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 organochlorine chemicals, five trace elements and four polynuclear aromatic hydrocarbons (PAHs) to the Great Lakes. Intercomparison of this 1994 estimate is made with earlier loading estimates made in 1988 and 1992 by Strachan and Eisenreich. The flux calculations include wet deposition, dry deposition and two-film vapour transfer across each of the lakes. Of these 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 OC chemicals. PCBs, dieldrin, HCB, DDE, phenanthrene and pyrene are currently showing net loss from the lakes to the atmosphere via volatilization. p,p'-DDT is still being loaded into the lakes from the atmosphere. alpha- and gamma-HCH are near equilibrium with the water bodies and show volatilization in the summer and fall for alpha-HCH but net deposition 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 atmospheric deposition routes for this trace element. The results taken from the IADN program provide a detailed data set for the interpretation of atmospheric impact on the lakes. Relative assessment in relation to other sources of input is difficult due to sparsity of data in other media of the lakes. Particularly important is the inconsistent intercomparison of air and water concentrations from different years leading to gas transfer estimates which could be dated or incorrect. For chemicals which are showing rapidly changing concentrations in the lakes, the calculation of gaseous mass transfer should be made on the basis of short-term, concurrent measurements in both air and water. Crown copyright (C) 1996 Published by Elsevier Science Ltd