Environmental models, transformation products

There are many areas into which environmental organic chemistry and environmental engineering can advance as a result of developments in various analytical techniques. All of this information will provide a much clearer picture on the chemodynamics of organic compounds, their biodegradation residues, and transformation products. Information such as this is important for modeling the fate and transport of organic compounds in the environment. 

The behavior of MTBE through the different environmental compartments has been investigated using various modelling approaches. For example, the EU risk assessment used the simplest type of fugacity models (a Level 1 model) and concluded that from diffuse sources 93.9% of MTBE is in the air phase, 6.0% in the water phase, and 0.05% in the soil phase [2]. However, another study by Environment Canada for Southern Ontario [61] used the Level III model and predicted 56% of MTBE in the air, 42% in surface water, and 0.5% in soil and sediment. As can be observed, models developed so far differed in their predictions of relative MTBE concentrations for relevant environmental compartments and of seasonal concentration variations further, they have hardly considered the formation of transformation products [62]. Moreover, limitations in pollutant environmental data or key physicochemical parameters often make it difficult to validate model predictions. 

Modelling Environmental Exposure to Transformation Products of Organic Chemicals... 

Environmental Fate Models for Transformation Products An Overview. . 124... 

One can differentiate between three types of transformation products of environmental pollutants. First, environmental pollutants can be metabolized during the toxicokinetic phase of uptake/metabolism/distribution/elimination in organisms (Table 1). Here, the observed effect is actually due to the combined effect of different metabolites. Taking these transformation reactions into account will help to understand mechanisms of toxicity, species sensitivity differences, and time dependency of effects. Lee and Landrum [8,9] developed a model to describe the mixture effects of PAH and their metabolites in Hyalella azteca. This combined toxicokinetic/toxicodynamic models convincingly demonstrated the importance of accounting for metabolite formation and how different mixture toxicity concepts can be incorporated into such models. 

We propose a simple and versatile model for the prediction of the toxic potential of mixtures of environmental pollutants and their transformation products. This model assumes concentration addition between the parent compound and its metabohtes, which is strictly only applicable if the parent and all metabohtes act according to the same mode of toxic action. 

For most of the compounds considered, their environmental presence may not only result from direct release during present production or use but also from historical production and use, natural formation or transformation of other products. Therefore, to derive predicted environmental concentrations (PECs), data collected during analytical monitoring programmes are preferred to modelling data provided they are reliable and representative [1]. 

Farmer P Committee on Mutagenicity of Chemicals in Food, Consumer Products and the Environment ILSl/HESl research programme on alternative cancer models results of Syrian hamster embryo cell transformation assay. International Life Sciences Institute/Health and Environmental Science Institute. Toxicol Pathol 2002 30 536-8. 

At a minimum, the modeling capability must encompass industry models to reflect the nation s heavy industry at the core of the fossil energy and materials sector (electric power, petroleum refining, basic chemicals). This industry core generates the nation s electricity, refines the nation s petroleum products, and transforms the nation s chemicals into useable endproducts. New trends in production costs, resource use, and environmental quality will generally be influenced significantly by what happens in this heavy industrial core. 

Alvarez-Cohen, L. McCarty, P. L. (1991). Product toxicity and cometabolic competitive inhibition modeling of chloroform and trichloroethylene transformation by methano-trophic resting cells. Applied and Environmental Microbiology, 57, 1031-7. 

---