09/11/2003
Pinholes and Perchlorates
Last week I mentioned the fact that the word plumbing derives from the Latin word for lead, plumbum. Pb, the chemical symbol for lead, is also derived from the same word. Many older homes still have plumbing containing lead and one is advised to allow the water to run for a while before drinking so as to flush out any lead that might have dissolved overnight. In newer and in replumbed older homes, a popular plumbing choice is copper.
Now it seems that there is trouble in copper land, especially in copper-piped homes in central Maryland. According to an article by Louisa Wray Dalton in the August 18 issue of Chemical and Engineering News (C&EN), residents of central Maryland are suffering a rash of pinhole leaks in their copper plumbing. A pinhole leak may not sound serious but the article cites the case of one resident who, after spending some $13,000 on repairs, had to replumb her whole house! Could this be a harbinger of a nationwide epidemic of pinhole leaks? Marc Edwards, of Virginia Polytechnic Institute and state University, thinks we may be in the midst of a “catastrophic” pinhole problem in the U.S. Edwards, a corrosion researcher, gets continuing calls concerning pinhole leaks from residents in states ranging from Alaska to Florida.
I paid a visit to the Web site of the Washington Suburban Sanitary Commission, the water utility that supplies about a half million customers in the Maryland area. This water company takes pinhole leaks quite seriously. On the site you can read a letter, dated December 18, 2002, from the commission to Christie Whitman, then head of the Environmental Protection Agency (EPA), expressing their concern about the problem. In fact, the letter suggests that an EPA regulation meant to clean up our water may inadvertently be one of the causes of pinhole leaks. The letter points out that these leaks not only can result in costly repairs but also can be a source of mold and of increases in the cost of or even cancellation of home insurance policies.
There is nothing unusual about water pipes corroding. However, the typical corrosion is of a uniform variety in which the corrosion product or products form a film or coating that blocks or drastically slows down further corrosion. In a recent column we touched on an example of beneficial corrosion, the oxidation of aluminum. Aluminum oxidizes (corrodes) to form a very thin aluminum oxide film that is super protective and tough, blocking further oxidation. Otherwise, aluminum, being quite reactive, would just keep corroding away and aluminum objects ranging from baseball bats to airplanes would be useless.
Pinhole corrosion is another matter. You might have just a pinhole or two in a hundred feet of piping. And duplicating pinhole corrosion in the lab is not easy. According to the C&EN article, Edwards and his students spent 8 years trying. Finally, last year, he and a student, Jason Rushing, found a set of three conditions that did the trick with a vengeance. If chlorine, commonly added to water to keep bacteria at bay, is present between 0.5 and 2 milligrams per liter and if aluminum is also present at between 10 and 500 parts per billion and if the pH is between 8.2 and 10, experimental copper tubes corroded like crazy. For those not familiar with pH, this range corresponds to alkaline solutions.
The alkaline part is somewhat surprising. Typically, acidic conditions are associated with corrosion and, in the past, water utilities encountering corrosion problems tended to deliberately make the water more alkaline. How does the EPA enter the picture? Back in 1991, EPA formulated a so-called “Lead and Copper Rule” designed to cut down leaching of copper and lead into the drinking water. The rule was targeted at uniform corrosion, not pinhole leaks and in some cases the rule mandates raising the pH.
Water also contains “natural organic material” (NOM). The EPA also ruled that the water utilities should make an effort to get rid of NOM. Why? The organic material can react with chlorine in the water to form carcinogenic compounds. The only problem is that NOM tends to coat the pipes and block corrosion. How do you get rid of NOM? One approach is to precipitate it out using a coagulant. But a popular coagulant used in the water industry contains aluminum! So, in attempting to better the environment and make our water more fit to drink, we’ve added chlorine and aluminum and raised the pH. Everything leads to the conditions Edwards and student found to promote pinhole corrosion!
How to correct the problem? Many water utilities are adding a known corrosion inhibiter, orthophosphate. If you’re worried about the addition of another chemical to your drinking water, take heart. You’re already imbibing roughly a thousand or so milligrams of orthophosphate a day from all manner of foods ranging from soft drinks to cereals to cured meats to dairy products. The water company in Maryland is talking the adding of a milligram of orthophosphate per liter of water. If you drink a couple liters a day, it’s only a couple milligrams of phosphate, a tiny fraction of your current intake. Ironically, after adding the phosphate to the drinking water, the company is required to take it out of wastewater to the tune of about $300,000 a year! Nothing is simple these days.
If pinhole leaks don’t concern you, perhaps you should be concerned about the lettuce you’re eating and what’s in the water in the lower Colorado River. Another article, by Cheryl Hogue in the same issue of C&EN, is titled “Rocket-Fueled River” and deals with perchlorates. Perchlorates are a class of compounds that have many uses, notably in rocket fuels, matches, flares, airbag inflators, etc. I used lithium perchlorate as an electrolyte in my lithium battery studies at Bell Labs.
Here we’re concerned with perchlorate that originated from two plants outside Las Vegas that were involved in manufacturing perchlorate salts during the latter half of the 20th century. One of the plants blew up in 1988, killing 2 and injuring 300 people. Perchlorate can be dangerous! It is estimated that the operations of these plants have resulted in plumes of shallow groundwater contaminated with over 20 million pounds of perchlorate in some 18 billion gallons of water – big numbers indeed!
Today, hundreds of pounds of perchlorate flow every day into the lower Colorado River. Among the cities that get a goodly share of their water from the lower Colorado are Phoenix, Tucson and San Diego. The water is also used to irrigate large areas of California that grow the lettuce and other vegetables shipped all across the country. Perchlorate has been found in the lettuce grown in these areas. Chances are good that we’ve all eaten some of that lettuce.
How much of a health problem does perchlorate pose? To date, there are no federal standards. It is known that perchlorate can interfere with the uptake of iodine, thus affecting thyroid functioning. This can be a problem for fetuses and newborns. Members of the Torrez Martinez Indian (Native American) tribe on a reservation in the lower part of California are prone to hypothyroidism, which means that the thyroid doesn’t produce the normal amounts of hormones. These individuals are at increased risk in the presence of perchlorates and, needless to say, are not happy with the contamination of their water supply.
Efforts are being made to address the perchlorate pollution problem but at the current rate of remediation, it will take over two decades to clean it up. Meanwhile, the EPA has to come up with safe levels for perchlorates in our water. From pinhole leaks to perchlorates, the EPA is under the gun. Our state of New Jersey’s former governor, Christie Whitman, should be breathing a sigh of relief that she no longer has the responsibility for either the EPA or, in these times of budget deficits, our state!
Allen F. Bortrum
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