ATMOSPHERIC DEPOSITION OF TOXIC-CHEMICALS TO THE GREAT-LAKES - A REVIEW OF DATA THROUGH 1994

An update is presented of the atmospheric loadings of 11 organochlorin e chemicals, five trace elements and four polynuclear aromatic hydroca rbons (PAHs) to the Great Lakes. Intercomparison of this 1994 estimate is made with earlier loading estimates made in 1988 and 1992 by Strac han and Eisenreich. The flux calculations include wet deposition, dry deposition and two-film vapour transfer across each of the lakes. Of t hese processes, confidence is highest for wet deposition estimates and lowest for the gas transfer component. This is unfortunate since gas transfer has been estimated to be the most important process for the O C chemicals. PCBs, dieldrin, HCB, DDE, phenanthrene and pyrene are cur rently showing net loss from the lakes to the atmosphere via volatiliz ation. p,p'-DDT is still being loaded into the lakes from the atmosphe re. alpha- and gamma-HCH are near equilibrium with the water bodies an d show volatilization in the summer and fall for alpha-HCH but net dep osition for the rest of the year. Hg assessment for the net loading to Lake Superior is given and points out the importance of each of the a tmospheric deposition routes for this trace element. The results taken from the IADN program provide a detailed data set for the interpretat ion of atmospheric impact on the lakes. Relative assessment in relatio n to other sources of input is difficult due to sparsity of data in ot her media of the lakes. Particularly important is the inconsistent int ercomparison of air and water concentrations from different years lead ing to gas transfer estimates which could be dated or incorrect. For c hemicals which are showing rapidly changing concentrations in the lake s, the calculation of gaseous mass transfer should be made on the basi s of short-term, concurrent measurements in both air and water. Crown copyright (C) 1996 Published by Elsevier Science Ltd