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One of the more common types of cancer is bladder cancer, accounting for about 68,000 cases a year in the USA, with an annual mortality of about 14,000. Although the exact causes of the disease remain a mystery, there are a series of risk factors that influence the likelihood of a particular person developing bladder cancer. These include age, the use of tobacco, occupation, gender (men three times more likely than women) and race (whites twice as likely as African Americans or Hispanics). In spite of these factors, the US National Cancer Institute notes that "most people with known risk factors do not get bladder cancer, and many who do get this disease have none of these factors." It also comments on the ongoing search for a link between chlorinated drinking water and the occurrence of bladder cancer, declaring that there is no proof, as yet, that chlorination causes cancer. However, recent epidemiological studies have suggested that there is an increased risk of bladder cancer associated with chlorinated drinking water and swimming pools, although the chemical agents responsible have not been identified. Now, scientists from the Department of Chemical Engineering at Yale University have proposed that nitrosamines might be the perpetrators. William Mitch and Spencer Walse pointed out that nitrosamines are highly carcinogenic to bladder tissue and are employed as biomarkers of human bladder cancer. Appropriately, they have recently been found in water that had been disinfected with chlorine. If they are in chlorinated drinking water, then they could well be produced in chlorinated swimming pools too, subjecting swimmers to the risk of exposure. The researchers tested their hypothesis by examining water from 27 public pools: 6 hot tubs, 8 indoor swimming pools, 9 outdoor pools, 1 indoor/outdoor pool and 3 outdoor aquaria for sea lions, whales and penguins. The majority of the pools had been disinfected with sources of free chlorine such as hypochlorite. Others were treated with UV light/free chlorine, bromochlorodimethylhydantoin, or ozone/free chlorine. The levels of N-nitrodimethylamine and 7 nitrosamines, including the highly carcinogenic N-nitrosodimethylamine (NDMA) were measured by GC/MS/MS with positive chemical ionisation using methanol as reagent gas in an ion trap mass spectrometer. Their protocol followed EPA Method 521 for the measurement of nitrosamines in drinking water. The water samples were passed over an SPE cartridge containing coconut charcoal and the analytes eluted with dichloromethane. Following the addition of a deuterium-labelled nitrosamine internal standard, the solutions were analysed. The nitrosamines were quantified by comparing the product ion responses with that of the internal standard. NDMA was the most abundant nitrosamine detected, its amount varying significantly between the different types of pool. Indoor pools contained about 6 times more NDMA (32 ng/L median) than outdoor pools (5.3 ng/L), whereas those in hot tubs were about 10-fold higher (313 ng/L) than those in indoor pools. Although these levels may seem low, they are approximately 500-fold greater than the level in drinking water (0.7 ng/L) that is associated with a one-in-a-million lifetime cancer risk. Of course, the routes of exposure to chemicals in drinking and swimming water are quite different, but swimmers can still be at risk from several routes, including skin absorption, inhalation and ingestion. The effects of pool environment on NDMA levels were also considered. The lower concentrations in indoor pools appear to correlate with the suppression of NDMA destruction routes, such as sunlight photolysis, since the indoor/outdoor pool with a retractable roof had an NDMA level between those of the indoor and outdoor pools. The higher temperatures of the hot tubs also appeared to raise levels of the carcinogen. The NDMA concentration in an outdoor penguin pool was 88 ng/L, far higher than the average value for outdoor swimming pools. This was attributed to the fact that there were greater amounts of amine precursors in the penguin pool from animal urine, leading to more NDMA formed. The actual identities of these precursors in the swimming pools and hot tubs remain unknown. One of them is likely to be dimethylamine, because it is a component of human urine and sweat. Similarly, trimethylamine from urine is a candidate. There is sparse experimental data on the toxicological significance of nitrosamines in swimming water but they are known to be volatilised and to be dermally absorbed in occupational settings. The skin permeability of NDMA is predicted to be the same as hydrocortisone, a drug used in topical skin treatments, so passage through the skin barrier is a real possibility. The results suggest that the risk of human exposure to nitrosamines in chlorinated recreational water should be evaluated. Mitch and Walse suggest that epidemiological studies are one of the better ways to examine the link between bladder cancer and exposure to nitrosamines, and to estimate the contributions from chlorinated drinking water and chlorinated swimming water. Related Links:
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. |
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