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Arsenic and Old Laws
A Scientific and Public Health Analysis of Arsenic Occurrence in Drinking Water, Its Health Effects, and EPA's Outdated Arsenic Tap Water Standard

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Arsenic in drinking water poses a significant public health risk in the United States. According to our most conservative analysis of new EPA data covering only 25 states, at least 34 million Americans in over 6,900 communities drank tap water supplied by systems containing arsenic, a known toxin and carcinogen, at average levels that pose unacceptable cancer risks.[1] Our "best" estimate, based on what we believe to be the most reasonable (but less conservative) analytical techniques, indicates that 56 million Americans in over 8,000 communities in those 25 states drank water with arsenic at these risky levels.[2]

These newly public figures are based on more than 100,000 arsenic samples collected from 1980 to 1998 by more than 24,000 public water systems in 25 states, which were then compiled by the U.S. Environmental Protection Agency (EPA). The Natural Resources Defense Council (NRDC) obtained the data under the Freedom of Information Act and analyzed them. While arsenic levels can vary with time, when considering cancer risk, the average levels generally are of primary concern. For this reason, NRDC calculated average arsenic levels in the systems evaluated. Because data were available for only half of the states in the nation, these are likely to be significant underestimates of the total U.S. population exposed to arsenic in tap water.

NRDC also has generated maps for this report showing the geographic distribution of arsenic problems for all 25 reporting states. This marks the first time that EPA’s drinking water database has been publicly analyzed using a Geographic Information System (GIS) to generate maps of drinking water problems.

This report includes a summary of the adverse health effects of arsenic in drinking water by an eminent expert on the subject, based upon a 1999 National Academy of Sciences (NAS) report and a review of peer-reviewed literature. The NAS report and other scientific literature discussed here have concluded that arsenic in drinking water is a known cause of bladder, lung, and skin cancer. In addition, the NAS report and many previous studies have found that arsenic in drinking water may also cause kidney and liver cancer.

Arsenic’s known noncancer toxic effects include toxicity to the central and peripheral nervous systems, heart and blood vessel problems, and various precancerous lesions on the skin, such as hyperkeratosis (a pronounced scaly skin condition) as well as changes in pigmentation. The NAS report and peer-reviewed animal studies have found that arsenic may also cause birth defects and reproductive and other problems, although some of these effects are less documented than arsenic's cancerous, skin, nervous, and cardiovascular effects.

The NAS concluded in 1999 that EPA’s 57 year-old arsenic standard for drinking water of 50 parts per billion (ppb), set in 1942 before arsenic was known to cause cancer, "does not achieve EPA’s goal for public health protection and, therefore, requires downward revision as promptly as possible" (NAS, 1999, p. 9). In fact, the academy said that drinking water at the current EPA standard "could easily" result in a total fatal cancer risk of 1 in 100 -- about a 10,000 times higher cancer risk than EPA would allow for carcinogens in food, for example.


  • EPA must immediately adopt a strict, health-protective standard for arsenic in tap water. The Safe Drinking Water Act (SDWA) Amendments of 1996 required EPA to propose a revised arsenic standard (to replace the old standard set in 1942) by January 1, 2000, a deadline the agency has missed. This is the third time EPA has violated a statutory mandate to update the arsenic standard. EPA is required to finalize a new standard by January 1, 2001. We conclude -- as did NAS -- that EPA should expeditiously issue a stricter Maximum Contaminant Level standard for arsenic. EPA must consider that many Americans also have unavoidable exposure to arsenic in their food, so relatively low levels of arsenic in tap water can cause safety levels to be exceeded. A health-protective tap water arsenic standard should allow a maximum lifetime cancer risk no greater than that EPA has traditionally accepted (a level presenting a lifetime cancer risk from 1 in 1,000,000 to at most 1 in 10,000 for vulnerable or highly exposed individuals).

    This would require EPA to set a drinking water standard well below the current 50 ppb standard -- in the range of 1 ppb. Limitations in the analytical techniques widely used for measuring arsenic in water, however, would likely necessitate a standard of 3 ppb, rather than a standard of 1 ppb, because reliably quantifying arsenic at levels below this would be difficult using current standard lab equipment and practices. Based on an extrapolation of NAS's risk estimates, even a relatively strict arsenic standard of 3 ppb could pose a fatal cancer risk several times higher risk than EPA has traditionally accepted in drinking water. EPA data, which the agency recently said probably overestimate costs, indicate that the cost per household of a 2 ppb standard would be from $5 to $14 per month for the vast majority (87 percent) of affected consumers; users of small systems may have to pay significantly more. EPA’s (admittedly high) estimates also project that nationally an arsenic standard of 2 ppb would cost $2.1 billion per year, and a 5 ppb standard would cost $686 million per year.

  • EPA should reduce its cross-media guidance level for arsenic and should fund improved analytical methods to lower detection limits for arsenic. Health data indicate that EPA's current guidance level establishing the maximum recommended daily arsenic exposure, called a reference dose (which is unenforceable itself, but is used by EPA in developing enforceable standards in all environmental media, including water), is too high and may not protect vulnerable populations, such as children. To protect children, EPA should reduce this reference dose from 0.3 micrograms per kilogram per day (µg-kg per day) to at most 0.1 µg-kg per day, and should immediately reevaluate the reference dose in light of the 1999 NAS risk estimates, suggesting that the cancer risk at this level would still be unacceptable. In addition, EPA should fund efforts to reduce the level at which arsenic can be reliably detected in drinking water, so that it can be found down to levels at which it may pose a health risk (below 1 ppb).

  • Water systems should be honest with their customers about arsenic contamination and potential health risks. Only if water systems tell their customers the truth about arsenic contamination in their tap water, and about the health threat it poses, will the public support efforts (including possible rate increases) to remedy the problem.

  • Systems with arsenic problems should work with government officials to clean up their source water. Some systems may be able to reduce arsenic levels by cleaning up or changing the source of their water. For example, some arsenic contamination results from leaching of arsenic from old waste dumps, mines, or tailings, or from past use of arsenic-containing pesticides. Government officials and water systems should team up with citizens to remedy contamination at these sites so water supplies are not arsenic-contaminated. In addition, recent studies have shown that high groundwater pumping rates have increased arsenic levels in some wells. It should be investigated whether reducing pumping rates or reworking wells can reduce some systems’ arsenic levels.

  • Water systems unable to get cleaner source water should treat to remove arsenic; state and federal funds should be increased to assist smaller Systems in paying for upgrades. As noted above, there is readily available treatment technology that can remove arsenic from tap water, at a cost of about $5 to $14 per month per household for the vast majority of people (87 percent) served by systems with arsenic problems. Very small systems serving a small fraction of the population drinking arsenic-contaminated water, however, will often be more expensive to clean up per household (due to the lack of economies of scale). For these systems, federal and state assistance to improve treatment is available, and arsenic contamination should be a high priority for these drinking water funds. Additional federal and state funding through State Revolving Fund (SRF), USDA's Rural Utility Service, and other programs may also be needed. The SRF established by the SDWA Amendments of 1996 should be funded at least to the full authorized amount ($1 billion per year) to help smaller systems with arsenic problems.

  • EPA should improve its arsenic and other drinking water databases. EPA should upgrade its drinking water database, known as the Safe Drinking Water Information System (SDWIS) so that it includes all of these arsenic data, as well as unregulated contaminant data, as required by the Safe Drinking Water Act -- and makes them accessible to the public. The SDWIS database must also be upgraded to include more accurate latitude and longitude ("lat-long") data. The ready availability and low cost of new GPS (global positioning system) units for recording lat-long coordinates -- available for a few hundred dollars -- should drive EPA to require accurate lat-long data for the distribution systems, treatment plants, and intakes of each public water system. Such data will have a wealth of uses for water systems, state and local officials, EPA, and the public in using GIS systems for protecting source water, for developing targeted and well-documented rules, and for other purposes.


1. The phrase "unacceptable cancer risk" is used here to mean water containing arsenic at a level posing a lifetime risk of dying from cancers in all internal organs -- bladder, kidney, liver, and lung -- of over 1 in 10,000, based on the methodologies, estimates, and cancer risk characterizations described in the National Academy of Sciences’ recent report, Arsenic in Drinking Water, at 8, 301 (1999), and based on the standard assumption that a person consumes two liters of water per day. A 1 in 10,000 cancer risk traditionally is the highest cancer risk EPA ever allows in tap water when setting standards, although the agency usually seeks to set standards at a stricter level, posing a lower cancer risk. See Chapters 1 and 2 for details.

2. As discussed in Chapter 1, the 56 million population exposed figure is our best estimate of the average arsenic exposure levels of consumers in the 25 states included in the new EPA database analyzed in this report. While this analysis is conservative (it may underestimate the extent of exposure), an even more conservative analysis would suggest that a minimum of 34 million people in these 25 states drank water posing a significant cancer risk. The latter highly conservative low average estimate assumes, when calculating average arsenic levels, that no arsenic was in the water at times when early crude tests with a high reporting limit of, for example, 10 ppb, found none, even though subsequent more sensitive tests found arsenic. On the other hand, the mid-average approach assumes that arsenic was present at half the reporting limit if, in some tests, arsenic was not detected using a high reporting limit, and other more sensitive tests found arsenic. See Chapter 1 for details.

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