Haloacetic Acids in the Environment

Haloacetic acids (HAAs) have been found in lakes, groundwater, drinking water, glacial ice, precipitation, air and soil. At high enough concentrations, they are poisonous to plants, and some are suspected carcinogens. Although HAAs have been studied extensively in Europe, little was known about their extent and concentration in Canada until recently, when Environment Canada's National Water Research Institute (NWRI) devised a unique in situ method of measuring these substances in freshwater and marine systems.

Haloacetic acids include many different compounds, such as monochloroacetic, dichloroacetic, trichloroacetic and trifluoroacetic acids. Some HAAs are believed to occur naturally, while others are found in the environment as a consequence of human activities. For example, trichloroacetic acid is thought to form in the atmosphere from degradation of the industrial chemicals tetrachloroethene and 1,1,1-trichloroethane.

NWRI used its new technique, which is based on traditional analytical methods, to conduct the first Canada-wide testing for HAAs in freshwater systems. The research team chose lakes from diverse locations across the country — Ontario's Great Lakes, Loon Lake in British Columbia, Great Slave Lake in the Northwest Territories, Lake Winnipeg in Manitoba, and Lake Kejimkujik in Nova Scotia — and also tested precipitation samples at seven departmental sites across Canada.

Results of the precipitation tests showed concentrations of haloacetic acids ranging from below detectable limits to 2400 nanograms per litre, with higher concentrations in rainfall from air masses that had passed near or over highly populated, industrialized areas. The lake studies revealed a similar pattern, with those associated with industrial activities found to contain higher HAA levels. Lake Superior, which has some industry and a low population, had trifluoroacetic acid concentrations of about 18 nanograms per litre. This figure increased through the Great Lakes system, with Lake Ontario having concentrations of approximately 150 nanograms per litre. Chloroacetic acid concentration levels were relatively constant throughout the Great Lakes at approximately 450 nanograms per litre. Lake Winnipeg, situated downstream from urban sources, contained high concentrations, while the lakes in more isolated regions contained the lowest.

To build on this first effort to establish concrete information on the presence of these contaminants in Canadian freshwaters, NWRI scientists next conducted a study with international partners comparing HAA levels in the northern and southern hemispheres. Their efforts involved collecting and analyzing samples of precipitation and soil from Canada, Malawi and Chile, and soil samples from the United Kingdom.

The lowest trichloroacetic acid concentrations in the precipitation samples were found in Malawi and the highest in Canada. Malawi had low monochloroacetic acid concentrations as well, but they were slightly higher than those taken in Canada or Chile. In soil samples, HAA concentrations were highest in the United Kingdom and lowest in Malawi, with Chilean samples having higher levels than Canadian ones. Malawi soil and precipitation samples also contained small amounts of monobromoacetic acid, but this particular HAA was found in only one of 11 Chilean sites. In general, dichloroacetic acid was the most prevalent HAA found in all samples.

Overall, results showed that concentrations of HAAs were greatest in the industrialized northern hemisphere —supporting the NWRI's earlier Canadian research, and the theory that levels of these substances are higher in industrialized areas. Although substantial quantities of some HAAs were also found in the southern hemisphere, the pattern there was by no means uniform.

Haloacetic acids are an emerging environmental issue, and much work remains to be done to determine their sources, how they are transported in the atmosphere, and the exact nature of the threats they may pose to the Canadian and global environment. Environment Canada researchers continue to work with national and international partners to find the answers to these questions and to lay the scientific groundwork for actions to control these substances.

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