DISSOLVED AND TOTAL THALLIUM IN GREAT-LAKES WATERS

While being a highly tonic element, thallium (Tl) has been studied to a much lesser degree than other toxic elements such as lead, cadmium or mercury. This is mainly because Tl is often undetected by classical analytical methods which tend to have poorer sensitivity for TI than for other elements. This is clearly evidenced by our findings that Tl is more concentrated than Cd in Great Lakes waters, yet there have been no published Tl data compared to a good amount of published Cd data for this ecosystem. Recently, we have developed art ultrasensitive Laser-Excited Atomic Fluorescence Spectrometric (LEAFS) method which made possible the direct determination of thallium in lake waters. This paper reports for the first time the concentration and the distribution of dissolved and total Tl in the waters of three Great Lakes and some point sources. The median dissolved concentration of Tl are 1.2, 5.7, 9.4, and 25.7 ng/L (6, 27, 45, and 124 x 10(-12) M) in Lakes Superior, Ontario, Erie, and Hamilton Harbor, respectively. A range of sub-ng/L to 50 ng/L of Tl was found The overall average ratio of dissolved over total Tl is 87% with a standard deviation of 8%. To our knowledge these Tl data are the first ones ever reported for this important ecosystem.