Extraction and analysis of low concentrations of DDT, DDE and DDD in small volumes of sediment pore water

As a result of effluent discharges by a previous chemical manufacturer, sediments in the Huntsville Spring Branch-Indian Creek (HSB-IC) near Huntsville, AL are contaminated with DDT and its metabolites. This area was selected as a field location at which to evaluate equilibrium partitioning theory (EqP) to predict the bioavailability of nonionic organic chemicals associated with sediments. An important component of the evaluation of EqP features determination of contaminant concentrations in the sediment interstitial (pore) water. The objective of our study was to develop an analytical method to measure o,p′- and p,p′-DDE, DDD and DDT at low concentrations (< 1 ng/mL) in small volumes (ca., 30 mL) of sediment pore water. Initially, pore water from a clean, uncontaminated (control) sediment was spiked with DDT and its metabolites and extracted with hexane. The extracts were applied to chromatography columns packed with acid silica gel or acid celite to remove interfering compounds. Gas chromatograms of extracts treated with acid celite exhibited lower background interferences and were easier to interpret than chromatograms for samples processed using acid silica gel. The acid celite technique was further assessed by spiking uncontaminated pore water over a range of DDE, DDD and DDT concentrations and evaluating recovery efficiencies for each target analyte. Polychlorinated biphenyl congener, 2,3,5,6-tetrachlorobiphenyl (PCB 065) was determined to be a good compound for monitoring method performance (e.g., analyte recovery). Pore water samples were obtained from nine sampling sites in the HSB-IC system and analyzed for DDT and its metabolites where concentrations ranged from 0.020 ng/mL (detection limit) to 8.200 ng/mL in 30 mL of pore water.