Vertical Soil Analysis of Cypress Creek
April 29, 2003 Kate Burgess Nick Van Sant Environmental Geology 214
Introduction
The Cypress Creek floodplain is known to contain pesticides.
– Previous studies have found aldrin, chlordane, dieldrin, endrin, and others
About Cypress Creek
These pesticides are known as persistent organic pollutants and impose serious health risks.
The floodplain is downstream from Velsicol, Buckeye Cellulose and Cretox Chemical, all of which used the creek for waste discharge in the 50s and 60s.
– Velsicol produced chlordane until 1997, although discharge into the creek was ended before the 1970s.
– The floodplain is in a residential area, and local community organizations hope to safely develop the area.
Persistent Organic Pollutants
Carbon containing chemical compounds that resist photochemical, biological and chemical degradation. Characterized by low water solubility and high lipid solubility. Linked by a growing body of evidence to cancer and reproductive problems.
About Chlordane
Chlordane is a POP that has been found near Cypress Creek. Chlordane does not dissolve easily in water and can stay in the soil for over 20 years. It breaks down very slowly and can build up in the tissues of exposed fish, birds and mammals. People are exposed to chlordane when they eat crops grown in soil that contains chlordane or when they breath air near or touch soil in sites that have been contaminated by chlordane.
Chlordane Molecule
C10H6Cl8
Previous Studies
Fall 2002, Jack Stewart and Dan Paull
Bioremediation Project, Dr. Redfearn, Dr. Stinemtz, Prof. Ekstrom, Mr. Aquadro
– Analyzed a series of samples extending from creek – Found presence of POPs in all samples, but higher quantities closer to creek
Lab Analysis, VECA Grant, September 1999-May 2000, Prof. Ekstrom and Emily Pacini
– Quantitative analysis found evidence of several different POPs in soil
– Found presence of POPs in soil but not in plants around Cypress Creek
Purpose
We looked for vertical variation from the surface to a depth of five feet in the soil in the northwest corner of the Cypress Creek floodplain. No previous research has examined the pollution present at different depths in the soil.
Collection of Samples
Samples were collected near Cypress Creek in the floodplain. Six soil samples were taken from a vertical core through the floodplain sediments at spacings of one foot apart to a depth of five feet, which was below the water table when samples were taken.
Soxhlet Extraction
We performed a soxhlet extraction in order to separate the compounds from the soil. A portion of the sample was weighed and placed in a clean soxhlet thimble. The thimble was placed in a soxhlet apparatus comprised of the extractor mounted over a round bottom flask containing about 500mL of Methylene Chloride (and boiling stones). A condenser was placed on top. The solvent was brought to a boil, causing a “percolating action” that washed the soil sample with solvent. The process proceeded for about 24 hours. After completion the solvent was evaporated.
Gas Chromatography – Mass Spectroscopy
The extract was injected into the GC-MS for analysis. The gas chromatograph rapidly heats the sample so that all the components are converted to gases. The organic compounds are swept through a very long, thin tube or column. Each compound can be separated from all other ones because the compounds with lower boiling points will move along faster than the ones with higher boiling points. Thus, a compound will emerge from the column at a specific time called the retention time. The separated compound then goes into the mass spectrometer where it is analyzed based on how it decomposes when shot with an “electron gun.” Each compound has its own mass spectrum which makes it identifiable.
Mass Spectrum for Chlordane
Results from tests done on sample of chlordane from Velsicol Corporation Shows presence of molecule at 15.68 minutes
Results
A comparison of the GC-MS results showed the presence of POPs in all but the 4 ft. sample. The most common compound detected had a retention time of about 15.7 minutes. Analysis of the mass spectrums indicate this compound to be C7H3Cl7, a known degradation product of chlordane.
Indicator Molecule
Relative Abundance of Indicator Molecule
0 ft deep 1 ft deep 2 ft deep 46.061 28087.167 16161.616
3 ft deep
4 ft deep 5 ft deep
844.444
0.000 62589.928
Relative Abundance of Indicator Molecule
70000.000 60000.000 50000.000 40000.000 30000.000 20000.000 10000.000 0.000 0 ft deep 46.061 1 ft deep 2 ft deep 844.444 3 ft deep 0.000 4 ft deep 28087.167 16161.616 62589.928
5 ft deep
Discussion
The type of soil affects presence of POPs
– The sample taken at four feet was much sandier than the surrounding soil, which contained more clay. – Because clay is more dense, the compounds are unable to move as quickly through it.
Discussion Cont.
The chlorinated pesticides are found at the surface and at least as deep as five feet, meaning the POPs migrate through the soil. The large abundance of the indicator molecule at five feet suggests that it is also present at lower depths. The abundance of other POPs may be different at different levels, and this will need to be looked at.
Applications
Because of the presence of POPs in the soil at least as deep as five feet, any attempt to clean the floodplain by removing the top layer of soil would be very expensive. It is likely that pollutants are present at even deeper levels. Bioremediation has been suggested as a way to clean the area, but the depth of these pesticides would present a serious obstacle.
Future Research
Looking for the presence of POPs at even greater depths. Analysis of vertical cores in other areas of the floodplain. Further identification of POPs in the soil at different depths (endrin, dieldrin, heptachlor, isodrin).
References
http://www.atsdr.cdc.gov/tfacts31.html Agency for Toxic Substances and Disease Registry www.chemfinder.com http://pops.gpa.unep.org/01what.htm Global Programme of Action for the Protection of the Marine Environment from Land-based Activites
Acknowledgements
• Professor Ekstrom, Department Physics • Dr. Redfearn, Chemistry Department
Thank You