The behavior of selenium and arsenic in the Zhujiang (Pearl River) Estuary, South China Sea

Two cruises were undertaken to study the selenium species and arsenic, and their relationship with marine production in the Zhujiang (Pearl River) Estuary, covering both wet (July, 1999) and dry (January, 2000) seasons. Concentrations of dissolved Se (IV), Se (VI) and arsenic in the Zhujiang River are generally within the range of Chinese rivers and other large systems, like the Rhone River and Panama River. In January 2000, the concentration of selenium was lower than that in the July 1999. Total dissolved inorganic selenium averaged 2.77 nmol L−1 in the winter and 4.15 nmol L−1 in the summer, with Se (VI) accounting for 55% and 58%, respectively. Total dissolved inorganic arsenic averaged 25.8 nmol L−1 in the winter and 22.3 nmol L−1 in the summer. The data indicated that dissolved arsenic and selenium did not behave conservatively in the estuary. An important mobilization of dissolved selenium and arsenic was observed from the river up to halfway in the estuary. Both input flux (from river to estuary) and output flux (from estuary to coastal zone) of dissolved selenium and arsenic were calculated from statistical interpretations of the salinity profiles.