Trend of trace metals in precipitation around Okinawa Island, Japan

Abstract

Okinawa Island is located between mainland Japan to the northeast, Taiwan to the southwest and China to the west. In recent years, precipitation with relatively low pH has been observed in the island during winter seasons. This study was conducted to evaluate the potential sources and factors affecting distribution of trace metals in the atmosphere around the northern area of Okinawa Island. The results showed that the trace metal contamination was low comparable to rural areas of less industrialized countries. The annual average depositions were 6.0, 5.2, 4.4, 2.7 and 20.4 kg km − 2 y − 1 for Al, Fe, Mn, Cu, and Zn, respectively. The metals in the precipitation were mainly derived from the dissolution of wind-blown soil particles. The distribution of trace metals across the island showed the influence of road traffic as a source and cause of atmospheric pollution. Aluminium and Fe were found to be high closer to the main road and decreased further away from the road, while Zn and Cu were strongly correlated with average mean pH of precipitation. The variation of concentrations in the island was attributed to the distance from the main road, average rain pH at a particular sampling location and wind speed and direction. A strong correlation between lithological elements (Al and Fe) and anthropogenic elements (Zn and Cu) indicates that they were carried by the same particles and experienced similar scavenging mechanism during dissolution process.