MP9 Metals and Bioaccumulation
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(TSU-1115-809290) Relative significance of dissolved organic carbon and cations influencing metal toxicity during biosorption process.

Tsui, Martin^{1, 2}, Wang, Wen-Xiong³, Wong, M¹, ¹ Croucher Institute for Environmental Sciences, Hong Kong Baptist University, Hong Kong, China² Department of Environmental Toxicology, Clemson University, Pendleton, South Carolina, USA³ Department of Biology, Hong Kong University of Science and Technology (HKUST), Hong Kong, China

ABSTRACT- Biosorption of metals using macroalgae can release dissolved organic carbon (DOC), which may influence metal toxicity and bioavailability of metals in wastewater effluents. In this study, we examined how the macroalgae-derived DOC (from Sargassum hemiphyllum) could affect the acute toxicity of copper (Cu) and cadmium (Cd) to a freshwater cladoceran, Daphnia magna. In the first experiment, different amounts of potassium (K)-loaded macroalgae were added in artificial hard water (M7 medium) to generate different DOC levels, and the 48-h LC50s of Cu and Cd to D. magna were assessed. The Cu toxicity decreased with DOC levels but became relatively constant after DOC = 8.1 mg/L, while Cd toxicity decreased with DOC levels but increased sharply after DOC = 22 mg/L. One mechanism underlying the constant or increasing toxicity with DOC concentrations was the release of a large amount of K and the simultaneous biosorption of protective cations (i.e. magnesium or Mg and calcium or Ca). In the second experiment, K-loaded macroalgae were incubated with ultrapure water only. The DOC-containing water was spiked with the constituents of the M7 medium to prevent the removal of Mg and Ca from the water. The Cu toxicity decreased linearly with increasing DOC levels (while maintaining the Mg and Ca levels), but Cd toxicity was not related to DOC levels. In the third experiment, a short-term Cu accumulation test using D. magna with or without macroalgae-derived DOC (at comparable Mg and Ca levels) was conducted. It was noted that Cu uptake decreased in the presence of DOC, suggesting that DOC-Cu complex reduced the Cu bioavailability. It can be concluded that biosorption could release DOC, as well as remove the protective cations in the treated effluent. The final metal toxicity and bioavailability would depend on the relative magnitude of the two processes.

Key words: Biosorption, Sargassum hemiphyllum, Daphnia magna, Metal toxicity