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.