SOURCES OF PAHS IN THE ST-LAWRENCE-RIVER (CANADA) AND THEIR RELATIVE IMPORTANCE

Water and suspended particulate matter samples were collected in the S t. Lawrence River and its tributaries and analyzed for 12 PAHs at diff erent seasons. Mean total concentrations of PAHs in raw water were hig hest in the spring (xBAR = 27.9 ng/L) and autumn (xBAR = 21.0 ng/L) sa mples. The higher concentrations in the spring and in the fall are mos t likely caused by snow melt and increased runoff, respectively. The p redominant compound is phenanthrene. High molecular weight PAHs are de tected more frequently in the spring and fall samples. A mass balance equation is proposed to evaluate the relative importance of the princi pal sources of PAHs in the St. Lawrence River. The contributions of th e principal sources of PAHs in the autumn were found to be: atmospheri c deposition (52%), tributaries (17%), Great Lakes (8%) and other sour ces (22%). The atmospheric contribution could decrease to approximatel y 15% in the spring.