Quarterdeck 2.2
By Deborah L. Hesse
Biodegradation is the transformation of an organic chemical to another form by biological metabolic processes. These processes use oxygen and can produce carbon dioxide as a final product. Respiration methods measure the amount of oxygen used or amount of CO(2) produced. Organics other than pollutants are transformed by the same basic process, so this method cannot determine if the oxygen loss (or CO[2] production) is due to the degradation of the pollutant or another organic chemical. The loss-of-parent-compound methods measure the amount of pollutant that has disappeared over time. Unfortunately, this method cannot determine if the loss is due to biological or physical (transportation) processes. Radio-labeled tracers (14-C) help trace degradation of single compounds but do not always reflect the behavior of complex mixtures such as petroleum hydrocarbons. Investigation of the "ratio of 13-C of CO(2)" procedure was performed because it combines the advantages of respiration and radio-label methods and can be applied to both single compounds and complex mixtures. Hopefully this research will lead to an on-site method to determine biodegradation rates at chemical-spill sites and a way to maximize them.
[9K] The use of stable carbon isotope
ratios allowed me to differentiate between CO(2) produced from the biodegradation
of estuarine grasses (e.g. Spartina alterniflora) and the biodegradation
of crude oil. I used a mass spectrometer to compare the amount of 13-C in
the CO(2) to a standard and reported the results as a value for the proportion
of 13-C in units of parts per thousand (o/oo). Estuarine grasses typically
have a proportion of 13-C of -16 to -10 o/oo and estuarine phyto-plankton
values typically range from -22 to -18 o/oo, while crude oil values typically
range from -32 to -28 o/oo. These ranges and the importance of estuaries
in marine life cycles made them an excellent place to determine the efficacy
of this procedure. The abundance of bacteria in estuarine sediments allowed
me to use naturally occurring bacteria from Galveston Bay.
The research performed indicated that the precision of the stable isotope procedure was sufficient to distinguish between degradation of oil and degradation of estuarine organic matter. The "ratio of 13-C of CO(2)" pattern observed in the experiments corresponded to and expanded the information obtained through simultaneous radio-label and loss-of-parent-compound experiments. The "ratio of 13-C of CO(2)" produced by the bacteria was similar to the proportion of 13-C of the substrate (Spartina alterniflora, crude oil, a mixture of the previous two, or no substrate) during the middle section of the experiment. Therefore, the "ratio of 13-C of CO(2)" procedure can provide useful information in determining the efficacy of various bioremediation techniques in many environments and on many pollutants as long as the pollutant and the environment have different proportions of 13-C.
Editor's Note: Debby currently works with Toxicological Evaluations, Research and Risk Assessments (TERRA), Inc. in Tallahassee, FL, where she forms part of the scientific support staff. After only a short time there, she has already learned a great deal about risk assessments and is looking forward to learning more. She also hopes to become involved in the litigation work that TERRA, Inc. performs.
Oceanography, Texas A&M
University
rshatto@ocean.tamu.edu
URL=http://oceanography.tamu.edu/Quarterdeck/QD2.2/Hesse/hesse.html
Updated July 24, 1995