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Reductive dechlorination rate data for 4,4'-DDE in sediments of the Palos Verdes Shelf, CA (1981-2010)

Metadata Updated: October 29, 2023

Wastes from the world’s largest manufacturer of DDT were released into the Los Angeles County municipal sewer system from 1947 to 1971. Following primary treatment, the effluent was discharged from a submarine outfall system whereupon a portion of the DDT and associated degradation products were deposited in sediments of the Palos Verdes Shelf (PVS). Parent DDT is present only in trace amounts in the sediments today, the vast majority having been transformed to DDE shortly following deposition. Previously believed to be inert, DDE is slowly being converted to DDMU and DDMU to DDNU via microbially-mediated reductive dechlorination (RDC). Kinetic and compositional data suggest that this process began sometime in the mid- to late 1970s. Rates of DDE RDC in shelf sediments are spatially variable and have proven difficult to determine accurately. This limits our ability to understand the factors controlling RDC rates and to predict the course of natural recovery. In the present study, concentrations of ten DDT compounds and twelve PCB (polychlorinated biphenyl) congeners were determined in cores collected at two locations on the PVS (stations 3C, 6C, ~7 km and ~2 km downcurrent from the outfalls, respectively). DDE inventories, normalized to those of non-degrading PCB congeners having similar physico-chemical properties, were modeled to yield first-order RDC rates for the period 1981-2010. Average rates at the two sites were 0.044 ± 0.004 (3C) and 0.008 ± 0.002 yr-1 (6C), respectively, with depth-dependent RDC rates at station 3C (1992-2003) ranging from 0.0025 to 0.102 yr-1. Comparison of RDC and total loss (i.e., RDC + physical loss) rates suggests that the average per cent loss of DDE due to RDC is ~90% at station 3C (1981-2010) and ~57% at station 6C (1992-2010). Trajectories of adjusted molar inventories of DDE, DDMU, and DDNU were forecast using a first-order multi-step reaction series model. The results for DDE are consistent with the normalization procedure, RDC rates at stations 3C and 6C were 0.036 ± 0.002 yr-1 and 0.010 ± 0.001 yr-1, respectively. At station 6C, the DDE to DDMU transformation appears to be the rate limiting step in the reaction sequence, DDE (k_1 ) ⃗ DDMU (k_2 ) ⃗ DDNU (k_3 ) ⃗ unidentified compound(s), whereas at station 3C RDC rates for DDE and DDMU are roughly equivalent. At both locations the transformation rate of DDNU is 7-20 times that of the other steps. Estimated half-lives of DDE at stations 3C and 6C based on the M-SRS model results are ~19 and 72 years, respectively.

Access & Use Information

Public: This dataset is intended for public access and use. License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Metadata Created Date June 1, 2023
Metadata Updated Date October 29, 2023

Metadata Source

Harvested from DOI EDI

Additional Metadata

Resource Type Dataset
Metadata Created Date June 1, 2023
Metadata Updated Date October 29, 2023
Publisher U.S. Geological Survey
Identifier USGS:5980bc7fe4b0a38ca278a8af
Data Last Modified 20200831
Category geospatial
Public Access Level public
Bureau Code 010:12
Metadata Context
Metadata Catalog ID
Schema Version
Catalog Describedby
Harvest Object Id 2d6327ae-9979-4dd9-949f-f716a8070f41
Harvest Source Id 52bfcc16-6e15-478f-809a-b1bc76f1aeda
Harvest Source Title DOI EDI
Metadata Type geospatial
Old Spatial -118.96270751841,33.426491758717,-117.62786865128,34.197811214321
Publisher Hierarchy White House > U.S. Department of the Interior > U.S. Geological Survey
Source Datajson Identifier True
Source Hash e18751fe161ba469337e1550a44bbfd1785dc971d8fa57caaf255147a326ef87
Source Schema Version 1.1
Spatial {"type": "Polygon", "coordinates": -118.96270751841, 33.426491758717, -118.96270751841, 34.197811214321, -117.62786865128, 34.197811214321, -117.62786865128, 33.426491758717, -118.96270751841, 33.426491758717}

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