Most of fresh water on earth exists in the frozen state but chemical reactions in frozen solutions have been less investigated. When aqueous solutions freeze, dissolved substrates are excluded from the ice lattice and concentrated in ice grain boundaries. As a result, many environmental reactions taking place in ice are significantly different compared to aqueous counterparts. We have investigated several homogeneous and heterogeneous redox chemical reactions in ice, especially those which have environmental significance. First, we studied the reductive dissolution of iron oxides and manganese oxides trapped in ice and investigated their relevance to bioavailability. When iron or manganese oxides were trapped in ice, the release of metal ions (Fe2+, Fe3+, and Mn2+) upon thawing was significantly accelerated. The enhanced dissolution of naturally occurring metal oxides in ice can serve as an efficient pathway for supplying bioavailable metal ions to organisms in the environment. We also studied the redox conversion of chromate and arsenite as model inorganic oxyanion contaminants in ice. The simultaneous redox transformation of chromate (Cr(VI)) and arsenite (As(III)) was greatly enhanced in ice. Another example is the photooxidation of iodide to triiodide and I2 in ice phase. The production of triiodide through iodide photooxidation, which was negligible in aqueous solution, was significantly accelerated in ice phase. All the above environmental redox chemical reactions occurring in ice may have significant effects on the chemical transformation processes in the icy environment such as polar region, upper atmosphere, and frozen soil.

Ice grain boundary interface as a non-conventional reaction medium of environmental chemical processes

251st National Meeting (2016)

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