Learn More Topic: Criteria Types
Local water quality conditions.
Potential reactions between the chemical of concern and other chemicals that could increase or reduce the toxicity of the chemical of concern.
Expressed as a pollutant concentration based on a toxicological assessment and an exposure scenario.
Calculated for ingestion of aquatic organisms AND for ingestion of water and organisms.
Bacteriological criteria are developed to protect waters that are designated for contact recreational uses. The bacteria criteria describe a level of a bacterial indicator of fecal contamination that is associated with an acceptable level of risk (to humans). The indicator bacteria are not generally pathogenic themselves, but indicate the presence of pathogens at levels that increase the risks of gastroenteritis illness (G.I.) above an acceptable level.
Expressed as a bacterial indicator concentration based on epidemiological studies and a selected unacceptable illness rate.
Intended to protect recreational uses from unacceptable rate of gastrointestinal illness during swimming.
An aquatic life criterion establishes the level of exposure to a pollutant in water above which the pollutant is expected to pose a significant risk to animals and plants. Typical components of an aquatic life criterion include:
- Concentration or magnitude of exposure. (How much exposure?)
- Time period or duration of exposure. (How long was the exposure?)
- Frequency of exposure. (How often did the exposure occur over time?)
Where data are available, using an aquatic life criterion for water quality management decisions involves calculating the following:
|Saltwater||4-day average||1-hour average|
|Freshwater||4-day average||1-hour average|
In some cases, EPA's criteria may be either overly or insufficiently protective of aquatic life in a particular water body—for example, if the physical and chemical characteristics of the particular water body alter the biological availability or toxicity of the pollutant of concern. In such cases, site-specific criteria should be developed.
Contaminated sediments can pose threats to human health and the environment by serving as a persistent source of toxic chemicals. Desirable sediment quality is established based on assessments conducted on the organic and inorganic material that has settled at the bottom of a water body.
The types of assessments typically conducted to establish desirable sediment quality focus on the following:
|Sediment chemistry||Utilizes both empirically and theoretically derived sediment quality guidelines (or "values") that support prediction of impacts on benthic-dwelling organisms based on contaminants found in the sediment.|
|Utilizes exposure of surrogate organisms to sediments to support measurement of direct impacts on the benthic community (i.e., measurement of impacts on survival and/or on growth and reproduction).|
|Benthic community||Involves measuring impacts on the benthic community (e.g., increases in pollutant-tolerant species or decrease in species diversity).|
|Bioaccumulation||Involves measuring the uptake of bioaccumulative compounds in the food chain. (May utilize lab tests and/or food-chain models.)|
Biological criteria establish threshold levels or guidelines that describe the desired conditions of biological integrity for protecting aquatic communities of surface waters. The criteria can be numeric or expressed in a narrative.
Criteria development is based on an appropriate reference condition that characterizes segments of the water body that are the least impaired by human activities. The underlying premise is that the structure and function of an aquatic biological community in a type of water body provide critical information about the quality of the surface waters.
Key Point. Biological criteria can help identify water quality degradation that cannot be identified by chemical or physical test procedures alone.
An example of biological criteria:
- Narrative criteria: Waters shall be free from substances in concentrations or combinations that would adversely alter the structure and function of aquatic communities as defined by the reference condition.
- Numeric criteria: Class 1 Cool Water Aquatic Life:
- Taxa richness: 5
- EPT index: 3
Nutrient criteria are expressions of allowable levels of nutrient-related biological and chemical response variables for protecting aquatic life and recreational uses. Nutrients are any substances that enhance the growth of plants or animals (e.g., fertilizer phosphorus, nitrogen compounds).
Because incidents of water quality degradation around the country have been linked to nutrient over-enrichment, EPA is in the process of developing numeric criteria. The criteria are being developed for specific ecoregions and waterbody types based on a reference condition or other scientifically defensible approach.
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