Simultaneous determination of methylmercury (MeHg) and ethylmercury (EtHg) in natural waters was developed using propylation-headspace (HS)-GC/MS. Sodium tetra (n-propyl) borate was used as a propylating agent. Mercury compounds were extracted as dithizon-complex by toluene, then back extracted into water by evaporating the toluene. The mercury species in the water was propylated in the headspace vial and analyzed with HS-GC/MS. The limits of detection of MeHg and EtHg for 1 L water sample were 0.005 and 0.007 ng/L, respectively. The average recoveries of MeHg and EtHg, performed for several natural water samples, were 91 and 87%, respectively. Using this method, determinations of a small amount of MeHg and EtHg in natural waters are applicable.

Since the eruption of Mt.Ioyama, Miyazaki Pref., Japan on 19^th April 2018, arsenic was detected in the river exceeding the regulatory limit, which affected the planting of rice in 2018. In this study, we collected water and sediments along the Akago-Nagae River from the Ebino Bridge to the Hishikari canoe Stadium in order to clarify the dynamics of the drained arsenic in the river. Arsenic concentration in the river water decreased toward the downstream, however, from the Ebino Bridge to the Nagae Bridge, it was diluted by the increase of the river water. On the other hand, the adsorption of oxoanion by ferrihydride from the Nagae Bridge to the Yuda Bridge removed arsenic from river water.