Overview

• A PNAS Nexus study sampled sediment around five barrels, including three with white halos, and found pH near 12 along with carbonate enrichment and brucite concretions.
• DDT and its breakdown products were elevated across the region yet showed no increase with proximity to the barrels, indicating the halos are unrelated to DDT leakage.
• Recent mapping has identified roughly 25,000 to 27,000 barrels in the San Pedro Basin, with halos seen around many, but the overall share of affected barrels remains unclear.
• The extreme alkalinity suppresses typical microbial communities and favors alkaliphilic species, pointing to localized ecological disruption that could persist for centuries.
• Researchers cite major unknowns about the specific wastes and extent of contamination and are prioritizing expanded mapping, targeted chemical analyses, long-term monitoring, and noninvasive remediation rather than risky removal.