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

Water and suspended particulate matter samples were collected in the St. Lawrence River and its tributaries and analyzed for 12 PAHs at different seasons. Mean total concentrations of PAHs in raw water were highest in the spring (xBAR = 27.9 ng/L) and autumn (xBAR = 21.0 ng/L) samples. The higher concentrations in the spring and in the fall are most likely caused by snow melt and increased runoff, respectively. The predominant compound is phenanthrene. High molecular weight PAHs are detected more frequently in the spring and fall samples. A mass balance equation is proposed to evaluate the relative importance of the principal sources of PAHs in the St. Lawrence River. The contributions of the principal sources of PAHs in the autumn were found to be: atmospheric deposition (52%), tributaries (17%), Great Lakes (8%) and other sources (22%). The atmospheric contribution could decrease to approximately 15% in the spring.