Environmental fate modeling, main

Environmental fate models make use of chemical properties to describe transfer, partitioning, and degradation (Mackay et al. 1992a Cahill et al. 2003). For organic chemicals, quantitative structure-property relationships (QSPRs) may be used to predict partitioning from physical-chemical properties, such as Kow and Kov Such properties may also allow for a prediction of the transfer of chemicals between compartments. Recently, some successful attempts have also been made to predict persistency of chemicals (Raymond et al. 2001), although this mainly concerns... 

When comparing priority setting methodologies it is important to identify additional external information. For all the methods considered a choice is made by choosing the descriptors. The choice of descriptors is however often based on key parameters from risk assessment schemes or environmental fate models, which makes it less subjective. In the present chapter exposure (given by production volume), aquatic toxicity, bioaccumulation and persistence were chosen as descriptive parameters. For HDT the selection of the descriptors is the main contribution of subjectivity. Additionally, some indirect weighting can be added if the data are separated into classes. 

Estimation of the Main Exposure Routes by Environmental Fate Modeling... 

Despite the existence of several databases for certain substances, it is not possible to find physicochemical and/or toxicological parameters to assess the risk for all substances. The lack of data is one of the main problems in risk assessment. This is especially true for emerging pollutants. One solution to solve this problem is the use of QSAR or estimation tools. QSAR models correlate the structure of the substance with their activities (physicochemical properties, environmental fate, and/or toxicological properties). 

Environmental Fate. Experimental data are available regarding the transport and partitioning properties of chloroform in surface waters (Bean et al. 1985 Clark et al. 1982 Class and Ballschmidter 1986 Dilling 1977 Ferrario et al. 1985 Piwoni et al. 1986 Sawhney 1989). Chloroform partitions mainly into the atmosphere and into groundwater. Empirical measurements or model predictions on half-disappearance times in such media as soil could not be identified in the literature. Chloroform can be transported long distances in air. Data are available regarding the degradation of chloroform in the... 

Chemical reactivity and biological activity can be related to molecular structure and physicochemical properties. QSAR models can be established among hydrophobic-lipophilic, electronic, and steric properties, between quantum-mechanics-related parameters and toxicity and between environmental fate parameters such as sorption and tendency for bioaccumulation. The main objective of a QSAR study is to develop quantitative relationships between given properties of a set of chemicals and their molecular descriptors. To develop a valid QSAR model, the following steps are essential ... 

Environmental Fate. Zinc partitions to the air, water, and soil (Callahan et al. 1979 Guy and Chakrabarti 1976 Houba et al. 1983 Pita and Hyne 1975). Zinc occurs in the environment mainly in the +2 oxidation state (Lindsey 1979). Adsorption is the dominant fate of zinc, resulting in enrichment of zinc in suspended and bed sediments (Callahan et al. 1979). The mobility of zinc in soil has been characterized (Base and Sharp 1983 Bergkvist et al. 1989 EPA 1980d Hermann and Neumann-Mahikau 1985 Kalbasi et al. 1978 Saeed and Fox 1977 Tyler and McBride 1982). No estimate for the atmospheric lifetime of zinc is available. Development of pertinent data on the atmospheric processes important for zinc speciation in the atmosphere would be helpful. Development of this information would permit construction of a comprehensive model for the transport and interaction of zinc not only in air but in other media as well. Transformation in air and water can occur as a result of changes in chemical speciation (Anderson et al. 1988 Callahan et al. 1979 EPA 1980d Stokinger 1981). Data that describe the transformation processes for zinc in soil or the fate of zinc in soil are needed. A model of zinc flux from all environmental compartments would be useful for providing information on the overall environmental fate of zinc. 

At high pressures, a non-covalent ionic complex can be regarded as a microsolvated ion. It represents the simplest model for ions generated in a dynamic environment, such as in a solvent cage in solution. The main difference is that the behavior of a microsolvated ion is not perturbed by those environmental factors (solvation, ion pairing, etc.) which normally affect the fate of intimate ion-dipole pairs in solution. Hence, a detailed study of the dynamics and the reactivity of microsolvated ions may provide valuable information on the intrinsic factors governing the reaction and how these factors may be influenced by the solvent cage in solution.4 493... 

On the quantitative side, an environmental concentration is either measured by experimental monitoring or evaluated by means of predictive models. For both, experimental or predictive, approaches information on the use patterns of the substance, on its intrinsic properties, on its persistence in relation to the different environmental compartments and on the main environmental processes influencing distribution and fate of the chemical are needed. In the case of predictive models, this information... 

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