Sanitation report: post‑fire ocean testing shows no immediate lethal threats; arsenic and some PAHs within pre‑fire ranges

Los Angeles Sanitation environmental monitoring staff outlined coordinated sampling and testing in Santa Monica Bay after the Palisades fire and said recent results do not indicate an immediate lethal threat to human health or marine life. However, staff and council members said continued monitoring, coordination with county and state partners, and preparation for wet‑season first‑flush risks remain priorities.

What the testing showed Stacy Karnia, laboratory manager in LA Sanitation’s environmental monitoring division, described efforts by local, regional and academic groups to assemble coordinated sampling across the shoreline and nearshore bay. Various agencies (LA County Public Health, the Los Angeles Regional Water Board, SCCWRP/SCCWRP partners and academic institutions including Scripps) collected samples for heavy metals, polycyclic aromatic hydrocarbons (PAHs), bacteria and other analytes.

Karnia said that initial samples showed elevated levels of some metals (arsenic, copper, zinc) and PAHs in very early sampling events but that subsequent review by the Regional Water Board and LA County Public Health concluded most measurements were below EPA risk‑based screening levels for recreation and ocean plan objectives for fish consumption. Arsenic concentrations were noted at multiple sites and events, but water‑board reviewers found those arsenic levels were within pre‑fire background concentrations historically observed in the Los Angeles region and therefore not likely attributable to the fire.

Ongoing monitoring and coordination LA Sanitation conducts routine NPDES‑required monitoring across Santa Monica Bay (sampling more than 54 miles of beaches at multiple stations), operates quarterly water‑quality surveys (CTD profiles and multi‑depth sampling), and collects fish and sediment samples for long‑term comparison. Sanitation staff said sampling plans and an LA County dashboard (public health) provide accessible results; the dashboard was updated as recently as 09/12/2025.

Sanitation emphasized two practical points: (1) there are currently no standardized health thresholds tied to “post‑fire ocean” recreational use, so agencies have used EPA risk‑based screening tools and ocean plan benchmarks to interpret results; and (2) wet‑season “first flush” runoff remains a risk, and agencies are coordinating to trigger watershed task‑force activities and alert/warning systems when rain‑driven debris flows are forecast.

Quote "Overall, recent testing does not reveal any urgent lethal threats. Data is below the calculated risk thresholds for human health," Stacy Karnia said, summarizing the combined multi‑agency review.

Next steps LA Sanitation and partner agencies will continue shoreline bacteria monitoring, sediment chemistry testing, trawl surveys and a local seafood safety survey scheduled to begin in October. City staff are participating in a multi‑agency post‑fire aquatic habitats working group and in a satellite‑enabled monitoring advisory project with JPL and SCCWRP to enhance remote sensing of fire‑impacted waters.

Ending Committee members thanked sanitation staff and urged continued vigilance ahead of the rainy season, noting the need for long‑term monitoring to inform future policy and mitigation choices.