UC San Diego

The San Pedro Basin (SPB) contains thousands of DDT-production waste barrels dumped on the seafloor from 1947 to 1961. DDT, a harmful pesticide now banned, still impacts California marine life. This study evaluates the relationship between these waste barrels, DDX concentrations (DDT + related metabolites), and benthic macrofaunal assemblages. It analyzed sediment samples from around six waste-barrels and three background sites to address (1) the DDX concentration and depth in relation to the barrels, (2) barrel-proximity effects on macrofaunal (> 300 µm) community structure, vertical distribution, or diversity of the macrofauna, (3) the potential relationship between DDX and macrofauna density, and (4) the potential role of the macrofauna to mix or mobilize DDX. DDX concentration was highest in the 2-6 cm fraction but showed no correlation with macrofaunal density. Macrofauna densities, relatively low (1553-11802 ind/m2) compared to other low-oxygen areas of similar depth. Dominant among the macrofauna were Entoprocta (Barentsiidae), but nematodes were by far the most numerically abundant group. Paraonid, dorvilleid, and cirratulid polychaetes were present. Diversity was lowest within the bacterial halos surrounding the barrels and highest adjacent to the barrels. There is potential for the macrofauna to remobilize DDX into the water column and ultimately the SPB food web, but macrofaunal densities are low. Overall, the study suggests waste barrels have minimal impact on macrofauna communities. However, a broader regional survey, including megafauna and pelagic biota, is necessary for a more comprehensive understanding of how DDX is mobilized in the Southern California Borderland.