Organic pollutants such as the pesticide DDT and related compounds are often found in contaminated aquatic sediments. However, variations in the composition of these sediments have often thwarted efforts to determine the presence of DDT and other hydrophobic organic contaminants (HOCs), because of the dependence of traditional methods on measuring bulk sediment concentrations and using equilibrium partitioning. Even measuring free dissolved HOC concentrations in pore water calls for time-consuming, expensive and difficult procedures.
Newer, passive sampling methodology exposes polymeric samplers to sediment matrices or water isolated from sediments, so that HOCs can partition into the sampler’s extraction phase. HOCs in the polymer can then be extracted with solvents or thermally desorbed. Robert Eganhouse of the US Geological Survey and Erica DiFilippo of the groundwater consulting firm S.S. Papadopulos and Associates recently announced a method using solid-phase microextraction (SPME) and several GERSTEL techniques, including the Thermal Desorption System, microvial inserts, MAESTRO software and Multi Purpose Sampler. Using optical fiber SPME and automated GERSTEL desorption and analysis equipment allowed for higher temporal and spatial resolution studies, enabling the scientists to meet quality control objectives more cost effectively. The researchers published their results recently in the Journal of Chromatography A.
Using solutions of 10 DDT compounds from well-known DDT-contaminated sediments off the coast of Palos Verdes, California, where as much as 1,000 tons of DDT had been discharged for about 20 years, the researchers found that SPME fibers needed to be coated with PDMS (the same polydimethylsiloxane phase used with the GERSTEL Twister) and allowed to equilibrate in contact with the sample, a process that can take weeks to months.
SPME fibers were readied for sediment exposure by placing them into GERSTEL Thermal Desorption System (TDS) tubes and baking them in a GERSTEL TC 2 tube conditioner. After exposure of the SPME fibers to sediment cores for 79 days, the fibers were prepared and transferred to GERSTEL micro-vial inserts in an autosampler vial. The micro-vial inserts were placed inside glass GERSTEL TDU tubes, and automated TD-GC/MS analysis was performed using the GERSTEL Multi Purpose Sampler with the ATEX (Automated Tube Exchange) option and a GERSTEL TDU. Gas chromatography was performed on a GC apparatus with a GERSTEL Cooled Injection System (CIS4), and operations were automated and data was integrated with GERSTEL MAESTRO software.
Of the 10 DDT-related analytes, six were detected in almost all sediment core sections, and one compound, 4,4’-DDD was occasionally detected. One compound, 4,4’-DDMS was subject to interference from releases of oligomeric siloxanes.
The automated TD-GC/MS method developed by the researchers was found to be simpler and less expensive than standard extraction and analytical methods, and was efficient, accurate and precise. Because of the greater sample replication that is possible with this method, data was not lost if SPME fibers were lost during the process. The method’s flexibility, in addition to its other benefits, made the techniques useful for determining HOCs at sub-parts per trillion levels.
You can learn more details about Eganhouse and DiFilippo’s work by reading their paper in Journal of Chromatography A here. Or we would be happy to talk with you about how you may incorporate this new method into your HOC analysis.