Persistence-Directed Testing of Chemicals Discharged from Offshore Oil Platforms Combined with Nontargeted Analysis

Persistent chemicals discharged into the sea can pose long-term, irreversible risks. New approaches are needed to elucidate the number and type of persistent chemicals, particularly in complex mixtures and high-volume discharges. We introduce a novel "Persistence-Directed Testing" approach that combines environmentally relevant biodegradation tests with nontarget analytical methods. Complex produced waters from two offshore oil platforms in the North Sea served as case studies. In the biodegradation tests, produced waters were diluted 1:200 with seawater from the site of discharge (inoculum). Biotic test systems and abiotic controls were incubated at 9 °C. At day 60 nontarget analyses were performed by Solid Phase Microextraction coupled to GC-MS and Solid Phase Extraction coupled to LC-HRMS. Primary biodegradation and persistence were determined based on biotic/abiotic peak area ratios. Over 600 chemicals passed the quality control filtering criteria, and the persistent fraction of chemicals discovered by GC-MS was 4% and that discovered by LC-HRMS was 32-44%. Spectral library matches and computational modeling of the LC-HRMS data annotated several persistent chemicals as N-substituted aromatic ring structures. These findings demonstrate the value of a persistence-directed approach in uncovering the hidden burden of unidentified persistent chemicals in environmental discharges and highlight the urgent need for enhanced treatment of produced water discharges.