Using The RAIS to Accomplish Your Goals
MODULE #1: RISK ASSESSMENT INFORMATION SYSTEM OVERVIEW
The Risk Assessment Information System (RAIS) is a web-based system used to disseminate risk tools and supply information for risk assessment activities. Taking advantage of searchable and executable databases, menu-driven queries, and data downloads using the latest Web technologies, the RAIS offers essential tools and information for the risk assessment process and can be tailored to meet site-specific needs.
This tutorial is designed to assist the user in understanding and applying available RAIS tools to the risk assessment process. Using the tutorial, the user is guided through a focused case study which will demonstrate to the user how to utilize many of the tools and information available on the RAIS. This tutorial will assist the user in:
- developing a conceptual site model,
- determining appropriate preliminary remediation goals for screening/comparisons,
- identifying and selecting the chemicals of potential concern,
- extracting information for a toxicity assessment,
- calculating risk/hazards, and
- documenting portions of the risk assessment report.
MODULE #2: PROBLEM IDENTIFICATION
As an example for this tutorial, the following hypothetical, yet realistic, situation is described.
An industrial area upstream of Site A has accidentally released contaminants into the environment and they have found their way into the nearby stream. This stream is classified for domestic, fish and aquatic life, recreational, and irrigation uses. At Site A there is a residential community which uses the water in this stream for domestic household uses; they also occasionally catch and eat the fish from this stream. Surface water and fish samples were taken from the stream at Site A and the results of the chemical analyses are provided in the data set below for use in this tutorial.
Data Set for Site A:
|Trichloroethane, 1,1,1-||10098972||2/4||12,600||µ/L||Surface Water|
MODULE #3: DEVELOPING A SITE CONCEPTUAL MODEL
Now that you have a brief overview of the hypothetical problem identified and the tools available on the RAIS, we will demonstrate how various tools on this system can be utilized to help you through the risk assessment process.
As one of the first steps in performing a risk assessment, a conceptual site model (CSM)> is developed after reviewing all existing data. The CSM helps to identify all potential or suspected sources of contamination, types and concentrations of contaminants detected at the site, potentially contaminated media, and potential routes of exposure, exposure pathways, and receptors (in this case residents of the community).
Various types of CSMs may be formulated to identify this information.
- Example 1: Classic Graphical Conceptual Model>
- Example 2: Stem-and-Leaf Conceptual Model>
- Example 3: Table-Style Conceptual Model>
In addition, the DOE Office of Environmental Policy and Assistance has developed a Site Conceptual Exposure Model (SCEM) Builder to streamline the process in preparing CSMs. If you are not familiar with designing conceptual models or would like a standard model for doing so, this model would be useful for you to obtain. This computer graphics planning tool is free and can be downloaded to generate site-specific conceptual models.
Once you have developed a CSM and identified:
- all potential or suspected sources of contamination,
- the types and concentrations of contaminants detected at the site,
- all potentially contaminated media,
- potential exposure routes and pathways, and
- potential receptors,
you are ready to begin the selection of chemicals of potential concern.
MODULE #4 SELECTION OF COPCs
Once the user has reviewed the available data for Site A and developed the conceptual site model, the user can proceed with selecting the chemicals of potential concern (COPCs). COPCs are chemicals that are potentially site-related and whose data are of sufficient quality for use in the quantitative risk assessment.
4.1 Background Data Screen
The data set should first be screened against background data to ensure that naturally occurring or anthropogenic levels of chemicals are evaluated/screened-out if appropriate. [Different regions have various guidance concerning if and how comparisons of site data with background data should be performed.] The RAIS has tools which can assist the user in determining appropriate background concentrations for their site. Please see the background tool on the Tools Page. Also, guidance concerning how to compare background data to site-related contaminant data is provided in the Guidance for Conducting Risk Assessments and Related Risk Activities for the DOE-ORO Environmental Management Program [BJC/OR-271], Appendix C. This background comparison guidance has been consistently used for the Oak Ridge Reservation; however, the user should consult with their Regional Program Manager and appropriate Stakeholders before the background screen is performed to determine the appropriate method for your site. For the purposes of this tutorial, we will assume that the data for Site A has already been screened against background.
4.2 Preliminary Remediation Goal Screen
Site A data should now be screened against preliminary remediation goals (PRGs) which are concentration goals for individual chemicals, in specific medium and land use combinations (e.g., residential use of water). PRGs are often used: 1) as long-term targets during the analysis and selection of remedial alternatives; 2) to facilitate development of appropriate detection limits for chemical sampling purposes; 3) as screening tools to focus concern on a specific medium or specific COPCs; 4) to support no further action recommendations; and 5) as a toxicity screen. There are two general sources of PRGs which include: 1) concentrations based on potential Applicable or Relevant and Appropriate Requirements (ARARs) and 2) concentrations based on risk assessment (i.e., risk-based PRGs).
PRGs are appropriately used as a toxicity screen to identify COPCs in the baseline risk assessment, by eliminating chemicals at a site that pose insignificant risk/hazard to human health. For the purpose of this tutorial, the Federal ARARs and residential risk-based water and fish PRGs will be used in the toxicity screen to determine which analytes in the Site A data are COPCs.
4.3 Preliminary Remediation Goal Screen: ARARs Screen
First a screen of the Site A data against the appropriate Federal or State ARARs will be conducted. Before performing an ARARs screen, be sure to check with your regulators to see if this is appropriate (e.g., EPA Region IV does not perform the ARARs screen as part of the baseline human health risk assessment). In some cases, states may only require that the ARARs for the detected analytes be reported, for example, in the remedial investigation report.
In order to screen against the Federal ARARs, choose ARAR Search from the Tools Page. Then within "Select ARAR Source" choose "Federal". The user is now able to retrieve Federal and Tennessee primary and secondary drinking water standards and water quality criteria from the available options. At this point, the user should consult with appropriate regulatory agencies to determine which, if any, ARARs should be screened against and the appropriate selection criteria. The user will need to determine the classification of the water body under consideration to determine which ARARs should be addressed. As stated in the problem identification, we are evaluating a water body source that is classified as "domestic, fish and aquatic life, recreational, and irrigation uses." For the purposes of this tutorial and since we are considering domestic use of the water (most conservative use), we will check all options from the first and second selection box. The user should note that radionuclides are divided into separate categories for Promulgated Federal and State Primary Drinking Water MCLs and Proposed Federal Primary Drinking water MCLs.
From the "Select Individual Chemicals" selection box, choose the names of the four analytes identified in our data set. Note, when choosing more than one name, the user MUST press the CTRL key and hold it down continuously until all selections are made. Each selection will be highlighted if chosen properly. After all analyte selections are made, the user can then select the ARARS to retrieve. For the purpose of this tutorial all ARARs are selected.
Once the user has chosen to "Retrieve", the selected data will appear as below. [The data will be displayed horizontally on the screen; but in order to demonstrate the results for this tutorial, the data are displayed in two tables.]
The user will then evaluate the chosen guidelines based on Federal guidance, referring to all appropriate footnotes.
For the purposes of this tutorial and because of variance in state guidance which may require that the ARAR comparisons be performed at a different stage in the remedial investigation process, we will assume that none of the contaminants are screened out at this stage. However, the user should note that the maximum detected concentration for toluene is below the ARARs and could drop out of the assessment at this stage if these criteria were being used.
4.4 Preliminary Remediation Goal Screen: Risk-Based PRGs
Next, the user should compare the data from Site A against risk-based PRGs. PRGs can be calculated using the Chemical PRG Tool. To learn more about the PRGs, the user may refer to the Chemical PRG User Guide. The specific PRG Equations for each land use are presented.
The user should be familiar with each of the landuse scenarios presented in the Chemical PRG Tool. For the purposes of this tutorial, select the Residential landuses, default PRG type and the 4 analyte names and press retrieve.
Results are given for Residential soil, air, tapwater and fish. Each section gives a table with the default exposure parameters followed by a table of the cancer and noncancer PRGS and any chemical-specific inputs that were required. In accordance with the problem identified for Site A in Module 2, the Tapwater and fish PRGs are needed to screen Site A. The PRG results are summarized and reproduced below.
Resident Preliminary Remediation Goals for Tap Water
Resident Preliminary Remediation Goals for Fish
The user should note that for each land use and exposure route combination, a definition table precedes the result table. The user may review the definition table to ensure that the appropriate criteria have been selected.
Use these results to compare the maximum detected analyte concentrations from the Site A data against the residential risk-based PRGs for water and fish. The user should note the source of the toxicity values used in the PRG calculation to be sure the sources are acceptable to local authorities.
The most protective of the cancer and noncancer PRGS are selected for screening. Note that for toluene, the maximum detected concentration (4.3 µ/L)at Site A is below the residential tapwater PRG of 1.93E+03 µ/L; therefore this analyte is not a COPC. All other analytes have concentrations above their corresponding PRGs and are considered to be COPCs (in this tutorial).
MODULE #5: TOXICITY ASSESSMENT
Once the chemicals of potential concern (COPCs) for Site A have been determined using the background and PRG screens, the toxicity assessment is conducted. The purpose of the toxicity assessment is to consider the types of adverse health or environmental effects associated with chemical exposures, the relationship between magnitude of exposure and adverse effects, and related uncertainties. In the toxicity assessment, the toxicity values for each COPC are identified and retrieved from the Risk Assessment Information System (RAIS). There are many types of toxicity values that come from many sources.
5.1 Types of Toxicity Values
5.1.1 Reference Doses
The current, or recently completed, EPA toxicity assessments used in these screening tables (IRIS and PPRTV) define a reference dose, or RfD, as an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, or using categorical regression, with uncertainty factors generally applied to reflect limitations of the data used. RfDs are generally the toxicity value used most often in evaluating noncancer health effects at Superfund sites. Various types of RfDs are available depending on the exposure route (oral or inhalation), the critical effect (developmental or other), and the length of exposure being evaluated (chronic or subchronic). Some of the PRGs in this calculator also use Agency for Toxic Substances and Disease Registry (ATSDR) chronic oral minimal risk levels (MRLs) as oral chronic RfDs and intermediate oral MRLs as subchronic RfDs. The HEAST RfDs used in these PRGs were based upon then current EPA toxicity methodologies, but did not use the more recent benchmark dose or categorical regression methodologies.
22.214.171.124 Chronic Oral Reference Doses
A chronic oral RfD is defined as an estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a daily oral exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable risk of deleterious effects during a lifetime. Chronic oral RfDs are specifically developed to be protective for long-term exposure to a compound. As a guideline for Superfund program risk assessments, chronic oral RfDs generally should be used to evaluate the potential noncarcinogenic effects associated with exposure periods greater than 7 years (approximately 10 percent of a human lifetime). Chronic oral reference doses and ATSDR chronic oral MRLs are expressed in units of mg/kg-day.
126.96.36.199 Subchronic Oral Reference Doses
EPA has begun developing subchronic oral RfDs, which are useful for characterizing potential noncarcinogenic effects associated with shorter-term exposures by the oral route. As a guideline for Superfund program risk assessments, subchronic oral RfDs should generally be used to evaluate the potential noncarcinogenic effects of exposure periods between two weeks and seven years. Such short-term exposures can result when a particular activity is performed for a limited number of years or when a chemical with a short half-life degrades to negligible concentrations within several months. Subchronic oral reference doses and ATSDR intermediate oral MRLs are expressed in units of mg/kg-day. IRIS defines the subchronic RfD to be: "An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure for a subchronic duration (up to 10% of average lifespan) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used."
188.8.131.52 Short Term Oral Reference Doses
IRIS defines short-term oral RfDs as "An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure for a short-term duration (up to 30 days) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used."
184.108.40.206 Acute Oral Reference Doses
IRIS defines acute oral RfDs as "An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure for an acute duration (24 hours or less) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used."
5.1.2 Reference Concentrations
The current, or recently completed, EPA toxicity assessments used in these screening tables (IRIS and PPRTV assessments) define a reference concentration (RfC) as an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, or using categorical regression with uncertainty factors generally applied to reflect limitations of the data used. Various types of RfCs are available depending on the exposure route (oral or inhalation), the critical effect (developmental or other), and the length of exposure being evaluated (chronic or subchronic). These screening tables also use ATSDR chronic inhalation MRLs as chronic RfCs, intermediate inhalation MRLs as subchronic RfCs and California Environmental Protection Agency (chronic) Reference Exposure Levels (RELs) as chronic RfCs. These screening tables may also use some RfCs from EPAs HEAST tables.
220.127.116.11 Chronic Inhalation Reference Concentrations
The chronic inhalation reference concentration is generally used for continuous or near continuous inhalation exposures that occur for 7 years or more. EPA chronic inhalation reference concentrations are expressed in units of mg/m3. Cal EPA RELs are presented in g/m3 and have been converted to mg/m3 for use in these screening tables. Some ATSDR inhalation MRLs are derived in parts per million (ppm) and some in mg/m3. For use in this table, all were converted into mg/m3.
18.104.22.168 Subchronic Inhalation Reference Concentrations
The subchronic inhalation reference concentration is generally used for inhalation exposures that are between 2 weeks and 7 years. Subchronic inhalation reference concentrations are expressed in units of mg/m3. As noted above, some ATSDR (intermediate) inhalation MRLs were derived in ppm and converted for use in this table into mg/m3. IRIS defines the subchronic RfC to be: "An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure for a subchronic duration (up to 10% of average lifespan) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used."
22.214.171.124 Short Term Inhalation Reference Concentrations
IRIS defines short-term inhalation RfCs as "An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure for short-term duration (up to 30 days) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used."
126.96.36.199 Acute Inhalation Reference Concentrations
IRIS defines acute inhalation RfCs as "An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure for an acute duration (24 hours or less) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used."
5.1.3 Slope Factors
A slope factor and the accompanying weight-of-evidence determination are the toxicity data most commonly used to evaluate potential human carcinogenic risks. Generally, the slope factor is a plausible upper-bound estimate of the probability of a response per unit intake of a chemical over a lifetime. The slope factor is used in risk assessments to estimate an upper-bound lifetime probability of an individual developing cancer as a result of exposure to a particular level of a potential carcinogen. Slope factors should always be accompanied by the weight-of-evidence classification to indicate the strength of the evidence that the agent is a human carcinogen. The ATSDR does not derive cancer toxicity values (e.g. slope factors or inhalation unit risks). Some slope factors used in these screening tables were derived by the California Environmental Protection Agency, whose methodologies are quite similar to those used by EPAs IRIS and PPRTV assessments.
188.8.131.52 Oral Slope Factors
An upper bound, approximating a 95% confidence limit, on the increased cancer risk from a lifetime oral exposure to an agent. This estimate, usually expressed in units of proportion (of a population) affected per mg/kg-day, is generally reserved for use in the low-dose region of the dose-response relationship, that is, for exposures corresponding to risks less than 1 in 100.
184.108.40.206 Inhalation Unit Risk
The IUR is defined as the upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 µg/m3 in air. The interpretation of inhalation unit risk would be as follows: if unit risk = 2 × 10-6 per µg/m3, 2 excess cancer cases (upper bound estimate) are expected to develop per 1,000,000 people if exposed daily for a lifetime to 1 µg of the chemical per m3 of air. Inhalation unit risk toxicity values are expressed in units of (mg/m3)-1.
220.127.116.11 Inhalation Slope Factor
Inhalation slope factors are no longer recommended for use.
18.104.22.168 Oral Unit Risk
The upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 µg/L in water, or 1 µg/m3 in air. The interpretation of unit risk would be as follows: if unit risk = 2 × 10-6 per µg/L, 2 excess cancer cases (upper bound estimate) are expected to develop per 1,000,000 people if exposed daily for a lifetime to 1 µg of the chemical per liter of drinking water.
5.2 Sources of Toxicity Values
In a 2003 memo, EPA Superfund revised its hierarchy of human health toxicity values, providing three tiers of toxicity values. Three tier 3 sources were identified in that guidance, but it was acknowledged that additional tier 3 sources may exist. The 2003 guidance did not attempt to rank or put the identified tier 3 sources into a hierarchy of their own; however, when developing this calculator for the RAIS, a hierarchy was needed for all sources. The toxicity values used in this calculator are consistent with the 2003 guidance. Toxicity values from the following sources, in the order in which they are presented below, are used as the defaults in this calculator.
EPA's Integrated Risk Information System (IRIS)
Federal Register. Thursday December 7, 2000. Part II, Environmental Protection Agency. 40 CFR Parts 9, 141, and 142 - National Primary Drinking Water Regulations; Radionuclides; Final Rule. p 76713.
World Health Organization toxicity equivalence factors (TEFs). Van den Berg et al. (2006) presents the WHO 2005 TEFs for carcinogenic dioxins and furans and polychlorinated biphenyls. Ahlborg et al. (1994) presents the WHO 1994 TEFs for carcinogenic polychlorinated biphenyls 170 and 180 inToxic equivalency factors for dioxin-like PCBs: Report on a WHO-ECEH and IPCS consultation, December 1993. Chemosphere, Vol. 28, No. 6, 1049-1067. Polycyclic aromatic hydrocarbon TEFs are presented in Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons.
The Provisional Peer Reviewed Toxicity Values (PPRTVs) derived by EPA's Superfund Health Risk Technical Support Center (STSC) for the EPA Superfund program.
The California Environmental Protection Agency/Office of Environmental Health Hazard Assessment's toxicity values-http://www.oehha.ca.gov/risk/ChemicalDB/index.asp
The Agency for Toxic Substances and Disease Registry (ATSDR) minimal risk levels (MRLs)-http://www.atsdr.cdc.gov/mrls/index.html
Other sources such as NCEA that were provided to the RAIS for use on the Oak Ridge Reservation.
The EPA Superfund program's Health Effects Assessment Summary Table (HEAST).
Values withdrawn from IRIS or archived from PPRTV or HEAST. The archived values are no longer present on the EPA source websites.
When using toxicity values other than tier 1, users are encouraged to carefully review the basis for the value, and to document its use in decision documentation on a site.
5.3 Toxicity Metadata
In order to obtain the information needed for the toxicity assessment, for Site A COPCs (arsenic, carbon tetrachloride, and 1,1,1-Trichloroethane)the user will need to go to the Toxicity Values tool and select the appropriate metadata needed. Tables of the related meta data for the four COPCs are presented below. For noncancer risk it may be appropriate to sum risk across target organs. (Remember that toluene dropped off the COPC list during the risk-based PRG screen and is not considered further.)
EPA Cancer Classification
|Chemical||"Inhalation Chronic Reference Concentration Basis"||"Inhalation Chronic Reference Concentration Confidence Level"||"Inhalation Chronic Reference Concentration Critical Effect"||"Inhalation Chronic Reference Concentration Modifying Factor"||"Inhalation Chronic Reference Concentration Species"|
|Trichloroethane, 1,1,1-||NOEL (HEC)||medium||liver histopathologic changes||1||rat, mouse|
|Chemical||"Inhalation Chronic Reference Concentration Basis"||"Inhalation Chronic Reference Concentration Study Date"||"Inhalation Chronic Reference Concentration Study Reference"||"Inhalation Chronic Reference Concentration Target Organ"||"Inhalation Chronic Reference Concentration Uncertainty Factor"|
|Toluene||human||'1990 (multiple studies)||Foo et al. (multiple studies)||10|
|Trichloroethane, 1,1,1-||1988, 1984||Quast et al.||liver||100|
|Chemical||"Oral Chronic Reference Dose Basis"||"Oral Chronic Reference Dose Confidence Level"||"Oral Chronic Reference Dose Critical Effect"||"Oral Chronic Reference Dose Modifying Factor"||"Oral Chronic Reference Dose Species"|
|Arsenic, Inorganic||NOAEL/LOAEL||medium||hyperpigmentation, keratosis and possible vascular complications||human|
|Toluene||BMDL||medium||increased kidney weight||rat|
|Trichloroethane, 1,1,1-||BMDL10||low/medium||reduced body weight||1||mouse|
|Chemical||"Oral Chronic Reference Dose Study Date"||"Oral Chronic Reference Dose Study Reference"||"Oral Chronic Reference Dose Target Organ"||"Oral Chronic Reference Dose Uncertainty Factor"|
|Carbon Tetrachloride||1986||Bruckner et al.||liver||1000|
Oral Slope Factor Metadata
|Chemical||CAS||"Oral Slope Factor Species"||"Oral Slope Factor Study Date"||"Oral Slope Factor Study Reference"||"Oral Slope Factor Target Organ"||"Oral Slope Factor Tumor Type"|
|Arsenic, Inorganic||007440-38-2||human||U.S. EPA||skin||cancer|
|Carbon Tetrachloride||000056-23-5||hamster/mouse/rat||1977||NCI||liver||carcinomas / hepatomas|
Inhalation Unit Risk Metadata
|Chemical||CAS||"Inhalation Unit Risk Species"||"Inhalation Unit Risk Study Date"||"Inhalation Unit Risk Study Reference"||"Inhalation Unit Risk Target Organ"||"Inhalation |
|Arsenic, Inorganic||007440-38-2||human||Brown and Chu||lung||cancer|
|Carbon Tetrachloride||000056-23-5||See Oral||See Oral||See Oral||See Oral||carcinomas / hepatomas|
5.4 Chemical-specific factors
In order to obtain the information needed for the toxicity assessment, for Site A COPCs (arsenic, carbon tetrachloride, and 1,1,1-Trichloroethane)the user will need to go to the Toxicity Values tool and select the appropriate chemical-specific factors needed. A table is presented below with a few of the parameters offered by the RAIS.
|Chemical||CAS||Diffusivity in Air (cm2/s)||Diffusivity in Water (cm2/s)||Fish Bioconcentration Factor (L/kg)||Unitless Henry`s Law Constant||Soil-Water Partition Coefficient (cm3/g)|
5.5 Toxicity Profiles
Now that all of the appropriate toxicity values and chemical-specific factors have been obtained, toxicity profiles may also be retrieved for Site A COPCs.
The user should return to the Main Tools Menu and select " Toxicity Profiles". From the main Toxicity Profile screen, the user may choose to select the Formal Version, Condensed Version, or a RAGs Part A format version of any one of the available analytes listed (see example below).
|Analyte||CAS Number||Formal Version||Condensed Version||RAGs Part A Format|
|Antimony (metallic)||7440360||Formal||Summary||RAGs A|
This convenient tool is provided to eliminate the effort needed to produce the toxicity profiles presented in the toxicity assessment chapter of a risk assessment report and to supplement the human health risk-based PRGs. Our three COPCs at Site A each have toxicity profiles within this system.
At the bottom of each summary profile, the user may choose to return to the main toxicity profile menu to "Retrieve Toxicity Profiles" or proceed to review the "Formal Version" of the same profile. The user may also select the Condensed Profile from the bottom of the Formal versions.
MODULE #6: RISK CALCULATIONS
Using the data from Site A, we will now use the Contaminated Media (Risk) Calculator on the RAIS to determine the potential human health risks and hazards from exposure to the Site A COPCs from residents using the water in their households and from eating the fish.
This portion of the risk assessment process is generally referred to as "Risk Characterization". This step incorporates the outcome of the previous activities and calculates the risk or hazard resulting from potential exposure to chemicals via the pathways and routes of exposure determined appropriate for the source area.
The basic equation for calculating excess lifetime cancer risk is:
Risk = CDI × SF
Risk = a unitless probability of an individual developing cancer over a lifetime;
CDI = chronic daily intake or dose [mg/kg-day; and risk/pCi]
SF = slope factor, expressed in [(mg/kg-day)-1; pCi/risk]
The basic equation for calculating systemic toxicity (i.e., noncarcinogenic hazard) is:
Noncancer Hazard Quotient = CDI/RfD
CDI = chronic daily intake for the toxicant expressed in mg/kg-day, and
RfD = chronic reference dose for the toxicant expressed in mg/kg-day.
From the main page of the Calculator, the user should select the residential Landuse Scenario and the COPCs to begin the risk calculations.
After selecting the Landuse and COPCs, hit the "Retrieve" button.
On the next screen input the media concentrations and modify any of the exposure parameters necessary. In this case study (Site A), the Residential Land Use; Exposure to Contaminants in Tap Water and Fish are appropriate for our risk calculations/analysis. The Tap Water media is used rather than Surface Water because the residents at Site A are using the water for household purposes.
Scrolling down the page, the user can change the exposure parameters and view the chronic daily intake equations by clicking on the exposure rout name. The ingestion of fish route is displayed below.
Hitting the "Retrieve" button will display excess lifetime cancer risk and noncancer hazard results for each medium and exposure pathway along with the primary parameters used in each equation.
Resident RISK for Tap Water
Resident RISK for Fish
The excess lifetime cancer risk and noncancer hazard results are then displayed for each medium and exposure pathway along with the primary parameters used in each equation.
These risk/hazard values can then be included in the risk characterization section of a risk assessment report. In the case of Site A, carbon tetrachloride poses a slight concern for cancer risk for a lifetime consumption of fish in our baseline risk assessment. A site-specific risk assessment should be conducted to:1) determine if the stream in question can support a large enough population of fish to supply the residents and 2) determine the actual amount of fish consumed by the residents. Arsenic and 1,1,1-trichlorethane pose a significant cancer and noncancer risk to residents who use the stream for drinking water and household purposes. Possible solutions could be to provide the residents with an alternative water source or remediate the source of the contamination at the upstream industrial site.
MODULE #7: DOCUMENTATION
Finally, the user must document the risk assessment process. The purpose for documentation is to:
- determine if additional action is necessary at the site,
- provide a basis for determining residual chemical levels that are adequately protective of public health,
- provide a basis for comparing potential health impacts of various remedial alternatives, and
- help support selection of the "no-action" remedial alternative, where appropriate.
The EPA has published guidance for documentation purposes and is entitled, "Risk Assessment Guidance To Superfund: Volume 2 Human Health Risk Evaluation - Part D Standardized Planning, Reporting, and Review of Superfund Risk Assessments". Provided in this guidance are standardize tables for presentation of all risk results, including COPCs, background, ARARs, toxicity values, toxicity information (e.g., critical effects, target organs, uncertainty factors), excess lifetime cancer risks, hazard indices, and chemicals of concern (COCs). The user should check with their Regional Program Manager, Stakeholders, and state regulatory agencies to see if this guidance is applicable to their site.
In general, the risk assessment documentation includes sections/chapters containing the: introduction, data evaluation, exposure assessment, toxicity assessment, risk characterization, summary of risks, conclusions, and remedial goal options. The RAGS Part D guidance standardizes the format of the tables presented within each of these sections of the risk assessment report/documentation.