Disinfection Byproducts and the Wrath of Unintended Consequences

In the past century, drinking water chlorination has dramatically reduced the incidence of waterborne disease wherever it has been adopted, contributing to greater life expectancy and healthier societies.  A recent article in the journal Science (The Chlorine Dilemma, January 7) takes a fresh look at water chlorination by stacking the “pros” of this technology against its “cons” and tracing the unintended consequences of switching to alternative disinfectants.

Why entertain the notion of moving away from a technology that represents one of the greatest public health advancements of all time?  The answer lies in the discovery in the 1970s of the presence of low levels of disinfection byproducts (DBPs) in chlorinated drinking water. These unwanted compounds are products of chemical reactions between chlorine and naturally occurring organic matter in source water.  Some DBPs are of potential health concern, but, as the International Programme on Chemical Safety notes:

The health risks from these byproducts at the levels at which they occur in drinking water are extremely small in comparison with the risks associated with inadequate disinfection. Thus, it is important that disinfection not be compromised in attempting to control such byproducts.

EPA regulates several chlorination DBPs to safe levels and is considering further regulating these compounds in groups as part of its new Drinking Water Strategy.  Interestingly, all chemical disinfection methods are associated with byproducts, but chlorinated DBPs are the most well studied; there are hundreds of other DBPs for which health effects data are scarce.

The authors of The Chlorine Dilemma explain that in an effort to reduce levels of regulated DBPs, many water systems switched from chlorine to chloramine disinfection. One unintended consequence of the switch to chloramines, however, is lead leaching from plumbing in aging infrastructure. Another unexpected result of this decision is that an unregulated family of DBPs of potentially greater health risk—nitrosamines–have made an unwelcomed appearance in drinking water. Not surprisingly, EPA lists nitrosamines among the top groups of compounds headed for future regulation.

How can U.S. water quality be maximized by minimizing DBP levels? Which DBPs are of the highest concern? When will there be enough data to regulate all problematic DBPs confidently? One of the goals of EPA’s new Drinking Water Strategy is to “foster development of new drinking water technologies to address health risks posed by a broad array of contaminants.”  The common culprit in all reactions that form DBPs is organic matter.  If water systems could use an innovative, affordable technology to remove organic matter prior to disinfection, DBP levels of all types in drinking water could be minimized.  Perhaps then we would stop inviting the wrath of unintended consequences.

Joan Rose, PhD, is the Homer Nowlin Chair in Water Research at Michigan State University and a member of the Water Quality and Health Council.