The production and mobility of DDT metabolites within sediments as controlled by the local diagenetic environment

Currently, there is no routine analytical method for sensitively measuring concentrations of most of the known DDT+ breakdown products and related byproducts. Berelson and partners will develop an identification and quantification method for at least 23 DDT+ compounds at very low concentrations at various ocean depths. Berelson will also investigate whether “fingerprinting” (‘isotomics’) of DDT sources is possible—in other words, this work will reveal if it will be feasible to trace DDT contamination from marine animals back to exact sources of DDT contamination on the seafloor. Berelson will weave the various threads of this project together into a model depicting DDT+ migration in deep water sediments. The produced model and novel analytical techniques will be critical for accurate and efficient future risk assessments for human and ecological health.

Detailed Research Objectives:

  1. Develop a sensitive and efficient ion-monitoring GC/MS/MS method to quantify DDT+ compounds in sediments and water at low (sub-ppb) concentrations.
  2. Measure the vertical distribution of soluble DDT+ metabolites, particularly DDA, in sediment porewaters using gold-standard sampling methods. Samples will be collected via an in-situ pore water sampler coupled to a large multicorer device at three contrasting sites between Los Angeles Harbor and Dumpsite #2 (i.e., shelf near the Whites Point Outfall, slope, deep basin) 
  3. Understand how the sedimentary diagenetic environment impacts the pathway and rate of DDT+ degradation. Using the analytical method established in objective 1, the spatial distribution of  DDT+ compounds will be measured, along with a suite of other measurements to fully characterize the diagenetic environment (e.g., DIC, ammonium, nitrate, Fe, Mn and sulfide), in both sediments and porewaters from 3 distinct sites between LA Harbor and Dumpsite #2 (i.e., shelf near the Whites Point Outfall, slope, deep basin).
  4. Assess whether DDT from the Palos Verdes shelf and deep-basin Dumpsite #2 have unique isotopic profiles in order to determine the viability of ‘fingerprinting’ DDT sources.
  5. Develop a reaction-transport model of soluble DDA migration in deep water sediments to understand how much DDT metabolite could be escaping the sediment column and thus transported back into the water column.

 

Key Results to Date:

  • In a 2023 research cruise, nearly every  DDT+ compound targeted by the new methods was detected, some at very high levels.
  • Some of the highly-detected molecules are not targeted by Environmental Protection Agency (EPA) methods. If these patterns persist in sediments from the deeper San Pedro basin, it indicates there are many more compounds of concern in the sediments than just the 6 DDT+ congeners targeted by EPA methods and previously studied.
  • The newly developed protocols will be used by multiple teams now studying  DDT+ in the Palos Verdes channel.

 

Principal Investigators:

  • William Berelson, Ph.D., University of Southern California
  • Alex Sessions, Ph.D. California Institute of Technology 
  • Hope Alisa Johnson, Ph.D., California State University, Fullerton
  • Lisa Collins, Ph.D., Santa Monica College

 

Funding:

California State Water Resources Control Board

 

Additional Info and Publications: 

 

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