Adsorption of Pb, Cd to Fe, Mn oxides in natural freshwater surface coatings developed in different seasons

Metal oxides(Fe, Mn oxides) in natural surface coatings(biofilms and associated minerals) are believed to play a significant role in the fate and transport of trace metal in aquatic environments. Seasonal variation of Fe, Mn oxides and organic materials in surface coatings, which were developed periodically on glass slides in Nanhu Lake, Jilin Province, China over the time frame of three seasons, was investigated in order to understand the influence of metal oxides on Pb and Cd adsorption to heterogeneous surface coating materials(biofilm). Pb and Cd adsorption was measured under controlled laboratory conditions(mineral salts solution with defined speciation, ionic strength 0 05 mol/L, 25℃ and pH 6 0). The classical Langmuir adsorption isotherm was applied to estimate equilibrium coefficients of Pb and Cd adsorption to the surface coatings. In general, components in the surface coatings varied greatly with seasons altering and obtained higher concentrations in summer while the content of iron oxides always exceeded that of manganese oxides. Correlation analyses between the maximum adsorption of Pb and Cd and components in the surface coatings developed periodically indicated that Pb phase association with Mn oxides and Cd phase association with Fe oxides as well as Mn oxides were statistically significant. Effect of Mn oxides on Cd adsorption was confirmed in view of its higher content in the surface coatings. The importance of ferromanganese oxides for Pb and Cd adsorption to the natural surface coatings developed in different seasons was evidenced.

Screening,Identification,Metal-tolerance Cadmium Biosorption and Application of a Cadmium-Resistant Trichoderma asperellum

This study was designed to screen and identify cadmium-resistant fungi and characterize its cadmium adsorption.A cadmium-resistant strain(HD228)was isolated from cadmium-polluted paddy soil by using the Cd^2+concentration gradient pressure domestication method.According to the morphological characteristics and the analysis of internal transcribed spacers(ITS)region gene sequence phylogenesis,the strain was identified as Trichoderma asperellum.This strain was resistant to Cd at 22 mmol/L with a Cd adsorption rate of up to 79.88%,and it was also resistant to other heavy metals such as Pb,Zn and Cu.The colony diameter decreased as the heavy metal concentration increased,and the colony was out-of-shape when the Cd^2+concentration was 20 mmol/L.The strain HD228 was found to grow well at pH 4 to 8 and a temperature between 20 and 35℃.The optimal growth conditions were established to be pH 5 and temperature of 30℃.Fermented liquid of the strain is neither disease-causing nor inhibitory to rice seedling emergence,and indeed it improves rice seedling and root growth and enhances rice’s detoxification ability under Cd stress.Thus,the Cd-resistant fungus HD228 has the potential for the treatment of Cd-polluted rice paddies.