Adsorption of aqueous anions, such as sulfate, arsenite, and oxalate, to oxide surfaces is important in the retardation of toxic species in the environment, but predicting the surface speciation as a function of environmental parameters is a major challenge. Recent laboratory spectroscopic studies defining surface speciation must be integrated with surface complexation models. However, the latter have neglected the electrostatic work of desorption of water dipoles in treating anion adsorption by ligand exchange. Taking this effect into account permits close quantitative description of anion adsorption and the prediction of anion surface speciation as a function of pH, ionic strength, and surface coverage in agreement with spectroscopic results.

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Abstract. At stations on the Natsui River and the Same River in Fukushima Prefecture, Japan, effects of a heavy rain event on radiocesium export were studied after Typhoon Roke during 21-22 September 2011, six months after the Fukushima Dai-ichi Nuclear Power Plant accident. Radioactivity of 134 Cs and 137 Cs in river waters was 0.009-0.098 Bq L −1 in normal flow conditions during July-September 2011, but it increased to 0.85 Bq L −1 in high flow conditions because of heavy rains occurring with the typhoon. The particulate fractions of 134 Cs and 137 Cs were 21-56 % of total radiocesium in the normal flow condition, but were close to 100 % after the typhoon. These results indicate that the pulse input of radiocesium associated with suspended particles from land to coastal ocean occurred because of the heavy rain event. Export flux of 134 Cs and 137 Cs attributable to the heavy rain accounts for 30-50 % of the annual radiocesium flux from inland to coastal ocean region in 2011. Results show that rain events are one factor contributing to the transport and dispersion of radiocesium in river watersheds and coastal marine environments.

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