Can water dating trace the transport history of HCHs in the ocean?

Long-range atmospheric and oceanic transport play a crucial role in the accumulation of persistent organic pollutants (POPs), including hexachlorocyclohexanes (HCHs), in the Arctic Ocean. Herein, transient tracers, specifically chlorofluorocarbon-12 and sulfur hexafluoride, were used to determine the ventilation time of HCHs. Results revealed that dissolved HCHs can penetrate to a depth of ~500 m in the western Arctic Ocean, corresponding to water masses with a mean age of 45 ± 14 years. The average long-range transport time for α-HCH from initial atmospheric release to entering the western Arctic Ocean was estimated to be >30 ± 5 years, indicating continued moderate to high ecological risks from HCHs in the Arctic. This study demonstrates that transient tracers serve as effective water dating tools to elucidate the transport history of stable POPs in the ocean, contributing to a better understanding of their environmental characteristics and fate.