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Overcome by Dishwashing
April 29, 2005
Trevor Butterworth
Cancer panic over U.S. research showing chlorine and antibacterial soap produce chloroform; toothpaste pulled from British department stores.

In the past few weeks, a cancer scare has traveled around the world - and it all started in a kitchen sink in Virginia.

Peter Vikesland, an environmental chemist at Virginia Tech, discovered that in some cases, the chlorine in water interacted with triclosan, an antibacterial agent in some soaps, to produce chloroform. Though the conditions for this happening were experimental – the amount of both chemicals and the acidity and temperature of the water were all controlled factors in the reaction – the possibility existed that they could be replicated in a normal household kitchen sink.

Not that this portended people keeling over while washing dishes: the amount of chloroform was nowhere near that required to simulate a movie-style kidnapping. In fact, the actual amount of chloroform likely to be absorbed either by inhalation or through the skin in a real-life sink reaction is unclear. But because the Environmental Protection Agency (EPA) classifies chloroform as a probable human carcinogen, it was a story primed to deliver a hysterical reaction somewhere.

As it turned out, ground zero for this antibacterial apocalypse was, unsurprisingly enough, Britain, which employs more journalists turning scientific data into omens of doom than any other modern post-Enlightenment society. “Researchers have discovered that triclosan, a chemical in the products, can react with water to produce chloroform gas. If inhaled in large enough quantities, chloroform can cause depression, liver problems and, in some cases, cancer,” reported The Evening Standard (15 April 05).

“An Evening Standard investigation found dozens of products on supermarket shelves containing the chemical, from brand names including Colgate, Aquafresh, Dentyl and Sensodyne. Marks & Spencer confirmed today it was removing products containing triclosan from all its stores and has been working with Greenpeace to develop alternative products. Asda said it was investigating the problem and would be urgently talking to its suppliers. Giles Watson, a toxicology expert at wildlife charity WWF, warned that the long-term effects of exposure to chloroform were still unknown and advised consumers to check the bottles before buying products.”

Then it spread to Israel. The Jerusalem Post warned that:

“…those scrubbing away for hours for Pessah should be informed about a new study by researchers at the Virginian Institute of Technology who say the use of antimicrobial soaps and other products may unnecessarily be directly exposing consumers to significant quantities of chloroform. (17 April 05)”

Then it was China’s turn. As the China Daily News observed (20 April 05):

“An international cancer scare over anti-bacterial soap and toothpaste is being investigated by Chinese authorities. Research carried out by a professor in the United States found chlorine in tap water and the bacteria-busting chemical triclosan in some soaps and other products can react together to create the probable carcinogen chloroform.”

However, Chinese journalists were a little more circumspect about the risk:

“Professor Wu Weikai of the China Centre for Disease Control and Prevention yesterday said he believed the risk posed by use of the toothpaste is almost "negligible," as in toothpaste triclosan is only present in very small amounts, and the chloroform produced when it is mixed with chlorinated water is also minimal.”

The most bizarre aspect of this health scare is that it had major supermarket chains in Britain scrambling to remove toothpaste from store shelves. The thing is, triclosan and chlorine only produced chloroform in Vikesland’s experimental sink when the water was 40 degrees celsius – which is hot enough to facilitate removing grease and be bearable to human skin. How many people clean their teeth using water the same temperature as they would to wash dishes?

Here’s the rub
Chloroform is actually a byproduct of chlorination, the most effective chemical way of ensuring our drinking water is safe from potentially lethal microbial agents. Chlorination is responsible for largely or entirely eliminating such infectious diseases as cholera, typhoid, dysentery, and hepatitis A.

But the upshot of being protected from diseases which still claim millions of lives each year in the developing world is that we are actually exposed to trace amounts of chloroform in drinking water – and have been since 1908, when chlorination was first introduced.

The EPA considers chloroform a probable human carcinogen on the basis of rodent studies. But this is like one of those automated “out-of-office” responses you get when you send an e-mail to someone on vacation. Any substance that can be shown to cause cancer in an animal automatically gets labeled a ‘probable’ human carcinogen.

There is, however, a caveat: there has to be no evidence to suggest that the cancer risk is non-linear. A linear risk means that as the degree of exposure decreases, the risk of cancer decreases – but does not wholly disappear. Many health activists believe that the risk from all carcinogens is linear. Most toxicologists, on the other hand, understand that risk can be linear or non-linear. A non-linear risk means that there is a threshold below which trace amounts of the chemical will have no adverse effect.

In 1998, the EPA examined the risk from chloroform in water and looked at research by a panel of experts under the auspices of the International Life Sciences Institute. The research, which was peer-reviewed, concluded that the cancer risk from chloroform was non-linear: it caused cancer through damaging cells (cytotoxicity), but not through damaging the cells’ DNA (genotoxicity). This means that at exposure levels below a certain threshold, cell damage is repairable.

As a consequence of this research, the EPA set a maximum safe dosage for chloroform in water at 300 parts per billion (ppb), a level that also takes into account evidence of liver toxicity in animals. The level for cancer alone is 600 ppb – a figure, it should be noted that has a 1000-fold safety margin. (When the EPA tried to keep the legal limit for chloroform in water at zero, the agency was reprimanded by a federal court for ignoring its own scientific research without having any legitimate scientific grounds for doing so.)

Back to the kitchen sink
Vikesland’s experiment to see how much chloroform would be produced in typical dishwashing conditions resulted in chloroform levels of 50ppb, which is six times lower than the EPA’s maximum safe dosage.

Even if someone were to be chained to the kitchen sink, the key question is whether they would be likely to absorb the chloroform at these levels. The study warned that “the potential exists for substantial chloroform production to occur via daily household use of triclosan-containing products;” but, crucially, it did not try to examine whether the chloroform could be inhaled or absorbed by an unwitting dishwasher.

Vikesland’s research is certainly interesting, and it points to the problem of unintended reactions among common household chemicals. But there are few reasons to conclude that anyone is putting their health at serious risk from using antibacterial soap and hot water. “I think people are jumping to conclusions,” Vikesland told the Roanoke Times. “There isn’t a huge need to worry at present.”

Of course, Virginia Tech didn’t help matters by putting out a press release that overstated the risk, viz, “Being too clean can be hazardous to your health and the environment.” But this is a well-established trend when it comes to publicizing academic studies: hook the press in with a catchy synopsis or headline, and then leave it to the reporters to find out that things aren’t quite so clear cut in the study itself. Except that they don’t.