Exposure Assessment Tools by Media - Water and Sediment
Overview
Contaminated media to which people may be exposed include air, water and sediment, soil and dust, food, aquatic biota, and consumer products. Surface water can be contaminated by direct discharges or indirect discharges. Examples of direct discharges are those coming from industrial, commercial, agricultural, or residential sites. Examples of indirect discharges are groundwater contaminants that have migrated to surface water, storm water runoff, or settling of contaminants from the atmosphere.
Pollutants in surface water can sink and contaminate sediments. Groundwater can become contaminated when pollutants in subsoil leach to groundwater. Contaminated surface water or groundwater might be used as a source of drinking water.
Exposure to contaminants in water can occur by direct ingestion (e.g., drinking water) or indirect ingestion (e.g., consuming foods and drinks made with water). Incidental ingestion (e.g., swallowing water while swimming), dermal contact (e.g., during showering or bathing, while swimming or wading in surface water), or inhalation (e.g., inhaling vapors during showering) can also occur.
Exposure to contaminants in sediment would likely occur through dermal contact (e.g., while wading or playing in water). The concentrations of contaminants in water or sediment at the point of exposure may differ from the concentration at the source as a result of fate and transport processes (e.g., dilution, biodegradation).
Various tools are available for evaluating sources and releases of contaminants to water and sediment, fate and transport processes, and potential exposure concentrations. Exposure factors, calculation tools, and guidance for assessing exposure to contaminants in water are also provided.
Information about EPA’s Water Programs can be found here:
Water Topics
The National Primary Drinking Water Regulations (NPDWRs or primary standards) are legally enforceable standards that apply to public water systems to protect public health by limiting the levels of contaminants in drinking water. Maximum Contaminant Levels (MCLs) for various chemicals are available at:
Drinking Water Contaminants
EPA’s Watershed Assessment, Tracking & Environmental ResultS (WATERS) program provides a comprehensive listing of resources for assessing water quality:
Watershed Assessment, Tracking and Environmental Results System (WATERS)
Information from the US Geological Survey on water resources can be found at:
Water Resources of the United States
State, USGS, and EPA Regional water websites are provided in the following tables.
| EPA Region | URLs |
|---|---|
| 1: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont | New England Drinking Water Program |
| 2: New Jersey, New York, Puerto Rico , U.S. Virgin Islands | EPA Region 2 |
| 3: Delaware, Maryland, Pennsylvania, Virginia, West Virginia, District of Columbia | Impaired Waters and TMDLs |
| 4: Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee | Impaired Waters and TMDLs |
| 5: Illinois, Indiana, Michigan, Minnesota, Ohio, Wisconsin | Impaired Wters and TMDLs |
| 6: Arkansas, Louisiana, New Mexico, Oklahoma, Texas | Impaired Waters and TMDLs |
| 7: Iowa, Kansas, Missouri, Nebraska | Impaired Waters and TMDLs |
| 8: Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming | Drinking Water Operations |
| 9: Arizona, California, Hawaii, Nevada, territories of Guam and American Samoa | Pacific Southwest, Region 9 Water Program |
| 10: Alaska, Idaho, Oregon, Washington | EPA Region 10 |
Sources
Contamination of water and sediment can occur from anthropogenicResulting from human activity. (manmade) sources or natural sources. Examples of anthropogenic sources include point and nonpoint sources. Natural sources that may contaminate water and sediment include volcanic activity, hurricanes and other storms, forest fires, and earthquakes.
- Point sources involve releases of pollutants to surface water and sediment from a specific source, such as an outfall pipe or ditch. Examples of common point sources of water pollution include sewage treatment plants, industrial facilities, mining operations, construction sites, and storm drains. Contaminants in the surface water column have the potential to settle and contaminate sediments.
- Nonpoint sources of water contamination are area-wide releases of pollutants to surface water and sediment, including nutrient runoff from agricultural sites or storm water runoff from urban or suburban sites. Storm water runoff can become contaminated when rain water comes into contact with contaminated soil and either dissolves the contamination or carries contaminated soil particles. Surface water can also be contaminated when contaminated groundwater migrates to surface water or when contaminants in the air are deposited on the surface water. Pollutants in the surface water column have the potential to settle and contaminate sediments.
Contamination of groundwater is not classified as resulting from point or nonpoint sources. Contaminants may leach from soil into the groundwater causing contamination of the aquifer.
Contamination of drinking water can occur at the source (surface water or groundwater), during treatment (e.g., byproducts of chlorination), or after treatment (e.g., lead contamination from corrosion of plumbing materials).
For more information on drinking water contaminants, public water treatment systems, primary drinking water regulations, and private drinking water wells, see the text box on the right and the list of resources provided under Guidance in this module.
Fate and Transport
Fate and transport processes “link” the release of contaminants at a source with the resultant environmental concentrations to which receptors can be exposed. When a contaminant is released from a source, it is subject to transportMovement within a medium or between media. and transformationChange in a chemical or physical state. in the environment. Compounds can also transfer from one environmental medium to another.
| Migration Process | Examples Relevant to Water and Sediment |
|---|---|
| Transport |
|
| Transformation |
|
| Transfer – Environment to Biota |
|
For additional information on the uptake of contaminants from water to fish, refer to the Aquatic Biota Module of the Media Tool Set.
The characteristics of water and sediment play a large role in the transport processes of contaminants through these media. For example, if surface water is a key exposure pathway, data on flow rates and water characteristics like pH, salinity, water hardness, and levels of dissolved oxygen may be needed.
Environmental factors such as percent organic matter can play a large role in the mobility and bioavailability of contaminants in sediment. Physicochemical characteristics—such as water solubility, octanol/water partition coefficient (Kow), and solid/water partition coefficients (Kd or Koc)—are also important for predicting fate and transport behavior of contaminants in the aqueous phase.
There are a number of sources of information related to the environmental fate and transport of contaminants in surface water and sediment.
Models
Environmental fate and transport models can be used with monitoring data to help characterize media-specific exposure concentrations. A variety of mathematical methods or models are available to describe the multimedia transport and fate of pollutants in the environment. There are also several resources that contain information on input parameters necessary for fate and transport models.
Concentrations
Estimates of contaminant concentrations in water and/or sediment are needed for assessing exposure via potential exposure pathways involving these media. These media concentrations may also be needed as data inputs for modeling the fate and transport of contaminants in water and the transfer of contaminants to other media.
Characterizing contaminant concentrations for an exposure scenario is typically accomplished using some combination of the following approaches:
- Sampling water and sediment and measuring contaminant concentrations
- Modeling the concentration distribution based on source strength, media transport, and chemical transformation processes
- Using existing, available measured concentration data collected for related analysis or compiled in databases
EPA ExpoBox provides information on measuring or modeling water and sediment concentrations and on available monitoring data. Information on sampling techniques and analytical methods is available to support the measurement of contaminants in water and sediment.
In some cases, available measurement data may be used alone to estimate exposures. In the absence of monitoring data, a variety of models can be used to estimate contaminant concentrations in these media. Models may also be used in conjunction with monitoring data to estimate water and sediment concentrations at the point-of-contact with receptors considering fate and transport processes.
Measuring Concentrations
A number of sampling techniques or protocols have been established for monitoring and characterizing water and sediment contamination. Sampling protocols are necessary to ensure that samples are collected in a proper manner using suitable equipment to account for environmental conditions.
Analytical methods for measuring concentrations of contaminants in water and sediment may include methods required for specific contaminants or groups of contaminants that are regulated by EPA, or methods for unregulated contaminants or groups of contaminants of interest.
Modeling Concentrations
In the absence of monitoring data, models may be used to estimate the concentrations of contaminants in water and sediment, such as the following. By modeling contaminant movement and concentrations in freshwater, marine, and estuarine environments, researchers can better understand how these contaminants affect the quality of water, sediment, and aquatic biota.
Groundwater models simulate groundwater flow through the subsurface (and possible migration to surface water) and inform subsurface contaminant transport models.
Available Data
There are a number of information sources that provide monitoring data on contaminant concentrations in surface water and sediment (also see the Aquatic Biota Module of the Media Tool Set).
Some of these data come from national surveys that help to characterize the chemical, biological, and physical water quality of the Nation’s waters. They may also identify actions to prevent pollution, and evaluate the effectiveness of protection and restoration efforts
Exposure Scenarios
People may be exposed to contaminants in water when consuming water directly as a beverage, indirectly from foods and drinks made with water, or incidentally while swimming. Dermal absorption of water contaminants could occur during activities such as hand washing, bathing, and swimming in a pool or surface water body. People could also contact contaminants in sediment while fishing, clamming, wading, or swimming in a lake, river, or other water body.
Inhalation exposures to contaminants in tap water through showering or bathing could also occur.
Exposure to contaminants in water can be estimated by first defining the exposure scenarioA set of facts, assumptions, and inferences about how exposure takes place that aids the exposure assessor in evaluating or quantifying exposure. of interest. Exposure scenarios typically include information on the sources and pathways of exposure, as well as the contaminants of concern, and receptor populations. They might describe a receptor population’s location or activities that may affect exposure and the timeframe over which exposure occurs. For example, ingestion of contaminated water may occur at a residence or at work and be associated with different types of activities (e.g., recreational swimming or consuming tap water used to make coffee). Exposures might occur over short durations (e.g., swimming event) or longer timeframes (e.g., a lifetime drinking water scenario). For any exposure scenario of interest, concentrations of the contaminants in the medium are needed to estimate the exposure dose.
After characterizing the exposed population and identifying exposure concentrations, it is important to define all appropriate exposure factor inputs used to estimate potential exposures and risks. These inputs (intake rates, dermal contact rates, and other relevant patterns of behavior) can be obtained from the Exposure Factors Handbook: 2011 Edition (see Exposure Factors tab).
The table below provides some examples of scenarios involving contaminants in water or sediment. The list of examples is not meant to be exhaustive. There are numerous other ingestion, dermal, and inhalation scenarios that may be constructed based on the specific needs of the assessment. There are also numerous variations of the examples provided in the table.
Additional information on exposure scenarios involving contaminated water and/or sediment may be found in the Indirect Estimation Module of the Approaches Tool Set in EPA ExpoBox.
| Source/Pathway | Population | Activity/Timeframe | Intake or Contact Rate | Exposure Period |
|---|---|---|---|---|
| Indoor air; volatilization from water while showering | Residential adults and children | Showering daily [Table 16-1] |
Short-term, activity-specific [Table 6-2] |
Chronic or sub-chronic, depending on lifestage |
| Outdoor or indoor air; volatilization from swimming pool water | Recreational users | Swimming over less than lifetime [Table 16-1] |
Short-term, activity-specific [Table 6-2] |
Sub-chronic |
| Tap water | General population; adults | Drinking water at home and away from home over lifetime | Daily total tapwater intake [Table 3-1] |
Chronic |
| Tap water; localized | School children | Drinking water during time at school; elementary school years [Table 16-17] |
Portion of daily community tapwater ingestion rate [Table 3-1] |
Sub-chronic |
| Swimming pool water | Adults and children recreational users | Swimming over the short-term [Table 16-1] |
Ingestion rate while swimming [Table 3-5] |
Acute |
| Tap water | General population; adults | Showering; lifetime | Total surface area [Table 7-1] |
Chronic |
| Surface water; localized | Children | Wading | Surface area of legs and feet [Table 7-2] |
Subchronic |
| Swimming pool water | Adults and children recreational users | Swimming over the short-term [Table 16-1] |
Total skin surface area [Table 7-1] |
Acute |
| Sediment; localized | Adults | Clamming | Surface area and solid adherence to skin for face, arms, hands, legs, feet [Table 7-2, 7-4] |
Subchronic |
Several resources are available that illustrate ingestion and dermal scenarios involving exposure to contaminants in water and/or sediment.
Exposure Factors
To estimate human exposure to contaminants in water, exposure factor information is needed. Exposure factors are human behaviors and characteristics that help determine an individual's exposure to an agent.
Several chapters of EPA’s Exposure Factors Handbook: 2011 Edition contain information that might be relevant for a scenario involving exposure to contaminants in water as shown in the table below. Other exposure factors that may be needed for assessing ingestion, inhalation, or dermal exposures include body weight (Chapter 8) and life expectancy values, specifically when evaluating cancer risk (Chapter 18).
| Chapter | Exposure Factors for Evaluating Exposure to Contaminated Water |
|---|---|
| Chapter 3: Water Ingestion Rates |
|
| Chapter 7: Dermal Exposure Factors |
*Note that chemical-specific factors related to dermal absorption and internal dose are not provided in Chapter 7. |
| Chapter 6: Inhalation Rates |
|
| Chapter 16: Activity-Specific Factors |
|
Drinking water ingestion rates are reported in units of mL/day or mL/kg-day (adjusted for body weight). Ingestion rates should be selected to represent the age, lifestage, gender (if appropriate), and activity level for the exposure scenario of interest.
Drinking water intake rates are provided as per capita or consumer-only data. Per capita rates include all survey participants whether or not they ingested any water from the source during the survey period. Consumer-only rates exclude individuals who did not ingest water from the source during the survey period. Per capita intake rates are typically used in exposure assessments of the general population for which average dose estimates are of interest.
Exposure factor data may be accessed from the Exposure Factors Tab of the Indirect Estimation Module.
Calculation Tools
A variety of tools are available for quantifying exposures (dose) and risks to human populations associated with contaminants in water and/or sediment. These tools have typically been developed for specific situations or program offices but may be tailored to meet the needs of the user.
Guidance
A number of guidance documents are available to support various components of EPA programs involving water and/or sediment. EPA regularly issues guidelines to states, tribes, territories, and interstate organizations to improve the consistency and comprehensiveness of water quality monitoring, assessment, and reporting methods and to help build stronger water monitoring programs.