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Biodegradation of γ-hexachlorocyclohexane (lindane) by a nitrogen-fixing cyanobacterium isolated from Chinese paddy soils, Anabaena azotica 118, was investigated. Lindane with an initial concentration of 0.2 mg L −1 in the cultures had no negative effect on the chlorophyll a concentration of A. azotica after 5 d exposure. The tolerance of this cyanobacterium to lindane indicates that it has the potential to biodegrade lindane. The degradation experiments show that the percentage of lindane removal efficiency by A. azotica was 48.8% after 5 d, at an initial lindane concentration of 0.2 mg L −1 and initial A. azotica chlorophyll a concentration of 50 mg L −1 . The calculated half-life was 4.78 d. Elevated culture temperature, irradiation, and usage of nitrate as the nitrogen source in the cultures could increase the biodegradation efficiency of lindane. γ-Pentachlorocyclohexene was detected as a metabolite of lindane. The ability of A. azotica to biodegrade lindane has potential use in the bioremediation for this organochlorine pesticide.

The shallow city river of Baoyang located in China had been eutrophicating with nutrients from domestic sewages for many years. A heavy bloom of Microcystis.aeruginosa in Baoyang River was recorded in 2004 and microcystin-RR (MCRR), the most popular cyanobacterial hepatotoxin microcystins in China, could be detected in the river in the next several years in the filtered waters. To determine the environmental variable factors associated with concentrations of MCRR, samples taken from the beginning of April 2008 to the end of March 2009, were analyzed by high-performance liquid chromatography with photodiode array detection. MCRR, the main microcystins found in the filtered water samples from spring to winter, ranged from undetectable to 4.37μg/L. The highest concentrations of MCRR were found in the late summer in October 2008, and the concentrations of MCRR at the bottom waters were higher than that at the aquatic surfaces. Significant positive relationships (p<0.01) were observed between MCRR and NO 3 -N; but significant negative relationships (p<0.01) were observed between MCRR and pH, COD, NO 2 -N and TN. This research indicated NO 3 -N would be very important for the biosynthesis of MCRR. The relationships between MCRR concentrations and environmental factors were complicated and further researches should be focused on the prediction methods of microcystins by the nonlinear models for their potential health risks.

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