What is in Our Drinking Water?

What is in Our Drinking Water?

Identification of New Chemical Disinfection By-products (DBPs)

What is a DBP? A drinking water disinfection by-product (DBP) is formed when the chemical used for disinfecting the drinking water reacts with natural organic matter and/or bromide/iodide in the source water. Popular disinfectants include chlorine, ozone, chlorine dioxide, and chloramine. Source waters include rivers, lakes, streams, groundwater, and sometimes seawater. We have only known about DBPs since 1974, when chloroform was identified by Rook as a DBP resulting from the chlorination of tap water. Since then, hundreds of DBPs have been identified in drinking water.

So what? Millions of people in the U.S. are exposed to these drinking water DBPs every day. While it is vitally important to disinfect drinking water, as thousands of people died from waterborne illnesses before we started disinfection practices in the early 1900s, it is also important to minimize the chemical DBPs formed. Several DBPs have been linked to cancer in laboratory animals, and as a result, the U.S. EPA has some of these DBPs regulated. However, there are many more DBPs that have still not been identified and tested for toxicity or cancer effects. Currently, we have only identified <50% of the total organic halide (TOX) that is measured in chlorinated drinking water. There is much less known about DBPs from the newer alternative disinfectants, such as ozone, chlorine dioxide, and chloramine, which are gaining in popularity in the U.S. Are these alternative disinfectants safer than chlorine? What kinds of by-products are formed? And, what about the unidentified chlorine DBPs that people are exposed to through their drinking water--both from drinking and showering/bathing? The objective of our research is to find out what these DBPs are--to thoroughly characterize the chemicals formed in drinking water treatment--and to ultimately minimize any harmful ones that are formed.

Our research approach

• Gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), and gas chromatography/infrared spectroscopy (GC/IR) techniques are used to identify the unknown by-products

• NIST and Wiley mass spectral databases are used first to identify any DBPs that happen to be present in these databases

• Because many DBPs are not in these databases, most of our work involves unconventional MS and IR techniques, as well as a great deal of scientific interpretation of the spectra

• High resolution MS provides empirical formula information for the unknown chemical (e.g., how many carbons, hydrogens, oxygens, nitrogens, etc. are in the chemical’s structure)

• Chemical ionization MS provides molecular weight information when this is not provided in conventional electron ionization mass spectra

• IR spectroscopy provides functional group information (e.g., whether the oxygens are due to a carboxylic acid group, a ketone, an alcohol, or an aldehyde)

• LC/MS is used to identify compounds that cannot be extracted from water (the highly polar, hydrophilic ones). This is a major missing gap in our knowledge about DBPs--so far, most DBPs identified have been those that are easily extracted from water

• Novel derivatization techniques are also applied to aid in the identification of highly polar DBPs

• Formation and fate & transport studies are conducted to better understand how certain priority DBPs are formed and transformed in treatment and distribution systems

• Once DBPs are identified, ones that are predicted to have adverse health effects are studied in order to determine how they are formed (so that the treatment can be modified to ultimately minimize their presence in drinking water)

Currently

We recently completed a major nationwide DBP occurrence study EPA/600/R-02/068, where we sampled drinking water across the U.S. (disinfected with the different disinfectants and with different water quality, including elevated levels of bromide in the source water). A group of >50 DBPs that resulted from a prioritization of >500 DBPs in the literature for predicted adverse health effects was quantified in these drinking waters. Fate and transport studies were also conducted in the drinking water distribution systems to determine whether these DBPs changed in concentration or were transformed in the distribution systems. In addition to obtaining important quantitative information on these new DBPs (to help in prioritizing health effects testing), important new discoveries were made regarding the use of alternative disinfectants. While the use of alternative disinfectants lowered the levels of the four regulated trihalomethanes and five haloacetic acids (as compared to chlorine), many of the other prioritized DBPs were formed at higher levels with these alternative disinfectants. For example, the highest levels of iodinated DBPs were found in chloraminated drinking water, the highest levels of trihalonitromethanes were found in pre-ozonated drinking water, and dihaloaldehydes were highest at a plant using chloramines and ozone.

Our new work includes obtaining quantitative occurrence information on the iodo-acids that were identified for the first time in the Nationwide DBP Occurrence Study. Chloraminated waters (where levels are expected to be highest) are targeted for this work. In addition, a toxicity-based identification approach (using mammalian cell and medaka fish assays) will be used to ensure toxicologically important DBPs are not being missed. The full study of the Four Lab Study is also expected to begin in 2005 (where drinking water is treated and concentrated, comprehensive DBP identifications are carried out, and drinking water concentrates are tested in a battery of in vivo and in vitro toxicity assays, with an emphasis on newer reproductive and developmental health effects). This Four Lab Study involves the collaboration of EPA's national laboratories and centers (NHEERL, NERL, NRMRL, and NCEA). Finally, work continues in determining how the toxicologically significant bromonitromethane DBPs are formed. These bromonitromethanes are more genotoxic and cytotoxic to mammalian cells than most of the DBPs currently regulated and are also currently the focus of in vivo testing at NHEERL (RTP, NC) and at the National Toxicology Program (NTP, NIEHS).

Recent results

• A recent Nationwide DBP Occurrence Study has provided important new quantitative information on unregulated DBPs that have the potential to cause adverse health effects based on a structure-activity analysis (Woo et al., 2002); several of these DBPs have concentrations similar to some that are already regulated

• The use of alternative disinfectants can produce higher levels of these DBPs, as compared to chlorine

• A recent study reveals that iodoacetic acid (one of five new iodo-acids recently identified in chloraminated drinking water) is a potent cytotoxin and genotoxin in mammalian cells (Plewa et al., 2004a) (work is in progress on the toxicity of other iodo-acids)

• The presence of natural bromide in the source water results in a tremendous shift from chlorine-containing DBPs to bromine-containing DBPs when chlorine or chloramine is used as a disinfectant (even in combination with ozone)

• New analytical methods have been developed (and are continuing to be developed) for the analysis of highly polar DBPs

• Collaborations have been forged with health effects researchers to study selected DBPs for potential adverse health effects

Upcoming event

There will be a new Gordon Research Conference on drinking water DBPs on August 13-18, 2006, at Mount Holyoke College in South Hadley, Massachusetts. Title of meeting: Drinking Water Disinfection By-products: Integrating Occurrence and Formation, Exposure, Toxicity, and Epidemiology. Updates on this meeting can be found at www.grc.org/programs/2006/drinking.htm. Contact Susan Richardson for more information (richardson.susan@epa.gov).


Source http://www.epa.gov/athens/research/process/drinkingwater.html