The photoconversion of gamma-hexachlorocyclohexane under UV irradiation in water, snow and ice

The photochemistry of organic pollutants has received increasing attention in ice and snow. In this work, the photoconversion of gamma-hexachlorocyclohexane (γ-HCH) under UV irradiation was investigated in water, snow and ice. The photoconversion rate, products and mechanisms were inspected, and the effect of inorganic ions (NO₂⁻, NO₃⁻, HCO₃⁻ and Fe²⁺) was discussed. The results showed that γ-HCH could be photoconverted in water, snow and ice, with the photoconversion rate being fastest in snow, and slowest in ice. All photoconversion could be described by the first-order kinetics model. In water, snow and ice, the common photoproducts of γ-HCH were alpha-hexachlorocyclohexane (α-HCH) and pentachlorocyclohexene. α-HCH was generated by a change in the bonding of a chlorine atom in γ-HCH; pentachlorocyclohexene was generated by the removal of a molecule of chlorine hydride from a molecule of γ-HCH. Different concentrations of NO₂⁻, NO₃⁻ and HCO₃⁻ all inhibited the photoconversion of γ-HCH, and the inhibition effect decreased with increasing concentrations of NO₂⁻ and NO₃⁻, but increased with the increasing concentrations of HCO₃⁻. Different concentrations of Fe²⁺ promoted the photoconversion of γ-HCH in water and ice, but had little effect in snow.