- Email: [email protected]
Hazard identification for contaminants
Toxicology 205 (2004) 195–199
Hazard identification for contaminants M¨umtaz Iscan∗ Department of Toxicology, Faculty of Pharmacy, Ankara University, 06100 Tandogan-Ankara, Turkey Available online 31 July 2004
Abstract In recent years, the recognition of generation of large quantities of toxicants and their by-products due to the industrial and/or cultural activities and transport and their persistence in the environment and biological activities brings out the necessity and importance of their assessment of risk they pose to the ecosystems (e.g. aquatic environment-coastal waters, rivers, lakes and ground water). Indeed, understanding the impacts of contaminants on the environment, including the organisms which live in it, is rather complicated. Nevertheless, the need for protection of the scarce natural resources in the environment and wiser use of them brings the necessity and importance of focusing more attention to the issue. Accordingly the process of ecological risk assessment (ERA) has evolved rapidly since the Environmental Protection Agency (EPA) issued a framework for ecological risk assessment in 1992. The ecological risk assessment involves three stages in a continuous process: (1) problem formulation (problem identification-hazard identification), (2) the analysis of exposure and effects and (3) risk characterisation. Risk management follows the risk characterisation. Of these stages, problem identification is the most critical one which establishes the direction and scope of the ecological risk assessment. The stage involves identifying the actual environmental value(s) to be protected (assessment endpoints) and selecting ways in which these can be measured and evaluated (measurement endpoints). The accuracy of the risk estimation is largely based on the availability of the key information about the contaminant characteristics, ecosystem at risk and ecological effects and the less uncertainty associated with them. The key information required during this phase of the risk assessment process are as follows: (a) potential/actual contaminant of concern, (b) source of contaminant; current and historic use, (c) mode of action of the contaminant, (d) contaminant characteristics (e.g. physical/chemical properties and environmental behaviour, persistence in the ecosystem, transformation products and bioaccumulation), (e) ecosystem potentially at risk and (f) areas of uncertainty. Finally based on these information a conceptual model has to be developed to define the possible exposure and assessment scenarios. Herein, the aforementioned key issues concerning the problem-hazard identification stage of ecological risk assessment for contaminants have been briefly reviewed. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Ecological risk assessment; Contaminants; Problem-hazard identification
1. Introduction ∗
Corresponding author. Tel.: +90 312 212 2921; fax: +90 312 212 2921. E-mail address: [email protected] (M. Iscan).
Understanding the impacts of environmental chemicals (contaminants) on the environment, including the organisms which live in it, is rather complicated.
0300-483X/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.tox.2004.06.051
196
M. Iscan / Toxicology 205 (2004) 195–199
For example, fresh water and marine environments contain complex systems, such as rivers, lakes, wetlands and estuaries. Each of these contain unique biota, that may be represented by thousands of animals, plants and micro-organisms (Gore, 1992). In this system, they interact with the physical and chemical environment and climate conditions. Thus, if the overall health of the ecosystem is to be properly evaluated and understood, the impact of chemicals on interactions of organisms with each other and with their environment must be assessed in addition to their effects on individuals. The bioata (e.g. aquatic ecosystem), both fauna and flora, are often exposed to a variety of toxicants, which, in most cases result from anthropogenic activities. These contaminants are organic chemicals, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides and heavy metals. They are released to the ecosystem (e.g. aquatic environment) from numerous sources. Typical sources are: (a) municipal wastewater-treatment plants, (b) manufacturing industries, (c) mining, (d) oil spills and (e) rural agricultural cultivation and fertilization. As a result, they may damage the environment and produce their deleterious effects on the organisms living in it. Hence, this brings the need for protection of the scarce natural resources in the environment and wiser use of them. While the process of ecological risk assessment (ERA) has been applied for decades this process has evolved rapidly since the Environmental Protection Agency (EPA) issued a framework for ecological risk assessment in 1992 (US Environmental Protection Agency, 1992).
2. Ecological risk assessment process ERA involves three stages in a continuos process (US Environmental Protection Agency, 1998; http:// www.epa.gov/ncea/pdfs/riskcom/menzie.pdf). This process is generally more complex and lasts longer than are most human health risk assessments due to the fact that ERA consider effects at population community and ecosystem levels as well as to the individual species. In addition the relevant assessments are not universally accepted. Moreover, it frequently deals with the effects of mixtures of chemicals that interact in a complex chemical and physical environment rather
than the single chemical. The stages of ERA are: 1) Problem Formulation (problem identificationhazard identification). 2) The analysis of exposure and effects. 3) Risk characterisation. 2.1. Problem Identification This critical stage establishes the direction and scope of the ecological risk assessment. The process involves identifying the actual environmental value(s) to be protected (assessment endpoint(s)) and selecting ways in which these can be measured and evaluated (measurement endpoint(s)) (http://www. epa.gov/ncea/pdfs/riskcom/menzie.pdf). 2.2. Analysis of exposure and effect During this stage of ERA, the exposure level or concentration of the contaminant of concern on the environment resource must be established and the effects assessed. The effects assessment should include potential toxicological effects and ecological effects (http://www.epa.gov/ncea/pdfs/riskcom/menzie.pdf; Fairbrother et al., 2001). 2.3. Risk characterisation This stage is to integrate the exposure of the resource to the contaminants with the observed and the predicted effects within the context of the problem identification to estimate the degree of risk and the probability of adverse environmental changes actually being observed (http://www.epa.gov/ncea/pdfs/riskcom/menzie.pdf; Fairbrother et al., 2001). Risk management follows the risk characterisation. Risk managers should be provided with scientifically sound quantitative and precise assessment results so that they can take effective measures in the management of the ecosystem.
3. Problem identification At this stage of the risk assessment process it is crucial to identify and document the following:
M. Iscan / Toxicology 205 (2004) 195–199
1) 2) 3) 4) 5) 6) 7)
Potential/actual contaminant of concern. Source of contaminant; current and historic use. Mode of action. Contaminant characteristics. Ecosystem potentially at risk. Areas of uncertainty. Conceptual model.
3.1. Potential/actual contaminant of concern There is a need for identification of the contaminant of concern exceeding the benchmark. It should be emphasised that the benchmarks are numerical values used to guide risk assessors at various intended uses. They should not applied to the situations for which they are not intended because the limitations and uncertainties surrounding benchmarks is a key aspect of their effective use (Clark et al., 1999). 3.2. Source of contaminant; current and historic use The information about the contaminant of concern, such as where, when and in what quantities of the contaminant has been/is being used should be provided. 3.3. Mode of action The most important key information required for this stage of ERA to assess the risk estimation accurately is the mode of action of contaminant of concern. Understanding the toxic mechanism of a contaminant helps to evaluate the importance of potential exposure pathways and selection of sensitive ecological targets. For example, a contaminant may selectively affect higher vertebrates by interfering with organ systems not found in invertebrates, or a contaminant may be present at a level that may not be toxic to most organisms, but which will threaten top predators through food chain biomagnification. 3.4. Contaminant characteristics The characteristics of contaminant determines the fate and transport of the contaminant and exposure and thus its toxicity. These are: (a) physical/chemical properties and environmental behaviour, (b) persistence in the ecosystem, (c) transformation products and
197
(d) bioaccumulation (Kendall, 1996; Fairbrother et al., 2001). 3.4.1. Physical/chemical properties and environmental behaviour Environmental behaviour of the contaminant is of great importance and this depends on the physical and chemical behaviour of the contaminant in question. This also provides the information about the bioavailability of the toxic substance and thus exposure. These properties are: (i) water solubility and lipophilicity, (ii) soil adsorption and (iii) vaporisation 3.4.1.1. Water solubility and lipophilicity (Kow or P octonal/water partition coefficient). It is a key property of a contaminant and related to soil and sediment adsorption and bioconcentration of a chemical in aquatic organisms. It is well known that the highly soluble contaminants are transported in large quantities through the hydrologic cycle and thus are found widely distributed at large distances from their points of introduction into the environment. In contrast, hydrophobic compounds tend to be more static and move little through the hydrologic cycle. Generally, the more water soluble the contaminant, the less sorbed to soils and sediments and the less bioconcentrated it is. On the other hand, the more hydrophobic it is, the more sorbed to soils and sediments and more bioconcentrated it is. 3.4.1.2. Soil adsorption. The contaminants in aqueous phase of ecosystems can be adsorbed by soil and sediment. Koc soil sorption constant is the most frequently used value to describe the adsorption of a contaminant to soil or sediment. This constant is relatively independent of the type of soil or sediment. 3.4.1.3. Vaporisation. Evaporation from a solid or aqueous phase is an important mass transfer process. There are several factors that control volatilisation, such as diffusibility of contaminant, its water solubility, vapour pressure, temperature and Henry’s Law constants. However, the most important consideration in evaluating the extent of such movement is the Henry’s Law constant. The tendency of contaminants to move into the air will have an impact on their potential for toxic effects in organisms that may be exposed.
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M. Iscan / Toxicology 205 (2004) 195–199
3.4.2. Persistence in the ecosystem Persistence in the ecosystem depends on the degradability (breakdown) of contaminants. As they move in the environment they are subjected to breakdown by microorganisms (e.g. these are the primary converters of complex organic chemicals to inorganic substances), metabolism by higher organisms, photochemically and chemically. Some compounds, however, may not be degraded at all (Kendall, 1996; Fairbrother et al., 2001). Thus, the ones which are not degradable easily persist in the ecosystem. Some examples for such contaminants are DDT, PCBs and tetrachloro dibenzo p-dioxin (TCCD). 3.4.3. Transformation products Transformation products are the degradation products of the contaminants. The fate and exposure of these intermediates should also be evaluated. Some metabolic products could be more toxic than the parent chemicals (e.g. PAHs). The photooxidation can also enhance the toxicity of various contaminants (e.g. PAHs). 3.4.4. Bioaccumulation Certain contaminants tend to bioaccumulate in aquatic organisms. Many examples exists being concentrated in food chain to the point that toxic effects are exhibited in organisms that may have no direct exposure to chemical itself at its point of application, e.g. DDT, Hg. This feature of such a contaminant is described by its bioconcentration factor. It is calculated as concentration of chemical in the organism/concentration in the water. This value generally gives an idea about the degree of uptake (and intake) and storage of the contaminant by the aquatic organism. However, it does not take into account the metabolism of the chemical by the organism (Kendall, 1996; Fairbrother et al., 2001). 3.5. Ecosystem potentially at risk It is crucial to define the ecosystem, the species and population or community at risk. Accordingly based on the aforementioned information so far the answers to the questions what is likely to be affected, how is likely to be affected, what is to be protected should be searched for to address assessment endpoint (the actual environmental value that is to be protected) and measurement endpoint (measurable responses to a con-
taminant that can be related with or used to predict changes in the assessment endpoint). For the assessment endpoint generally the most susceptible species are chosen. In order the assess the environmental hazard of a contaminant the toxicity data is needed. This is achieved by toxicity tests that are generally performed in a tiered (level) approach. This approach consists of conducting lower tier-laboratory based tests and higher tier-field based tests (US Environmental Protection Agency, 1975; Mc Kim, 1977; American Society for Testing and Materials, 1991; Fairbrother et al., 2001). Lower tier tests involve standard battery of acute and chronic ecotoxicological tests where lethal and sublethal (growth, reproduction, behaviour, physiology and histology) effects are considered. On the other hand, higher tier tests consists of field based (or model ecosystems e.g. microcosms or mesocosms) acute and chronic tests. In these tests, as in lower tier tests, the lethal and sublethal (growth, reproduction, behaviour, physiology and histology) effects are also examined. In addition sediment toxicity tests are performed in this category. 3.6. Areas of uncertainty Uncertainty represents the lack of knowledge about the factors affecting the risk estimation. Hence, uncertainty can lead to inaccurate or biased estimates (Solomon et al., 1996; Paustenbach, 2001). In risk assessment uncertainty has three sources: (1) Imperfect knowledge of things that should be known e.g. if the assessment is based on the data only obtained from the laboratory testing, the estimates of risk would have to be conservative (i.e. wider margins of uncertainty), (2) Systematic errors (e.g. computational, analytical or data transforming errors) and (3) Non-systematic errors (i.e. random or stochastic errors and variability that originate in the system being assessed) (Solomon et al., 1996). Therefore, there is a need to reduce the uncertainty in risk estimation. Accordingly uncertainty analysis is recommended for the entire process of ERA to define and quantify the uncertainty as much as possible. 3.7. Conceptual model At this stage it is advisable to establish a conceptual model for the problem (Solomon et al., 1996; Fair-
M. Iscan / Toxicology 205 (2004) 195–199
brother et al., 2001). This involves the generation of a wide range of hypotheses about the effects of the contaminant on ecosystem. In a broader sense, this model defines the possible exposure and effect scenarios by using the preliminary analysis of the ecosystems at risk, contaminant characteristics and ecological effects. 4. Conclusion The problem (hazard) identification stage of the ERA process is very critical for the accurate estimates of risk. However, this requires the proper toxicological evaluation of the necessary information about the mode of action of the contaminant, contaminant characteristics and ecosystems at risk, and as acknowledged in the Framework for ERA, professional judgement in the selection of risk hypothesis-establishing conceptual model. At this stage it is advisable and useful to involve also the risk managers and stakeholders in discussions so that the result of the assessment will be most effective.
References American Society for Testing and Materials, 1991. Standard guide for assessing the hazard of a material to aquatic organisms and their uses. In: Annual Book of ASTM Standards. E1022-84, vol. 11.04. American Society for Testing and Materials, Philadelphia, PA, USA, pp. 624–640.
199
Clark, J.R., Reinert, K.H., Dorn, P.B., 1999. Development and application of benchmarks in ecological risk assessment. Environ. Toxicol. Chem. 18, 1869–1870. Fairbrother, A., Lewis, M.A., Menzer, R.E., 2001. Methods in environmental toxicology. In: Hayes, A.W. (Ed.), Principles and Methods of Toxicology, 4th ed. Taylor & Francis, Ann Arbor, MI, pp. 1759–1801. Gore, R.H., 1992. The Gulf of Mexico. An assessment of the Risk assessment paradigm for ecological risk assessment. Pineapple Press, Sarasota, FL, USA, 1996, http://www.epa.gov/ ncea/pdfs/riskcom/menzie.pdf. Kendall, R.J., 1996. Aquatic and terrestrial ecotoxicology. In: Klaassen, C.D. (Ed.), Toxicology, The Basic Science of Poisons, 5th ed. McGraw-Hill, New York, pp. 883–905. Mc Kim, J.M., 1977. Evaluation of tests with early life stages of fish for predicting long-term toxicity. J. Fish Res. Board Can. 34, 1148–1154. Paustenbach, D.J., 2001. The practice of exposure assessment. In: Hayes, A.W. (Ed.), Principles and Methods of Toxicology, 4th Ed. Taylor & Francis, Ann Arbor, MI, pp. 387– 448. Solomon, K.R., Baker, D.B., Richards, R.P., Dixon, K.R., Klaine, S.J., LaPoint, T.W., Kendall, D.J., Weisskopf, C.P., Giddings, J.M., Giessy, J.P., Hall, L.W., Williams, W.M., 1996. Ecological risk assessment of atrazine in north american surface waters. Environ. Toxicol. Chem. 15, 31–76. US Environmental Protection Agency, 1975. Committee on Methods for Acute Toxicity Tests with Aquatic Organisms: Methods for acute Toxicity, Macroinvertebrates and Amphibians. EPA-660/375-009, US EPA, Washington, DC. US Environmental Protection Agency, 1992. Framework for Ecological Risk Assessment. EPA/630/R-92/001, US EPA, Washington, DC. US Environmental Protection Agency, 1998. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F, US EPA, Washington, DC.
Hazard identification for contaminants M¨umtaz Iscan∗ Department of Toxicology, Faculty of Pharmacy, Ankara University, 06100 Tandogan-Ankara, Turkey Available online 31 July 2004
Abstract In recent years, the recognition of generation of large quantities of toxicants and their by-products due to the industrial and/or cultural activities and transport and their persistence in the environment and biological activities brings out the necessity and importance of their assessment of risk they pose to the ecosystems (e.g. aquatic environment-coastal waters, rivers, lakes and ground water). Indeed, understanding the impacts of contaminants on the environment, including the organisms which live in it, is rather complicated. Nevertheless, the need for protection of the scarce natural resources in the environment and wiser use of them brings the necessity and importance of focusing more attention to the issue. Accordingly the process of ecological risk assessment (ERA) has evolved rapidly since the Environmental Protection Agency (EPA) issued a framework for ecological risk assessment in 1992. The ecological risk assessment involves three stages in a continuous process: (1) problem formulation (problem identification-hazard identification), (2) the analysis of exposure and effects and (3) risk characterisation. Risk management follows the risk characterisation. Of these stages, problem identification is the most critical one which establishes the direction and scope of the ecological risk assessment. The stage involves identifying the actual environmental value(s) to be protected (assessment endpoints) and selecting ways in which these can be measured and evaluated (measurement endpoints). The accuracy of the risk estimation is largely based on the availability of the key information about the contaminant characteristics, ecosystem at risk and ecological effects and the less uncertainty associated with them. The key information required during this phase of the risk assessment process are as follows: (a) potential/actual contaminant of concern, (b) source of contaminant; current and historic use, (c) mode of action of the contaminant, (d) contaminant characteristics (e.g. physical/chemical properties and environmental behaviour, persistence in the ecosystem, transformation products and bioaccumulation), (e) ecosystem potentially at risk and (f) areas of uncertainty. Finally based on these information a conceptual model has to be developed to define the possible exposure and assessment scenarios. Herein, the aforementioned key issues concerning the problem-hazard identification stage of ecological risk assessment for contaminants have been briefly reviewed. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Ecological risk assessment; Contaminants; Problem-hazard identification
1. Introduction ∗
Corresponding author. Tel.: +90 312 212 2921; fax: +90 312 212 2921. E-mail address: [email protected] (M. Iscan).
Understanding the impacts of environmental chemicals (contaminants) on the environment, including the organisms which live in it, is rather complicated.
0300-483X/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.tox.2004.06.051
196
M. Iscan / Toxicology 205 (2004) 195–199
For example, fresh water and marine environments contain complex systems, such as rivers, lakes, wetlands and estuaries. Each of these contain unique biota, that may be represented by thousands of animals, plants and micro-organisms (Gore, 1992). In this system, they interact with the physical and chemical environment and climate conditions. Thus, if the overall health of the ecosystem is to be properly evaluated and understood, the impact of chemicals on interactions of organisms with each other and with their environment must be assessed in addition to their effects on individuals. The bioata (e.g. aquatic ecosystem), both fauna and flora, are often exposed to a variety of toxicants, which, in most cases result from anthropogenic activities. These contaminants are organic chemicals, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides and heavy metals. They are released to the ecosystem (e.g. aquatic environment) from numerous sources. Typical sources are: (a) municipal wastewater-treatment plants, (b) manufacturing industries, (c) mining, (d) oil spills and (e) rural agricultural cultivation and fertilization. As a result, they may damage the environment and produce their deleterious effects on the organisms living in it. Hence, this brings the need for protection of the scarce natural resources in the environment and wiser use of them. While the process of ecological risk assessment (ERA) has been applied for decades this process has evolved rapidly since the Environmental Protection Agency (EPA) issued a framework for ecological risk assessment in 1992 (US Environmental Protection Agency, 1992).
2. Ecological risk assessment process ERA involves three stages in a continuos process (US Environmental Protection Agency, 1998; http:// www.epa.gov/ncea/pdfs/riskcom/menzie.pdf). This process is generally more complex and lasts longer than are most human health risk assessments due to the fact that ERA consider effects at population community and ecosystem levels as well as to the individual species. In addition the relevant assessments are not universally accepted. Moreover, it frequently deals with the effects of mixtures of chemicals that interact in a complex chemical and physical environment rather
than the single chemical. The stages of ERA are: 1) Problem Formulation (problem identificationhazard identification). 2) The analysis of exposure and effects. 3) Risk characterisation. 2.1. Problem Identification This critical stage establishes the direction and scope of the ecological risk assessment. The process involves identifying the actual environmental value(s) to be protected (assessment endpoint(s)) and selecting ways in which these can be measured and evaluated (measurement endpoint(s)) (http://www. epa.gov/ncea/pdfs/riskcom/menzie.pdf). 2.2. Analysis of exposure and effect During this stage of ERA, the exposure level or concentration of the contaminant of concern on the environment resource must be established and the effects assessed. The effects assessment should include potential toxicological effects and ecological effects (http://www.epa.gov/ncea/pdfs/riskcom/menzie.pdf; Fairbrother et al., 2001). 2.3. Risk characterisation This stage is to integrate the exposure of the resource to the contaminants with the observed and the predicted effects within the context of the problem identification to estimate the degree of risk and the probability of adverse environmental changes actually being observed (http://www.epa.gov/ncea/pdfs/riskcom/menzie.pdf; Fairbrother et al., 2001). Risk management follows the risk characterisation. Risk managers should be provided with scientifically sound quantitative and precise assessment results so that they can take effective measures in the management of the ecosystem.
3. Problem identification At this stage of the risk assessment process it is crucial to identify and document the following:
M. Iscan / Toxicology 205 (2004) 195–199
1) 2) 3) 4) 5) 6) 7)
Potential/actual contaminant of concern. Source of contaminant; current and historic use. Mode of action. Contaminant characteristics. Ecosystem potentially at risk. Areas of uncertainty. Conceptual model.
3.1. Potential/actual contaminant of concern There is a need for identification of the contaminant of concern exceeding the benchmark. It should be emphasised that the benchmarks are numerical values used to guide risk assessors at various intended uses. They should not applied to the situations for which they are not intended because the limitations and uncertainties surrounding benchmarks is a key aspect of their effective use (Clark et al., 1999). 3.2. Source of contaminant; current and historic use The information about the contaminant of concern, such as where, when and in what quantities of the contaminant has been/is being used should be provided. 3.3. Mode of action The most important key information required for this stage of ERA to assess the risk estimation accurately is the mode of action of contaminant of concern. Understanding the toxic mechanism of a contaminant helps to evaluate the importance of potential exposure pathways and selection of sensitive ecological targets. For example, a contaminant may selectively affect higher vertebrates by interfering with organ systems not found in invertebrates, or a contaminant may be present at a level that may not be toxic to most organisms, but which will threaten top predators through food chain biomagnification. 3.4. Contaminant characteristics The characteristics of contaminant determines the fate and transport of the contaminant and exposure and thus its toxicity. These are: (a) physical/chemical properties and environmental behaviour, (b) persistence in the ecosystem, (c) transformation products and
197
(d) bioaccumulation (Kendall, 1996; Fairbrother et al., 2001). 3.4.1. Physical/chemical properties and environmental behaviour Environmental behaviour of the contaminant is of great importance and this depends on the physical and chemical behaviour of the contaminant in question. This also provides the information about the bioavailability of the toxic substance and thus exposure. These properties are: (i) water solubility and lipophilicity, (ii) soil adsorption and (iii) vaporisation 3.4.1.1. Water solubility and lipophilicity (Kow or P octonal/water partition coefficient). It is a key property of a contaminant and related to soil and sediment adsorption and bioconcentration of a chemical in aquatic organisms. It is well known that the highly soluble contaminants are transported in large quantities through the hydrologic cycle and thus are found widely distributed at large distances from their points of introduction into the environment. In contrast, hydrophobic compounds tend to be more static and move little through the hydrologic cycle. Generally, the more water soluble the contaminant, the less sorbed to soils and sediments and the less bioconcentrated it is. On the other hand, the more hydrophobic it is, the more sorbed to soils and sediments and more bioconcentrated it is. 3.4.1.2. Soil adsorption. The contaminants in aqueous phase of ecosystems can be adsorbed by soil and sediment. Koc soil sorption constant is the most frequently used value to describe the adsorption of a contaminant to soil or sediment. This constant is relatively independent of the type of soil or sediment. 3.4.1.3. Vaporisation. Evaporation from a solid or aqueous phase is an important mass transfer process. There are several factors that control volatilisation, such as diffusibility of contaminant, its water solubility, vapour pressure, temperature and Henry’s Law constants. However, the most important consideration in evaluating the extent of such movement is the Henry’s Law constant. The tendency of contaminants to move into the air will have an impact on their potential for toxic effects in organisms that may be exposed.
198
M. Iscan / Toxicology 205 (2004) 195–199
3.4.2. Persistence in the ecosystem Persistence in the ecosystem depends on the degradability (breakdown) of contaminants. As they move in the environment they are subjected to breakdown by microorganisms (e.g. these are the primary converters of complex organic chemicals to inorganic substances), metabolism by higher organisms, photochemically and chemically. Some compounds, however, may not be degraded at all (Kendall, 1996; Fairbrother et al., 2001). Thus, the ones which are not degradable easily persist in the ecosystem. Some examples for such contaminants are DDT, PCBs and tetrachloro dibenzo p-dioxin (TCCD). 3.4.3. Transformation products Transformation products are the degradation products of the contaminants. The fate and exposure of these intermediates should also be evaluated. Some metabolic products could be more toxic than the parent chemicals (e.g. PAHs). The photooxidation can also enhance the toxicity of various contaminants (e.g. PAHs). 3.4.4. Bioaccumulation Certain contaminants tend to bioaccumulate in aquatic organisms. Many examples exists being concentrated in food chain to the point that toxic effects are exhibited in organisms that may have no direct exposure to chemical itself at its point of application, e.g. DDT, Hg. This feature of such a contaminant is described by its bioconcentration factor. It is calculated as concentration of chemical in the organism/concentration in the water. This value generally gives an idea about the degree of uptake (and intake) and storage of the contaminant by the aquatic organism. However, it does not take into account the metabolism of the chemical by the organism (Kendall, 1996; Fairbrother et al., 2001). 3.5. Ecosystem potentially at risk It is crucial to define the ecosystem, the species and population or community at risk. Accordingly based on the aforementioned information so far the answers to the questions what is likely to be affected, how is likely to be affected, what is to be protected should be searched for to address assessment endpoint (the actual environmental value that is to be protected) and measurement endpoint (measurable responses to a con-
taminant that can be related with or used to predict changes in the assessment endpoint). For the assessment endpoint generally the most susceptible species are chosen. In order the assess the environmental hazard of a contaminant the toxicity data is needed. This is achieved by toxicity tests that are generally performed in a tiered (level) approach. This approach consists of conducting lower tier-laboratory based tests and higher tier-field based tests (US Environmental Protection Agency, 1975; Mc Kim, 1977; American Society for Testing and Materials, 1991; Fairbrother et al., 2001). Lower tier tests involve standard battery of acute and chronic ecotoxicological tests where lethal and sublethal (growth, reproduction, behaviour, physiology and histology) effects are considered. On the other hand, higher tier tests consists of field based (or model ecosystems e.g. microcosms or mesocosms) acute and chronic tests. In these tests, as in lower tier tests, the lethal and sublethal (growth, reproduction, behaviour, physiology and histology) effects are also examined. In addition sediment toxicity tests are performed in this category. 3.6. Areas of uncertainty Uncertainty represents the lack of knowledge about the factors affecting the risk estimation. Hence, uncertainty can lead to inaccurate or biased estimates (Solomon et al., 1996; Paustenbach, 2001). In risk assessment uncertainty has three sources: (1) Imperfect knowledge of things that should be known e.g. if the assessment is based on the data only obtained from the laboratory testing, the estimates of risk would have to be conservative (i.e. wider margins of uncertainty), (2) Systematic errors (e.g. computational, analytical or data transforming errors) and (3) Non-systematic errors (i.e. random or stochastic errors and variability that originate in the system being assessed) (Solomon et al., 1996). Therefore, there is a need to reduce the uncertainty in risk estimation. Accordingly uncertainty analysis is recommended for the entire process of ERA to define and quantify the uncertainty as much as possible. 3.7. Conceptual model At this stage it is advisable to establish a conceptual model for the problem (Solomon et al., 1996; Fair-
M. Iscan / Toxicology 205 (2004) 195–199
brother et al., 2001). This involves the generation of a wide range of hypotheses about the effects of the contaminant on ecosystem. In a broader sense, this model defines the possible exposure and effect scenarios by using the preliminary analysis of the ecosystems at risk, contaminant characteristics and ecological effects. 4. Conclusion The problem (hazard) identification stage of the ERA process is very critical for the accurate estimates of risk. However, this requires the proper toxicological evaluation of the necessary information about the mode of action of the contaminant, contaminant characteristics and ecosystems at risk, and as acknowledged in the Framework for ERA, professional judgement in the selection of risk hypothesis-establishing conceptual model. At this stage it is advisable and useful to involve also the risk managers and stakeholders in discussions so that the result of the assessment will be most effective.
References American Society for Testing and Materials, 1991. Standard guide for assessing the hazard of a material to aquatic organisms and their uses. In: Annual Book of ASTM Standards. E1022-84, vol. 11.04. American Society for Testing and Materials, Philadelphia, PA, USA, pp. 624–640.
199
Clark, J.R., Reinert, K.H., Dorn, P.B., 1999. Development and application of benchmarks in ecological risk assessment. Environ. Toxicol. Chem. 18, 1869–1870. Fairbrother, A., Lewis, M.A., Menzer, R.E., 2001. Methods in environmental toxicology. In: Hayes, A.W. (Ed.), Principles and Methods of Toxicology, 4th ed. Taylor & Francis, Ann Arbor, MI, pp. 1759–1801. Gore, R.H., 1992. The Gulf of Mexico. An assessment of the Risk assessment paradigm for ecological risk assessment. Pineapple Press, Sarasota, FL, USA, 1996, http://www.epa.gov/ ncea/pdfs/riskcom/menzie.pdf. Kendall, R.J., 1996. Aquatic and terrestrial ecotoxicology. In: Klaassen, C.D. (Ed.), Toxicology, The Basic Science of Poisons, 5th ed. McGraw-Hill, New York, pp. 883–905. Mc Kim, J.M., 1977. Evaluation of tests with early life stages of fish for predicting long-term toxicity. J. Fish Res. Board Can. 34, 1148–1154. Paustenbach, D.J., 2001. The practice of exposure assessment. In: Hayes, A.W. (Ed.), Principles and Methods of Toxicology, 4th Ed. Taylor & Francis, Ann Arbor, MI, pp. 387– 448. Solomon, K.R., Baker, D.B., Richards, R.P., Dixon, K.R., Klaine, S.J., LaPoint, T.W., Kendall, D.J., Weisskopf, C.P., Giddings, J.M., Giessy, J.P., Hall, L.W., Williams, W.M., 1996. Ecological risk assessment of atrazine in north american surface waters. Environ. Toxicol. Chem. 15, 31–76. US Environmental Protection Agency, 1975. Committee on Methods for Acute Toxicity Tests with Aquatic Organisms: Methods for acute Toxicity, Macroinvertebrates and Amphibians. EPA-660/375-009, US EPA, Washington, DC. US Environmental Protection Agency, 1992. Framework for Ecological Risk Assessment. EPA/630/R-92/001, US EPA, Washington, DC. US Environmental Protection Agency, 1998. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F, US EPA, Washington, DC.