PARENT SESSION

PT16 Biological Testing Data in Sediment Management Decisions
Exhibit Hall
8:00 AM - Tuesday

(PT260) Effects of TOC levels and grain size distributions on sediment DDT analysis and bioaccumulation potential.

Bodensteiner, S¹, Wiechmann, M², Zinkl, M¹, McCloskey, J¹, Word, J¹, ¹ MEC Analytical Systems - Weston Solutions, Inc., Tiburon, CA, USA² U.S. Army Corps of Engineers, San Francisco District, San Francisco, CA, USA

ABSTRACT- As an ecologically persistent pesticide, DDT continues to pose a threat to various aquatic ecosystems within the U.S. despite the 32-year ban on its use. In many cases, large-scale clean-up efforts have mitigated the extent and magnitude of ecological impairment caused by DDT contamination in affected coastal areas. However, clean-up efforts are typically unsuccessful in complete elimination of the presence or threat of DDT in contaminated sediments. Many sites are left with sediment DDT concentrations near the threshold for eliciting adverse biological effects, including bioaccumulation. Therefore, it is critical to understand how common sediment characteristics can influence DDT uptake in aquatic organism tissues when this pesticide is present at reduced but not assuredly innocuous concentrations. It is also critical to understand the significance of analytical precision when measuring sediment DDT concentrations within this range. The two study objectives were to 1) evaluate the effect of varying TOC levels and grain size distributions on bioaccumulation potential of DDT present in moderately contaminated sediments, and 2) assess the analytical variability expected when measuring DDT concentrations. Sediment samples were collected from a marine harbor with wide variations in TOC and grain size distributions, and DDT concentrations previously measured up to 303 g/kg dry weight. Four samples exhibiting the greatest variation in TOC and grain size were selected for steady-state bioaccumulation testing using the clam Macoma nasuta and polychaete Nephtys caecoides. Samples were also split three ways and submitted to three chemistry labs certified for pesticide analysis (EPA 8081). Bioaccumulation results showed significant correlations between tissue uptake and both TOC and grain size distributions. Results of sediment DDT analysis submitted by the laboratories showed significant intra-sample variability (12 to 43% CV). Data normalization based on surrogate spike recoveries allowed for an accurate estimation of the variability that can be expected with sediment DDT analysis.

Key words: Sediment, DDT, Bioaccumulation, Variability