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 b-hexa-chlorocyclohexane (b-HCH), an isomer comprising 5-12% 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%). b-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 b-HCH and a-HCH (60-70% 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 a-HCH with the long-range atmospheric transport (LRAT) as its major transport pathway, b-HCH reached the Arctic mainly through long-range oceanic transport (LROT). The much higher tendency of b-HCH to partition into the water, mainly due to its much lower Henry's Law Constant than a-HCH, produced an exceptionally strong pathway divergence with b- HCH favoring slow transport in water and a-HCH favoring rapid transport in air. The concentration and burden of b-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.(c) 2022 The Authors. Published by Elsevier B.V. on behalf of Chinese Society for Environmental Sciences, Harbin Institute of Technology, Chinese Research Academy of Environmental Sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Using a mass balance box model, the historical loading, removal, and cumulative burden of b-hexa-chlorocyclohexane (b-HCH) in the Arctic Ocean from 1945 to 2020 were investigated. The majority of the loading occurred through ocean currents and river inflow, while atmospheric transport contributed only a small portion. b-HCH accumulated in the Arctic Ocean starting in the late 1940s, reached a peak in 1986, and decreased by 2020. The pathways of b-HCH entering the Arctic differed from those of a-HCH, with b-HCH primarily transported through long-range oceanic transport.