Supplementary Training Materials - Background
1.1 Why did EPA update its freshwater copper criteria?
To reflect the latest scientific knowledge on metals speciation and bioavailability, EPA updated its national recommended aquatic life criteria for copper to include a new means of quantifying copper toxicity and to utilize a more advanced modeling approach for developing water quality criteria. This update incorporates the use of the BLM in the criteria derivation procedures.
1.2 What is the Biotic Ligand Model? Where can I obtain a copy?
The BLM is a metal bioavailability model that uses information on water chemistry conditions in a water body to calculate a site-specific water quality criterion. The BLM is based on the premise that toxicity is primarily related to the amount of metal bound to a biochemical receptor on an organism (e.g., gill membrane on a fish). Many water quality characteristics, including pH, alkalinity,1 dissolved organic carbon (DOC), and hardness, can affect the bioavailability, and thus the toxicity, of a metal like copper.
The BLM software and user's guide may be downloaded from EPA's website.
1.3 What is a ligand? What is a biotic ligand?
A "ligand" is an ion, molecule, or molecular group that binds to another chemical to form a larger complex. Carbonate, sulfate, chloride, and organic matter are all ligands that may interact with copper.
A "biotic ligand" is a biochemical receptor that is metal-binding and is treated similarly to other ligands in the exposure water, except that it is on the organism. An example of a biotic ligand is a fish gill.
1.4 What is the history and scientific basis of the BLM?
The BLM is based on conceptual modeling and experimental work that began in the early 1980's, with development continuing to the present day. In 1999, the BLM approach was presented to EPA's Science Advisory Board (SAB). The SAB found that the BLM can "significantly improve predictions of the acute toxicity of certain metals across an expanded range of water chemistry parameters compared to the WER [Water-Effect Ratio]". EPA refined the BLM and incorporated it into the 2003 Draft Update of Ambient Water Quality Criteria for Copper. The BLM-based freshwater aquatic life criterion is now final with the publication of EPA's Aquatic Life Ambient Freshwater Quality Criteria – Copper 2007 Revision (EPA-822-R-07-001). The criteria document contains additional information on the history and scientific basis of the BLM. EPA has not yet developed recommendations regarding BLM-based criteria for saltwater systems.
1.5 Why is copper important?
Copper is a naturally occurring metal found in the earth's crust. Copper is also generally present in surface waters, with cupric ion (Cu+2) as the primary form in natural surface waters. In freshwater systems, naturally occurring concentrations of copper range from 0.2 µg/L to 30 µg/L (Bowen 1985).
At low concentrations, copper is an essential element to virtually all plants and animals, including humans. Copper is a reddish colored metal and is a good conductor of heat and electricity. It is used in a variety of products, including electrical wiring, plumbing materials, cookware, automobile brake pads, and coins.
1.6 How is copper released into the environment?
Some examples of how copper may be released into the environment are through copper mining activities, agricultural activities (e.g., through its use as a mildewcide, fungicide, and/or algaecide), and manufacturing activities (e.g., manufacturing of leather and leather products, fabricated metal products, electrical equipment, and automobile brake pads). Copper may also enter the environment through natural processes, such as volcanic eruptions, windblown dusts, decaying vegetation, and forest fires. These examples are not an exhaustive list of all sources of copper. Additionally, copper is found in most municipal effluents due to the corrosion of copper plumbing.
1.7 How many rivers in the U.S. are impaired for copper? How many Total Maximum Daily Loads (TMDLs) are approved for copper?
As of January 2007, there were 629 river and stream segments listed as impaired (e.g., not meeting their water quality standards) for copper in 36 states plus Puerto Rico. Additionally, five river and stream segments were listed as impaired for contaminated sediments due to copper in one state.
As of January 2007, there were 258 TMDLs approved for copper in 21 states plus the District of Columbia. Additionally, one TMDL is approved for copper in sediments in one water body in Colorado.
1.8 Is copper toxic to freshwater aquatic organisms? How does copper affect human health?
Elevated levels of copper are toxic in aquatic environments and may adversely affect fish, invertebrates, plants, and amphibians. Acute toxic effects may include mortality of organisms; chronic toxicity can result in reductions in survival, reproduction, and growth.
In humans, small amounts of copper are necessary to maintain good health; however, higher concentrations of copper may cause health effects such as irritation of the nose, mouth, and eyes; nausea; and diarrhea.
The freshwater copper criteria presented in EPA's revised aquatic life copper criteria recommendation document and discussed in these supplementary training materials are based on protection of aquatic life, not human health.
1.9 How are the updated national freshwater copper criteria expressed?
The revised national recommendations are contained in EPA's Aquatic Life Ambient Freshwater Quality Criteria – Copper 2007 Revision (EPA-822-R-07-001). The freshwater acute and chronic criteria recommendations for copper are expressed differently than traditional criteria, in that the criteria maximum concentration (CMC) and the criteria continuous concentration (CCC) are expressed as outputs of a computer model, the BLM, rather than as regression-based hardness formulas (see Question 1.2 for a definition of the BLM). The BLM utilizes acute toxicity data for copper and calculates chronic criteria using the final acute-chronic ratio (FACR).
1.10 How is the updated freshwater criterion recommendation different from the previous recommended criterion?
The 1986 and 1995-updated copper criteria are based on an empirical relationship of toxicity to water hardness,2 and do not explicitly consider the effects of other water quality parameters on copper toxicity. EPA's earlier recommendations provided for sitespecific adjustments using the 1994 and 2001 WER3 procedures to account for variations in water chemistry other than hardness. (The 1994 and 2001 WER guidance documents can be found online).
The freshwater criteria recommended in EPA's Aquatic Life Ambient Freshwater Quality Criteria – Copper 2007 Revision are instead formulated as a BLM-based calculation. Unlike the empirical hardness relationship, the BLM explicitly accounts for ten individual water quality variables, is not linked to a particular correlation among these variables, and can address variables that were not a factor in the hardness relationship. Adoption of site-specific criteria developed using the BLM would eliminate the need for the site-specific toxicity testing that is otherwise recommended as part of the WER method, thereby decreasing costs and providing an approach that can be applied more frequently across spatial and temporal scales.
1.11 Will the updated freshwater criterion be more or less stringent than the previous (1986 and 1995) criterion? How might BLM-derived copper criteria values compare with hardness-based criteria and WERadjusted criteria values?
"Stringency" likely varies depending on the specific water chemistry of the site. The 1986 hardness-based equation and resulting copper criteria reflected the effects of water chemistry factors such as hardness (and any of the other factors that were correlated with hardness, chiefly, pH and alkalinity). However, the hardness-based criteria, unadjusted with the WER, did not explicitly consider the effects of DOC and pH, two of the more important parameters affecting copper toxicity. This application resulted in copper criteria that were potentially under-protective (i.e., not stringent enough) at low pH and potentially over-protective (i.e., too stringent) at higher DOC levels.
By contrast, the BLM-based recommended criterion should more accurately yield the level of protection intended to protect and maintain aquatic life uses. By using the latest science currently available, application of the BLM-derived copper criteria should be neither under-protective nor over-protective for protection and maintenance of aquatic life uses affected by copper. For sites where the hardness criteria may be overly stringent and WERs have been used to develop site-specific criteria, the BLM-based criteria would be expected to result in criteria values similar to the WER-adjusted criteria. In Colorado, WER-adjusted criteria were compared with BLM-derived criteria and the values were similar.
1.12 How are EPA's metals criteria expressed?
EPA's recommended 304(a) criterion for copper (and certain other metals) is expressed as a dissolved metal concentration. This is based on the knowledge that the concentration of dissolved metal better approximates the toxic fraction than does the concentration of total metal.
1 Alkalinity is a measure of the capacity of water to neutralize acids.
2 Hardness is a measure of the concentration of many dissolved ions in water, but principally calcium and magnesium.
3 The WER method is a biological method to compare bioavailability and toxicity in receiving waters versus laboratory test waters. A WER is calculated by dividing the acute
LC50 of the metal, determined in water collected from the receiving water of interest, by the LC50 of the metal determined in standard laboratory water, after adjusting both test
waters to the same hardness. The hardness-based criteria concentrations are then multiplied by this ratio (e.g., the final WER calculated as a geometric mean of two or more
WERs) to establish site-specific criteria that reflect the effect of site water characteristics on toxicity.