The Lake Michigan contaminant transport and fate model, LM2-toxic: Development, overview, and application

The Lake Michigan contaminant transport and fate model LM2-Toxic was developed to gain a better understanding of PCB cycling dynamics and to predict environmental exposure concentrations of 54 polychlorinated biphenyl (PCB) congeners in Lake Michigan water and sediment from 1994 to 2055 as a function of a variety of forcing functions including constant conditions, continued recovery forecasts, and load reduction scenarios. LM2-Toxic couples the organic carbon sorbent and chemical dynamics conceptualized for a natural water system. Based on 1994-1995 model results, a mass budget analysis showed that air-water exchange was the most important mass transfer process. Volatilization was the largest PCB loss and gas absorption was the largest PCB input to Lake Michigan. Model-predicted environmental exposure concentrations suggest that the water quality criterion for protection of wildlife (0.074 ng/L) and human health (0.026 ng/L) will be attained in approximately 2018 and 2045, respectively, based on a slow recovery scenario. For this scenario, atmospheric components, including vapor phase concentration and wet and dry particulate loadings, were assumed to decline with a 20 year half-life, and tributary loadings were assumed to decline with a 13 year half-life.