Toxicological Considerations of Contaminants in the Terrestrial Environment for Ecological Risk Assessment

The terrestrial environment acts as a “sink” for contaminants that have been purposely or accidentally released into the environment. Science and policy that support protective measures for terrestrial ecosystems have run behind those of aquatic toxicology and water quality concerns. As a result ecological risk assessment (ERA) involving terrestrial environments tends to be conducted at a simplistic level, relying on numeric targets (soil quality criteria) as a basis for decision-making. However, soil criteria for ecological receptors are somewhat deficient in terms of the numbers available and the data that supports these numbers. Direct toxicity assessments (DTA) for terrestrial environments, such as those used for water quality evaluations, can provide additional useful information about the toxicity and bioavailability of mixtures of contaminants present in soils. This article outlines the approaches used for assessing the toxicity of soil contaminants in terrestrial environments and critiques their advantages and pitfalls.     

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.     

Treatments of Uncertainty and Variability in Ecological Risk Assessment of Single-Species Populations

The selection of the most appropriate model for an ecological risk assessment depends on the application, the data and resources available, the knowledge base of the assessor, the relevant endpoints, and the extent to which the model deals with uncertainty. Since ecological systems are highly variable and our knowledge of model input parameters is uncertain, it is important that models include treatments of uncertainty and variability, and that results are reported in this light. In this paper we discuss treatments of variation and uncertainty in a variety of population models. In ecological risk assessments, the risk relates to the probability of an adverse event in the context of environmental variation. Uncertainty relates to ignorance about parameter values, e.g., measurement error and systematic error. An assessment of the full distribution of risks, under variability and parameter uncertainty, will give the most comprehensive and flexible endpoint. In this paper we present the rationale behind probabilistic risk assessment, identify the sources of uncertainty relevant for risk assessment and provide an overview of a range of population models. While all of the models reviewed have some utility in ecology, some have more comprehensive treatments of uncertainty than others. We identify the models that allow probabilistic assessments and sensitivity analyses, and we offer recommendations for further developments that aim towards more comprehensive and reliable ecological risk assessments for populations.     

The Intersection of Independent Lies: Increasing Realism in Ecological Risk Assessment

In 1966, Levins presented a philosophical discussion on making inference about populations using clusters of models. In this article we provide an overview of model inference in ecological risk assessment, discuss the benefits and trade-offs of increasing model realism, show the similarities and differences between Levins' model clusters and those used in ecological risk assessment, and present how risk assessment models can incorporate Levins' ideas of truth through independent lies. Two aspects of Levins' philosophy are directly relevant to risk assessment. First, confidence in our interpretation of risk is increased when multiple risk assessments yield similar qualitative results. Second, model clusters should be evaluated to determine if they maximize precision, generality, or realism or a mix of the three. In the later case, the evaluation of each model will differ depending on whether it is more general, precise, or realistic relative to the other models used. We conclude that risk assessments can be strengthened using Levins' idea, but that Levins' caution that model outcome should not be mistaken for truth is still applicable.     

The Anna Karenina Principle Applied to Ecological Risk Assessments of Multiple Stressors

Successful ecological risk assessments are all alike; every unsuccessful ecological risk assessment fails in its own way. Tolstoy posited a similar analogy in his novel Anna Karenina: “Happy families are all alike; every unhappy family is unhappy in its own way.” By that, Tolstoy meant that for a marriage to be happy, it had to succeed in several key aspects. Failure on even one of these aspects, and the marriage is doomed. In this paper, I argue that the Anna Karenina principle also applies to ecological risk assessments involving multiple stressors. In particular, I argue that multiple stressors assessments and environmental decision making will not have a happy marriage unless the following can be achieved: (1) there must be societal and political buy-in to the assessment and decision-making process; (2) the assessment must have the latitude to consider a wide range of stressors and potential risk management options; (3) there must be a commitment to following a rigorous focusing of the assessment and to expending resources for model development and data collection; and (4) an adaptive management strategy must be adopted wherein risk management actions are undertaken, system response intensively observed and assessed, and revised management actions taken as appropriate. Failure to meet any of the above criteria for success will doom a multiple stressors assessment and prevent its use in effective decision-making.     

A diatom functional-based approach to assess changing environmental conditions in temporary depressional wetlands

Functional-based assessments to identify the effects of human-induced disturbances on diatom communities are increasingly used. However, information on the response of functional groups to natural disturbances in temporary depressional wetlands is limited although important for the development of temporary wetland biological assessments. We assessed how diatom life-form and ecological guilds responded to a seasonal hydrological and hydrochemical gradient in three least human-disturbed, temporary depressional wetlands. We assigned species to their respective life-form and ecological guild groups and compared metric composition along the gradient. Overall, temporal variability in alkalinity and ionic composition, essentially Na⁺, as well as hydrological factors, wetland depth and total relative evapotranspiration (ETo), were good predictors of diatom species and functional group composition. Low profile guilds dominated by pioneer life-forms showed the strongest relationship with higher disturbance levels (i.e. increasing Na⁺, alkalinity with a decrease in depth). Similarly, the planktonic guild and tube-living, rosette and adnate life-forms dominated at higher disturbance levels whereas the high profile diatoms displayed the reverse trend. Our study shows the effectiveness of functional-based assessments beyond traditional species-based approaches for understanding and predicting community responses to temporal changes in environmental conditions. We also highlight the benefit of using both life-forms and ecological guilds where a broad set of metrics can enhance our understanding of the mechanisms relating diatom composition to environmental stressors and provide signs of underlying ecological processes.     

A quantitative risk ranking model to evaluate emerging organic contaminants in biosolid amended land and potential transport to drinking water

A quantitative risk ranking model was developed for human exposure to emerging contaminants (EC) following treated municipal sewage sludge (“biosolids”) application to Irish agricultural land. The model encompasses the predicted environmental concentration (PEC) in soil, surface runoff, groundwater, and subsequent drinking water ingestion by humans. Human exposure and subsequent risk was estimated for 16 organic contaminants using a Monte Carlo simulation approach. Nonylphenols ranked the highest across three environmental compartments: concentration in soil (PEC_soil), runoff (PEC_runoff), and groundwater (PEC_groundwater), which had mean values of 5.69 mg/kg, 1.15 × 10^?2 µg/l, and 2.22 × 10^?1 µg/l, respectively. Human health risk was estimated using the LC₅₀ (chemical intake toxicity ratio, (RR)) as a toxicity endpoint combined with PEC_runoff and PEC_groundwater. NP ranked highest for LC₅₀ combined with PEC_runoff and PEC_groundwater (mean RR values 1.10 × 10^?4 and 2.40 × 10^?3, respectively). The model highlighted triclocarban and triclosan as ECs requiring further investigation. A sensitivity analysis revealed that soil sorption coefficient and soil organic carbon were the most important parameters that affected model variance (correlation coefficient –0.89 and –0.30, respectively), highlighting the significance of contaminant and soil properties in influencing risk assessments. This model can help to prioritize emerging contaminants of concern requiring vigilance in environmental compartments.     

Application of the Hazard Quotient Method in Remedial Decisions: A Comparison of Human and Ecological Risk Assessments

This paper evaluates the relative roles of the human health hazard index (HI) and the ecological risk assessment hazard quotient (HQ) in remedial decision-making. Through an analysis of HI outcomes drawn from Superfund Records of Decision, the reduced importance of the HI statistic in human health risk assessments is demonstrated, and the high visibility of the ecological risk assessment (ERA) HQ for terrestrial receptors (birds and mammals) is underscored. Three HQ method limitations common to both HHRA and ERA, deriving either from the mathematical construct of the HQ (a simple binary measure, indicating that an animal's exposure either exceeds its toxicity value or does not) or from dose-response outcomes in animal trials, are reviewed. Two additional HQ limitations unique to ERA (i.e., a propensity for the HQ to easily exceed its threshold value, and a propensity for it to assume values that are unreasonably high), and deriving from the complexities of estimating bird and mammal dietary intakes of contaminants and the availability of toxicological effects information, are also identified. The paper cautions of the potential to err in concluding that terrestrial site receptors are at risk when the HQ threshold is exceeded, and regardless of the toxicological information (NOAELs, LOAELs, etc.) used. It recognizes that because other methods of terrestrial assessment are presently unavailable, HQs are sometimes, out of necessity, used to justify a remedial action. The analysis and discussion are intended to remind ecological risk assessors that the HQ is a measure of a level of concern only and not a measure of risk     

Reconstruction and forecast of doses due to ingestion of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr after the Chernobyl accident

The assessment doses due to ingestion of ¹³⁷Cs and ⁹⁰Sr for the population suffering from the Chernobyl accident was performed on the basis of the new mechanistic ecological model for assessment of radiological consequences of agricultural lands contamination (EMARC). The EMARC model allows estimation of internal doses based on ecological factors influencing the contamination of foodstuff, for the post-accidental years in the countries of the former Soviet Union. The EMARC model allows estimation of all quantities required in radiation hygiene practice. For example, the proposed analytical method may be used for both retrospective dose reconstruction and prospective estimates of annual dose and integrated “life-time” dose, for different age intervals. According to the EMARC model, estimated reference “life-time” doses for adults are between 7 and 269 μSv kBq⁻¹ m² for ¹³⁷Cs, and between 25 and 235 μSv kBq⁻¹ m² for ⁹⁰Sr. Maximal doses were estimated for persons who were 3, 9 and 11 years old, at the time of the accident and these doses exceed those for adults by a factors of 1, 5 for ⁹⁰Sr, and 1.4 for ¹³⁷Cs.     

External radiation doses from <Superscript>137</Superscript>Cs to frog phantoms in a wetland area: in situ measurements and dose model calculations

For assessment of external radiation doses to frogs in a wetland area contaminated with ¹³⁷Cs, frog phantoms were constructed from polymethyl methacrylate (PMMA). The frog phantoms contained thermoluminescence (TL) chips and were used in situ at two study sites to measure doses. To test if higher doses are received by the sensitive skin of frogs, extra-thin TL chips were applied close to the surface of the frog phantoms. In addition, the measured doses were compared with those calculated on the basis of soil sample data from the wetland multiplied with dose-conversion coefficients from the US Department of Energy’s RESRAD-BIOTA code and from the ERICA assessment tool. Measured doses were generally lower than those calculated to ellipsoids used to model frogs. Higher doses were measured at the frog phantoms’ surfaces in comparison to inner parts at one of the two sites indicating that the frogs’ thin skin could receive a higher radiation dose than expected. In the efforts to assure protection of non-human biota, in situ measurements with phantoms provide valuable dose information and input to dose models in site-specific risk assessments of areas contaminated with radionuclides.     

Issues in Ecological Risk Assessment of Inorganic Metals and Metalloids

Ecological risk assessment (ERA) is a process that evaluates the potential for adverse ecological effects occurring as a result of exposure to contaminants or other stressors. ERA begins with hazard identification/problem formulation, progresses to effects and exposure assessment, and finishes with risk characterization (an estimate of the incidence and severity of any adverse effects likely to occur). Risk management initially sets the boundaries of the ERA and then uses its results for decision-making. Key information required for an ERA includes: the emissions, pathways and rates of movement of contaminants in the environment; and, information on the relationship between contaminant concentrations and the incidence and (or) severity of adverse effects. Because of specific properties and characteristics of metals in general and of certain metals in particular, a generalized ERA process applicable to organic substances is inappropriate for metals. First, metals are naturally occurring and can arise, sometimes in very high concentrations, from non-anthropogenic sources; organisms can and do adapt to a wide range of metal concentrations. Second, certain metals (e.g., copper, zinc) are essential for biotic health, which means there is an effect threshold for both deficiency and excess, and that standard body burden indices such as bioaccumulation factors (BCFs) can be misleading. Third, metals can occur in the environment in a variety of forms that are more or less available to biota but adverse biological effects can only occur if metals are or may become bioavailable. Fourth, whereas the bioavailability and hence the possibility of toxicity of persistent organic substances are mainly dependent on their intrinsic properties (i.e., lipophilicity), those of metals are generally controlled by external environmental conditions. Examples include pH and ligands, which affect the metal speciation and coexisting cations (e.g., H⁺, Ca²⁺) which compete with the metal ions. ERAs involving metals must include the above four major considerations; other considerations vary depending on whether the ERA is for a site, a region, or is global in scope.     

The Apache Longbow–Hellfire Missile Test at Yuma Proving Ground: Introduction and Problem Formulation for a Multiple Stressor Risk Assessment

An ecological risk assessment was conducted at Yuma Proving Ground, Arizona, as a demonstration of the Military Ecological Risk Assessment Framework (MERAF). The focus of the assessment was a testing program at the Cibola Range, which involved an Apache Longbow helicopter firing Hellfire missiles at moving targets, that is, M60-A1 tanks. The problem formulation for the assessment included conceptual models for three component activities of the test, helicopter overflight, missile firing, and tracked vehicle movement, and two ecological endpoint entities, woody desert wash communities and desert mule deer (Odocoileus hemionus crooki) populations. An activity-specific risk assessment framework was available to provide guidance for assessing risks associated with aircraft overflights. Key environmental features of the assessment area include barren desert pavement and tree-lined desert washes. The primary stressors associated with helicopter overflights were sound and the view of the aircraft. The primary stressor associated with Hellfire missile firing was sound. The principal stressor associated with tracked vehicle movement was soil disturbance, and a resulting, secondary stressor was hydrological change. Water loss to desert washes and wash vegetation was expected to result from increased ponding, infiltration, and/or evaporation associated with disturbances to desert pavement. A plan for estimating integrated risks from the three military activities was included in the problem formulation.     

Regional distribution characteristics and ecological risk assessment of heavy metal pollution of different land use in an antimony mining area – Xikuangshan,China

Abstract

Mining activities have introduced various heavy metals and metalloids to surrounding soil environments, causing adverse impacts to the ecological environment system. The extremely high concentration of various heavy metals and metalloids make the Xikuangshan (Hunan, China) an excellent model to assess their ecological risk. In this study, the soil samples from 26 locations of different land use methods in four areas (smelting area, road nearby ore, mining area, and ore tailing area) in Xikuangshan with different levels of various heavy metals and metalloids (Sb, As, Pb, and Cd) were analyzed; in addition, the index of geo-accumulation and the potential ecological risk index were used to evaluate ecological risk. The results showed that the average contents of Sb, As, Pb, and Cd in all soil samples were 4368.222?mg·kg^?1, 40.722?mg·kg^?1, 248.013?mg·kg^?1, and 40.941?mg·kg^?1, respectively, implying serious contamination of compound pollution of heavy metals in soil. The concentration of heavy metals in soil among smelting area, road nearby ore, mining area, and ore tailing area showed significant distribution characteristics of region because different mining activities such as smelting, mining, transportation, and stacking caused different pollution intensity. Moreover, the contents of Sb in soil samples decreased successively in residue field, wasteland, forestland, sediment, grassland, and vegetable field, and the contents of Sb in vegetable-field and ecological restoration grassland were relatively low, which indicate that the method of grassland ecological restoration is an effective method to control antimony pollution in soil. The results of ecological risk assessment showed that the antimony mining area was seriously polluted by Sb, As, Pb, and Cd, and had strong ecological risk, and Sb and Cd were the most important pollution factors, which indicated that the pollution of Sb and Cd should be a major concern of relevant departments of environment and health.     

Development & application of Conceptual Framework Model (CFM) for environmental risk assessment of contaminated lands

Dumping sites are the most common types of contaminated lands as they pollute the environment. Environmental management of contaminated sites cannot be delivered effectively and efficiently without robust holistic & integrated risk assessment. Previous studies reveal the absence of a risk assessment model that holistically integrates all essential factors progressively and categorically. The study aimed to develop a holistic & integrated Conceptual Framework Model (CFM) for environmental risk assessment and to apply developed CFM on real-world existing Mahmood Booti Open Dumping Site (MBODS). CFM developed in this study had three main tiers i.e., baseline study, hazard identification & exposure assessment, and risk estimation. For the application of CFM, baseline data were collected and assessed. Water, leachate & soil samples were collected within 1000 m across the site and analyzed for physio-chemical parameters and heavy metals to estimate risk. Results of applied CFM depicted that Physico-chemical analysis of leachate, water, and soil revealed significant pollution levels. Heavy metal analysis exhibited that Ni, Pb, Mn, and Cr levels exceeded the allowable limits of the “World Health Organization” in leachate, water, and soil samples. It also revealed the existence of metals at the source (dumping site itself), pathway, and receptor of the dumping site. Eⁱ_r value for Ni, Pb and Cd from the study area manifested a serious probable risk to ecological integrities. Results for PERI from dumpsite demonstrated a serious ecological risk. It can be concluded that although Mahmood Booti dumping site has been at post-closure stage, it is a momentous source of hazardous toxic contaminants to the nearby inhabitants. The work presented in this paper may reproduce repeatedly to create site-specific risk assessment models of other contaminated lands in a cost-effective, consistent and cohesive manner. Application of CFM at Mahmood Booti Dumping site described detailed risk assessment which helps further in risk management.     

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.     

Investigations of the chemical distribution of heavy metals in street dust and its impact on risk assessment for human health,case study of Radom (Poland)

Abstract

This work investigated the ecological and health hazards caused by heavy metals present in urban street dust of Radom (Poland). The objectives of this study were to improve the estimation of exposure doses of toxic metals based on their distribution patterns in street dusts and to assess the noncarcinogenic health risk for the residents. Zinc (Zn), manganese (Mn), and lead (Pb) were mainly associated with the reducible fraction, copper (Cu) with the oxidizable fraction, and iron (Fe), nickel (Ni), and chromium (Cr) with the residual fraction. The contents of short-term and long-term labile fractions of the metals were used to assess a direct health risk, a potential health risk and an overall human health risk. The level of the overall risk quantified by the cumulative total labile fraction-HI (tlf-HI^c ): 3.91E-01 (children) and 3.85E-02 (adults) was lower than the safety limit of unity. The metal that contributed the most to the overall health risk was Pb: 34% (children) and 31% (adults), while Zn and Ni had the least contribution (3% and 2% for both children and adults). It was shown that the risk assessment based on the pseudo-total content of metals can overestimate the health risk by nearly two times when compared to the assessments based on the total content of labile fractions.     

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.     

Developing Conceptual Models for Complex Ecological Risk Assessments

Conceptual models are representations of the assumed relationship between sources and effects. They serve three important purposes. (1) Their creation compels assessors to think through and clarify their assumptions concerning the activities being assessed. (2) They serve as a communication tool for conveying those assumptions to risk managers and stakeholders. (3) They provide a basis for organizing and conducting the risk assessment. Conceptual models for risk assessments of chemical contaminants have not been problematical because they simply portray the flow of the contaminant from a source to a receptor that experiences toxic effects. However, ecological risk assessments must increasingly deal with direct and indirect effects on multiple endpoint receptors and with multiple complex activities including both physical effects and toxic effects. This complexity may result in conceptual models that are incomplete, ambiguous, or simply too complex to be understood. This paper presents a strategy for creating conceptual models for complex ecological risk assessments that are not only complete but also clear and comprehensible. The strategy also promotes efficiency by creating modular component models for activities, sites, and receptors that can be reused in different combinations in different assessments.     

Risk analysis and management decisions for weed biological control agents: Ecological theory and modeling results

Biologically based control methods offer many advantages for the control of invasive plant species; however, these methods are not without risks to native species. Thus, there is a need for more effective and efficient methods of risk analysis for biological control agents. We show how the process of ecological risk assessment established by the United States’ Environmental Protection Agency may be adapted to improve assessment of the risks of proposed biological control agents. We discuss the risks posed by weed biological control agents, and present a simple individual-based model of herbivorous insect movement and oviposition on two species of host plant, a target invasive plant species and a non-target native species, in simulated landscapes. The model shows that risks of non-target impacts may be influenced by the details of the movement behavior of biological control agents in heterogeneous landscapes. The specific details of insect movement that appear to be relevant are readily measured in field trials and the general modeling approach is readily adapted to real landscapes. Current biological control risk assessments typically emphasize effects analysis at the expense of exposure analysis; the modeling approach presented here provides a simple and feasible way to incorporate exposure analyses. We conclude that models such as ours should be given serious consideration as part of a comprehensive strategy of risk assessment for proposed weed biological control agents.