Department of Earth Sciences, University of Bristol
Prof. D.M. Sherman
Lecture 3: Organic Geochemistry
Natural organic compounds in the environment result from the breakdown of biomass.
In aquatic systems, biomass (principally lignin) from plants breaks down into humic and fulvic acids.
Lipids hydrolyse to fatty acids, carbohydrates to sugars and proteins to amino acids.
In sediments, humic/fulvic acids transform to kerogen which, in turn, transforms to petroleumand natural gas.
Synthetic organic compounds comprise a major fraction of chemical pollutants in soil and
groundwater. However, these compounds (if the carbon is in a low oxidation state) can be broken down by microbial respiration if electron acceptors (e.g., O2, SO4-2) are present.
Chlorinated hydrocarbons are a very serious type of organic pollutants; they usually have carbon in a high oxidation state; these compounds
can be broken down by methanogens under very anaerobic conditions.