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

Abstract

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.