996. Most of the stations were located in the Virginia waters of Chesapeake Bay, primarily the James, Elizabeth and York Rivers. In Maryland waters of the Bay, various marina, harbor and river systems were also sampled. As expected, the highest environmental concentrations of tributyltin (based on 90th percentiles) were reported in and near marina areas. The sources of TBT causing these high concentrations were primarily boat hulls and painting/depainting operations. Lower concentrations of TBT were reported in open water areas, such as the Potomac River, Choptank River and C and D Canal, where the density of boats was minimal. Temporal data from a ten year data base (1986-1996) from two areas in Virginia showed that TBT water column concentrations have declined since 1987 legislation prohibited the use of TBT paints on recreation boats (<25?m). Acute saltwater and freshwater TBT toxicity data were available for 43 and 23 species, respectively. Acute effects for saltwater species were reported for concentrations exceeding 420?ng/L; the lowest acute value for a freshwater species was 1110?ng/L. The acute 10th percentiles for all saltwater and freshwater species were 320 and 103?ng/L, respectively. The order of sensitivity from most to least sensitive for saltwater trophic groups and corresponding acute 10th percentiles were as follows: zooplankton (5?ng/L), phytoplankton (124?ng/L), benthos (312?ng/L) and fish (1009?ng/L). For freshwater species, the order of sensitivity from most to least sensitive trophic groups and corresponding acute 10th percentiles were: benthos (44?ng/L), zooplankton (400?ng/L), and fish (849?ng/L). Chronic data for both saltwater and freshwater species were limited to a few species in each water type. Based on these limited data, the saltwater and freshwater chronic 10th percentiles were 5 and 102?ng/L, respectively. Limited mesocosm and microcosm studies in saltwater suggested that TBT concentrations less than 50?ng/L did not impact the structure and function of biological communities. The saltwater acute (320?ng/L) and chronic (5?ng/L) 10th percentiles were used to determine ecological risk because all exposure data were from saltwater areas of the Chesapeake Bay watershed. Highest ecological risk was reported for marina areas in Maryland waters of Chesapeake Bay and for areas in Virginia such as the Elizabeth River, Hampton Creek and Sarah Creek. Low ecological risk was reported for areas such as the Potomac River, Choptank River, C and D Canal and Norfolk Harbor. Regulation of TBT on recreational watercraft in 1987 has successfully reduced water column concentrations of this organometallic compound. However, various studies have showed that TBT may remain in the sediment for years and continue to be source for water column exposures.     

An Ecological Risk Assessment of Inorganic Chloramines in Surface Water

Inorganic chloramines are formed when chlorine and ammonia are combined in water. These substances are frequently used as a secondary disinfectant for drinking water and are by-products of processes involving the disinfection of wastewaters and the control of biological fouling in cooling water systems. For chloraminate drinking water, the total residual chlorine (TRC) concentration may be almost completely due to monochloramine. Based on 1995 and 1996 survey data, the most significant and prevalent TRC loading to the Canadian environment is from municipal wastewater releases. Drinking water releases are the next most important source of chloramine entry into the Canadian environment, while TRC releases from other sources, such as cooling water, zebra mussel control practices and industrial wastewater, are much less important. A probabilistic water quality model was used to model two wastewater discharges and a cooling water discharge to different freshwater systems. The resulting exposure distributions were then compared with three incipient lethality endpoints, i.e., 50% mortality to the invertebrate Ceriodaphnia dubia and 50% and 20% mortality to juvenile chinook salmon (Oncorhynchus tshawytscha). For each discharge scenario studied, there were moderate to high probabilities of significant adverse effects on aquatic life up to 1.9?km from the effluent sources.     

Ecological Risk Assessment of Organochlorine Pesticides in Surface Waters of Lake Taihu,China

The residues of organochlorine pesticides (OCPs) in surface waters from Meiliang Bay, Gonghu Bay, and Xukou Bay of Lake Taihu, China, were investigated, and their ecological risks were assessed using the risk quotient method and probabilistic risk assessment. Environmental concentrations of OCPs in surface water of these bays were relatively lower compared with other rivers or lakes in China. Calculation of risk quotient associated with taxonomic groups indicates moderate ecological risks from OCPs for crustaceans and insects in these bays, while the ecological risks were low for fish and negligible for phytoplankton. The ecological risk quotients associated with individual OCPs were lower than 0.01 in these bays, suggesting a negligible risk to aquatic organisms. Ecological risk from α-HCH was relatively lower compared with DDTs, endosulfans, and γ-HCH. The combined ecological risks were evaluated using probabilistic risk assessment for only eight OCPs owing to a lack of available toxicity data for β-HCH and δ-HCH. The percentage of species with the potential to be at risk from mixture of OCPs was lower than the criteria of 5% in each bay, indicating that the combined ecological risks were acceptable.     

Bioindicators Versus Biomarkers in Ecological Risk Assessment

The biomarker approach, adopted from medical toxicology, is subject to several theoretical and practical difficulties when used to address environmental problems. The problems are related to the definition that emphasizes measurement but does not specify a requirement to establish cause-effect linkages. An improved definition for a bioindicator is reviewed. The sentinel species approach is judged to be a biomarker rather than a bioindicator, and therefore of limited use for environmental risk assessment. An empirical weight of evidence approach to improve the utility of sentinel species is proposed.     

生态风险研究述评

生态风险(ＥｃｏｌｏｇｉｃａｌＲｉｓｋ,ＥＲ),指一个种群、生态系统或整个景观的正常功能受外界胁迫,从而在目前和将来减小该系统健康、生产力、遗传结构、经济价值和美学价值的一种状况[20]。生态风险评估(ＥｃｏｌｏｇｉｃａｌＲｉｓｋＡｓｓｅｓｓｍｅｎｔ,ＥＲＡ)指受一个或多个胁迫因素影响后,对不利的生态后果出现的可能性进行的评估。美国环保局(ＥＰＡ)把这种尚不为人们所重视的领域叫做生态风险评估[20,48]。随着新技术和新方法的应用,ＥＲＡ的研究领域迅速扩展。早期的生态风险评估主要是针对人类健康而言的,也就是人类健康风险…     

An Ecological Risk Assessment of Formaldehyde

A multi-tiered environmental risk assessment of formaldehyde determined the possibility of harmful effects on organisms in certain environmental compartments in Canada. A review of the relevant information indicates that biota are exposed to formaldehyde primarily in air and, to a lesser extent, in water. Worst-case scenarios predict that the estimated exposure values likely to be encountered in Canada for water and air are not expected to exceed estimated no-effects values. Therefore, the environmental risks associated with concentrations of formaldehyde likely to be found in Canada are low.     

Role of Ecological Modeling in Risk Assessment

Ecological models are useful tools for evaluating the ecological significance of observed or predicted effects of toxic chemicals on individual organisms. Current risk estimation approaches using hazard quotients for individual-level endpoints have limited utility for assessing risks at the population, ecosystem, and landscape levels, which are the most relevant indicators for environmental management. In this paper, we define different types of ecological models, summarize their input and output variables, and present examples of the role of some recommended models in chemical risk assessments. A variety of population and ecosystem models have been applied successfully to evaluate ecological risks, including population viability of endangered species, habitat fragmentation, and toxic chemical issues. In particular, population models are widely available, and their value in predicting dynamics of natural populations has been demonstrated. Although data are often limited on vital rates and doseresponse functions needed for ecological modeling, accurate prediction of ecological effects may not be needed for all assessments. Often, a comparative assessment of risk (e.g., relative to baseline or reference) is of primary interest. Ecological modeling is currently a valuable approach for addressing many chemical risk assessment issues, including screening-level evaluations.     

Ecological Risk Assessment and Ecological Epidemiology for Contaminated Sites

After 20 years of development, ecological risk assessment is widely accepted. However, it is evolving in response to a variety of technical and societal pressures. First, pressure for greater simplicity and standardization arise from the expectation that risk assessments should require little time and resources but be defensible. Second, the advance of the environmental sciences and increasing awareness of the complexity of ecological responses generate pressure for greater realism. Third, the dominance of human health risk assessment generates a pressure to integrate ecological risk assessment with that dominant field. Fourth, the demand for cost-benefit analysis creates pressure for integration with environmental economics. Finally, the need to connect the practice of ecological epidemiology with risk-based decision-making creates a pressure of the formation of a single integrated ecological assessment practice.     

An Ecological Risk Assessment of Nonylphenol and Its Ethoxylates in the Aquatic Environment

Nonylphenol ethoxylates (NPEs) are a group of surfactants that are widely used for industrial, commercial, institutional and household purposes in Canada. Ethoxylation of nonylphenol (NP) occurs upon reaction with ethylene oxide, producing NPEs, although NP is also used in the production of the antioxidant tris(nonylphenol)phosphite. NP and NPEs are not produced naturally, and the primary route of environmental exposure to NP and NPEs is via textile mill, pulp and paper mill and municipal wastewater treatment plant effluents. NPEs occur as complex mixtures and are described by the average ethoxylate chain length, which ranges from 1 to 100. The environmental fate of NPEs is strongly dependent on the effluent and, the degree and type of treatment to which the effluent is subjected. An ecological risk assessment was performed to determine if exposure to NP and NPEs results in effects on the Canadian environment, based on current use patterns. The Canadian ecological risk assessment found that adverse effects on aquatic organisms are likely, although assumptions were made with respect to appropriate dilution factors.     

Ten Years of the Relative Risk Model and Regional Scale Ecological Risk Assessment

It has been 10 years since the publication of the relative risk model (RRM) for regional scale ecological risk assessment. The approach has since been used successfully for a variety of freshwater, marine, and terrestrial environments in North America, South America, and Australia. During this period the types of stressors have been expanded to include more than contaminants. Invasive species, habitat loss, stream alteration and blockage, temperature, change in land use, and climate have been incorporated into the assessments. Major developments in the RRM have included the extensive use of geographical information systems, uncertainty analysis using Monte Carlo techniques, and its application to retrospective assessments to determine causation. The future uses of the RRM include assessments for forestry and conservation management, an increasing use in invasive species evaluation, and in sustainability. Developments in risk communication, the use of Bayesian approaches, and in uncertainty analyses are on the horizon.     

Terrestrial Metals Bioavailability: A Comprehensive Review and Literature-Derived Decision Rule for Ecological Risk Assessment

Interstudy variation among bioavailability studies is a primary deterrent to a universal methodology to assess metals bioavailability to soil-dwelling organisms and is largely the result of specific experimental conditions unique to independent studies. Accordingly, two datasets were established from relevant literature; one includes data from studies related to bioaccumulation (total obs = 520), while the other contains data from studies related to toxicity (total obs = 1264). Experimental factors that affected toxicity and bioaccumulation independent of the effect of soil chemical/physical properties were statistically apportioned from the variation attributed to soil chemical/physical properties for both datasets using a linear mixed model. Residual bioaccumulation data were then used to develop a non-parametric regression tree whereby bootstrap and cross-validation techniques were used to internally validate the resulting decision rule. A similar approach was employed with the toxicity dataset as an independent external validation. A validated decision rule is presented as a quantitative assessment tool that characterizes typical aerobic soils in terms of their potential to sequester common divalent cationic metal contaminants and mitigate their bioavailability to soil-dwelling biota.     

Approaches for Integrated Risk Assessment

Recognizing the need to enhance the effectiveness and efficiency of risk assessments globally, the World Health Organization's International Programme on Chemical Safety, the U.S. Environmental Protection Agency, the European Commission, and the Organization for Economic Cooperation and Development developed a collaborative partnership to foster integration of assessment approaches used to evaluate human health and ecological risks. The objectives of this effort included: improving understanding of the benefits of integration, identifying obstacles to the integration process, and engaging key agencies, organizations, and scientific societies to promote integration. A framework with supporting documentation was developed to describe an approach for integration. Four case studies were constructed to illustrate how integrated risk assessments might be conducted for chemical and nonchemical stressors. The concepts and approaches developed in the project were evaluated in an international workshop. The goal of this effort was international acceptance of guidance for integrated risk assessment.     

An Ecological Risk Assessment of Phenol in the Aquatic Environment

A probabilistic ecological risk assessment of phenol was undertaken to determine the risks posed to biota as a result of phenol release to the Canadian environment. A three-tiered approach was used to estimate risks, with progressively more realistic assumptions being applied at each tier. In Canada, the major sources of phenol are municipal wastewater treatment plants, pulp, paper and wood products mills, steel and metal products facilities and refineries. Thus, the highest exposures will occur in receiving waters near these point sources, primarily due to the short half-life of phenol in the aquatic environment. Sensitive aquatic organisms include salmonids (e.g., rainbow trout Oncorhynchus mykiss) and amphibians (e.g., leopard frog Rana pipiens). The results of the risk assessment indicate that species are exposed to elevated levels of phenol near point sources, but these levels represent only a minor risk to aquatic biota.     

The Fox River Risk Assessment Teaching Tool

In 1999 and 2000, two environmental consulting companies independently prepared risk assessments of the Lower Fox River waste site in Wisconsin. Because the two assessments produced somewhat different risk characterizations, the Association for Environmental Health & Sciences was asked by the site's Potentially Responsible Party to form a peer review panel to critique and compare the two assessments. The panel found interesting differences between the two risk assessments and recommended that their observations, together with the two risk assessments, be made available as a Teaching Tool for persons interested in conducting human and ecological risk assessments. An accompanying CD contains these and other materials useful for teaching purposes.     

Extrapolation in Human Health and Ecological Risk Assessments: Proceedings of a Symposium

A symposium was conducted in April 1998 by the U.S. Environmental Protection Agency's National Health and Environmental Effects Research Laboratory (NHEERL) to explore issues of extrapolation in human health and ecological risk assessments. Over the course of three and one half days, leading health and ecology experts presented and discussed research methods and approaches for extrapolating data among taxa and across levels of biological organization, through time, and across spatial scales. The intended result of this symposium was enhanced interaction among a diverse array of scientists, policymakers, and risk assessors to promote identification of approaches for reducing the uncertainties of extrapolation in risk assessment.     

Metals in Northern Forest Ecosystems: Role of Vegetation in Sequestration and Cycling,and Implications for Ecological Risk Assessment

Mass estimates of phytoaccumulated trace metal contaminants and transfers to soils are necessary to properly evaluate the impact of historic and continued anthropogenic metal deposition to northern forest ecosystems. An investigation of Cu, Ni, Pb, and Zn mass balances in plant communities subject to metal contamination from smelter emissions in Canada, found that accumulation of metals differed significantly among plant vegetation compartments (foliage, fine roots, bark, trunk, and branches). Analysis of plant community biological accumulation factors (BAFs), calculated using total soil metal and free soil metal ion (Me²⁺) found that free soil metal BAFs were more similar among locations than total soil metal BAFs, but that disparity still existed. Fine roots were found to dominate annual vegetation transfer of Cu, Ni, and Pb to soils, relative to foliage; fine root mortality played a smaller role than foliage for Zn plant-soil transfer. Plant-associated metal inputs were found to rival or exceed current estimates of atmospheric metal deposition, suggesting that potential benefits of future reductions in emissions to forests need to be evaluated within the context of phytocycling of metals already present.     

Ecological Risk Assessment and the Precautionary Principle

The Precautionary Principle, generated during the late 1980s as a unifying principle for regulating discharge of hazardous material into the North Sea, has been broadened to include a shifting of the burden of proof to the proponent of a proposed activity, adoption of a more holistic assessment process, and encompassing all environmental management decisions, not just pollution prevention activities. We argue that the Precautionary Principle remains a management philosophy, not a substitute for risk assessment. Risk assessment is a tool for organizing information used in environmental management decisions. However, increasing attention to reducing the Type II error of risk assessment studies would significantly reduce the skepticism with which many view the risk assessment process. A critical review of default assumptions used in risk assessments, inclusion of indirect effects within an ecologically relevant spatial/temporal framework, and better communication between risk assessors and risk managers also would enhance the acceptability of the process. Risk assessment can provide a sound basis for management decisions regardless of the underlying philosophies of environmental conservation or utilitarianism, but only if the inherent biases in the risk assessment assumptions are acknowledged explicitly throughout the assessment and management processes.     

Applications of Background Data in Ecological Risk Assessment: Various Shades of Gray

This paper discusses general approaches for evaluating the utility and manner of conducting background analyses in soil for ecological risk assessments. The types and sources of background data are discussed, and advantages and disadvantages of using literature-based versus site-specific background data are presented. The value of background evaluations is discussed with regard to the goals and objectives for a project. A comparison of literature-based ecological soil screening levels with generic metal background concentrations is presented to illustrate a typical problem in incorporating background data in ecological risk assessments, which is that many generic background concentrations are higher than ecological screening levels. This brings into question both the relevance of ecological screening levels and generic background levels. These issues are discussed along with cost-benefit considerations in an attempt to provide recommendations for determining the most appropriate type of background evaluation to conduct at a given site.     

The Ecological Component of Ecological Risk Assessment: Lessons from a Field Experiment

To improve ecological relevance, regulatory agencies are promoting assessments of effects at higher levels of organization, an objective that requires an understanding of current ecological theories. One such theory, hierarchy theory, contends that the effects of a disturbance acting at one level of organization (e.g., population) are not, as a rule, transmitted to higher levels of organization (e.g., community). Conversely, effects at higher levels of organization only occur if lower level variables have been affected. Further, responses to disturbance depend on disturbance history. In this study, I determined the effects of a disturbance treatment at the population, guild, and community levels of organization for vegetation in five wetlands with a disturbance history ranging from highly to rarely disturbed. The 2-year field experiment revealed that the effects of the disturbance treatment were most strongly felt at the population level of organization in wetlands without a history of disturbance. These observed impacts took place against a backdrop of constant change. Thus, the eventual disappearance of treatment effects was not due to a return to the pre-treatment state, but rather a return to a trajectory similar to that exhibited by the control plots. The implications of these results for ecological risk assessment are: (1) the observed effects of a stressor in a system cannot be extrapolated to other systems unless they have similar disturbance histories, (2) detecting effects before they become serious requires monitoring at lower levels of organization, (3) recovery to a naturally innate state is not a viable concept, and (4) the traditional approach of using one post-treatment measurement to determine if reference and impact sites differ is of very questionable value.