State Water Board hears contaminants‑of‑emerging‑concern update; 6PPD‑quinone monitoring and Caltrans adaptive management highlighted

State Water Board staff updated members June 16 on the board’s contaminants‑of‑emerging‑concern (CEC) program and presented early results from a pilot monitoring effort that coupled targeted chemistry with cell bioassays and untargeted analysis.

Pilot monitoring and bioassays: Dr. Manuela Romano de Orta described a CEC pilot that augmented the SPoT (stream pollution trends) monitoring network with water‑column testing, cell bioassays and untargeted chemical analysis. The pilot compared traditional whole‑organism toxicity tests (water flea and amphipod endpoints) with multiple cell bioassays that probe biological pathways (hormone signaling, oxidative stress). "Cell bioassays show strong potential as early screening tools for water quality," Romano de Orta said, noting some sites were bioactive in cell tests even where whole‑organism toxicity was not yet observed.

Why it matters: Staff said bioassays can prioritize sites for more intensive follow‑up and that comparing bioassay responses to literature effect‑based trigger values (EBTs) helped identify locations of concern. The pilot is expanding to more sites and broader diversity to strengthen proof of concept and calibrate EBTs.

6PPD‑quinone monitoring and Caltrans findings: Caltrans representatives (Alan Laca and consultant Dr. Khalil Abusaba) briefed the board on a four‑year stormwater monitoring program focused on 6PPD‑quinone, a tire additive oxidation product first linked to salmon kills in 2020. Caltrans reported more than 700 measurements at 56 locations and used a conceptual receiving‑water model (edge‑of‑pavement concentration × attenuation ÷ dilution) to assess risk to sensitive fish (coho salmon, rainbow trout). Of 12 fish‑passage sites evaluated, 10 generally were not at risk of exceeding EPA guidance levels for coho (11 ng/L) after accounting for attenuation and dilution; two sites occasionally showed higher readings but were not coho habitat, and none exceeded about 100 ng/L. Caltrans also reported before‑and‑after and side‑by‑side pavement studies that detected no field‑level increase in 6PPD‑quinone after installation of rubberized asphalt layers and emphasized that rubberized asphalt mixes include crumb rubber bound into bitumen, which reduces leachability in bench studies.

DTSC alternatives work: Kelly Grant (DTSC) summarized the Safer Consumer Products alternatives analysis process for tires. Most of the tire market submitted preliminary alternative analyses; DTSC added PPD derivatives as a candidate chemical class to prevent simple substitution of one PPD for another with similar hazards. Grant cautioned that developing and certifying new anti‑degradants that maintain tire performance and scale manufacturing could take years.

Public comment and interagency coordination: Staff and board members emphasized coordination with EPA, Caltrans, DTSC and regional boards. Public commenters urged the board to pursue numeric objectives and permit limits to prevent discharges to sensitive coho streams and to restrict crumb rubber uses where runoff may concentrate 6PPD‑quinone.

Next steps: CEC staff will expand pilot monitoring, support a North Coast collaborative effort for coho habitat sites, and bring draft data‑quality and communications documents for broader staff workshops later this year. Caltrans will finish remaining fish‑passage site monitoring over the next one or two wet seasons and update its white paper with new rubberized asphalt and treatment‑effectiveness data.

Ending: The board heard that CEC methods and interagency responses are evolving; staff said new monitoring and coordination will inform whether and where regulatory action is needed.