Assessment of Pollution-Induced Microbial Community Tolerance to Heavy Metals in Soil Using Ammonia-Oxidizing Bacteria and Biolog Assay

This study attempted to investigate if the tolerance of soil bacterial communities in general, and autotrophic ammonia-oxidizing bacteria (AOB) in particular, evolved as a result of prolonged exposure to metals, and could be used as an indigenous bioindicator for soil metal pollution. A soil contaminated with copper, chromium, and arsenic (CCA) was mixed with an uncontaminated garden soil (GS3) to make five test soils with different metal concentrations. A modified potential ammonium oxidation assay was used to determine the metal tolerance of the AOB community. Tolerance to Cr, Cu, and As was tested at the beginning and after up to 13 months of incubation. Compared with the reference GS3 soil, the five CCA soils showed significantly higher tolerance to Cr no matter which form of Cr (Cr³⁺, CrO₄ ^2?, or Cr₂O₇ ^2?) was tested, and the Cr tolerance correlated with the total soil Cr concentration. However, the tolerance to Cu²⁺, As³⁺, and As⁵⁺ did not differ significantly between the GS3 soil and the five CCA soils. Community level physiological profiles using Biolog microtiter plates were also used to examine the chromate tolerance of the bacterial communities extracted after six months of exposure. Our results showed that the bacterial community tolerance was altered and increased as the soil Cr concentration was increased, indicating that the culturable microbial community and the AOB community responded in a similar manner.     

The Role of Soil Microbial Tests in Ecological Risk Assessment: Differentiating between Exposure and Effects

The use of soil microorganisms in ecological risk assessment is hampered by an unclear dose-response relationship for most contaminants. Establishing dose-response curves for soil microbial communities requires that one have a clear estimate of exposure at the site of toxic action and a response free of confounding environmental factors. It is not clear what methods can estimate toxicant dose at the site of toxic action or determine microbial response to a toxicant. Pollution-induced community tolerance (PICT) is one possible estimate of microbial toxicant exposure. The PICT hypothesis is that the tolerance of a microbial community is proportional to the in situ dose. This method automatically corrects for differences due to differences in soil physical-chemical variables between samples. Various components of the soil nitrogen cycle can act as microbial bioindicators of toxicant impacts. Estimating denitrifica-tion activity presents a number of advantages over other components of the nitrogen cycle. Denitrifying bacteria come from a diversity of habitats, can be autotrophic or heterotrophic, and denitrification is a well-defined enzymatic system, which allows the use of molecular tools. Determining denitrification may be a good estimate of effects of toxicants on microbial communities. However, given the state of our ignorance regarding soil microbial community structure and function, redundant estimates of exposure and effect are necessary to adequately characterize the response of microbial communities to toxicants.     

Adaptation,Ecological Impacts,and Risk Assessment: Insights from Research at Foundry Cove,Bayou Trepagnier,and Pass Fourchon

This paper takes a detailed look at the occurrence of genetic adaptations and ecological impacts at three contaminated sites (Foundry Cove, Bayou Trepagnier, Pass Fourchon) to assess the co-occurrence of adaptation and ecological impacts and the implications for risk assessment. Community-level ecological impacts were reported for all three sites. However, there was little evidence of population-level impacts (on the six populations that were also assessed for adaptation). Similarly, adaptation was found in only one of the populations. While this review provides an incomplete picture (adaptation was assessed on only a small subset of the species present and the reasons behind the lack of adaptation in the five populations remained unknown), it indicates that adaptation is uncommon even where ecological impacts are obvious. Theoretical considerations also predict that contaminants can have large impacts without resulting in an adaptation. While adaptation to a contaminant reflects an impact by that contaminant, the three case studies indicate that determining whether or not resistance has evolved does not appear to be a very efficient tool for detecting ecological impacts. Nevertheless, assessing the occurrence of adaptation does have a place in risk assessment, especially when assessing the likelihood of local extinction of a particular population     

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.     

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.     

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.     

Consideration of Background Radiation in Ecological Risk Assessments

Background or ambient concentrations are often considered in the evaluation of potential risks to ecological receptors from exposure to hazardous chemicals in the environment. Such an evaluation may be a component of the screening or final risk management process and sets the baseline from which risks contributed by site-related activities can be addressed. Although the process for the evaluation of potential radiological risks to ecological receptors is less formalized than the chemical hazard assessment process, background remains an issue that should be addressed when considering potential site-related impacts. This paper briefly presents the ecological risk assessment approaches used to address background radionuclide concentrations at three United States Department of Defense Facilities. The concepts of total radiation dose, and tolerance and adaptation of populations to radiation are also discussed within the context of background radiation.     

Utility and relevance of aquatic oligochaetes in Ecological Risk Assessment

Ecological risk assessment (EcoRA) provides both a process and a framework to evaluate the potential for adverse ecological effects occurring as a result of exposure to contaminants or other stressors. EcoRA begins with problem formulation/hazard identification, progresses to effects and exposure assessment, and culminates with risk characterization (an estimate of the incidence and severity of any adverse effects likely to occur). Key components of EcoRA include determining: stressors/contaminants of concern; sensitive, exposed biota; and, appropriate tests and organisms for evaluating effects. Aquatic oligochaetes are not generally used directly in EcoRA because of three major perceptions. First, EcoRA personnel are generally not familiar with or comfortable using this group of organisms. Second, there is believed to be a paucity of widely accepted toxicity tests with these organisms. Third, their taxonomy is considered difficult and uncertain. In fact, aquatic oligochaetes potentially have great utility and relevance to EcoRAs because of factors including: their importance in the aquatic food chain (e.g. prey to fauna including fish and waterfowl; as a vector for contaminant movement through the food chain from bacteria); many species are widely distributed and well studied; representatives include fresh, estuarine and marine species; as a group, they range from sensitive to insensitive over a wide range of environmental insults; they have a long history of use in pollution monitoring and assessment; and, relevant toxicity and biaccumulation tests exist. Toxicity testing under defined conditions is appropriate for problem formulation while more realistic testing for effects assessment (e.g. microcosms) is logistically easier with this group of organisms than with others due to their relatively small size. The importance of aquatic oligochaetes for EcoRA, in particular of sediments, is particularly compelling.     

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.     

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.     

Determination of Field Effects of Contaminants—Significance of Pollution-Induced Community Tolerance

The concept of pollution-induced community tolerance (PICT) consists of the phenomenon that communities in an ecosystem exhibit increased tolerance as a result of exposure to contaminants. Although a range of ‘classic’ ecological principles explains the processes that increase tolerance of a community, the value of PICT for ecological risk assessment was recognized only recently (Blanck et al. 1988). The following issues are recognized: First, regarding the question on the role of suspect compounds causing ecological effects, the PICT approach covers the issue of causality better than ‘classical’ ecological community response parameters like species densities or species diversity indices. This relates to the fact that the level of PICT is assumed to be relatively constant (compared to density and diversity), whereas the suspect compound causing the observed effect can be deduced with relative clear inference from artificial exposure experiments. Second, PICT directly addresses a level of biological organization (the community), the level of concern for many ecological risk assessment methods. Other methods for risk assessment, like toxicity testing or bioassays, focus on individual or population-level effects, and need extrapolation of the results to the field. Such extrapolation step may pose problems regarding validity of the outcome of risk assessment. The occurrence of PICT is, however, not (yet) a community endpoint that is sufficiently underpinned to trigger risk mitigation activities. This paper especially focuses on the possibility to improve risk assessment approaches by incorporation of PICT assessments, especially focusing on the issue of causality and on the ecological meaning of PICT. Despite the advantages over ‘classical’ parameters, literature analysis suggests that the PICT approach may be strengthened by determining to which degree the PICT approach relates to ecological changes, like shifts in community structure, functioning, and stability. The aim of this paper is to summarize some literature, putting the emphasis on terrestrial studies, to get insights whether PICT is a sensitive and powerful tool to quantify ecological effects in field conditions, to link them to toxicant stress, and thus to determine whether PICT may be taken into consideration in risk assessment.     

An Ecological Risk Assessment of Hexachlorobutadiene

Hexachlorobutadiene (HCBD) has never been commercially produced in Canada and was imported in the past for use as a solvent. Anthropogenic activity is linked with the entry of this substance into the environment. While current Canadian sources of HCBD involve low-level releases, potentially they can be numerous. Until recently, the most significant point source of HCBD in Canada appeared to be the Cole Drain, which discharges into the St. Clair River at Sarnia, Ontario, and includes outfalls from an industrial landfill and a few industrial companies. HCBD has been detected in Canadian surface waters, sediments, aquatic organisms and, occasionally, air. Considering the properties of the substance, including its persistence and bioaccumulation characteristics, the environmental risk assessment of HCBD was focused on the aquatic environment. The results of a conservative assessment suggest that there is a risk of harmful effects for benthic organisms exposed to sediments contaminated by HCBD in the most contaminated part of the St. Clair River.     

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.     

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.     

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.     

A Critical Review of Procedures and Approaches Used for Assessing Pollution-Induced Community Tolerance (PICT) in Biotic Communities

Pollution-induced community tolerance (PICT) is used for the detection of minor effects of toxicants in biotic communities. Organisms survive in toxic environments only if they are tolerant to the chemicals present in their habitat. In the selection phase, toxicants hinder the success of sensitive individuals and species and replace them by more tolerant ones. The resulting increase in community tolerance is quantified in the detection phase by short-term toxicity tests. In this way PICT can establish causal linkages between contaminants and effects. An increase in community tolerance compared to the baseline tolerance at reference sites suggests that the community has been adversely affected by toxicants. PICT has been used in aquatic and terrestrial environments with communities of periphyton, phytoplankton, bacteria, nematodes and insects. A variety of methods have been used for quantification of community tolerance including photosynthesis, sulfolipid synthesis, respiration, thymidine and leucine incorporation, survival, and substrate utilisation patterns. PICT has been observed for copper, zinc, nickel, mercury, cadmium, arsenate, monomethylarsonic acid, diuron, tributyl tin, 4,5,6-trichloroguaiacol, irgarol 1051, seanine 211, atrazine, and trinitrotoluene. It is necessary to validate PICT, at least by showing that it is related to the preexposure concentration of the toxicants and that it is coupled to a toxicant-induced succession (TIS) in the community. Care must also be taken to ascertain that PICT interpretation is not confounded by co-tolerance or bioavailability differences. Co-tolerance patterns, which are indicative of the specificity of PICT, have only been investigated for arsenate, diuron and a few metals. For the further improvement of PICT methodology special attention should be given to co-tolerance patterns and development of new integrating short-term tests for quantification of tolerance. It is also important to broaden the scope of organisms and toxicants used. Properly validated, PICT is a powerful tool for detection of community effects and its use in monitoring and site-specific risk assessment should be encouraged.     

Human Health Risk Assessment: Required Reading

Over the past 30 years, risk assessment has developed into a scientific discipline. It is critical that the next generation of risk assessors understand the history of our field, and recognize the numerous successes and failures that have taken place. This short Perspective identifies and describes specific books, monographs, and reports that are required reading for any nascent risk assessor.     

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…     

Ecological Risk Assessment Guidance and Procedural Documents: An Annotated Compilation and Evaluation of Reference Materials

The scientific approach toward ecological risk assessment (ERA) has advanced greatly during the 1990s. This growth has been accompanied by the development of ERA guidance by USEPA Headquarters, individual USEPA Regions, state environmental agencies, as well as international agencies. This compilation of ERA guidance and procedural documents identifies many of the existing ERA reference materials from the regulatory and/or governmental agency arena. In addition, this compilation provides annotations pertaining to the focus of each reviewed document, and compares/contrasts the approaches presented in the documents. As such, the evaluation provides insight into some of the qualities and levels of detail provided by each document. Examples of documents which are highlighted include recently published USEPA's “Guidelines for Ecological Risk Assessment;” USEPA's “Ecological Risk Assessment Guidance for Superfund;” the U.S. Army's “Procedural Guidelines for Ecological Risk Assessments;” and Environment Canada's “Ecological Risk Assessments Under the Canadian Environmental Protection Act.”