Modeling historical budget for β-Hexachlorocyclohexane(HCH)in the Arctic Ocean:A contrast to α-HCH

The historical annual loading to,removal from,and cumulative burden in the Arctic Ocean for β-hexachlorocyclohexane(β-HCH),an isomer comprising 5e12%of technical HCH,is investigated using a mass balance box model from 1945 to 2020.Over the 76 years,loading occurred predominantly through ocean currents and river inflow(83%)and only a small portion via atmospheric transport(16%).β-HCH started to accumulate in the Arctic Ocean in the late 1940s,reached a peak of 810 t in 1986,and decreased to 87 t in 2020,when its concentrations in the Arctic water and air were~30 ng m^(-3)and~0.02 pg m^(-3),respectively.Even though β-HCH and α-HCH(60e70%of technical HCH)are both the isomers of HCHs with almost identical temporal and spatial emission patterns,these two chemicals have shown different major pathways entering the Arctic.Different from α-HCH with the long-range atmospheric transport(LRAT)as its major transport pathway,β-HCH reached the Arctic mainly through long-range oceanic transport(LROT).The much higher tendency of β-HCH to partition into the water,mainly due to its much lower Henry's Law Constant than α-HCH,produced an exceptionally strong pathway divergence with β-HCH favoring slow transport in water and α-HCH favoring rapid transport in air.The concentration and burden of β-HCH in the Arctic Ocean are also predicted for the year 2050 when only 4.4-5.3 t will remain in the Arctic Ocean under the influence of climate change.