Models of natural organic matter and interactions with organic contaminants

Adsorption of organic contaminants onto soils, sediments and other:particul ates has the potential to be a major controlling factor in their bioavailab ility, fate and behavior in the environment. Models for estimating the amou nt and stability of sorbed organic contaminants based on the fraction of or ganic carbon in a soil or sediment can oversimplify the process of sorption in the environment. In order to help understand sorption of organic contam inants in soils and sediments, we modeled various components of natural org anic matter (NOM) that are possible substrates for sorption, These substrat es include soot particles, lignin. humic and fulvic acids. The molecular sc ale interactions of selected aromatic hydrocarbons with different substrate s were also simulated. Results of the simulations include the 3-D structure s of the NOM components, changes in structure with protonation state and so lvation and the sorption energy between PAH and substrate. This last parame ter is an indicator of the amount of contaminant that will sorb and the ene rgy required to free the contaminant from the substrate. Although the simul ation results presented in this paper represent a first-order examination o f NOM and contaminant interactions, the findings highlight a number of esse ntial features that should be included in future molecular models of NOM an d contaminant sorption. (C) 1999 Elsevier Science Ltd. All rights reserved.