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.