High cadmium concentration in the estuarine sediment of the Miyara River (Ishigaki Island)

Anthropogenic pollutants, such as pesticides, heavy metals, and petroleum hydrocarbons discharged into marine coastal regions, are currently receiving considerable attention because of their potential to damage coral reefs and their cumulative damage to the ecosystem (Ramos and Ohde 2004 Fabricius 2005). Cadmium (Cd) is a nonessential trace heavy metal, and its polluting effects and toxicity for organisms on a global scale are serious problems (e.g., Satarug et al. 2003). Anthropogenic activities, such as agriculture, are a possible source of the Cd that enters the coastal marine ecosystem (de Boo 1990 Bennet-Chambers et al. 1999). Cadmium from phosphate fertilizer used in agricultural fields is transferred by river discharge and ground water, leading to considerable accumulation of the element in the estuarine sediment and marine organisms (Gifford et al. 2005). This short paper reports a preliminary study of the Cd concentration in sediments and benthic animals collected from three river estuaries of Ishigaki Island. The study suggests the outflow of Cd with an agricultural origin into the coastal areas of the island. STUDY SITES