An Evaluative Screening Level Model of the Fate of Organic Chemicals in Sludge-Amended Soils Including Organic Matter Degradation

Abstract

The Biosolids-Amended Soil: Level IV (BASL4) evaluative screening level model of the fate of organic chemicals introduced to a two-layer soil in association with contaminated biosolids amendments is described. The model is intended for use in assessing the likely month-to-month and year-to-year fate and possible build-up of chemicals in sludge-amended soils in which there can be relatively rapid degradation of the organic matter (OM) present in the applied sludge. To accomplish this goal, processes of chemical degradation, inter-layer transport, volatilization, leaching, diffusion, sorbed phase transport due to bioturbation, and degradation of both fast and slow degrading OM present in the soil and amendment are quantified. Chemical can be introduced as pure compound or in biosolids; it may be applied to the surface layer of the soil or injected into a deeper layer of soil, and it may be ploughed into the surface and deeper layer. BASL4 was applied illustratively to three dissimilar chemicals: DDT, benzene, and phenol for a 12-month simulation period. Several simulations of DDT fate in different amended and unamended soil scenarios demonstrate the capabilities of the model. Degradation of OM is shown to significantly affect partitioning between solids, pore water, and pore air and hence the fate of the chemicals. A preliminary evaluation of the model is described by simulating three field and laboratory studies and the results are regarded as being in reasonable accord with observations. A sensitivity analysis is included with the objective of determining the relative importance of the various parameters describing chemical and soil properties. The model is a useful tool for evaluating the potential for soil contamination under conditions of OM degradation, for identifying the need for soil monitoring studies, and as a basis for estimating concentrations in soil-dwelling organisms.