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Study Finds LA Seafloor ‘Halo’ Barrels Are Leaking Caustic Alkaline Waste, Not DDT

The findings reframe the dump site’s risk by identifying persistent high‑pH zones that can be used to map contamination.

The toxic barrels, which came to public attention in 2020, appear to have "halos" around them — and researchers have finally figured out why.
© Schmidt Ocean Institute
As the sediment dissolves, it creates the odd-looking halos around each barrel.
A discarded barrel on the seafloor off the coast of Los Angeles, California.

Overview

  • Peer‑reviewed research from Scripps Institution of Oceanography in PNAS Nexus analyzed 2021 ROV samples from five barrels in the San Pedro Basin near Santa Catalina Island.
  • Sediments around halo barrels registered about pH 12 and contained a concrete‑like brucite crust, with surrounding white rings formed by calcium carbonate.
  • Regional sediments are contaminated with DDT, but concentrations did not rise nearer the barrels, indicating the halo drums are not the source of that pesticide.
  • Microbial life at halo sites was sparse and dominated by alkaliphilic bacteria, pointing to localized biodiversity loss that has persisted for decades.
  • The total number of affected barrels remains uncertain, early visuals suggest roughly one‑third show halos, and scientists are focusing on mapping and microbial remediation since physical removal could spread pollutants.