Title page for ETD etd-06132006-072250

Type of Document Master's Thesis
Author Rodriguez, Maria D
Author's Email Address mrodr23@lsu.edu
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
  • soil
  • bioturbation
  • earthworms
  • soil solid phase
  • diffusion coefficients
Date of Defense 2006-05-10
Availability unrestricted
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.


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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