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. You are guided through a focused case study that will demonstrate how to utilize many of the tools and information available on the RAIS. This tutorial will assist 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.
Before beginning this tutorial, a brief overview of risk assessment can be gained from the mini tutorial What is Risk Assessment?
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 that 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||µg/L||Surface Water|
Now that you have a brief overview of the hypothetical problem, we will demonstrate how various RAIS tools 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.
Once you have developed a CSM and identified:
you are ready to select chemicals of potential concern.
Once you have reviewed the available data for Site A and developed the conceptual site model, 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.
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 can assist you in determining appropriate background concentrations for their site. Please see the background values tool under the Chemical Tools menu. 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, you should consult with your 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.
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: 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.
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). For example, some states may only require that the ARARs for the detected analytes be reported in the remedial investigation report.
In order to screen against the Federal ARARs, choose ARAR Search from the chemical Tools menu. Then within "Select ARAR Source", choose "Federal". Next, select Federal and Tennessee primary and secondary drinking water standards and water quality criteria from the available options. At this point, you should consult with appropriate regulatory agencies to determine which, if any, ARARs to screen against and the appropriate selection criteria. You will need to define the classification of the water body under consideration to determine which ARARs should be addressed. As stated in the problem identification step, 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. 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, press the Arrow button to move the analytes into the Selected box.
Press "Submit Form" to retrieve the data (as shown 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.]
Evaluate the results (make sure to refer to all appropriate footnotes) based on Federal guidance.
For the purposes of this tutorial, and because of variance in state guidance that 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. Note, however, that the maximum detected concentration for toluene is below the ARAR and could drop out of the assessment at this stage, if these criteria were being used.
Next, compare the data from Site A against risk-based PRGs. PRGs can be calculated using the PRG Calculator, available under the Chemical Tools menu. To learn more about the PRGs, the user may refer to the Chemical PRG User Guide, which presents specific PRG Equations for each land use.
For the purposes of this tutorial, select a Hazard Quotient of 1, Target Risk of 10-6, Residential landuse, Tap Water and Fish media options, default PRG type, Chronic values, and the 4 analytes 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
Note that for each land use and exposure route combination, a definition table precedes the result table. Review the definition table to ensure that the appropriate criteria have been selected.
Use these results to compare the maximum detected analyte concentrations from Site A data against the residential risk-based PRGs for water and fish. 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/gL) at Site A is below the residential tapwater PRG of 1.10E+03 µg/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).
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.
A reference dose (RfD) is defined 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. 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).
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 are expressed in units of mg/kg-day.
Subchronic oral RfDs 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 are expressed in units of mg/kg-day.
A short-term oral RfD is 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.
An acute oral RfD is 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.
A reference concentration (RfC) is 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).
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. Values with different units have been converted to mg/m3 for use in the RAIS tools.
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, values with different units have been converted to mg/m3 for use in the RAIS tools.
A short-term inhalation RfC is 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.
An acute inhalation RfC is 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.
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.
An oral slope factor (OSF) represents 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.
The Inhalation unit risk (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.
An oral unit risk is defiend as 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.
In a 2003 memo, EPA Superfund revised its hierarchy of human health toxicity values, providing three tiers of toxicity values. The toxicity values used for all RAIS calculators 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.
When using toxicity values, users are encouraged to carefully review the basis for the value and to document its use for a site.
In order to obtain the information needed for the toxicity assessment for Site A COPCs (arsenic, carbon tetrachloride, and 1,1,1-Trichloroethane), go to the Chemical Toxicity Metadata tool under the Chemical Tools menu and select the appropriate metadata needed. Tables of the related metadata 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
|Carbon Tetrachloride||000056-23-5||Likely to be Carcinogenic to Humans|
|Chemical||"Inhalation Chronic Reference Concentration Source"||"Inhalation Chronic Reference Concentration Basis"||"Inhalation Chronic Reference Concentration Confidence"||"Inhalation Chronic Reference Concentration Critical Effect"|
|Arsenic, Inorganic||Cal EPA|
|Carbon Tetrachloride||IRIS||BMCL10(HEC): 14.3 mg/m3||Medium||Fatty changes in the liver|
|Toluene||IRIS||NOAEL(ADJ): 46 mg/m3||High||Neurological effects in occupationally-exposed workers|
|Trichloroethane, 1,1,1-||IRIS||NOEL(HEC): 1553 mg/m3||Medium||Histopathologic changes|
|Chemical||"Inhalation Chronic Reference Concentration Species"||"Inhalation Chronic Reference Concentration Target Organ"||"Inhalation Chronic Reference Concentration Uncertainty Factor"||"Inhalation Chronic Reference Concentration Reference"|
|Carbon Tetrachloride||Rat||Liver||100||Nagano et al. 2007b, Japan Bioassay Research Center 1998|
|Toluene||Human||Neurological||10||Abbate et al. 1993, etc. (multiple studies)|
|Trichloroethane, 1,1,1-||Mouse||Liver||100||McNutt et al. 1975|
|Chemical||"Oral Chronic Reference Dose Source"||"Oral Chronic Reference Dose Basis"||"Oral Chronic Reference Dose Confidence"||"Oral Chronic Reference Dose Critical Effect"|
|Arsenic, Inorganic||IRIS||NOAEL: 0.0008 mg/kg-day||Medium||Hyperpigmentation, keratosis and possible vascular complications|
|Carbon Tetrachloride||IRIS||BMD2x(ADJ): 3.9 mg/kg-day||Medium||Elevated serum SDH activity|
|Toluene||IRIS||BMDL: 238 mg/kg-day||Medium||Increased kidney weight|
|Trichloroethane, 1,1,1-||IRIS||BMDL 10: 2155 mg/kg-day||Low-medium||Reduced body weight|
|Chemical||"Oral Chronic Reference Dose Species"||"Oral Chronic Reference Dose Target Organ"||"Oral Chronic Reference Dose Uncertainty Factor"||"Oral Chronic Reference Dose Reference"|
|Arsenic, Inorganic||Human||Skin and blood||3||Tseng, 1977, Tseng et al., 1968|
|Carbon Tetrachloride||Rat||Blood||1000||Bruckner et al. 1986|
|Trichloroethane, 1,1,1-||Mouse||Whole body||1000||NTP 2000|
Oral Slope Factor Metadata
|Chemical||"Oral Slope Factor Source"||"Oral Slope Factor Species"||"Oral Slope Factor Reference"||"Oral Slope Factor Target Organ"||"Oral Slope Factor Tumor Type"|
|Arsenic, Inorganic||IRIS||Human||Tseng, 1977, Tseng et al., 1968||Skin||Skin cancer|
|Carbon Tetrachloride||IRIS||Mouse and Rat||Nagano et al. 2007b, JBRC 1998||Liver||Hepatocellular adenoma or carcinoma|
Inhalation Unit Risk Metadata
|Chemical||"Inhalation Unit Risk Source"||"Inhalation Unit Risk Species"||"Inhalation Unit Risk Reference"||"Inhalation Unit Risk Target Organ"||"Inhalation |
|Arsenic, Inorganic||IRIS||Human||Brown and Chu 1983a,b,c, Lee-Feldstein 1983, Higgins 1982, Enterline and Marsh 1982||Lung||Cancer|
|Carbon Tetrachloride||IRIS||Mouse||Nagano et al. 2007b, JBRC 1998||Adrenal Gland||Pheochromocytoma|
Other information needed to complete the toxicity assessment for Site A COPCs (arsenic, carbon tetrachloride, and 1,1,1-Trichloroethane) are chemical-specific parameters. Go to the Chemical Parameters tool under the Chemical Tools menu 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)|
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.
Select "Toxicity Profiles" from the Chemical Tools menu. From the main Toxicity Profile screen, select the Formal or Condensed version for any analyte (see example below).
|Analyte||CAS Number||Formal Version||Condensed Version|
This convenient tool eliminates the effort to produce the toxicity profiles presented in the toxicity assessment chapter of a risk assessment report and supplements the human health risk-based PRGs. Our three COPCs at Site A each have toxicity profiles within this system.
Using the data from Site A, we will now use the Risk Calculator on the RAIS (found under Chemical Tools) to determine the potential human health risks and hazards to residents from drinking water and eating fish that may be exposed to Site A COPCs.
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 or risk/pCi]; and
SF = slope factor, expressed in [(mg/kg-day)-1 or 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, select the Resident Scenario, tap water and fish media, database defaults, and chronic values. Then select the applicable COPCs from the chemcial list.
Then, press 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.
Below the media concentration table are the exposure assessment details. Modify and exposure parameters, as applicable, and view the chronic daily intake equations by clicking on the exposure route name. The ingestion of fish route is displayed below.
Hit the "Retrieve" button to receive excess lifetime cancer risk and noncancer hazard results for each medium and exposure pathway, along with the primary parameters used in each equation. Since we did not change any parameters, the default values will be shown. If you changed any exposure parameters, these would be displayed on the results page.
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.
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 For 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). Check with your Regional Program Manager, Stakeholders, and state regulatory agencies to see if this guidance is applicable to your site.
In general, the risk assessment documentation includes sections/chapters containing the following: 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.