PCDDs and PCDFs in the environment: Physical measurements, levels and fate predictions.

摘要

The research reported here is divided into three separate sections: the measurement of selected physical parameters of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs); analysis of PCDDs, PCDFs and other organic pollutants in composts and the development of a surface soil model for predicting the fate of pollutants in such an environment and its application to PCDDs and PCDFs.; The physical parameters measured are as follows. First, enthalpies of desorption for PCDDs and PCDFs are calculated using the gas saturation method. The importance of relative humidity in effecting surface desorption is also investigated. Second, aqueous concentrations are determined for the same compounds using a generator column technique. This technique is further applied for the first time toward measurements of solubility enhancement by dissolved humic acid. Again PCDDs and PCDFs are studied. Henry's law constants for these compounds are calculated from the partial pressures and aqueous concentrations. Finally, partition coefficients important in the prediction of the soil fate of these compounds are calculated. A novel method for the prediction and measurement of {dollar}rm Ksb{lcub}MW{rcub}{dollar} is proposed and applied. The application of this method to {dollar}rm Ksb{lcub}P{rcub}{dollar} determination is also noted. These enthalpies of desorption, solubilities and partition coefficients are all important parameters in predicting the behavior and fate of PCDDs and PCDFs in soil. This information is utilized in the surface soil model.; Analysis of three types of composts, yard waste, municipal solid waste and municipal solid waste/sewage sludge, for levels of PCDDs, PCDFs and chlorinated phenols indicates two major sources of PCDDs and PCDFs in composts. The introduction of pentachlorophenol contaminated with dioxins and furans is one source. Biological formation, primarily of hepta- and octachlorinated dioxins, is the postulated second source. As composting is a biologically intensive process, PCDD/F formation in this way is likely.; The surface soil model that is developed uses the concepts of fugacity and partition coefficients. Insight into the behavior of PCDDs and PCDFs in surface soil is obtained as are fate predictions. Physical soil attributes such as air and water volumes, organic matter content and dissolved organic matter concentrations as well as distance of analyte from the soil surface were all observed to affect behavior. Predicted half-lives suggest long term residence times for both 2,3,7,8-tetrachlorinated dioxin and 1,2,3,4,6,7,8-heptachlorinated furan in many of the model soil systems.