Contamination by organochlorine pesticides from rivers

The contamination of organochlorine pesticides (OCPs) from the selected rivers in Okinawa Island was investigated to estimate the current status of pollution in water, plants and surface sediments in these rivers. The Aja River, Asato River, Houtoku River, Kokuba River and Okukubi River were selected for this study. The concentration of the total pesticides were in the range of 0.94-231.8 ng/L in river water, 0.006–191.6 ng/L dry weight in river sediments and 0.001–55.8 ng/L dry weight in plants. Among the OCPs, ΣHCB of α-BHC,β-BHC and Aldrin were the common detected compounds in river water. The α-BHC, Aldrin and Dieldrin were the most frequent detected compounds in river sediments and α-BHC and Dieldrin were the common OCPs detected in plants. Aldrin, Dieldrin and ΣHCB were in abundance. Various contamination patterns between the selected river water, sediments and plants were observed. Aja River, Asato River and Houtoku River were contaminated with α,β,δ,γ- BHC, Aldrin and Dieldrin (water and sediments) whereas the main OCPs in Kokuba River and Okukubi River were Dieldrin (plants) The OCPs levels in all rivers were generally below guideline values in Japan, but some sites displayed levels which exceeded the EC and WHO Standards for Aldrin, Dieldrin and α,β-BHC.     

Effects of dry density and exchangeable cations on the diffusion process of sodium ions in compacted montmorillonite

As a part of the safety assessment of the geological disposal of high-level radioactive waste, the effects of dry density and exchangeable cations on the diffusion process of Na⁺ ions in compacted bentonite were studied from the viewpoint of the activation energy for diffusion. The apparent self-diffusion coefficients of Na⁺ ions in compacted Na-montmorillonite and in a Na- and Ca-montmorillonite mixture were determined by one-dimensional, non-steady diffusion experiments at different temperatures and dry densities. A unique change in activation energy as a function of dry density was found for the Na⁺ ions in compacted Na-montmorillonite. The activation energy suddenly decreased from 18.1 to 14.1 kJ mol^− 1 as the dry density increased from 0.9 to 1.0 Mg m^− 3, whereas it increased to 24.7 kJ mol^− 1 as the dry density increased to 1.8 Mg m^− 3. Examination of the effect of exchangeable cations on the activation energies determined that the activation energies were almost constant, approximately 25 kJ mol^− 1, for the montmorillonite specimens at a dry density of 1.8 Mg m^− 3. However, three different activation energy values were obtained at a dry density of 1.0 Mg m^− 3. These findings cannot be explained by the conventional diffusion model (the pore water diffusion model), which suggests that the predominant diffusion process alternates among pore water diffusion, interlayer diffusion, and external surface diffusion.