Haloacetic acids in Canadian lake waters and precipitation

Haloacetic acids (HAAs) were measured in lake water and precipitation in di stinct geographical areas of Canada with the objective of determining preva iling levels and source regions of these phytotoxins. This included surface water samples from the Great Lakes and four lakes in widely separated geog raphical areas of Canada. These lakes had levels dependent on the degree of isolation from human activity, with the more isolated lakes having HAA con centration generally of <100 ng/L. Surface water from Lake Superior was sam pled at 11 sites during two separate cruises. This lake had HAA levels of < 100 ng/L except for dichloroacetic acid which generally was the most abunda nt of all the HAAs. Two sites from each of the other Great Lakes were sampl ed, one close to the inflow of the lake and the other close to the outflow. These HAA concentrations were generally 10 limes greater than in Lake Supe rior. For precipitation, the HAA levels were variable (<10-to 2400 ng/L) in daily event samples from seven sites situated across Canada. Five-day back -trajectories indicated that the sources of the air masses govern the types and amounts of HAAs in the precipitation. Urban centers appear to be sourc es of HAAs, particularly trifluoroacetic acid (TFA). The average daily even t precipitation fluxes of TFA were reasonably constant across Canada, excep t for samples from the station in the Northwest Territories, but those of t he chloroacetic acids increased from west to east.