Geospatial and Temporal Inventory for Industrial DDT Waste Disposal to a Deep Coastal Ocean Environment

Historical ocean
disposal of industrial DDT (dichloro-diphenyl-trichloroethane)
waste off Southern California is implicated in extensive ecological
impacts extending well beyond this region, but details around disposal,
transport, and fate are poorly characterized for deep ocean settings
such as this. Here, we present results from an 814 km2 survey
of a primary disposal area, San Pedro Basin, by mapping the spatial
distribution and depositional history of DDT and its immediate daughter
products DDD (dichloro-diphenyl-dichloroethane) and DDE (dichloro-diphenyl-dichloroethylene).
We find highly elevated concentrations for all three compounds throughout
the study area, with “hotspots” from primary deposition
and secondary migration processes. The majority of DDT and DDD is
buried within a thin sediment layer consistent with peak deposition
in the 1950s, whereas substantial amounts of DDE still linger in overlying
sediments with an apparent contribution from the Palos Verdes Shelf.
We characterize intense spatial variability across distance scales
and develop an approach to address the resulting uncertainty toward
estimating a total modern burden of ∼30–36 tonnes (DDT,
DDD and DDE) in this area. These results are foundational for informing
DDT’s deep-sea transport and transformation processes and for
defining the linkage of offshore disposal to current ecological problems
in this region and beyond.