Accumulation of Cr in different vegetables and derivation of soil Cr threshold using the species sensitivity distribution method.

Due to its high mobility and bioavailability, hexavalent chromium [Cr(VI)] in agricultural soil can be taken up by crops and pose threat to human being. In this study, two soils (Jiangxi red soil and Shandong fluvo-aquic soil) spiked with Cr(VI) and 8 common vegetable varieties were used to conduct the pot experiment. The bioconcentration factor (BCF) values based on the tetraacetic acid extractable Cr (EDTA-Cr) in soils were used to construct the species sensitivity distribution (SSD) curve. Afterwards, the soil Cr threshold was derived based on the critical BCF value and the permissible limit of Cr for vegetables. The results showed that when spiked with 5.6 mg kg-1 of Cr(Ⅵ), the soil EDTA-Cr concentrations were significantly increased compared with the control except Jiangxi red soil planted with carrot and radish, while the Cr concentrations in the edible parts of vegetables in both soils were below the permissible limit (0.5 mg kg-1 FW). However, there are dramatic differences in the accumulation of Cr by different varieties of vegetables. Apparent discrepancy was observed between the two soils for the bioconcentration of Cr by carrot. Among the leafy vegetables, lettuce and oilseed rape are the most and the least sensitive to Cr pollution, respectively. The safety threshold values of EDTA-Cr were 0.70 mg kg-1 for Shandong fluvo-aquic soil and 0.85 mg kg-1 for Jiangxi red soil, respectively. This study provides information on the safety production of vegetable products in Cr(Ⅵ) polluted soils and is helpful to the revision of soil quality standards of Cr.

[Analysis of structure changes of microbial community in medium biofilm by ERIC-PCR fingerprinting].

A new technique, with medium biofilms and hydrophytes as main components, with microbes, plankton, hydrophytes and aquatic animals as basic ecological elements, was adopted to deal with eutrophication water in Shanghai. A pilot-scale test was carried on, with influent as 6 m(3)/d, 7 ponds parallelly connected, and with continuous influent and effluent. Water qualities were analyzed and ERIC-PCR fingerprinting method was used to study the natures of biofilm microbes. The results show that, the device has obvious affection on eutrophication water pollution removal, COD, TN, NH4+-N and TP removal efficiencies are respectively 20.7% - 48.5%, 20.1% - 49.7%, 39.8% - 66.2 % and 60.0% - 73.9% higher than those of control experiment. Water plants contribute for N and P absorption and removal, the three ponds with plants have higher TN and TP removal efficiency than the tree ones without hydrophytes, the enhanced TN removal efficiencies are 30.1%, 24.9% and 17.6% respectively. ERIC-PCR fingerprinting indicate that the three ponds with water plants have more similar microbial community structure to each other than no hydrophyte ponds, and that mean pairwise similarity coefficient value are 71.8% , 86.9% and 91.0% respectively on 2nd, 15th and 30th day, and at the same time the population diversity indexes rang from 1.89 to 2.22, 2.17 to 2.43 and 2.28 to 2.68, respectively. The above discussions conclude that the systemic population diversity indexes and structure similarity increase, biofilm microbes have gradually abundant population and stable structure, which are in accord with pollution removal efficiencies.