Identifier

etd-06132006-072250

Degree

Master of Science in Chemical Engineering (MSChE)

Department

Chemical Engineering

Document Type

Thesis

Abstract

Large quantities of chemicals, such as pesticides, fertilizers, and industrial wastes, have been found throughout the environment raising concerns due to their ecological impacts and implications to human health. Soil is the most important repository of many organic chemicals in the environment. The objective of the present study was to determine the importance of the soil solid phase in the transport of chemicals in soils, and yield quantitative information to better describe bioturbation and its role in the movement of soil particles. Vertical movement of chemicals in the soil solid phase occurs by mixing mechanisms, such as bioturbation, cryoturbation, and dryoturbation. An extensive variety of soil-dwelling animals are responsible for bioturbation. Data on this process were located in the published literature, cataloged, and evaluated to estimate sorbed phase diffusion coefficients from soil turnover rates and effective depths reached by selected organisms. The impact of animals in soil processes varies depending on species, numbers, diversity, size, and feeding and burrowing behavior, which at the same time depend on soil properties, climate conditions, among others. Based on a 50% probability of occurrence, the approximated average depth of soil bioturbation was 20 cm. The periodic mixing of soil due to agricultural practices influences the sorbed phase transport of chemicals; representative numerical values of this type of “bioturbation” were estimated as well. Soil concentration profiles for selected PCBs were collected from literature and modeled. Model extracted sorbed phase diffusion coefficients of 4.03E-07, 5.98E-07, and 5.81E-07 m2/day were obtained for PCB-52, 153, and 101, respectively. These numerical chemical values were in agreement with bioturbation particle turnover values. For all congeners, percentage contribution of transport in the solid phase corresponded to more than 90% of the overall transport process. viii The model exercise provided valuable insights into the relative importance of the different soil transport mechanisms. It was concluded that PCBs are transported principally in association with the soil solid phase; their transport in air and water phases is insignificant. Therefore, chemical fate and transport models must account for the mixing of soil particles by bioturbation as it greatly influences the transport of chemicals sorbed to them.

Date

2006

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Louis J. Thibodeaux

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