Final synthesis report for factors controlling DDE dechlorination rates on the palos verdes shelf: A field and laboratory investigation

This project was organized into separate field and laboratory studies aimed at answering “18
questions” in the original Scope of Work (cf., section 2 of this report, Background, for
explanation). Because of some early results, certain questions became irrelevant and were,
therefore, not pursued. In other cases, there simply was not enough time to complete the
originally planned studies. On the other hand, additional work, not identified in any of the
original “18 questions”, was carried out for purposes of addressing specific issues of concern to
the USEPA (United States Environmental Protection Agency). Examples of the latter include: 1)
the analysis of an expanded list of sediment cores for DDX (DDX refers to the ten DDT-related
compounds of interest in this study; cf., Eganhouse et al., [1]) and selected PCB congeners to
facilitate estimation of site-specific reductive dechlorination (RDC) and total loss rates, 2)
analysis of gravity and box cores for trace elements to allow stratigraphic alignment, and 3)
determination of the extent of mineralization of p,p’-DDE (1-chloro-2-[2,2-dichloro-1-(4-
chlorophenyl)ethyl]benzene) in microcosm experiments.
In this Executive Summary, we offer a brief recapitulation of what was learned about the
factors controlling reductive dechlorination of p,p’-DDE in Palos Verdes Shelf (PVS) sediments
using the “18 questions” as a structural guide. The summary is written in narrative form, but
references to specific sections (corresponding to the “18 questions”) are identified
parenthetically in the text so that the reader can explore the expanded answers that appear later in
the report.