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NAWQA trace element schedules and selected water-quality criteria

In 1997-98 the Trace Element Synthesis Planning Team (TENSPT) identified a target list of trace elements to be analyzed in ground water, bed sediment, and tissues. With a few exceptions, 1991-start Study Units had analyzed trace elements only in bed sediment and tissues. All 1994-start Study Units analyzed trace elements in sediment and tissues; most also ran trace element schedule 2703, plus seven "add-on" constituents, on their SUS ground-water sites. Schedule 2710 is now a mandatory part of the 1997-start SUS samplings and Cycle II MAS samplings.

The following tables list those constituents and media that the TENSPT has prioritized for national synthesis.

Tables: Ground water | Bed sediment | Tissues

Ground water

Analytes and schedules

NWQL schedule 2710 has replaced schedule 2703 for ground water. Schedule 2710 includes several additional elements (boron, lithium, strontium, thallium, and vanadium), and changes the analytical methods for arsenic and selenium from GF/AA to ICP/MS (resulting in higher precision and lower reporting limits). The new methods are described in:
Garbarino, J.R., 1999, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--Determination of dissolved arsenic, boron, lithium, selenium, strontium, thallium, and vanadium using inductively coupled plasma-mass spectrometry: U.S. Geological Survey Open-File Report 99-093, 31 p.

Standards and criteria

We have selected four types of national drinking-water standards and criteria to compare against national NAWQA data on trace elements in ground water. For the purposes of national analysis, we will not use drinking-water standards or guidelines set by individual states. The standards and criteria on this page were selected according to the following rules:

1. Where available, the EPA maximum contaminant level (MCL) is the primary drinking-water standard to which our data should be compared. The MCL is a regulated level that Class A public water supply systems generally must meet.
2. Copper and lead are regulated according to Treatment Types rather than MCLs. For these elements, the Action Level (ACT, an enforceable drinking-water standard) will be used as analogous to an MCL.
3. For non-carcinogens that have no MCL, we will wherever possible use the EPA health advisory level (HAL) for a 70-kg adult consuming 2L of water per day over a 70-year lifetime. There is no regulatory requirement for public supply systems to meet the HAL.
4. For carcinogens that have no MCL, we will generally use the 70-year-lifetime risk-specific dose (RSD).
5. For elements that have no MCL but have both carcinogenic and non-carcinogenic effects (and so have both an RSD and an HAL), we will use whichever concentration (RSD or HAL) is lower.
6. We will not report any standard or criterion for elements that have no MCL, HAL, or RSD, or for elements whose standards or criteria are based on data not comparable with NAWQA analytical results.
7. Where a standard or criterion is proposed or draft, and not the final rule, it should be referenced in the form '1991 draft MCL' or some similar verbiage.

The EPA Office of Water maintains tables of all current drinking-water standards and criteria, in a PDF file at:
Drinking Water Regulations and Health Advisories (updated semiannually) and an accompanying fact sheet.
Our table of analytes, below, also includes links to EPA's "Consumer Fact Sheets on Inorganics" and "Technical Fact Sheets on Inorganics" for each element.

[ug/L, micrograms per liter; pCi/L, picocuries per liter; - -, no MCL, ACT, HAL, or RSD exists]

¹ On Jan. 16, 2001, EPA finalized a new MCL for arsenic in drinking water, at 10 ug/L. This new MCL is the appropriate level to which to compare NAWQA ground-water data, as 10 ug/L represents the current level deemed protective to the overall population (albeit at an unusually high risk level). However, public water systems serving less than 10,000 customers have a grace period of 5 years (until 1/17/2006) before exceedances of the new MCL are deemed "out of compliance;" the grace period is 3 years for larger public water systems.
Background-- The old MCL of 50 ug/L was set by EPA in 1975, based on a Public Health Service standard originally established in 1942. This old MCL did not take into account arsenic's carcinogenic effects. A March 1999 report by the National Academy of Sciences concluded that the 50ug/L standard should be lowered as soon as possible. On June 22, 2000, EPA proposed a new drinking-water standard of 5 ug/L for arsenic and requested comment on options of 3 ug/L, 10 ug/L and 20 ug/L. Following the comment period, EPA has now set the new arsenic standard for drinking water at 10 ug/L; see the EPA fact sheet on the rulemaking and EPA Project site for more detail.

² Copper and lead are regulated according to Treatment Types rather than MCLs. For these elements, the Action Level (an enforceable drinking-water standard) may be considered analogous to an MCL.

³ Comparing NAWQA gross-alpha and gross-beta results to the EPA MCLs may result in 'false exceedances.' EPA lists MCLs for gross alpha activity (15 pCi/L) and gross beta activity (4 mrem/yr), but these MCLs are based on activity from man-made radionuclides alone (i.e. waste from nuclear power and weapons-testing facilities). NAWQA analyses of gross alpha and gross beta include the man-made radionuclides as well as natural radionuclides (e.g. isotopes of U, Th, and Ra), some of which are strong alpha- or beta-emitters and may greatly increase the gross activity measured.

⁴ EPA lists an MCL of 5 pCi/L for the sum of Radium-226 and Radium-228.

⁵ In 1991, EPA proposed a radon MCL of 300 pCi/L; this proposal was subsequently withdrawn. More recently, EPA has proposed the 300 pCi/L MCL again, along with an alternative MCL (AMCL) of 4,000 pCi/L for those states that create Multimedia Mitigation programs to address radon in indoor air. Both the final concentration and the timing of the final standard are still uncertain. Trace Element Synthesis feels that both the proposed MCL (300 pCi/L) and the proposed AMCL (4,000 pCi/L) should be cited in NAWQA publications.

Bed sediment

We have selected two types of guidelines for comparison with NAWQA trace element concentrations in sediment. The first are sediment-quality guidelines (SQGs) developed by Environment Canada as a screening tool for potentially contaminated fresh-water sediments (MacDonald et al. 1992; CCME 1995). The second, for selenium only, is the "Toxicity threshold" from the National Irrigation Runoff Drainage Program. This "Toxicity threshold" is the value above which adverse effects have appeared in some fish and wildlife species in the western United States due to contaminated sediments. This second (selenium) guideline should be used only by study units in the Western United States, ie. within the Rocky Mountains and further west. The major difference between these two sets of guidelines: the Canadian guidelines are based on toxicological effects of a given concentration to the macro-invertebrate community, while the selenium guideline is based on effects on the vertebrate community as well as for its capacity to bioaccumulate.

In the Canadian guidelines, two concentration levels are listed for each element: the sediment quality guideline (SQG, also called the Threshold Effects Level or TEL) and the probable effects level (PEL). Sediment chemical concentrations below the SQGs are not expected to be associated with any adverse biological effects. Concentrations above the PELs are expected to be frequently associated with adverse biological effects. Concentrations between the SQGs and PELs are above "background", and effects are occasionally observed. NAWQA reports should use the PELs for comparisons and as a screening tool to identify sediment sample concentrations that are likely to be contaminated, either naturally or by human sources. These are not regulatory standards like the USEPA Maximum Contaminant Levels (MCLs) in water. PELs are, however, a useful tool for the indication of potential adverse biological effects.

Canadian sediment quality guidelines (SQGs) for fresh water sediments

[ug/g, micrograms per gram]

Tissues

There are no health standards or aquatic criteria for concentrations of trace elements in fish livers. Methods for comparing trace element concentrations in tissue samples collected by the NAWQA study units are currently being discussed by the Trace Element Synthesis team. Suggestions regarding methods for the comparison of liver, versus whole fish or fillets, much less of data from organisms other than fish, are greatly appreciated.

[ug/g, micrograms per gram]

¹ The methyl-mercury criterion does not apply to Cycle I NAWQA liver data, although some Study Units may have fillets or whole fish data that are appropriate for comparison with the criterion. Bear in mind that the criterion is given as wet weight, so any dry weight analyses will need to be converted before comparison. (The conversion factor from dry- to wet- weight is generally close to 3:1, but varies for each analysis.)
Note that approximately 41 states have established either state-wide or limited-area advisory levels for mercury (total- or methyl-) in edible fish.

² For selenium, we are aware of edible-fish consumption advisories in 5 states (CA, CO, NC, TX, UT). However, there is no national (FDA, etc.) edible-fish advisory for selenium, and these edible-fish advisories do not apply to the standard NAWQA liver data.

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