Perchlorate is both a naturally occurring and a manmade inorganic chemical. It is used in the manufacture of fireworks, explosives and is also used as rocket propellant. It is predominantly found in areas where the manufacture of rocket propellants took place over the last 50 years. The soil and the groundwater around these facilities in a number of states have been contaminated with perchlorates.

Perchlorates inhibit the absorption of iodine by the thyroid gland causing a decrease in the secretion of some thyroid hormones. Prolonged decrease in thyroid hormones is known to cause developmental and learning disabilities in children. Pregnant women and children are especially susceptible to this problem.

Occurrence

Occurrence of perchlorate contamination in drinking water in the United States has been determined by the U.S. Environmental Protection Agency (EPA) in 3,865 public water systems between the years of 2001 to 2005. Of these 160 systems located in 26 states the EPA detected at least one sample at a level of greater than 4 ppb (µg/L). The highest density of perchlorate was found in southern California, west central Texas, along the East Coast between New Jersey and Long Island and in Massachusetts. No perchlorate has been detected in the drinking water in the northern Great Plains, the central and northern Rocky Mountains, Alaska or Hawaii. Nowhere was the concentration of perchlorate greater than 12 ppb. Today, more than 11 million people have perchlorate concentration in their public drinking water at concentration of at least 4 ppb.

The Centers for Disease Control and Prevention (CDC) study of people all over U.S. showed that all the people tested had a detectable level of perchlorate in their urine.

Health impact

Health impact of perchlorate ingestion in human beings was studied by the National Research Council (NRC) of the National Academies of Science in 2005. Their task was to recommend the maximum concentration of perchlorate that a person can ingest per day without any harm. Based on their analysis and risk assessment, NRC came up with a no-observable-effect level (NOEL) for the inhibition of iodide uptake by the thyroid at 0.007-mg/kg weight per day (also called Reference dose or RfD). Assuming the weight of an "adult" at 70 kg and with a 10-fold safety factor this translates into Drinking Water Equivalent Level (DWEL) or Health Reference Level (HRL) of 24.5 ppb (µg/L). But, since water contributes about 62 percent of the total perchlorate ingested, the rest coming from food, the actual DWEL or HRL should be around 15 ppb. This is the Health Reference Level EPA currently recommends for U.S.

How EPA regulates a contaminant

When EPA wants to regulate a Drinking Water Equivalent Level or Health Reference Level for a chemical contaminant, it then refers to it as a Maximum Contaminant Level (MCL). There are MCLs for many contaminants, such as cadmium, mercury, nitrate and linden. This then becomes a legally enforceable level, the exceeding of which can cause appropriate penalties.

EPA thus regulates a contaminant when it sets a MCL for it. If EPA does not want or is not ready to set a MCL for a certain contaminant, it can then recommend an advisory or interim level (also referred to as a Maximum Contaminant Level Goal or MCLG or Health Reference Level HAL), which is not legally enforceable. Besides the EPA, states have their own regulatory entities that can also set both MCL and MCLG for their state territories.

Current situation

By not setting a MCL, EPA currently does not regulate perchlorate. In 2008, under the Bush Administration, it had come up with a decision to only set an Advisory MCLG level of 24.5 ppb and recommended the individual states to set their own MCL depending upon the occurrence and the level of perchlorate.

Currently, some states such as California and Massachusetts have MCL for perchlorate while some states such as Arizona and Texas operate on an advisory level.

EPA's 2008 decision on not regulating perchlorate came under fire from the scientific and environmental communities. Their objection was that in determining the DWEL or MCLG, the formula uses an adult weight of 70 kg. NRC had identified infants, developing children and people with iodine deficiency or thyroid disorder as a more vulnerable population.

Infants and children eat and drink more on a per-body-weight basis than adults. Therefore, eating a normal diet and drinking water with 15 ppb perchlorate may result in exposure greater than the reference dose for the adults. EPA estimated the effect on sensitive subgroups by using physiologically based pharmacokinetic modeling with certain assumptions, which still did not satisfy certain scientific and environmental communities. Hence under the Obama Administration a decision was made by EPA to revisit the earlier decision, and after due consideration it has reversed the earlier decision not to set the MCL.

The MCL has not yet been announced, pending public comment, but in all probability this MCL can be at a level equal to 4-5 ppb or lower. Anticipating this outcome, the American Water Works Association (AWWA) has vociferously complained about the decision to regulate perchlorate.

Setting of a MCL by EPA would result in public water systems whose water source exceeds the MCL being required to treat all the water that they supply to conform to the limit. This is usually a very expensive proposition and generally requires capital expenditure in building the treatment facility and maintaining it. Nationally, less than 1 percent of all municipalities or public water works will be impacted, if a MCL of 20 ppb (µg/L) were established. A MCL of 2 ppb (µg/L) could impact up to 4 percent of public water systems nationally. Regional impacts in California and Texas would be greater.

Naturally as a voice of national collective public water systems, AWWA wants to ensure that any expenditure of capital and other resources by their members is justified by the public good this decision achieves. So their resistance to the decision on regulating perchlorate by the EPA without further explanation as to how and why this reversal occurred is perfectly justified.

We know that EPA had earlier estimated the impact of perchlorates on the sensitive subpopulation with certain assumptions in making the 2008 decision not to regulate perchlorate. We need to know how these assumptions have changed. That is why EPA is currently seeking comments from various stakeholders. It is reported that EPA developed a new Health Reference Level based on exposure data for infants and children. It is also supposed to undertake a cost benefit analysis of any single value it has chosen. Until all of this information is available, it is hard to make a judgment on whether perchlorate should or should not be regulated.

We have reached a point in the Safe Drinking Water Act where increasingly some of the emerging contaminants are not going to be national in scope, but are going to be confined to some geographical or urban or rural area. Here it does not make sense to have a single national MCL. In such a case, we need to develop a thorough understanding of the health impact of that contaminant both on the general public and sensitive groups and have a flexible regulation at a local level.

This has already happened for perchlorate. Even though EPA has not yet set a MCL for perchlorate for all these years, some individual states such as California and Massachusetts have already set legally enforceable MCLs for their individual states. For the last few years this has been working and unless EPA has new information that suggests greater health risk for infants, children and pregnant women that outweighs the cost of implementation, a national regulation of perchlorate appears to be unnecessary.

One of the challenges we face is the dependence on treatment of all the drinking water by public water systems to eliminate a contaminant. If the contamination requires expensive treatment, it hardly makes economic sense to treat all the water for that contaminant when in actuality only a tiny fraction of it is used for ingestion, with the rest being used for bathing and flushing of toilets. We badly need to shift the treatment of contaminations in water by point-of-use (POU) devices so that we do not incur the high cost of constructing new treatment facilities to treat large amounts of water, when only a fraction of which is used for human consumption.

Technology to treat most of the emerging contamination by POU devices exists today. Regulating a contaminant will then only involve the scientific information on the health impact of that contaminant, without bringing special interest considerations into the decision.

Arvind S. Patil, Ph.D. is the vice president of technology at Ricura Water Technologies LLC — a filtration system and component manufacturer based in Huntersville, N.C. He is a member of NSF Joint Committee for Drinking Water Treatment Devices and is the leader of the Task Group on Perchlorate Treatment. He is also a member of the Government Relations and Water Sciences Committee of WQA.