Organic Geochemistry Lab

The organic geochemistry lab is closely associated with the microbiology lab, and Dr. Lenczewski oversees both.

The nature and extent of human impact on the environment is an important field of enquiry. Current and past practices in agriculture, manufacturing, and other activities, have introduced substances into the environment which are actually or potentially harmful to life. Study of these materials as they exist in and interact with rock, soil, and biological agents is necessary in order to understand how best to prevent adverse effects, and to find remedies for problems that already exist. The organic geochemistry lab, operated by Dr. Melissa Lenczewski is used to identify and study the contaminants themselves, including such things as gasoline and its additives, organic solvents, and pesticides.

Rosa Leal-Bautista with Varian GC/MSThe principal piece of equipment used in this research is a Varian Saturn 2100 T GC/MS, pictured here with Ph.D. student Rosa Leal-Bautista loading the sample carousel. As implied in the name, it actually consists of two distinct instruments coupled together, a gas chromatograph ( the "GC" part ) and a mass spectrometer ( the "MS" part ). The gas chromatograph is used to separate organic molecules according to their mass, and the separated concentrations are then introduced into the mass spectrometer where they can be identified on the basis of their molecular weight. Once the molecular species present are known, a simple study might involve determination of the distribution of a particular contaminant or contaminants in groundwater as it flows away from the site of introduction carrying a so-called contaminant plume. A more complex effort would perhaps involve the difficult business of working out what reactions, if any, may be taking place in an environment, and how they are taking place. It is not uncommon for the products of chemical reactions to be more harmful than the original substances they are derived from, and this can complicate clean-up, or remediation, programs immensely.

A project currently in progress in the lab serves to illustrate the method. It involves a chemical called "methyl tert-butyl ether," or MTBE for short. It has been used as an additive for gasoline to make it burn more cleanly, and it is required by law to be used in some areas as a pollution-abatement measure. Unfortunately, it is both mildly toxic and now very widespread in the environment because of its use in motor fuels since the 1970s (US EPA1). The effects of long-term human exposure are not known (US EPA2).

A source of uncontaminated water is needed in an industrialized area of Mexico, where MTBE contamination is believed to be commonplace. It is possible that near-surface lacustrine clays may adsorb the MTBE and prevent it from reaching the deeper groundwater, or that any MTBE present may be biodegraded within the sedimentary column and destroyed, removing the threat. Samples of the clay sediment were taken from the area using core drills and returned to the lab for analysis. The organic fraction is to be extracted by warming the sample and collecting the vapors. These will be analyzed in the GC/MS to see where MTBE is located spatially ( the map locations of the drilling sites ) and in the sedimentary sequence ( how far down or exactly where in the core it is found ). It is hoped that the deeper groundwater reservoirs, protected by the clay layer, will prove to be MTBE-free.