Ecological Risk Assessment - Part 7 (end) pptx

Part VII The Future of Ecological Risk Assessment Pursuing the whole spectrum of scientific activities essential for conservation requires taking creative advantage of all potential resources. Gell-Mann (1994) Since the publication of the first edition of this text, ecological risk assessment has become established as the dominant approach to informing decisions concerning the management of chemicals in the nonhuman environment. Now pressures from scientific advances and from changes in policy and public expectations are pushing the practice in different direc- tions. The following are prognostications based on those pressures and a little wishful thinking. Both the advance ofscience and the pressure of policy are pushing ecological risk assessment to be clearer and more specific in its predictions. Division of an LC 50 by a factor of 1000 to estimate a threshold for unspecified ecological effects is justifiable if the science does not support anything more. However, the sciences that support ecological risk assessment now provide the bases for more sophisticated methods. Perhaps more important, public policymakers increasingly desire assurance that regulations or other management actions are justified. In particular, cost–benefit criteria are increasingly applied to environmental regulations. Similarly, demands for stake- holder involvement in decision making result in increasing requirements that risk assessors explain what is at risk and what is likely to happen under alternative actions. Hence, both capabilities and demands are increasing and assessors must respond. If ecological risk assessors must apply more sophist icated tools and a wider range of data to estimate specific risks, those tools and data must be made more available and usable. Otherwise, ecological risk assessment will fail to meet the expectations of decision makers and stakeholders. This will require the development of better means of placing information and tools in the hands of assessors in forms that allow easy implementation. Publication in journals does not meet that need, and texts such as this one are a little more useful but can ß 2006 by Taylor & Francis Group, LLC. only skim the surfa ce. Assessors need bette r access to informat ion, better acce ss to mod els to analyze the infor mation, and help with organ izing asses sments and making proper inferen ces. Infor mation : Data bases of seco ndary da ta, such as the EPA’s ECO TOX, are us eful but are difficul t to susta in. Better platf orms for sharin g prim ary data are needed . Mod els an d modeling tool s : As discus sed in Chapt er 28, both standar d ecosyst em models and easy- to-use systems for simulat ion modeli ng ha ve beco me availab le. Ho wever, they sti ll requir e more ex pertise than is possess ed by mo st ecologi cal risk assessors. Asse ssment suppor t systems : Com puter-b ased systems like CADD IS (http: =cfpub.e pa.gov = cadd is=) should be the futur e of ecologi cal risk assessment practice. CA DDIS comb ines a framework and methodology of determining the most likely cause of ecological impairment, with worksheets, case studies, useful information, links to other useful information, and quantitative tools. Uncertainty is poorly handled in ecological risk assessment, and one can hope that this will change in the next decade. Currently, the state of practice is to list sources of uncertainty without even ranking them or estimating their approximate magnitudes. Many techniques are available, but guidance is needed for their application. The ongoing revolution in biology based on genomics, proteomics, and metabolomics will inevitably transform toxicology. In the coming years, organisms will be treated as systems responding to toxicological challenges rather than as black boxes. The resulting computa- tional toxicology will facilitate extrapolation among species, life stages, and exposure regimes as well as allowing greatly enhanced prediction of effects of new chemicals. In contrast, ecological risk assessment will become more attentive to the actual effects occurring in the field and more adaptively respond to those results. The increasing use of biological surveys by the US Environmental Protection Agency (US EPA) and other envir- onmental regulatory agencies amounts to a tacit recognition that not all effects are predict- able. This unpredictability results from both the complexity of ecological responses (e.g., Box 34.1) and the importance of unregulated agents such as agricultural runoff that affect ecosystems but are not subject to risk assessments. Increasingly in the coming years, predict- ive risk assessment and ecoepidemiological assessments based on field surveys must be linked by a common analysis of direct and indirect causal relationships. ß 2006 by Taylor & Francis Group, LLC. Glossary 1,2 abduction—Inference to the best explanation. An alternative logic to deduction and induction. accuracy—Closeness of a measured or computed value to its true value. acute—Occurring within a short period of time relative to the life span of an organism (conventionally <10%). Acute is also used to refer to severe effects, usually death, but that usage causes confusion. adaptive management—The use of management actions as experimental treatments to test management models and thereby provide a better basis for future management actions. advocacy science—Scientific studies performed for the purpose of supporting a particular position or sponsor. aged chemical—A chemical that has resided in contaminated soil or sediment for a long period (e.g., years). Generally it is less bioavailable than a chemical freshly added to soil. Also termed a weathered chemical. agent—Any physical, chemical, or biological entity or process that can potentially cause a response. It is synonymous with stressor but more general, because it includes nutrients, water flow, and other agents that may be beneficial or neutral rather than stressful. A synonym sometimes used in US Forest Service documents is affector. ambient media toxicity test—A toxicity test conducted with environmental media (soil, sediment, water) from a contaminated site. Usually the media contain multiple chemicals. analysis of effects—A phase in an ecological risk assessment in which the relationship between exposure to contaminants and effects on endpoint entities and properties and associated uncertainties are estimated. analysis of exposure—A phase in an ecological risk assessment in which the spatial and temporal distribution of the intensity of the contact of endpoint entities with contaminants and associated uncertainties are estimated. analysis plan—A plan for performing a risk assessment, including the data to be collected and the modeling and other analyses to be performed in order to provide the needed input to the environmental management decision. antagonism—The process by which two or more chemicals cause joint effects that are less than additive (either exposure-additive or response-additive). application niche—The range of conditions to which a model may be defensibly applied. assessment endpoint —An explicit expression of the environmental value to be protected. An assessment endpoint must include an entity and specific attribute of that entity. assessor—An individual engaged in the performance of a risk assessment or other assessment. asymptotic LC 50 —The minimum median lethal concentration, which occurs when exposure is extended until no more organisms die of toxicity. It is associated with the equilibrium receptor concen- tration in reversibly binding chemicals. background concentration—The concentration of a substance in an environmental medium that is not contaminated by the sources being assessed or any other local sources. Background concentra- tions are due to natural occurrence or regional contamination. baseline assessment—A risk assessment that determines the risks associated with current conditions so as to determine whether remediation is required. 1 Some of these definitions are taken directly from, or are modified from, the glossary in EPA (1998). 2 Terms within a definition that are also defined in this glossary are in italic font. ß 2006 by Taylor & Francis Group, LLC. Bayesian—A branch of statistics characterized by the updating of prior knowledge and estimation of conditional probabilities using Bayes’ theorem and by the treatment of probabilities as subject- ive degrees of belief. benchmark dose (BMD)—A dose of a substance associated with a specified low level of an effect (usually 10%). The term is used in the US EPA’s human health risk assessments and sometimes risk assessments for mammalian wildlife, equivalent to an ECp or ICp. benchmark dose limit (BMDL)—A lower confidence limit on a benchmark dose. bias—A systematic deviation of measured or computed values from true values. bioassay—A procedure in which measures of biological responses are used to estimate the concentration or to determine the presence of some chemical or material. See toxicity test. bioaccumulation—The net accumulation of a substance by an organism due to uptake from all environ- mental media. bioaccumulation factor—The quotient of the concentration of element or compound in an organism divided by the concentration in an environmental medium, when the concentrations are near steady state, and when multiple uptake routes may contribute. bioavailability—The extent to which a form of a chemical is susceptible to being taken up by an organism. A chemical is said to be bioavailable if it is in a form that is readily taken up (e.g., dissolved) rather than a less available form (e.g., sorbed to solids or to dissolved organic matter). bioconcentration—The net accumulation of a substance by an organism due to uptake directly from aqueous solution. bioconcentration factor—The quotient of the concentration of element or compound in an organism divided by the concentration in water, when the concentrations are near steady state and when only direct uptake from solution contributes. bioindicator—A species or group of species that, by their presence or abundance, are indicative of a property of the ecosystem in which they are found. Enchytraid worms are bioindicators of low dissolved oxygen. biomagnification—The increase in concentration of a chemical in a consumer species (or set of trophi- cally similar species) relative to concentration in food species in a food web. biomagnification factor—The ratio of the concentration of a chemical in organisms at a particular trophic level to the concentration at the next lower level. The factor may be defined for a particular consumer species and its food species or may be averaged across species at defined trophic levels. biomarker—A measurable change in a biochemical, cellular, or physiological characteristic that may be used as a measure of exposure or effect. biosurvey—A process of counting or measuring some property of biological populations or communities in the field. An abbreviation of biological survey. biota=sediment accumulation factor—The ratio of the concentration of a chemical in a benthic organism to the concentration in sediment. canopy cover—A measure of the degree to which the surface is covered by aboveground vegetation. It is related to the interception of solar radiation. carbon mineralization—The process of conversion of the carbon in organic compounds to the inorganic state (usually carbon dioxide). cation exchange capacity—A measure of the capacity of clay and organic colloids to remove positive ions from soil solution. chlorosis—An abnormally yellow color of plant tissues resulting from partial failure to develop chloro- phyll. chronic—Occurring after a long period of time relative to the life span of an organism or effectively infinite in duration relative to the response rate of the exposed system. Chronic is also used to refer to nonlethal effects or effects on early life stages, but that usage causes confusion. cleanup criterion—A concentration of a chemical in an environmental medium or other goal that is determined to be sufficiently protective of human health and ecological assessment endpoints. community—A biotic community consists of all plants, animals, and microbes occupying the same area at the same time. However, the term is also commonly used to refer to a subset of the community such as the fish community or the benthic macroinvertebrate community. The latter is more properly termed an assemblage. ß 2006 by Taylor & Francis Group, LLC. comparative risk assessment—Risk assessment used to rank or otherwise compare alternative actions to address a particular risk or to prioritize risks for remedial or regulatory action. compensation—In population ecology, compensation is the increase in growth of a population at low densities due to decreased mortality, more rapid growth and maturation, and increased fecund- ity. In ecosystem ecology, compensation is the increased rate of performance of a process by one or more species as the abundance or activity of other species decline. For example, increased growth and mass production by chestnut oak compensated for the loss of American chestnut trees in southern Appalachian forests. concentration additivity—A mode of combined toxicity in which each chemical behaves as a concentra- tion or dilution of the other, based on their relative toxicities. conceptual model—A representation of the hypothesized causal relationship between the source of a pollutant or other agent and the response of the endpoint entities. It typically includes a diagram and explanatory text. confounding—A situation in which the effects of multiple agents or processes cannot be separated. In ecological field studies, an apparently causal relationship between an agent and an effect may be confounded by an unrecognized agent that is spatially or temporally correlated with the agent being studied. contaminant—A substance that is present in the environment due to release from an anthropogenic source and is believed to be potentially harmful. corrective action goal—A concentration of a chemical in an environmental medium or other goal that is determined to be protective of human health and ecological assessment endpoints (cleanup criterion). cost–benefit analysis—Method for balancing the costs and benefits associated with an action or technology. credibility—The estimated probability of a unique event given the variability of the system and the assessor’s uncertainty. The credibilities of a series of events should equal their frequencies in the long term. cumulative distribution function (CDF)—A function expressing the probability that a random variable is less than, or equal to, a certain value. A CDF is obtained by integrating a probability density function (PDF) for a continuous random variable or summing the PDF for a discrete random variable. deduction—Inference from a theorem or set of axioms to a particular conclusion. For example, if bioconcentration factor (BCF) ¼ 0.89 log K ow þ 0.61, then one may deduce that for a chemical with K ow of 10, the BCF is 1.5. Deductive arguments are valid if the conclusions are always true when the premises are true. See abduction, induction. definitive assessment—An assessment that is intended to support a remedial decision by estimating the likelihood of endpoint effects and risks, and to provide the basis for management decisions. See scoping assessment and screening assessment. de manifestis—Sufficiently large to be obviously significant (i.e., risks so severe that actions are nearly always taken to prevent or remediate them). de minimis—Sufficiently small to be ignored (i.e., risks low enough not to require actions to prevent or remediate them). depensation—Depensation is the accelerated decline in a population at low densities due to reduced ability to find mates, increased predation, or decreased ability to condition the environment. It is the opposite of compensation. detection limit—The concentration of a chemical in a medium that can be reliably detected by an analytical method. It is defined statistically (e.g., as the concentration that has a prescribed probability of being greater than zero, given variability in the analytical method). deterministic—Having only one possible outcome. direct effect—An effect resulting from an agent acting on the assessment endpoint or other ecological component of interest itself, not through effects on other components of the ecosystem. Synonymous with primary effect. See also indirect effect and secondary effect. dose—The amount of a chemical, chemical mixture, pathogen, or radiation delivered to an organism. For example, mg of Cd per kg of mallard duck (mg=kg) administered by oral gavage. ß 2006 by Taylor & Francis Group, LLC. dose additivity—A mode of combined toxicity in which each chemical behaves as a concentration or dilution of the other, based on their relative toxicities. dose rate—The dose per unit time (e.g., mg=kg=d). dredge spoil—Sediments dredged from a water body and deposited as waste to land or another aquatic location. ecoepidemiology—The analysis of the causes and consequences of observed effects on ecological entities in the environment. ecological entity—An ecosystem, functional group, community, population, or type of organism that may be exposed to a hazardous agent or may itself be a hazardous agent. ecological risk assessment—A process that evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more agents. ecosystem—The functional system consisting of the biotic community and abiotic environment occupy- ing a specified location in space and time. effects range-low for sediments—The lower 10th percentile of effects concentrations in coastal marine and estuarine environments (NOAA). effects range-median for sediments—The median effects concentrations in coastal marine and estuarine environments (NOAA). efficacy assessment—Analysis of the effectiveness of remedial actions. empirical model—A mathematical model that is derived by fitting a function to data using statistical techniques or judgment. Purely empirical models summarize relationships in data sets and have no mechanistic interpretation. endpoint entity—An organism, population, species, community, or ecosystem that has been chosen for protection. The endpoint entity is one component of the definition of an assessment endpoint. environmental risk—A risk to humans or other entities due to hazardous agents in the environment. This definition applies to the United States, United Kingdom, and some other nations. However, some nations use environmental risk equivalently to ecological risk, as defined here. equilibrium partitioning—The transfer of chemical among environmental media so that the relative concentrations of any two media are constant. evidence—A summarization of data in the light of a hypothesis (a model). excess risk—The difference between the risk given an exposure and the risk without the exposure or with an alternative exposure. exotic species—A biological species that has been introduced from elsewhere, including species produced by biological engineering, selective breeding, or natural selection. exposure—The contact or co-occurrence of a contaminant or other agent with a biological receptor. exposure pathway—The physical route by which a contaminant moves from a source to a biological receptor. A pathway may involve exchange among multiple media and may include transform- ation of the contaminant. exposure profile—The product of characterization of exposure in the analysis phase of ecological risk assessment. The exposure profile summarizes the magnitude and spatial and temporal patterns of exposure for the scenarios described in the conceptual model. exposure–response—The functional relationship between the degree of exposure to an agent and the nature or magnitude of response of organisms, populations,orecosystems. exposure–response profile—The product of the characterization of ecological effects in the analysis phase of ecological risk assessment. The exposure–response profile summarizes the data on the effects of a contaminant, the relationship of the measures of effect to the assessment endpoint, and the relationship of the estimates of effects on the assessment endpoint to the measures of exposure. exposure–response relationship—A quantitative relationship between the measures of exposure to an agent and a measure of effect. Exposure–response relationships may take various forms includ- ing thresholds (e.g., effects occur at concentrations greater than x mg=L), statistical models (e.g., the probability of death as a probit function of concentration), or mathematical process models (e.g., dissolved oxygen concentration as a function of phosphorous loading and other variables). Dose–response, concentration–response, and time-to-death models are specific examples of exposure–response relationships. ß 2006 by Taylor & Francis Group, LLC. exposure route—The means by which a contaminant enters an organism (e.g., inhalation, stomatal uptake, ingestion). exposure scenario—A set of assumptions concerning how an exposure may take place, including assumptions about the setting of the exposure, characteristics of the agent, activities that may lead to exposure, conditions modifying exposure, and temporal pattern of exposure. extirpation—Effective elimination of a species from an ecosystem, watershed, or region. A synonym is functional extinction. extrapolation—(1) The use of related data to estimate an unobserved or unmeasured value. Examples include use of data for fathead minnows to estimate effects on yellow perch, for individual organisms to estimate effects on communities, or for oxidation rates in 108C water to estimate rates at 58C, and (2) estimation of the value of an empirical function at a point outside the range of data used to derive the function. feasibility study—The component of the CERCLA (Superfund) remedial investigation=feasibility study that is conducted to analyze the benefits, costs, and risks associated with remedial alternatives. frequentist—A branch of statistics characterized by the analysis of a data set as one of a potentially infinite number of samples drawn from population with a particular distribution and by the treatment of probabilities as frequencies. geographic information systems (GIS)—Software that uses spatial data to generate maps or to model processes in space. geophagous—Eating soil. Usually refers to deliberate or at least not incidental ingestion. habitat—An area that provides the needs of a particular species or set of species. hazard—A situation that may lead to harm. In risk assessment, a hazard is a hypothesized association between an agent and a potentially susceptible endpoint entity. Identification of a hazard leads to assessment of the risk that the harm will occur. hazard quotient—The quotient of the ratio of the estimated level of an agent divided by a level that is estimated to have no effect or to cause a prescribed effect. For example, the concentration of a chemical in water divided by its LC 50 . hyperaccumulator—An organism (usually plant) that accumulates high concentrations of an element or compound, relative to concentrations in soil or another medium. indicator—A simple observation that indicates something about the ecosystem that is important, but not easy to observe. indirect effect—An effect resulting from the action of an agent on components of the ecosystem, which in turn affect the assessment endpoint or other ecological component of interest. See direct effect. Indirect effects of chemical contaminants include reduced abundance due to toxic effects on food species or on plants that provide habitat structure. Equivalent to secondary effects but also includes tertiary and quaternary effects, etc. induction—In logic, induction is the derivation of general principles from observations. For example, a series of observations of bioconcentration of different chemicals may allow us to induce that the bioconcentration factor (BCF) is a function of octanol=water partitioning coefficients (K ow ); in particular, BCF ¼ 0.89 log K ow þ 0.61. Inductive arguments are valid if the conclusions are usually true when the premises are true. See abduction, deduction. inference—The act of reasoning from evidence. interested party—See stakeholder. intervention value—A screening criterion (the Netherlands) based on risks to human health and eco- logical receptors and processes. The ecotoxicological component of the intervention value is the hazardous concentration 50 (HC 50 ), the concentration at which 50% of species are assumed to be protected. junk science—Scientific results that are said to be false because of perceived political, financial, or other motives other than a desire for truth. The term is itself political, having been developed by industry groups to discredit environmental and public health concerns. The antonym is sound science. kinetic—Referring to movement. In particular, in toxicology and pharmacology, kinetic refers to the movement and transformation of a chemical in an organism (i.e., toxicokinetic or pharma- cokinetic). land farm—An area where organic wastes are tilled into the soil for disposal. ß 2006 by Taylor & Francis Group, LLC. life-cycle assessment—A method for determining the relative environmental impacts of alternative products and technologies based on the consequences of their life cycle, from extraction of raw materials to disposal of the product following use. likelihood—The hypothetical probability that events had a prescribed outcome. It may be thought of as the probability of evidence given a hypothesis [P(EjH x )] or as the probability of a sample (x 1 , x 2 , ,x n ) given a probability density function. Likelihoods are termed hypothetical probabilities, because the sum of likelihoods across a set of alternative hypotheses may be greater than 1. In ordinary English, it is synonymous with probability. line of evidence—A set of data and associated analyses that can be used, alone or in combination with other lines of evidence, to estimate risks or determine causes. A line of evidence (e.g., a fathead minnow LC 50 and a 24 h maximum concentration estimated using EXAMS) is an instance of a type of evidence (e.g., laboratory test endpoints and modeled exposure levels). loading—The rate of input of a pollutant or other agent to a particular receiving system (e.g., nitrogen loading to the Chesapeake Bay). lowest observed adverse effect level (LOAEL) —The lowest level of exposure to a chemical in a test that causes statistically significant differences from the controls in any measured response. measure of effect—A measurable or estimable ecological characteristic that is related to the valued characteristic chosen as the assessment endpoint (equivalent to the earlier term ‘‘measurement endpoint’’). measure of exposure—A measurable or estimable characteristic of a contaminant or other agent that is used to quantify exposure. mechanism of action—The specific process by which an effect is induced. It is often used interchangeably with mode of action but is usually used to describe events at a lower level of organization than the effect of interest. For example, if the effect of interest is a reduction in survival rates, the mode of action of an agent may be acute lethality and its mechanism of action may be crushing, acute narcosis, cholinesterase inhibition, or burning. mechanistic model—A mathematical model that estimates properties of a system by simulating its component processes rather than using empirical relationships. media toxicity test—A toxicity test of water, soil, sediment, or biotic medium that is intended to determine the toxic effects of exposure to that medium. It includes ambient media toxicity tests plus tests of site media that have been spiked or otherwise treated. median lethal concentration (LC 50 )—A statistically or graphically estimated concentration that is expected to be lethal to 50% of a group of organisms under specified conditions. mesofauna—Animals that are barely visible such as nematodes and rotifers, which are larger than microfauna such as protozoans but smaller than macrofauna such as earthworms. The term is usually applied to soil or sediment communities. mode of action—A phenomenological description of how an effect is induced. See mechanism of action . For example, if the effect of interest is local extinction of a species, the mode of action might be habitat loss and the mechanism of action might be fire, paving, or agricultural tillage. model—A mathematical, physical, or conceptual representation of a system. model uncertainty—The component of uncertainty concerning an estimated value that is due to possible misspecification of a model used for the estimation. It may be due to the choice of the form of the model, its component parameters, or its bounds. Monte Carlo simulation—A resampling technique frequently used in uncertainty analysis in risk assess- ments to estimate the distribution of a model’s output parameter. mycorrhiza—A symbiotic association of specialized mycorrhizal fungi with the roots of higher plants. The association often facilitates the uptake of inorganic nutrients by plants. natural attenuation—Degradation or dilution of chemical contaminants by unenhanced biological and physicochemical processes. net environmental benefits—The gains in environmental services or other ecological properties attained by remediation or ecological restoration, minus the environmental injuries caused by those actions. (Net benefits are also used in cost–benefit analysis as the difference between monetized benefits and costs.) nitrification—The oxidation of ammonium to nitrate. ß 2006 by Taylor & Francis Group, LLC. nitrogen fixation—The transformation of N 2 to ammonia by biological processes. no observed adverse effect level (NOAEL)—The highest level of exposure to a chemical in a test that does not cause statistically significant differences from the controls in any measured response. nonaqueous-phase liquid (NAPL)—A chemical or material present in the form of an oil phase. normalization—Alteration of a chemical concentration or other property (usually by dividing by a factor) to reduce variance due to some characteristic of an organism or its environment (e.g., division of the body burden of a chemical by the organism’s lipid content to generate a lipid- normalized concentration). octanol=water partitioning coefficient (K ow )—The quotient of the concentration of an organic chemical dissolved in octanol divided by the concentration dissolved in water if the chemical is in equilibrium between the two solvents. parties—The organizations that participate in making a decision. The representatives of all the parties are risk managers. phytoremediation—Remediation of contaminated soil via the accumulation of the chemicals by plants or the promotion of degradation by plants. phytotoxicity—Toxicity to plants. population—An aggregate of interbreeding individuals of a species occupying a specific location in space and time. precision—The exactitude with which a measurement or estimate can be specified or reproduced, usually determined by the similarity of independent determinations. The number of significant figures in a result is an expression of its precision. preliminary remedial goal (PRG)—A concentration of a contaminant in a medium that serves as a default estimate of a remedial goal for receptors exposed to the contaminated medium. primary data—Data obtained for the risk assessment and therefore designed to meet the assessor’s quality requirements and need to estimate a particular parameter or function. probability—Two definitions (at least) are commonly used. (1) Objectivist and frequentist: The relative frequency of occurrence of an event in repeated trials, and (2) subjectivist and Bayesian: The degree of belief assigned to a hypothesis. Probability is scaled 0 to 1, with 0 indicating impos- sibility and 1 indicating inevitability. probability density function (PDF)—For a continuous random variable, the PDF expresses the probabil- ity that the variable will occur in some very small interval. For a discrete random variable, the PDF expresses the probability that the variable assumes a prescribed value. probable effects level for sediments—The geometric mean of the 50th percentile of effects concentrations and the 85th percentile of no-effects concentrations in coastal and estuarine sediment (Florida Department of Environmental Protection). problem formulation—The phase in an ecological risk assessment in which the goals of the assessment are defined and the methods for achieving those goals are specified. pseudoreplication—The treatment of multiple samples from a single treated location or system as if they were samples from multiple independently treated locations or systems. For example, multiple samples of benthic invertebrates from a stream reach below a wastewater outfall are pseudoreplicates. quantal—Denoting an all-or-none response. quantile—Any of the values that divide the range of a probability distribution into a given number of equal, ordered parts; examples are the median, quartiles, and percentiles. Each value divides the range into two parts: the part below the value corresponding to a prescribed fraction p and the part above to 1 – p. quantitation limit—The concentration of a chemical in a medium that can be reliably quantified by an analytical method. Statistical definitions differ and are contentious, but are generally based on concentrations that can be estimated with prescribed precision (e.g., the true concentration that produces estimates having a relative standard deviation of 10%). receptor—An organism, population, or community that is exposed to contaminants. Receptors may or may not be assessment endpoint entities. record of decision—The document presenting the final decision resulting from the CERCLA remedial investigation=feasibility study process regarding selected alternative action(s). ß 2006 by Taylor & Francis Group, LLC. recovery—The extent of return of a population, community, or ecosystem process to a condition with valued properties of a previous state. Due to the complex and dynamic nature of ecological systems, the attributes of a ‘‘recovered’’ system must be carefully defined. reference, negative—A site or the information obtained from that site used to estimate the state of a receiving system in the absence of contamination or disturbance. reference, positive—A site or the information obtained from that site used to estimate the state of a system exposed to contaminants other than the system that is being assessed. reference value—A chemical concentration or dose that is a threshold for toxicity or significant contam- ination. relative risk—The ratio of the risk given an exposure to the risk without the exposure or with an alternative exposure. release—The movement of a contaminant from a source to an environmental medium. remedial action objective—A specification of contaminants and media of concern, potential exposure pathways, and cleanup criteria (remedial goal). remedial alternative—A potentially applicable remedial technology or action proposed in the feasibility study that is considered for remediation of a contaminated site. It may include controls on land use and the no action alternative (natural attenuation), as well as the usual engineered actions such as capping or thermal desorption. remedial goal—A contaminant concentration, toxic response, or other criterion that is selected by the risk manager to define the condition to be achieved by remedial actions. remedial goal option—A contaminant concentration, toxic response, or other criterion that is recom- mended by the risk assessors as likely to achieve conditions protective of the assessment end- points. remedial unit—An area of land or water to which a single remedial alternative applies. remediation—Actions taken to reduce risks from contaminants including removal or treatment of contaminants and restrictions on land use. Note that, in contrast to restoration, remediation focuses strictly on reducing risks from contaminants and may actually reduce environmental quality. removal action—An interim remedy for an immediate threat from release of hazardous substances. restoration—Actions taken to make the environment whole, including restoring the capability of natural resources to provide services to humans. Restoration goes beyond remediation to include restocking, habitat rehabilitation, and reduced harvesting during a recovery period. rhizosphere—The portion of a soil that is in the vicinity of, and influenced by, plant roots; includes enhanced microbial activity, nutrient mobilization, and other processes. riparian—Occurring in, or by the edge of, a stream or in its floodplain. risk assessor—An individual engaged in the performance of the technical components of risk assess- ments. Risk assessors may have expertise in the analysis of risk or specific expertise in an area of science or engineering relevant to the assessment. risk characterization—A phase of ecological risk assessment that integrates the exposure and the exposure–response profiles to evaluate the likelihood of adverse ecological effects associated with exposure to the contaminants. risk management—The processes of deciding whether to accept a risk or to take actions to reduce the risk, justifying the decision, and implementing the decision. risk manager—An individual with the authority to decide what actions will be taken in response to a risk. Examples of risk managers include representatives of regulatory agencies, land managers, and investment managers. rooting profile—The vertical spatial distribution of plant roots. scenario—A possible future condition, given certain assumed actions and environmental conditions. In risk assessment, a scenario is a set of hypothetical or actual conditions under which exposure may occur and for which risks will be characterized. scoping assessment—A qualitative assessment that determines whether a hazard exists that is appropriate for a risk assessment. For contaminated sites, it determines whether contaminants are present and whether there are potential exposure pathways and receptors. ß 2006 by Taylor & Francis Group, LLC. [...]... 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