I've been hearing about perchlorate in the news. What is it?

Perchlorate is a man-made compound used in the production of solid rocket fuel, fireworks, air bags, and munitions. It is odorless, colorless and tasteless and can form either an acid or salt in combination with other elements such as sodium or ammonium. Perchlorate is soluble, mobile in ground and surface water and degrades slowly in the environment.

What is perchlorate used for?

Perchlorate is a compound made up of chlorine and oxygen. Perchlorate salts, which have been used in propellants for rockets and missiles since World War II, have a relatively short shelf-life and therefore must be replaced periodically. This has resulted in large volumes of perchlorate being disposed of since the 1950s. Past outdated or improper disposal practices may have allowed perchlorate to contaminate both ground and surface water supplies.

Why has this suddenly become an issue?

In the southwest, perchlorate has been manufactured at two facilities near Henderson, Nevada - Pacific Engineering & Production Company of Nevada and Kerr-McGee Chemical Corporation - from World War II to the present. Considerable amounts of perchlorate were discharged in the liquid wastes from the facilities into unlined evaporation ponds. As a result of continuous percolation of perchlorate contaminated water into the underlying aquifer, the groundwater in the vicinity of the industrial complex has been contaminated. The groundwater contaminated with soluble ammonium perchlorate has been seeping into the Las Vegas Wash which drains into Lake Mead and ultimately into the Colorado River as it flows through Hoover Dam. First discovered in 1997 by Metropolitan Water District of Southern California, detectable concentrations of perchlorate have been found from Lake Mead to Yuma.

Is perchlorate a problem in Arizona?

Perchlorate has been found in Arizona at several industrial sites around military bases and at facilities catering to the defense and the aerospace industry. These sites are contaminated with perchlorate and other pollutants. ADEQ's Waste Programs Division has remediation oversight for these facilities which include: Navajo Army Depot at Bellemont; Apache Nitrogen near St. David; and Universal Propulsion and Phoenix-Goodyear Airport facilities in the metropolitan Phoenix area.

Low levels of perchlorate have also been found in some drinking water supplies which use Colorado River water as source water. In 1999, ADEQ directed a monitoring effort throughout the state and the Southwest. The study consisted of 112 samples collected from numerous locations including Lake Mead, the Colorado River mainstem, the Central Arizona Program (CAP) canal, groundwater recharge projects and community drinking water supplies. Results showed levels ranging from 480 parts per billion (ppb) in Lake Mead to between 4 ppb (the analytical detection limit at that time) and 11 ppb throughout the state. Because a significant amount of Colorado River water has been used for irrigated agriculture and recharged into the aquifer prior to the discovery of the perchlorate contamination and initiation of remediation activities, officials simply don't know whether perchlorate contamination is an issue in Arizona.

Remediation actions undertaken at the Nevada site have significantly reduced the levels of perchlorate in mainstem Colorado River water. Latest results from Willow Beach, Arizona, located just downstream of Hoover Dam, suggest that levels are now in the 4-6 ppb range. Both Arizona and California withdraw Colorado River water from Lake Havasu and deliver it inland for use in agriculture, municipal and industrial uses, as well as store it for future use in underground storage facilities and groundwater savings facilities permitted by the Arizona Department of Water Resources. Many communities along the river also withdraw water directly from the Colorado for domestic and agricultural uses.

What are the health effects from perchlorate?

Studies indicate that perchlorate disrupts iodine uptake in the thyroid gland which regulates hormone function. The thyroid gland helps regulate metabolism and in children it plays a major role in growth and development. Pregnant women and children are most vulnerable to the effects of perchlorate. Even though a form of perchlorate has been used to treat Grave's Disease, a disorder also known as hyperthyroidism which causes an overproduction of thyroid hormones, its use in medicine has been declining over the past few decades due to potentially negative or irreversible side effects such as aplastic anemia and bleeding disorders.

In 2003, perchlorate was found in the outer leaves of leafy vegetables grown in the Yuma area (e.g., lettuce). A study in Texas also revealed concentrations of perchlorate in milk, suggesting that perchlorate may be taken up in feed given to dairy animals. Studies are ongoing to determine the variation in uptake by various crops and what levels of consumption are safe for humans.

Is it safe to drink water with perchlorate?

Currently, there is no federal or Arizona state drinking water standard (or Maximum Contaminant Levels - MCLs) for perchlorate (see Safe Drinking Water Act ). A provisional federal health-based guideline developed by the U.S. Environmental Protection Agency in 1992 suggested concentrations of perchlorate in water ranging from four to 18 ppb would not pose a risk to human health. Based upon available research, Arizona has established a protective health-based guidance level for drinking water of 11 ppb. Drinking water at or below this concentration is believed to be safe for consumption.

What about swimming or showering?

Perchlorate is not well absorbed through the skin, therefore showering and bathing with water containing low levels of perchlorate should not be hazardous.

What is being done?

The U.S. EPA, the Nevada Department of Environmental Protection, Kerr-McGee and others are actively managing the Henderson, NV site and monitoring for perchlorate downstream in Lake Mead and the Colorado River. Perchlorate levels in Las Vegas Wash, Lake Mead and in the Colorado River have begun to decrease but final clean up will take many years.

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