Seasonal dynamics of the hepatotoxic microcystins in various organs of four freshwater bivalves from the large eutrophic Lake Taihu of subtropical China and the risk to human consumption

So far, little is known on the distribution of hepatotoxic microcystin (MC) in various organs of bivalves, and there is no study on MC accumulation in bivalves from Chinese waters. Distribution pattern and seasonal dynamics of MC-LR, -YR and -RR in various organs (hepatopancreas, intestine, visceral mass, gill, foot, and rest) of four edible freshwater mussels (Anodonta woodiana, Hyriopsis cumingii, Cristaria plicata, and Lamprotula leai) were studied monthly during Oct. 2003-Sep. 2004 in Lake Taihu with toxic cyanobacterial blooms in the summer. Qualitative and quantitative determinations of MCs in the organs were done by LC-MS and HPLC. The major toxins were present in the hepatopancreas (45.5-55.4%), followed by visceral mass with substantial amount of gonad (27.6-35.5%), whereas gill and foot were the least (1.8-5.1%). The maximum MC contents in the hepatopancreas, intestine, visceral mass, gill, foot, and rest were 38.48, 20.65, 1.70, 0.64, 0.58, and 0.61 mu g/g DW, respectively. There were rather good positive correlation in MC contents between intestines and hepatopancreas of the four bivalves (r = 0.75-0.97, p < 0.05). There appeared to be positive correlations between the maximum MC content in the hepatopancreas and the delta(13)C (r = 0.919) or delta(15)N (r = 0.878) of the foot, indicating that the different MC content in the hepatopancreas might be due to different food ingestion. A glutathione (GSH) conjugate of MC-LR was also detected in the foot sample of C. plicata. Among the foot samples analyzed, 54% were above the provisional WHO tolerable daily intake (TDI) level, and the mean daily intakes from the four bivalves were 8-23.5 times the TDI value when the bivalves are eaten as a whole, suggesting the high risk of consuming bivalves in Lake Taihu. (C) 2005 Wiley Periodicals, Inc.

Theoretical study on the formation mechanism of Iso-CH2I-Cl

The dissociation and isomerization reaction mechanism on the ground-state potential energy surface for CH2ClI are investigated by ab initio calculations. It is found that the isomer iso-CH2I-Cl can be produced from either the recombination of the photodissociation. fragments or the isomerization reaction of CH2ClI, rather than from isomerization reaction of iso-CH2Cl-I. Further explanations of experimental results are also presented. (C) 2003 Wiley Periodicals, Inc.

Study on the instability of organic field-effect transistors based on fluorinated copper phthalocyanine

The effects of positive and negative gate-bias stress on organic field-effect transistors (OFET) based on tantalum (Ta)/tantalum pentoxide (Ta2O5)/fluorinated copper phthalocyanine (F16CuPc) structure are investigated as a function of stress time and stress temperature. It is shown that gate-bias stress induces a parallel threshold voltage shift (DeltaV(T)) of OFETs without changes of field-effect mobility mu(EF) and sub-threshold slope (DeltaS). The DeltaV(T) is observed to be logarithmically dependent on time at high gate-bias appropriate to OFET operation. More importantly, the shift is directional, namely, be large shift under positive stress and almost do not move under negative stress. The threshold voltage shift is temperature dependent with activation energy of 0.51 eV We concluded that threshold voltage shift of the OFET with F16CuPc as active layer is due to charge trapping in the insulator in which trapped carriers have redistribution.

Study on cytocompatibility of carboxymethyl-chitosan membranes to skin fibroblasts

Chitosan and carboxymethl-chitosan (CM-chitosan) membranes with different molecular mass were prepared by a casting method. The cytocompatibility of two kinds of polysaccharide membranes to skin fibroblasts that cultured in vitro were studied. The methods were to culture the cells in soaking fluid of membranes and to culture the cells on the membranes directly. The results showed that the soaking fluid had no toxicity to fibroblasts and the biological security of lower molecular mass membranes were better than higher molecular mass membranes, and CM-chitosan membranes were better than chitosan membranes. In addition, the growth of fibroblasts on chitosan membranes was inhibited and the cells would fall off from chitosan membranes after a period of culture. However, the cells adhered and expanded well on CM-chitosan membranes. All these demonstrated that cytocompatibility of CM-chitosan membranes to skin fibroblasts was better than chitosan membranes.