Zhimei Ma

Simultaneous determination of microcystin contaminations in various vertebrates (fish, turtle, duck and water bird) from a large eutrophic Chinese lake, Lake Taihu, with toxic Microcystis blooms

This is the first to conduct simultaneous determination of microcystin (MC) contaminations in multi-groups of vertebrates (fish, turtle, duck and water bird) from Lake Taihu with Microcystis blooms. MCs (-RR, -YR, -LR) in Microcystis scum was 328 microg g(-1) DW. MCs reached 235 microg g(-1) DW in intestinal contents of phytoplanktivorous silver carp, but never exceeded 0.1 microg g(-1) DW in intestinal contents of other animals. The highest MC content in liver of fish was in Carassius auratus (150 ng g(-1) DW), followed by silver carp and Culter ilishaeformis, whereas the lowest was in common carp (3 ng g(-1) DW). In livers of turtle, duck and water bird, MC content ranged from 18 to 30 ng g(-1) DW. High MC level was found in the gonad, egg yolk and egg white of Nycticorax nycticorax and Anas platyrhynchos, suggesting the potential effect of MCs on water bird and duck embryos. High MC contents were identified for the first time in the spleens of N. nycticorax and A. platyrhynchos (6.850 and 9.462 ng g(-1) DW, respectively), indicating a different organotropism of MCs in birds. Lakes with deaths of turtles or water birds in the literatures had a considerably higher MC content in both cyanobacteria and wildlife than Lake Taihu, indicating that toxicity of cyanobacteria may determine accumulation level of MCs and consequently fates of aquatic wildlife.

Phytoplankton community succession shaping bacterioplankton community composition in Lake Taihu, China

PCR-denaturing gradient gel electrophoresis (DGGE) and canonical correspondence analysis (CCA) were used to explore the relationship between succession of phytoplankton community and temporal variation of bacterioplankton community composition (BCC) in the eutrophic Lake Taihu. Serious Microcystis bloom was observed in July-December 2008 and Bacillariophyta and Cryptophyta dominated in January-June 2009. BCC was characterized by DGGE of 16S rRNA gene with subsequent sequencing. The DGGE banding patterns revealed a remarkable seasonality which was closely related to phytoplankton community succession. Variation trend of Shannon-Wiener diversity index in bacterioplankton community was similar to that of phytoplankton community. CCA revealed that temperature and phytoplankton played key roles in structuring BCC. Sequencing of DGGE bands suggested that the majority of the sequences were affiliated with common phylogenetic groups in freshwater: Alphaproteobacteria, Betaproteobacteria, Bacteroidetes and Actinobacteria. The cluster STA2-30 (affiliated with Actinobacteria) was found almost across the sampling time at the two study sites. We observed that the family Flavobacteriaceae (affiliated with Bacteroidetes) tightly coupled to diatom bloom and the cluster ML-5-51.2 (affiliated with Actinobacteria) dominated the bacterioplankton communities during Microcystis bloom. These results were quite similar at the two sampling sites, indicating that BCC changes were not random but with fixed pattern. Our study showed insights into relationships between phytoplankton and bacterioplankton communities at species level, facilitating a better understanding of microbial loop and ecosystem functioning in the lake.

A systematic study on spatial and seasonal patterns of eight taste and odor compounds with relation to various biotic and abiotic parameters in Gonghu Bay of Lake Taihu, China

A systematic study was conducted on seasonal and spatial patterns of taste and odor (T&O) compounds with relation to biotic and abiotic parameters at fifteen sites in Gonghu Bay of Lake Taihu in 2008. We developed a sensitive and automated method to simultaneously analyze eight T&O compounds (boiling points ranging from 38°C to 239°C) by using Purge-and-Trap (P&T) coupled with GC/MS. Maximum particulate dimethyl trisulfide (DMTS, 69.6 ng/L) exceeded its odor threshold concentrations (OTC, 10 ng/L) and maximum dissolved DMTS was 6.1 ng/L, but still far below concentration in the drinking water pollution incident of Wuxi City in 2007 when DMTS reached 1768-11,399 ng/L. Geosmin (GEO), 2-methylisoborneol (MIB), β-cyclocitral, β-ionone and 2-isobutyl-3-methoxypyrazine (IBMP) occasionally or frequently exceeded their OTCs, whereas 2-isopropyl-3-methoxypyrazine (IPMP) and dimethyl sulfide (DMS) did not. We found for the first time significant correlations between particulate β-cyclocitral and β-ionon concentrations and intracellular and extracellular microcystin concentrations. Spatially, Nanquan Waterworks faced more risk by T&O contamination than Xidong Waterworks. High concentrations of NO(3)-N, TDN and TN could be risky signs of taste and odor events by DMS, DMTS, IPMP, IBMP and GEO.

Factors Affecting Temporal and Spatial Variations of Microcystins in Gonghu Bay of Lake Taihu, with Potential Risk of Microcystin Contamination to Human Health

A field survey of the seasonal variation of microcystin (MC) concentration was performed in Gonghu Bay (a total of 15 sampling sites) of Lake Taihu from January to December 2008. Microcystis spp. biomass and intra-/extracellular MCs were significantly correlated with water temperature, suggesting the importance of temperature in cyanobacterial blooming in the lake. Higher MC concentration was found in summer and autumn, and peaks of Microcystis biomass and intra-/extracellular MC concentrations were all present in October. Spatially, risk of MCs was higher in littoral zones than in the pelagic area. There were significant correlations between N or P concentrations, and Microcystis biomass or MC content, suggesting that N and P levels affected MC production through influencing Microcystis biomass. Intra-/extracellular MCs and Microcystis biomass had negative exponential relationships with TN:TP, and the maximum values all occurred when TN:TP was <25. Multivariate analyses by pcca indicated that intra- and extracellular MC concentrations had better correlations with biological factors (such as Microcystis biomass and chl-a) than physicochemical factors. The maximum concentration reached up to 17 µg/L MC-Lreq, considerably higher drinking water safety standard (1 µg/L) recommended who. So it is necessary take measures reduce exposure risk of cyanobacterial toxins human beings.

Microwave-assisted purge-and-trap extraction device coupled with gas chromatography and mass spectrometry for the determination of five predominant odors in sediment, fish tissues, and algal cells

Off-flavors are among the most troublesome compounds in the environment worldwide. The lack of a viable theory for studying the sources, distribution, and effect of odors has necessitated the accurate measurement of odors from environmental compartments. A rapid and flexible microwave-assisted purge-and-trap extraction device for simultaneously determining five predominant odors, namely, dimethyltrisulfide, 2-methylisoborneol, geosmin, β-cyclocitral and β-ionone, from the primary sources and sinks is demonstrated. This instrument facilitates the extraction and concentration of odors from quite different matrices simultaneously. This device is a solvent-free automated system that does not require cleaning and is timesaving. The calibration curves of the five odor compounds showed good linearity in the range of 1-500 ng/L, with correlation coefficients above 0.999 (levels=7) and with residuals ranging from approximately 77% to 104%. The limits of detection (S/N=3) were below 0.15 ng/L in algae sample and 0.07 ng/g in sediment and fish tissue samples. The relative standard deviations were between 2.65% and 7.29% (n=6). Thus the proposed design is ready for rapid translation into a standard analytical tool and is useful for multiple applications in the analysis of off-flavors.

Off-flavor compounds from decaying cyanobacterial blooms of Lake Taihu

The effect of cyanobacterial bloom decay on water quality and the complete degradation of cyanobacterial blooms in a short period were examined by an enclosure experiment in Gonghu Bay of Lake Taihu, China. Water quality parameters as well as taste and odor compounds during the breakdown of cyanobacterial blooms were measured. Results showed that the decay of cyanobacterial blooms caused anoxic water conditions, decreased pH, and increased nutrient loading to the lake water. The highest concentrations of dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), and beta-cyclocitral were observed in the anoxic water, at 62331.8, 12413.3, and 1374.9 ng/L, respectively. 2-Methylisoborneol was dominant during the live growth phase of cyanobacterial blooms, whereas DMS and DMTS were dominant during the decomposition phase. Dissolved oxygen, pH, and chlorophyll a were negatively correlated with DMS, DMTS, and beta-cyclocitral, whereas total phosphorus, total nitrogen, and ammonium (NH(4+)-N) were positively correlated with DMS, DMTS, beta3-cyclocitral, and beta-ionone. The experimental results suggested that preventing the anaerobic decomposition of cyanobacterial blooms is an important strategy against the recurrence of a malodor crisis in Lake Taihu.

Decrease of NH4+-N by bacterioplankton accelerated the removal of cyanobacterial blooms in aerated aquatic ecosystem

We used aerated systems to assess the influence of the bacterioplankton community on cyanobacterial blooms in algae/post-bloom of Lake Taihu, China. Bacterioplankton community diversity was evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. Chemical analysis and nitrogen dynamic changes illustrated that NH4+-N was nitrified to NO2--N and NO3--N by bacterioplankton. Finally, NH4+-N was exhausted and NO3--N was denitrified to NO2--N, while the accumulation of NO2--N indicated that bacterioplankton with completely aerobic denitrification ability were lacking in the water samples collected from Lake Taihu. We suggested that adding completely aerobic denitrification bacteria (to denitrify NO2--N to N2) would improve the water quality. PCR-DGGE and sequencing results showed that more than1/3 of the bacterial species were associated with the removal of nitrogen, and Acidovorax temperans was the dominant one. PCR-DGGE, variation of nitrogen, removal efficiencies of chlorophyll-a and canonical correspondence analysis indicated that the bacterioplanktonsignificantly influenced the physiological and biochemical changes of cyanobacteria. Additionally, the unweighted pair-group method with arithmetic means revealed there was no obvious harm to the microecosystem from aeration. The present study demonstrated that bacterioplankton can play crucial roles in aerated ecosystems, which could control the impact of cyanobacterial blooms in eutrophicated fresh water systems.

Microcystis aeruginosa/Pseudomonas pseudoalcaligenes interaction effects on off-flavors in algae/bacteria co-culture system under different temperatures

We conducted an experiment to study the interaction effects of Microcystis aeruginosa and Pseudomonas pseudoalcaligenes on off-flavors in an algae/bacteria co-culture system at three temperatures (24, 28 and 32°C). Gas chromatography-mass spectrometry was applied to measure off-flavor compounds dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), 2-methylisoborneol, geosmin (GEO) and β-cyclocitral. During the lag phase of co-cultured M. aeruginosa (first 15days), P. pseudoalcaligenes significantly increased the production of DMS, DMTS and β-cyclocitral at all three temperatures. In the exponential phase of co-cultured M. aeruginosa (after 15days), M. aeruginosa became the main factor on off-flavors in the co-culture system, and β-cyclocitral turned to the highest off-flavor compound. These results also indicated that DMS, DMTS and β-cyclocitral were the main off-flavor compounds in our M. aeruginosa/P. pseudoalcaligenes co-culture system. Univariate analysis was applied to investigate the effects of M. aeruginosa and P. pseudoalcaligenes on the production of off-flavors. The results demonstrated that both M. aeruginosa and P. pseudoalcaligenes could increase the production of DMS and DMTS, while β-cyclocitral was mainly determined by M. aeruginosa. Our results also provide some insights into understanding the relationship between cyanobacteria and heterotrophic bacteria.