Perchlorate Emerging as a Likely Arizona Water Quality Issue

Contaminant also poses food safety threat

Perchlorate is an increasingly familiar item in the water quality news of the day. It is, in fact, a breaking story, with work underway to determine at what levels it poses a risk to human health and to what extent the contaminant is present in water supplies and produce.

Further, although an issue of national significance — perchlorate is found in 23 states, mostly in groundwater — it is likely to be of far greater concern in western states. This brings up another angle to the developing story: How will perchlorate as a water quality concern affect Arizona?

The issue of perchlorate as a public health hazard is relatively new. The federal government began assessing its health risks in the mid-1990s. Studies indicate that perchlorate can affect thyroid functions, with the result that normal physical and mental growth in fetuses, infants and children can be disrupted. Also exposure to perchlorate can impair adult metabolism and cause thyroid tumors.

Perchlorate is a component of solid rocket fuel and also is used in roadside flares, air bag inflaters and in the manufacture of matches. It is highly soluble in water. Military bases, aerospace installations and defense contractors building rockets are the primary sources of perchlorate contamination.

The perchlorate contamination of the lower Colorado River is traced to a chemical manufacturing facility located outside of Las Vegas, with the contaminant entering Lake Mead and the lower Colorado River from Las Vegas Wash. From this single-source, perchlorate has become a contaminant to be reckoned with for all downriver users of Colorado River water.

The issue of perchlorate contamination therefore looms more largely in the West than in other parts of the country. In other areas, perchlorate is more likely to have contaminated groundwater, with its effects greatest on those drawing water from a particular aquifer. In the West, the lower Colorado River is the source of the contaminant, a river managed to provide maximum use of its waters, for irrigation and for drinking water throughout the region. This puts an estimated 15 to 25 million people in the region at risk from the contaminant including Arizona water users.

Fruits and vegetables produced in this region are distributed nationally and internationally further expanding the number of people potentially exposed to perchlorate. Along these lines a recent Texas Tech University study raised new concerns about perchlorate by finding the contaminant in milk. Much of the dairy feed in the West is produced with Colorado River water.

Perchlorate is generally acknowledged as posing a health threat. What is not generally acknowledged is an appropriate maximum contaminant level (mcl) for perchlorate. How much is safe? Establishing this figure is key to determining a suitable regulatory path. Complicating the task are the widely varying figures that have been proposed, from a 2002 U.S. Environmental Protection Agency draft assessment suggesting a health-protective standard of 1 part per billion (ppb) to some defense contractors’ contention that a level as high as 200 ppb would be plenty safe. The controversy prompted the Bush Administration to request the National Academy of Sciences to review the data and suggest a range for a drinking water standard.

Whatever perchlorate standards currently exist have been worked out by states patchwork fashion, with eight states having adopted advisory-standards. Three of those states draw water from the lower Colorado River: California, Arizona and Nevada. Nevada’s standard is 18 ppb. California is in the process of working out a standard, to be issued some time in 2004, probably before a federal standard is adopted. The state is looking at a range of between 2 to 6 ppb. Arizona has a 14 ppb standard.

Arizona’s 14 ppb perchlorate standard is an advisory health based guidance level or HBGL. This is in effect a non-enforceable advisory level. The Arizona Department of Health Sciences worked out the perchlorate HBGL through a risk assessment calculation. Initially the DHS came up with a 31.5 ppb based on adult exposure assumptions, later revising it to a 14 ppb to reflect children’s higher contaminant intake rates per body weight.

The Arizona Department of Environmental Quality is presently tracking the monitoring efforts of utilities using Colorado River water and awaiting the results of NAS deliberations. EPA’s unregulated contaminant monitoring rule requires that water systems serving more than 10,000 people monitor for perchlorate, with only a sampling of systems serving fewer than 10,000 needing to monitor.

Jeff Stuck, ADEQ safe drinking water sections manager, says, “We are helping to gather the information, keeping track of the results and comparing those results with our HBGL, looking for any points where we find the results in excess of the HBGL. It hasn’t occurred yet.”

Monitoring efforts along the mainstem of the Colorado River recorded perchlorate concentrations ranging from nondetection up to nine. In 1999, ADEQ monitored CAP canal water and found perchlorate concentrations of between 3 and 9 ppb.

ADEQ is looking to the results of the NAS review of the EPA risk assessment for guidance. Stuck says, “We are closely watching the NAS activities, to see what its findings are and then use that information as we move forward on further decisions.”

It (perchlorate) could be an issue in the state depending on what NAS comes up with in its review and how that translates into a risk assessment under EPA’s authority. That will tell us whether our utilities are confronting an issue.”

Charles Sanchez, director of the University of Arizona’s Yuma Agricultural Center, is studying the occurrence of the perchlorate in the state, in both water supplies and irrigated crops. He says, “It is a complicated issue, a water quality issue having food quality implications.”

Like many other researchers now studying perchlorate Sanchez got started relatively recently. He says, “It came on my radar screen about four years ago, from the implications of an EPA greenhouse study that lettuce accumulated perchlorate passively.”

Sanchez subsequently sampled various kinds of lettuce irrigated with Colorado River water to determine the presence of perchlorate. He found that in head lettuce most of the perchlorate was in the wrapper or frame leaves that are discarded, with little present in the edible portion. He says, “When we moved on to other kinds of lettuce like leaf and romaine we are finding more frequent hits in the edible portions.”

He also sampled sweet corn, tomatoes, peppers and cantaloupes. He says, “We are finding trace amounts in some of the fruiting crops, but mostly below our limits of quantitation.”

Sampling water at the Imperial Diversion of the Colorado River where over 4.2 million acre feet of irrigation water is diverted, Sanchez has found perchlorate in the range of 5 to 7 ppb.

Any possible perchlorate problem with lettuce could have adverse economic effects in the state. Lettuce is a prime cash crop, and a decline in sales would have an impact on the state’s agricultural community.

Sanchez has teamed up with toxicologist Bob Krieger from the University of California, Riverside, with Krieger working on exposure assessments, to find out how much perchlorate a person might be exposed to by eating produce that has been tested and found to contain the contaminant.

Krieger says, “We are using the amount of perchlorate established as a maximum contaminant level in drinking water as a standard. We estimate the exposure from the produce relative to the amount in water.” The mcl figures represent no-effect levels since they are the upper limits of a safe drinking water range. Water with perchlorate levels up to these figures is presumed safe, with no health effects.

Figuring that a person drinks two liters of water per day, Krieger then estimates the exposure from the produce relative to the amount in the water. He says he looks at different population groups with characteristic consumption patterns. “There is a lot of data for the consumption of various commodities. ... We can make age specific determinations; in some cases even geographical ones.”

Summarizing his research thus far Krieger says, “I can tell you categorically we have no alarming information, nor any information with toxicological implications.”

Krieger and Sanchez are now working on a more thorough survey, with more extensive sampling. They anticipate similar results.

Sanchez also wants to look into the extent that perchlorate has contaminated groundwater sources in the lower Colorado River region. He says, “We have no data to indicate to what extent groundwater sources have been tainted through their interaction with surface waters.” He says such a study would have broad implications for other areas in the western United States that are recharging Colorado River water.

Sanchez and coworkers are also seeking funds to study biotic and abiotic factors affecting the transport, transformations, and distribution of perchlorate in the environment.

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