Identification of Key CEC Variables Fact Sheet

This Fact Sheet has been organized into the following subsections:

• Section 1: Introduction
• Section 2: Process for Prioritizing CEC
  • Section 2.1: Occurrence
  • Section 2.2: Toxicity
  • Section 2.3: Physical-chemical Properties That Inform Fate and Transport and Chemical Behavior
• Section 3: Sources of Key Variables to Consider When Evaluating Potential Toxicity and Exposure
  • Section 3.1: Human Health Risk
  • Section 3.2: Ecological Risks
  • Section 3.3: Properties That Inform Fate and Transport
• Section 4. Schemes for Interpreting Information on Variables

1. INTRODUCTION

This Identification of Key CEC Variables Fact Sheet presents the key variables that may be used as criteria to prioritize actions to address a contaminant of emerging concern (CEC). In addition, this Fact Sheet contains suggested resources that can be used to determine the best available scientific information for these variables. The lack of scientific information on any one variable or multiple variables (e.g., exposure, toxicity, fate, and transport) poses a need for further research or data gathering to reduce the uncertainty and increase the accuracy when evaluating the risk posed by a CEC. 

Section 2 provides a process flowchart on how to approach the evaluation of CEC, the specific types of information about the CEC that need to be considered as part of prioritization, and the order in which the information should be considered. Section 3 summarizes key variables that are important for newly identified risks stemming from the exposure and toxicity domains and includes sources where both empirical and estimated (calculated) variable information can be found. Section 4 summarizes available schemes and tools for prioritizing and/or interpreting CEC data. 

Concerns about contaminants emerge because human activities relating to substances (e.g., the built environment, production, use, and disposal) release contaminants into the environment and/or lead to exposures that then may become public and environmental health concerns. These contaminants become recognized through detection and identification in environmental media locally, regionally, or globally. The term “CEC” refers to substances and microorganisms, including physical, chemical, biological, or radiological materials known or anticipated to be present in the environment, that may pose newly identified risks to human health or the environment. Thousands of chemicals are released into and identified in the environment, and communities, regulators, and policy makers need to know how to determine which of these CEC should be prioritized.  

The flowchart presented in Figure 1 was newly developed by the Interstate Technology and Regulatory Council (ITRC) CEC Team to identify a logical process for evaluating CEC other than pathogens and radiologicals. The process uses prioritization criteria and assumes the CEC (which has presumably been identified as the result of an event, a concern from the media or public, or a discovery of new information) can be measured in the environment (see the Adoption of Analytical Methods for CEC Fact Sheet). The process flowchart is intended primarily for chemical contaminants. Due to the unique characteristics of biological (microbials) and radiological materials and the lack of expert resources within the ITRC CEC Team, process flowcharts for those CEC are not currently available but may be considered in future efforts. Additionally, this Fact Sheet addresses CEC with direct effects to human and ecological endpoints and does not consider those that may have indirect effects, such as chemicals, for example, that may impact climate change or deplete ozone in the upper atmosphere. 

2. PROCESS FOR PRIORITIZING CEC

Figure 1. Process Flowchart for prioritizing CEC (download)

Ultimately, the intent of this process is to designate a CEC as low, medium, or high priority to inform the next evaluation steps and decision-making options (Table 1). The designations are based on occurrence, risk/toxicity, potential for exposure to receptors, and physical-chemical characteristics that inform mobility, bioaccumulation potential, and/or environmental degradation. These designations involve a certain degree of professional judgment that must be applied when weighing different factors and evidence. 

Table 1. CEC prioritization 

Table 1 summarizes the CEC prioritization scheme in terms of level of concern, monitoring follow-up, and potential additional steps. Each category is expanded on below: 

• Low-priority CEC: A CEC that is present in the environment, but current data suggest it does not pose a significant threat and does not require further monitoring at this time, either due to infrequent occurrence, low risk/toxicity, minimal potential for exposure to receptors or absence of receptors, or physical-chemical characteristics that may suggest poor mobility, low bioaccumulation potential, or high environmental degradation rate. Watching for new information is important for potential reprioritization. Additionally, the possibility of toxic breakdown products should be considered. 

• Medium priority CEC: A CEC that is present in the environment for which additional information is needed and should be sought out. Continued monitoring is recommended. New information (e.g., lower toxicity endpoint, sensitive health effect, new impacted medium (vapor/air), or new fate and transport characteristic) may require additional risk characterization to determine whether the medium-priority CEC is downgraded to a low priority, remains a medium priority, or is elevated to a high-priority CEC. 

• High-priority CEC: A CEC that, based on its physical-chemical characteristics and occurrence, risk/toxicity, potential exposure pathways, and/or presence of receptors, is recommended for expanded monitoring, additional risk characterization, and potential rulemaking. 

The science and information on CEC are evolving. Per- and polyfluoroalkyl substances (PFAS) are a notable example. Compound classes and mixtures may also emerge as CEC. CEC can be shifted between priority levels at any time. For example, a low-priority CEC can be reintroduced into the evaluation process at any time based on new data (e.g., new information on toxicity, exposure pathways or impacted media) and can result in reconsideration of its CEC status. As such, reevaluation, or reassessment of any given CEC should periodically occur depending on the latest information. As shown in the flowchart, additional data could result in the reclassification of a CEC’s priority. 

To differentiate among the low, medium, and high priorities, the CEC flowchart considers three categories of criteria for prioritizing CEC. These are, in sequence: occurrence, toxicity, and physical-chemical properties that inform fate and transport and chemical behavior. Following the risk assessment paradigm, occurrence and toxicity are considered first—the consideration of occurrence before toxicity was selected for practical purposes. These are discussed in the following sections. 

2.1 Occurrence 

The identification of a CEC in groundwater or surface water used for drinking water purposes is often a priority compared to other environmental media because of direct exposures to humans through drinking water and other household uses of water. For this reason, groundwater or surface water is often the first exposure source assessed and is highlighted in the flowchart. Depending on the situation, concerns over other exposure sources may predominate. For example, the occurrence of a CEC in soil may lead to a higher priority assignment depending on several factors, including land use (e.g., residential, day care, or school) or presence of sensitive subpopulations (e.g., children). Another example could be consumption of recreationally caught fish where a bioaccumulative CEC may be present at levels of concern even when it is nondetectable in surface water. CEC may also be identified in consumer products, which could lead to various exposure sources and pathways (e.g., dermal exposure, ingestion of contaminated food, inhalation of contaminated house dust, etc.). Overall, detection in multiple media adds to the concern due to the combined exposures to these multiple media (e.g., water, wastewater, air, soil, and biota) and likely multiple exposure routes (e.g., ingestion, dermal contact, inhalation) and higher potential for cross-media transfer. Importantly, an already regulated, well-established contaminant may be identified as a potential CEC. This could be due to new information that indicates potential for toxicity at lower exposure levels, its identification in a new media (e.g., air), or awareness of migration along a new exposure pathway (e.g., vapor intrusion). 

Proximity of the CEC to sensitive receptors, and the exposure sources (e.g., drinking water, bathing, ingestion, recreation) and exposure routes (e.g., ingestion, inhalation, and dermal absorption) for those receptors, are also critical inputs to the occurrence evaluation. For drinking water, the source type (private well, public water system, groundwater- vs. surface water–based system, etc.) would also need to be evaluated. Agencies may also consider analyzing wastewater samples from treatment plants to detect and quantify the presence of the CEC, which can provide valuable information on its occurrence and distribution, as CEC often enter the environment through wastewater effluent. 

An analogous process can be applied to ecological exposures. For example, occurrence in aquatic ecosystems (surface water and sediment) is often the first exposure question to evaluate if there is enhanced mobility and biological transfer potential within complex food webs. Occurrence in soil can lead to higher prioritization based on the presence of sensitive receptors (such as endangered species or valued keystone species), or the CEC may be susceptible to uptake by herbivorous or carnivorous animals via vegetation or soil biota. The priority assignment may also consider whether occurrence can affect the diversity and abundance of ecological communities. 

When evaluating the occurrence criteria, agencies will want to consider analytical data sufficiency factors such as those identified in Box 1. Adequate characterization can be taken into account when making a decision about whether a CEC needs further evaluation or should be prioritized as a CEC. When data are not sufficient to make a judgment, the flowchart recommends additional data collection and reassessment. If sufficient data are found to be available, the reviewer determines whether (1) the CEC is a low priority (in which case, it would not be evaluated further in the flowchart) or (2) evaluation should proceed to a risk/toxicity assessment to determine next steps (e.g., monitoring/surveillance). 

2.2 Toxicity 

The toxicities posed by a CEC are evaluated in relation to human health–based and/or ecological health effects. Many CEC may have information available on chemical characteristics but no available information on toxicity. For other CEC, toxicity information may be available but information about new exposure routes or exposure media may be lacking. In many cases, toxicity data may be limited and may not include the types of studies typically used to evaluate health effects in federal and/or state risk assessments. Toxicity data should be vetted to determine whether it can provide an adequate assessment of human health or ecological risks. Other potential considerations for evaluating CEC include the identification of toxicities at lower levels than previously known or identification of toxicities for one or more additional exposure routes. Toxicity evaluations (whether for human health or ecological receptors) will inform the degree to which a CEC poses a risk. This evaluation should also potentially include sensitive subpopulations that would be specific to a given site and CEC. Details regarding specific toxicity information are discussed in Section 3: Sources of Key Variables to Consider When Evaluating Potential Toxicity and Exposure. 

For a toxicity assessment to be meaningful, the extent and quality of information is a consideration. When incomplete toxicity data impede the development of numerical toxicity values, other tools may be used to develop or estimate toxicity values (see Section 3.3, Table 2: Sources of key variables information). For all estimates, an explanation of uncertainties, data sources, and assumptions should be provided to allow for clarity and transparency (see the Risk Perception and Communication Fact Sheet). 

After reviewing toxicity information, three questions are considered:  

• Does the CEC pose human and/or ecological health effects of concern?  
• Does the CEC pose toxicity at lower levels than previously known?  
• Does the CEC pose toxicity via exposure routes not previously identified?  

Pathways to consider should include the potential for toxicity by uptake via the food chain (e.g., via feed, animal products, or edible plants). If data are insufficient to assess these factors, additional data should be collected for reassessment (see Section 3: Sources of Key Variables to Consider When Evaluating Potential Toxicity and Exposure). If data are available, an assessment can be made as to whether a specific CEC should be prioritized. For ecological toxicity, it is important to note that a variety of endpoints may need to be considered in addition to acute mortality, such as behavioral changes, reproductive damage, sex changes, etc. If the assessment indicates sufficient toxicity data, the next step is to consider the physical-chemical property criterion. 

2.3 Physical-chemical Properties That Inform Fate and Transport and Chemical Behavior 

Physical-chemical properties influence how long a CEC remains in the environment and the environmental media in which it is present. They inform how the CEC’s potential for exposure could increase, through its persistence in the environment, bioaccumulation, mobility, toxic degradation products, cross-media transfer, or other factors. This is the final step for determining whether a CEC should be considered a high-priority CEC. See Table 3 in Section 3.3 for a brief description of various properties used to determine persistence, bioaccumulation, and mobility. 

These attributes reflect the potential for CEC to remain in the environment and cause exposure to human and ecological receptors. Physical-chemical properties may be empirical or estimated. Consideration may be given to the circumstances that dictate collection of site-specific data. Published data may be used when available. Data used to establish these properties also need to be of sufficient quality. Box 2 identifies additional considerations relative to physical-chemical mobility and transport. 

3. SOURCES OF KEY VARIABLES TO CONSIDER WHEN EVALUATING POTENTIAL TOXICITY AND EXPOSURE 

Assessments of CEC require some information on the CEC’s toxicity as well as information on potential exposures. When considering toxicity, regulatory agencies usually consider chronic (cancer or noncancer), subchronic (noncancer, reproductive, or developmental), and acute (noncancer) health effects. Federal and state environmental and health agencies establish toxicity values, but the values generated can vary due to several factors. These can include the scientific information available at the time the value was developed, the consideration of a sensitive health effect or endpoint, and the choice of uncertainty factors (for noncancer endpoints). When no federal or state-developed toxicity value is available, or when toxicologists need to consider new information, the state may need to conduct its own toxicological assessment to develop a value that is defensible based on best available information. Many states prefer to use existing toxicity values developed by authoritative agencies or do not have the resources to develop their own values, while other states develop their own toxicity values when necessary. Some states may choose to develop their own values if they do not agree with the scientific basis of available values; some states may be required to make different assumptions (e.g., regarding risk); and some states may also decide the available values are not applicable to or representative of conditions and situations present in their respective state (e.g., exposure of specific populations, water quality differences for aquatic life values, etc.). To facilitate a valid process for deciding which toxicity values should be applied in any given risk evaluation, the United States Environmental Protection Agency (USEPA) and many states use a hierarchy of sources (ECOS 2007; ITRC 2005; 2008; OSWER USEPA 2013, 3; 2009; ORD USEPA 2023d; 2015a). Table 2 presents a summary of sources relevant to the toxicity of a CEC. 

There is less consensus on standard toxicity values and source hierarchies for ecological risk than for human health values. This is due to the wide variety of potential plant and animal receptors and differences in responses from exposure to environmental CEC. Defensible values require careful attention to study validity, endpoints, and uncertainty factors. Information on CEC of interest may be available in various databases curated by state agencies, federal sources (e.g., National Oceanic and Atmospheric Administration (NOAA), USEPA, the Department of Defense, and the Department of Energy), or national and international organizations. 

When considering exposure pathways, physical-chemical criteria influence how long a chemical remains in the environment and the environmental media in which it is present and could increase the CEC’s potential for exposure (persistence, degradation products), influence how it is taken up and processed in biota, and affect how it behaves in the food chain (e.g., bioaccumulation, cross-media transfer). Table 3 presents a brief description of key variables used to help prioritize CEC in relation to persistence, bioaccumulation, and mobility. 

When standard approaches are not immediately applicable for use in evaluating CEC, the resources presented here can help states with decision-making regarding CEC. Table 2 summarizes sources of key variables and is explained in Sections 3.1 and 3.2.  

Table 3 summarizes properties that inform fate and transport and is explained in Section 3.3. 

3.1 Human Health Risk 

Suitable criteria for considering risk to human health (i.e., toxicity values) may be available in multiple sources of widely varying quality and applicability. The sources are discussed below in three groupings without ranking relative importance. Table 2 provides a summary of each. 

3.1.1 Group 1: U.S. Federal Values—IRIS, OW, ATSDR, PPRTV, and OPP 

This group includes U.S. federal sources of human health toxicity values. For chemical exposures, the Integrated Risk Information System (IRIS) (ORD USEPA 2023d) is typically the preferred source for toxicity values because they are based on high-quality assessments that include internal and external reviews. IRIS includes cancer slope factors and inhalation risk values. The IRIS database may not include a value for the contaminant of interest, or the IRIS assessment may not have considered newly available information. Values may be available from other USEPA offices such as the Office of Water (OW) Health Advisories (OW USEPA 2023h) or the Office of Ground Water and Drinking Water (OW USEPA 2023i). These OW values are toxicity values developed by USEPA OW for use in drinking water health advisories or ambient water quality criteria. Another widely accepted source is the Agency for Toxic Substances and Disease Registry’s (ATSDR) (ATSDR 2023) toxicity assessments for acute, intermediate, and chronic noncancer effects. ATSDR uses these to calculate peer-reviewed minimal risk levels for contaminants. The Provisional Peer Reviewed Toxicity Values (PPRTVs) (ORD USEPA 2023e) are developed to support the USEPA Superfund program for chemicals that do not have IRIS values or those with identified subchronic or acute health effects (which are not evaluated in IRIS). PPRTVs undergo both internal and external peer review but are considered a second-tier source by USEPA. The USEPA Office of Pesticide Programs (OPP) (OCSPP USEPA 2023c) generates health effects assessment for pesticides. 

3.1.2 Group 2: State Values, ECHA, OECD, Other International Values, PubChem 

Most states have their own processes for determining human health toxicity values. Generally, states use the Group 1 sources to initially identify their toxicity values; however, many states conduct their own toxicological assessments even when an IRIS value is available. Examples of these states are California (OEHHA 2016), New Jersey (NJDEP 2020), and Minnesota (MDH 2022). Toxicity values from the European Chemicals Agency’s (ECHA) Guidance on Information Requirements and Chemical Safety Assessment (ECHA 2023d) and REACH (ECHA 2023h) and other countries (e.g., Canada and its provinces (Health Canada 2007) and Australia (Australian Government 2022)) may be considered when selecting values. Selection of values from these sources when available will need to consider the toxicity assessment process, including evaluating principal studies (preferably peer reviewed and published/publicly available) and evaluating whether the risk assessment guidance used by other countries differs from USEPA’s guidance. The value should be appropriate and sufficiently protective for the exposure scenario of interest. The Organisation for Economic Cooperation and Development (OECD) Echem Portal (OECD 2023a) and the National Library of Medicine’s PubChem (PubChem 2023a) are excellent toxicity data resources but do not offer human health toxicity values that are used in human health risk assessment. 

3.1.3 Group 3: Other Sources of Toxicity Data That Provide Supporting Evidence to Health Effects 

If the level of concern for the CEC is potentially high based on other factors, and limited toxicity data are available, it may be advisable for the state to conduct a toxicological assessment. One resource that may provide additional weight of evidence to the assessment is the USEPA Toxicity Forecaster (ToxCast), which provides experimental and predictive data (ORD USEPA 2023g). ToxCast predictive capabilities are also available through the USEPA CompTox Dashboard (USEPA 2023a). A suite of models and tools are available for considering chemicals regulated under the Toxic Substances Control Act (OCSPP USEPA 2022b). Other estimation and modeling resources include the Toxicity Estimation Software Tool (TEST) (ORD USEPA 2023f), OPERA (NTP 2023), EpiSuite (OCSPP USEPA 2023a), Derex Nexus (Labcorp 2023), OncoLogic (OCSPP USEPA 2023b), and ToxTree (Jeliazkova et al. 2018). 

3.2 Ecological Risks 

Identification of suitable criteria for considering risk to the environment, wildlife, and water quality may be available from multiple sources of widely varying quality and applicability. 

3.2.1 Group 1: Established CEC Frameworks 

Many potential CEC may have already been evaluated as part of permitting requirements or other chemical management purposes using established CEC frameworks. A good starting point is the ECHA dossiers for new chemicals (ECHA 2023h), which assemble available information, including ecological and environmental toxicological data, as part of the European chemical classification process. As an example, for aquatic and terrestrial (soil) organisms, hazards may be represented under ECHA by the predicted no effect concentration values. The Chemicals Management Plan in Canada is a similar compilation of data (Government of Canada 2006). 

3.1.2 Group 2: Established Media Concentrations or Screening Values Deemed Protective of Various Ecological Endpoints 

Established media concentrations or screening values deemed protective of different ecological endpoints may have been established by various agencies. Unfortunately, they are typically established for well-known contaminants and may not be available for CEC. One source is the USEPA National Recommended Water Quality Criteria (OW USEPA 2022a) for surface water. Many states (e.g., Texas (TCEQ 2023), New Jersey (NJDEP 2010), and Oregon (Oregon DEQ 2023)) maintain surface water, sediment, and soil screening values for extensive lists of chemicals. Other sources include the USEPA regional office compilations for media concentrations (e.g., Region 3 (ORD USEPA 2015c), Region 4, (ORD USEPA 2015b), and Region 5 (USEPA 2023b)); the NOAA SquiRTs (NOAA 2023) screening value compilations for sediment, soil, and surface water; the Department of Energy (DOE) Oak Ridge National Laboratory Ecological Benchmark Tool for Chemicals (RAIS 2022a) as part of the Risk Assessment Information System (RAIS 2022b); and Los Alamos National Laboratory ECORISK Database (Kieling 2017). Many other countries also maintain similar databases. These values are generally, but not always, compilations developed from primary or secondary sources, can be based on widely different methodologies, and can be of varying quality and applicability. They are also generally limited to more common contaminants. Nevertheless, they are some of the primary sources to consider when evaluating a CEC. 

3.2.3 Group 3: Compilations of Measured Toxicity Criteria and Bioaccumulation Potential from Exposures to CEC 

These sources typically present a review of toxicity or bioaccumulation testing results available in the research literature and may or may not include the prioritization and selection of a preferred toxicity reference value (TRV). In the first group are databases of research results such as USEPA ECOTOX (Olker et al. 2022), which presents details of toxicity evaluations for a great many chemicals and species of aquatic and terrestrial biota. ECOTOX also now has several data summary tools that allow the user to summarize and manage data outcomes. A similar database for bioaccumulation and tissue residue studies in aquatic environments is the United States Army Corps of Engineers Environmental Residue Effects Database (USACE ERED) (USACE 2023). These sources present a wealth of information but require the user to have toxicological knowledge to determine the quality and applicability to the specific site and concern at hand. The scientific literature can be referenced for additional information. 

3.2.4 Group 4: Surrogates and Models 

Potential CEC may be lacking in published empirical evaluations of potential toxicity and hazard to the environment. It may therefore be useful to consider modeling approaches for such chemicals. Among these are the USEPA Ecological Structure Activity Relationships (ECOSAR) (OCSPP USEPA 2022a) Predictive Model, a quantitative structure activity relationships (QSAR) model to estimate aquatic toxicity for organic chemicals. QSAR models can be accessed through the OECD QSAR Toolbox (OECD 2023b) and VEGA (VEGA HUB 2023). In the absence of useful data on the chemical of interest, it may also be possible to consider similar chemicals as surrogates for the chemical of interest. This is a common approach for chemicals that exist as very similar congeners or isomers that can be extrapolated across the chemical class. Resources identified in the prior human health toxicity section “Group 3: State Toxicological Assessment Using Available Information” may also provide values that can be considered for evaluation of potential impacts on ecological receptors (see ,for example, James and colleagues (2023), where high-throughput laboratory in vitro cell-line bioassay exposure-response data are being used as a surrogate for ecological risk thresholds). 

3.2.5 Other Sources 

In the absence of useful information in complied data sources for either human health or ecological toxicity, it may also be necessary to search and evaluate the primary research literature for information not already reflected in many of these sources. Some manufactured chemicals are proprietary, and existing human health and/or ecological toxicological information may not be publicly available. Values based on published scientific research are generally preferred to modeled data. 

It is important to consider not only the exposure medium of concern, but also the biological organism level (individual, population, community, ecosystem) these data sources apply to. Toxicity data may be expressed in terms of toxicity (e.g., reference doses or effect concentrations) to an individual or populations of receptors or as values describing an effect at the community level (i.e., measures of diversity and abundance). 

3.3 Properties That Inform Fate and Transport 

Table 3 presents some indicators of persistence, bioaccumulation, and environmental partitioning. Persistence or bioaccumulation potential may be the result of direct empirical measurement or may be estimated from chemical-specific properties. 

Some common sources for primary data (measured and/or estimated) used in the evaluation of environmental presence and exposure include the following: 

• US EPA CompTox Dashboard (USEPA 2023a): The source presents chemistry, toxicity, and exposure information for more than 900,000 chemicals. Data and models presented in the dashboard can help with efforts to identify chemicals most in need of further testing. 
• ATSDR Toxicological Profiles (ATSDR 2023): Peer-reviewed information reflecting a comprehensive and extensive evaluation, summary, and interpretation based on available toxicological, epidemiological, and fate and transport information. 
• PubChem (PubChem 2023a): Comprehensive listing of chemicals and their physical-chemical, biological effect, and other attributes, including citations to original empirical data. 
• EPISuite (OCSPP USEPA 2023a): A compendium of empirical and estimated physical, chemical, degradation, and bioaccumulation parameters, searchable by CAS number, SMILES structure, or name. This database focuses on attributes useful for estimating whether a chemical should be identified as a CEC. 
• CRC Handbook of Chemistry and Physics (Rumble 2022): A classical source of comprehensive physical and chemical data for many chemicals. 
• National Institutes of Standards and Technology (NIST) Chemistry WebBook (NIST 2023) Includes collected information on chemical and physical property data curated by the NIST Standard Reference Data Program and others. 
• COSMOtherm (COLaN 2023): Computational chemistry software program to predict thermodynamic properties. 

Other countries also maintain compendia containing physical-chemical properties for thousands of chemicals. Some states specifically call out preferred sources for values to be used in a CEC evaluation. In addition, international and domestic specialized databases for bioaccumulation and bioconcentration data, biodegradability constants, and environmental degradation rates are available (e.g., USACE ERED, USEPA Envirofate) (USACE 2023; USEPA 2023c). 

Careful review and assessment of the data quality and applicability of the information from a data source, including any cited primary data, are essential to a comprehensive evaluation of the fate and transport characteristics of a chemical undergoing a CEC evaluation. Large ranges of empirical and measured values between sources may be present and could be problematic for the evaluation.  

Table 2. Sources of key variables information 

Table 3. Properties that inform potential fate and transport 

4. SCHEMES FOR INTERPRETING INFORMATION ON VARIABLES 

A number of published prioritization schemes/approaches for a range of environmental media and contaminant groups are available. Table 4 summarizes select schemes and frameworks used to prioritize emerging contaminants/chemicals and is intended to represent a broad spectrum of national, international, and state frameworks. Table 4 serves as a resource for the states to explore alternative prioritization approaches (in addition to the one presented in this Fact Sheet) to facilitate development of their own programs to monitor, identify, and evaluate CEC. 

Table 4. Schemes for interpreting information on variables 

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