Tap water between a rock and a hard place.

You may not have heard that very much of trihalomethanes. Yet, you are in a habit of drinking it every day. 

Trihalomethanes are halogenated carbons, substances like chloroform (CHCl3), bromoform (CHBr3), bromodichloromethane (CHBrCl2), and dibromochloromethane(CHClBr2),. They are one of the groups of disinfection by-products (DBPs) that are always present if ever in small amounts of the tap-water you drink and in the tap-water that is used to prepare your beverages and foods.

Today, the chemists at the municipal water plants, if they really try, can reduce almost any contaminant in the water to nondetectable levels. But when this is done, they will have to add residual disinfectants, usually some type of chlorine, in order to protect the water from microbiological infection in the transport from the water works to your tap.

When these disinfectants find bacteria, virus or other living or dead organics in the water, they attack the organics and oxidise them. The result is DBPs, most notably trihalomethanes.

To keep trihalomethanes levels as low as possible, and definitely below the Maximum Contaminant Level (MCL) of 80 parts per billion (ppb) (0.08 mg per litre), is a constant headache for the guys at the municipal water plants. The first order of importance is to keep the insides of the water mains as clean as possible. Increasingly difficult as the pipes grow older. The second order of importance is not to add excessive amounts of disinfectants. Also very difficult, since too little disinfectant means that bacteria and virus may slip through to your tap.

Other DBPs that pose similar problems are the haloacetic acids, i.e. monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid. The MCL of this group is 60 ppb.

Other by products such as haloacetonitriles, haloketones, chloropicrin and chloral hydrates are present at lower concentrations and there has been limited research on these classes of DBPs since they are known to level off or further degrade relatively rapidly after being formed.

For some DBPs, the MCLs are even lower, as for instance 10 ppb for bromate which may be formed when ozon is used as disinfectant. And for some it is higher, as for instance 1000 ppb for chlorite which is formed when chlorine dioxide is used as disinfectant.

In addition to these substances that have been identified and clasifid as to MCL, there are hundreds of DBPs that we know little about. Trihalomethanes are used as markers and it is assumed that if the trihalomethanes are below the MCL, other DBPs are also under safe limits.

You will probably be hearing more about trihalomethanes, and possibly other DBPs, in the years ahead!

One reason is that many of the water mains in most western cities are getting close to one hundred years old and sometimes more. Just like dental plaque partly consists of bacteria and becomes a breeding ground for additional bacteria, the build up of plaque inside a water main consists of mixture of rust, sediment and bacteria and becomes a breeding ground for additional bacteria and becomes more and more difficult to sanitize.

Small amounts of bacteria will always be in the water after treatment, but a more important source is that the mains tend to leak and break in regular intervals. According to a study published in February 2002 by Harvard School of Public Health the renovation of US municipal water systems needed to prevent waste water to get into the drinking water would cost 141 billion US dollars - probably an impossible sum to finance. The situation is similar in all countries where large municipal underground water purification systems have been built. 

Another reason why you will be hearing more about trihalomethanes and other DBPs is that we all become more and more observant on poisons in the air, in the water and in our foods. No matter that all poisons are below standards set by government, we are becoming convinced that all these small amounts of poison ad up ‚€“ in a negative synergy. That‚€™s why we feel exhausted, succumb to infections and fall prey to - another word you will be hearing about a lot - the metabolic syndrome.

But trihalomethanes are not only innocent co-workers in the general fog of unhealthiness around us. Medical science is convinced that it has lethal consequences of its own. Many studies have shown a convincing correlation between levels of trihalomethanes in tap water and cancers. And a clear correlation can also be found between trihalomethanes and adverse pregnancy outcomes, spontaneous abortion, still births and birth defects.

As of yet, there have been only a small number of studies and a great deal of apparent inconsistencies in the results. The small sample size and small number of cases in many of the studies has led to reduced statistical power. Only a limited number of confounders have yet been assessed. Many studies have also not considered the possibility of residential mobility, nor exposure to water sources outside the home. Sometimes use of private water supplies, bottled water or boiling of water before drinking have not been included in exposure assessment. To sum up, current epidemiological evidence is not entirely consistent. Therefore authorities have not acted forcefully. But for the consumer it must be better to be safe than sorry.

Research this far is convincing enough to prompt most responsible municipal authorities to try to reduce disinfectant use if possible and to change to different types of disinfectants. These attempts have not been successful. The change from chlorine to chloramines has been a very popular attempt, but instead of trihalomethanes, nitrosamine-like compounds may be formed if the source water contains secondary amines. These have positively been identified as carcinogenic. Today, it is open to speculation whether switching from chlorination to chloramination to achieve a reduction in trihalomethane levels may have the effect of increasing cancer risks by formation of nitrosamines rather than decreasing risks as is the intent.

Another example of the seriousness of the problem is that in 2001 a group of 214 women sued the municipal authorities in Chesapeake, Virginia, USA for failing to tell residents the drinking water contained high levels of trihalomethanes, which they believe caused them to have miscarriages. The women claim they had successful pregnancies after they stopped drinking the water in Chesapeake. The case was thrown out if court in 2005 because the court deemed it had no jurisdiction over the matter. However the claim was neither contested nor proven.

No matter how you try, you may fail. In October 2002, the regional municipality of Durham, Ontario, Canada, for instance, was charged with 15 counts of failure under Ontario's Drinking Water Protection Regulation to notify the ministry of water samples with low chlorine residual levels. Low chlorine residual levels are considered an indicator of poor water quality. 

Utilities are between a rock and a hard place. Either they dose too little and people may blame them for jeopardizing bacterial contamination, or they dose enough and people may accuse them for the perils of chlorination by-products, such as trihalomethanes.

Aapo Saask 2007-01-24

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