Distributions of Colloidal Trace Metals in Taihu Lake, China

Abstract

Contents of colloidal trace metals(1kD~1μm) in Meiliang Bay, an algal-bloom bay of Taihu Lake, and Gonghu Bay, a macrophytes dominanted bay of Taihu Lake, were investigated in April by using cross-flow ultrafiltration (CFF) technique. In each sampling site, 20 L surface water was pumped and filtrated by 63 μm nylon sieve. The filtered water was carried to laboratory in 2 hours, prefiltrated by 1μm Millipore membrane, and ultrafiltrated by CFF to obtain colloidal concentrated solution. Contents of Fe, Mn and Zn in the pre-filtrated water, colloidal concentrated solution and ultrafiltrate were measured by flame atomic absorption spectrophotometer (FAAS) after digestion with HNO3 and HClO4 mixture solution. Contents of Cd, Cu and Pb were measured by graphite furnace atomic absorption spectrophotometer (GFAAS). Results showed that contents of colloidal trace metals in Taihu Lake were 0.46~0.86 µg/L (22.3% of the totally dissolved partition) for Cu, 2.06~8.24 µg/L (26.3%) for Zn, 2.62~3.70 µg/L (20.7%) for Pb, 3.48~24.79 µg/L (58.9%) for Fe, 0.31~1.62 µg/L (40.4%) for Mn, and 6.71~17.94 ng/L (59.2%) for Cd. And averagely, the colloidal Cu, Pb, Fe, Mn, and Cd occupied 17.4%, 19.1%, 55.1%, 1.98%, and 52.8% of each total contents in lake water respectively. These indicated that the colloidal material in Taihu Lake was an important factor influencing the biogeochemical cycling of trace metals. Furthermore, except for Cd, average contents of colloidal Cu, Zn, Pb, Fe, and Mn in Meiliang Bay were all higher than those in Gonghu Bay. Contents of colloidal trace metals in Taihu Lake were higher than those in coastal oceans, shorter rivers, and lagoons, which may be mainly due to the higher colloidal content and the stronger affinity of colloids with trace metals in Taihu Lake, but were lower than those in longer rivers such as Namoi river in Australia possibly because of its smaller quality of colloids compared with that in Namoi river. It was also suggested that contents of colloidal trace metals largely depended on contents of colloids in natural water bodies.