Environmental Behavior Of Chemicals Research Articles

Kinetic Delay in Partitioning and Parallel Particle Pathways: Underappreciated Aspects of Environmental Transport.

We outline the general conditions under which chemicals of high hydrophobicity or, more generally, high partition ratios (HPRs) in water or air, may experience unexpectedly long kinetic delays in approaching equilibrium conditions with organic media. Such a "hydrophobic delay" in the case of K OW or an "aerophobic" delay in the case of KOA may be misinterpreted as being caused by a change in partitioning behavior or mechanism, resulting in development of nonlinear regression models describing intermedia partitioning. In fact, the partitioning is fundamentally linear but is distorted by a kinetic delay in partitioning. To illustrate this concept, we first compile the fundamental equations describing the diffusive equilibration processes, including a complementary transport mechanism termed a parallel particle pathway (PPP). Such a mechanism may occur simultaneously, shortening the HPR delay and complicating interpretation. Second, we describe five examples in which the HPR delay explains the observed and occasionally difficult-to-interpret environmental behavior of chemicals, namely studies of air-aerosol partitioning, chemical accumulation in indoor dust and surfaces, air-vegetation partitioning, internal transport in organisms, and fish bioaccumulation and toxicity. We believe that the general HPR delay and PPP issues deserve exposure as a commonly occurring and often underappreciated process.

Selecting and designing chemicals: application of a mass balance model of chemical fate, exposure and effects in the environment

The factors that are conventionally considered when selecting or designing more environmentally benign chemicals are described and discussed. A modelling strategy is described by which the environmental behaviour of chemicals can be compared and changes in molecular structure evaluated with the objective of contributing to this process. This is accomplished using a mass balance model for chemical fate, exposure and effects in an evaluative environment that depicts the likely environmental behavior of the substance and includes a mechanistic bioaccumulation and food web component, yielding estimates of both human and ecological exposures to the chemical. These exposures can be compared with levels known to exert toxic effects. The strategy thus provides a holistic characterization of chemical fate, persistence, bioaccumulation, exposure, proximity to levels of toxic concern, potential for long range transport and the effect of quantity of chemical released under steady-state conditions. Substances can be readily compared and the effects of proposed changes in molecular structure and hence properties can be evaluated. A key component is the use of the concepts of chemical fugacity and activity for describing the chemical's environmental distribution and potential to exert toxicity. The concept is applied to organic solvents, including alkanes, aromatics, halogenated aromatics and nitrogen-containing compounds.

Modeling the Environmental Fate of Atrazine

Mathematical simulation models of fate and transport of chemicals have been identified by researchers and regulators as potentially valuable tools for improving the understanding of the environmental behavior of chemicals which may be released to the environment as a consequence of routine (i.e., normal manufacturing, use, disposal) and non-routine (e.g., accidental spillage) events. In this context, CHEMFRANCE, a regional fugacity model level III, which calculates the environmental distribution of organic chemicals in 12 defined regions of France, or France as a whole, has been designed. The aim of this study is to show that CHEMFRANCE provides valuable simulation results for understanding the environmental fate behavior of atrazine.

Environmental hazard assessment of chemicals and products. Part VII. A critical survey of exposure data requirements and testing methods

Environmental exposure analysis may be used for a preliminary judgement — even in the absence of effect data — on the possible environmental behaviour of chemicals, based on relatively few, exactly measurable physico-chemical parameters from which the transfer between the media and (at least partly) also the degradation can be estimated. However, the data presently required by legislation (EU) are frequently based on concepts and experiences in the 70's, a period in which the highly lipophilic compounds were in the center of interest. Although these chemicals continue causing severe environmental problems, polar compounds have recently been identified as potentially dangerous substances. Therefore, it is to be expected that data requirements, testing procedures and modelling will have to be extended and improved in order to meet these new challenges. In order to identify the gaps in the present-day exposure analysis, the transfer- and degradations pathways and the most important parameters are identified and a survey of methods available for measuring the relevant parameters is attempted. Special emphasis is given to internationally agreed testing procedures (OECD).

A theoretical basis for Collander Equations

Biphasic partition coefficients are important parameters in describing environmental behaviour of chemicals. Collander Equations are linear expressions linking the logarithms of solvent/water partition coefficients (Ksw). Despite their importance, the theoretical basis for these equations is not well developed, limiting their predictive capability. Using Regular Solution Theory, a general equation is developed relating log Ksw to the logarithm of the octan‐1‐ol/water partition coefficient (Kow). As an example of the applicability of the expression, calculated hexadecane/water (Khw) and heptane/water (Khepw) partition coefficients are in satisfactory agreement with available experimentally determined values for homologous solute series of alkanes, alkenes and alkylbenzenes. Agreement is less satisfactory for alkan‐1‐ols and chlorobenzenes. The theoretical treatment predicts that Collander Equations relating log Ksw to log Kow are overall curvilinear, but linear over limited log Kow ranges.

The environmental behavior of chemicals in soil: Atrazine as an example

In this work a mathematical model has been developed and used to estimate the soil vertical distribution of Atrazine dispersed in the environment. Water transport, rise due to capillarity, and partition among soil-contained water, air, and organic matter, as well as degradation processes, are considered. As far as the vertical mobility in soil is concerned, the model has been derived from that proposed by P. H. Nichols, A. Walker, and R. J. Baker ((1982). Pestic. Sci. 12, 484–494). Such a model has been extended to include a procedure which takes into account the Atrazine mobility due to gravitational water flow. The organic carbon (O.C.) concentration gradient in soil was also considered in the evaluation when assessing partition processes, according to models by P. J. McCall et al. ((1983). Residue Rev. 13, 231–241) and D. McKay and S. Paterson ((1982). Environ. Sci. Technol. 16, 12, 654). The degradation processes are assumed to be first order, linearly related with O.C. content in soil. The application of this model to two sets of soil data demonstrated that Atrazine requires a long time (2 years or more, depending on soil features) in order to percolate at a depth comparable with those of a groundwater source.

SCOPE 25. Appraisal of Tests to Predict the Environmental Behaviour of Chemicals.

SCOPE 25. Appraisal of Tests to Predict the Environmental Behaviour of Chemicals.