Type of Document Master's Thesis Author Rodriguez, Maria D Author's Email Address email@example.com URN etd-06132006-072250 Title The Bioturbation Transport of Chemicals in Surface Soils Degree Master of Science in Chemical Engineering (M.S.Ch.E.) Department Chemical Engineering Advisory Committee
Advisor Name Title Louis J. Thibodeaux Committee Chair John W. Fleeger Committee Member Kalliat Valsaraj Committee Member Richard L. Bengtson Committee Member Keywords
- soil solid phase
- diffusion coefficients
Date of Defense 2006-05-10 Availability unrestricted AbstractLarge 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.
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.
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