Grantee Research Project Results
1998 Progress Report: Intrinsic Stable Isotopic Tracers of Environmental Contaminants
EPA Grant Number: R825420Title: Intrinsic Stable Isotopic Tracers of Environmental Contaminants
Investigators: Macko, Stephen A. , Kennicutt, Mahlon C.
Institution: University of Virginia , Texas A & M University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1996 through September 30, 1999 (Extended to September 30, 2000)
Project Period Covered by this Report: October 1, 1997 through September 30, 1998
Project Amount: $358,949
RFA: Exploratory Research - Water Engineering (1996) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Safer Chemicals
Objective:
The goal of this project is to determine if the stable isotopic compositions of individual pollutants can be used to uniquely identify the sources and monitor the fate of organic chemical contaminants in the environment.Progress Summary:
a) Biodegradation Studies - these are samples from coastal plots, salt water marshes, that have been treated with oil to determine the optimum conditions for promoting degradation in the field. These do not add bacteria but enhance the naturally occurring microbial populations by the addition of various nutrients. We have samples of the original undegraded oil that will serve as the time zero isotopic signature. The sites are enhanced with nitrate and phosphate to supplement the limiting nutrients. Controls are plots treated with oil and allowed to naturally degrade and weather. The elevated nutrients accelerate the degradation process thus accelerating any microbiologically mediated alteration of the original starting material. Samples are then collected as a time series over a period of months to track the degradation process. Therefore we will be able to look at various fractions and suites of compounds, particularly aromatics, to see if the removal of selective constituents is accompanied by a preferential loss of the lighter isotope or if the degradation process is non-isotopically selective. Within the oil there will be objective measures of the extent of degradation based on selective removal of compounds so we will be able to determine the relative level of alteration based on molecular ratios. This will be important in the field if we are to use the aromatics as relatively resistant tracers and particularly when the source oil is not known. It will also reveal if variations in environmental conditions are related to different degradation pathways and if there are recognizable or predictable shifts in compound specific stable isotopic labels. Unaltered compounds will serve as benchmarks to compare and contrast those suites of compounds that are demonstrably degraded. At some point we might also look for the altered compounds to try and mass balance any shifts in isotopes if the intermediates are present and the compounds have not been completely remineralized to CO2 and H2O.
b) NOAA Status and Trends Sites - in these locations there exists an extensive historical database on which the sites will be chosen for analysis. Most of the sites will have had a thirteen year history of monitoring that will provide a basis for interpreting the data. We will also be able to look at time series over this period to establish whether the site is stable or has had additions of contaminants over the course of the last decade. Also these sites are well characterized so that potential sources of pollutants will be known. Sites were purposely chosen away from point sources with the idea that the program is more interested in long term trends rather than one time acute discharges. So sediment samples will provide a long term integrated signature of the history of pollution as the ultimate repository and long term accumulator of contaminants. In addition, we have associated tissue samples from mussels or oysters. These organisms are seen as sentinel integrators as well but over shorter timeframes than the sediment. The comparisons will be twofold. First are the contaminants in the organisms traceable to the sediments? An assumption will be that the bioavailable fraction of the contaminants will be isotopically representative of the entire pollutant pool. This may or may not be true and may not be testable in the field. A first order question is whether the pollutants in the sediments are the source of the pollutants in the animal. At least we can establish whether they are the same chemicals. On the other hand we expect bivalves to be effective accumulators rather processors of pollutants because their ability to metabolize and depurate chemicals is limited. Thus we might expect a close one-to-one correspondence between abiotic and biotic occurrences. The enzymes (P450 system) that metabolize pollutants are primitive at best in these animals. Also there will be a suite of contaminants from PAH to pesticides to PCB that will likely have a range of reactivities and a range of responses to biological accumulation based on chemical structure. We can compare reactivities between classes of compounds and within classes of compounds based on molecular weight and structure. It is known that there is a shift in molecular weight distributions as these compounds are accumulated. If isotopic shifts are apparent it might be discernable that the compounds most readily accumulated show less of a shift than those most fractionated, being more susceptible to isotopic partitioning. It should also be noted that each class of chemicals also potentially has very different pathways to the ultimate site of collection with some being atmospherically transported, some being derived from urban runoff, and some being discharged at the site. These origins will be partially discernable based on composition and careful selection of sites.
c) Gulf of Mexico Seeps - we have matched pairs of tissues and sediments from ten sites. Here we have a simple case of one source of PAH so we know if it is accumulated it came from the seep. The key here is that the linkages are relatively unambiguous. We also have a range of PAH tissue concentrations over an order of magnitude so it might demonstrate if there is a concentration effect on the integrity of the isotopic signal. In other words is there a mass balance effect such that at low accumulation there may be a bigger fractionation and that this lessens as more of the pollutant is accumulated.
Future Activities:
We are now testing the capabilities of the TLC preparatory method. The TLC conditions are established, standards which have been processed through the entire procedure will be isotopically assessed. If the separation methods do not alter the isotope compositions of the analytes, further processing of the actual samples will continue. Ultimately the biodegradation effects will need to be ground-truthed in laboratory exposures. We have very a well-constrained sample sets available to give us insight into the processes controlling isotopic partitioning as contaminants travel through the biogeochemical cycle.Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
Scientific Discipline, Toxics, Waste, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Physics, pesticides, State, Chemistry, Fate & Transport, Engineering, Chemistry, & Physics, fate and transport, mass spectrometry, Georgia (GA), PCBs, gas chromatography, PAH, environmental contaminants, groundwater contamination, water qualityProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.