Arsenic species and leachability in the fronds of the hyperaccumulator Chinese brake (Pteris vittata L.)

Arsenic speciation is important not only for understanding the mechanisms of arsenic accumulation and detoxification by hyperaccumulators, but also for designing disposal options of arsenic-rich biomass. The primary objective of this research was to understand the speciation and leachability of arsenic in the fronds of Chinese brake (Pteris vittata L.), an arsenic hyperaccumulator, with an emphasis on the implications for arsenic-rich biomass disposal. Chinese brake was grown for 18 weeks in a soil spiked with 50 mg As kg(-1) as arsenate (AsO4(3-)), arsenite (AsO3(3-)), dimethylarsinic acid (DMA), or methylarsonic acid (MMA). Plant samples were extracted with methanol/water (1:1) and arsenic speciation was performed using high performance liquid chromatography coupled with atomic fluorescence spectrometry. The impacts of air-drying on arsenic species and leachability in the fronds were examined in the laboratory. After 18 weeks, water-soluble arsenic in soil was mainly present as arsenate with little detectable organic species or arsenite regardless of arsenic species added to the soil. However, arsenic in the fronds was primarily present as inorganic arsenite with an average of 94%. Arsenite re-oxidation occurred in the old fronds and the excised dried tissues. Arsenic species in the fronds were slightly influenced by arsenic forms added to the soil. Air-drying of the fronds resulted in leaching of substantial amounts of arsenic. These findings can be of significance when looking at disposal options of arsenic-rich biomass from the point of view of secondary contamination.     

Preliminary 3-D site-scale studies of radioactive colloid transport in the unsaturated zone at Yucca Mountain,Nevada

The U.S. Department of Energy (DOE) is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone (UZ) at Yucca Mountain (YM), Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids.     

Residues of Organochlorinated Pesticides in Eggs of Water Birds from Tai Lake in China

The levels of organochlorine compounds in eggs of water birds from the colony on Tai Lake in China were studied. The eggs were collected in 2000 and belonged to the following species: 65 samples of black-crowned night heron (Nycticorax nycticorax), 36 samples of little egret (Egretta garzetta), 26 samples of cattle egret (Bubulcus ibis) from 13 clutches and 43 samples of Chinese pond heron (Ardeola bacchus) from 17 clutches. Dichlorodiphenyltrichloroethane (DDT) and its derivates (DDE and DDD), hexachlorocyclohexane (HCH) and its isomers (-HCH, -HCH, -HCH, -HCH), heptachlor, heptachlor epoxide, aldrin, dieldrin, endrin, endrin aldehyde, -endosulfan, -endosulfan, and endosulfan sulfate were determined in the laboratory by gas chromatography. The data showed that DDE had the highest levels in all the samples, followed by -HCH. The mean levels of DDE among the water bird species were in the order as follows: black-crowned night heron (5464.26ng/g, dry weight) > Chinese pond heron (2791.12ng/g, dry weight) > little egret (1979.97ng/g, dry weight) > cattle egret (660.11ng/g, dry weight). DDT and its metabolites accounted for 90% of the total organochlorines, except that it was only 73% for cattle egret. The differences of the residue among the bird species were statistically significant and could be attributed to their variations in prey and habitat. Although the DDE burdens in Tai Lake were much lower than 8 g/g (wet weight) which are thought to have significant adverse effects on black-crowned night herons, they would be expected to increase the risk of adverse effects on survival of chicks of herons and egrets, particularly black-crowned night heron, based on the critical value of 1 g/g (wet weight) DDE. The burdens of HCHs in this study were higher and the cyclodienes were lower than those found elsewhere.     

Degradation of benzo[a]pyrene in soil with arbuscular mycorrhizal alfalfa

Mycorrhizal and non-mycorrhizal alfalfa (Medicago sativa) was grown in pots containing soil artificially contaminated with various levels of benzo[a]pyrene (B[a]P) (0, 1, 10 and 100 mg kg(-1)). Soil and plants were sampled after 30, 40, 50, 60 and 90 days and compared with unlanted pots. The percentage of mycorrhizal root length colonized by Glomus caledoniun was not significantly affected by the addition of B[a]P up to 10 mg kg(-1) but was significantly lower at 100 mg kg(-1)B[a]P compared with low concentrations (p < 0.05). There was no difference in soil polyphenol oxidase and dehydrogenase activity among the controls and applications of 1 and 10 mg kg(-1) of B[a]P. However, enzyme activities were significantly higher at 100 mg kg(-1) B[a]P compared with the other three treatments, and there was no mycorrhizal effect. Over a period of 90 days the concentration of B[a]P in soil in which alfalfa was grown was significantly lower than in unplanted soil (p < 0.05). Degradation rates of B[a]P added at 1, 10 and 100 mg kg(-1) without G. caledonium were 76, 78 and 53%, and with mycorrhizal inoculation were 86, 87 and 57%. The degradation rate in unplanted soil was significantly lower than in planted soil, and was significantly higher in medium- and low-B[a]P treatments than in the high B[a]P concentration tested. There is a possibility of enhancement phytoremediation of PAHs in rhizosphere soil with arbuscular mycorrhizal fungi.     

Degradation of Benzo[a]Pyrene in Soil with Arbuscular Mycorrhizal Alfalfa

Mycorrhizal and non-mycorrhizal alfalfa (Medicago sativa) was grown in pots containing soil artificially contaminated with various levels of benzo[a]pyrene (B[a]P)(0, 1, 10 and 100 mg kg^–1). Soil and plants were sampled after 30, 40, 50, 60 and 90 days and compared with unlanted pots. The percentage of mycorrhizal root length colonized by Glomus caledoniun was not significantly affected by the addition of B[a]P up to 10 mg kg^–1 but was significantly lower at 100 mg kg^–1B[a]P compared with low concentrations (p < 0.05). There was no difference in soil polyphenol oxidase and dehydrogenase activity among the controls and applications of 1 and 10 mg kg^–1 of B[a]P. However, enzyme activities were significantly higher at 100 mg kg^–1B[a]P compared with the other three treatments, and there was no mycorrhizal effect. Over a period of 90 days the concentration of B[a]P in soil in which alfalfa was grown was significantly lower than in unplanted soil (p < 0.05). Degradation rates of B[a]P added at 1, 10 and 100 mg kg^–1 without G. caledonium were 76, 78 and 53%, and with mycorrhizal inoculation were 86, 87 and 57%. The degradation rate in unplanted soil was significantly lower than in planted soil, and was significantly higher in medium- and low-B[a]P treatments than in the high B[a]P concentration tested. There is a possibility of enhancement phytoremediation of PAHs in rhizosphere soil with arbuscular mycorrhizal fungi.     

Simultaneous nitrogen and phosphorus removal under low dissolved oxygen conditions

ＩｎｔｒｏｄｕｃｔｉｏｎＮｉｔｒｏｇｅｎ(Ｎ)ａｎｄｐｈｏｓｐｈｏｒｕｓ(Ｐ)ｉｎｍｕｎｉｃｉｐａｌｓｅｗａｇｅ ,ｗｈｉｃｈｍａｉｎｌｙｃｏｍｅｆｒｏｍｄｏｍｅｓｔｉｃｗａｓｔｅｗａｔｅｒａｎｄｓｏｍｅｉｎｄｕｓｔｒｉａｌｗａｓｔｅｗａｔｅｒ,ｗｉｌｌｃａｕｓｅｍａｎｙｈａｒｍｓａｎｄｒｅｓｔｒｉｃｔｔｈｅｎｏｒｍａｌｆｕｎｃｔｉｏｎｏｆｗａｔｅｒｅｎｖｉｒｏｎｍｅｎｔａｆｔｅｒｅｎｔｅｒｔｈｅｗａｔｅｒｂｏｄｙ .Ｔｈｅｐｒｏｂｌｅｍｏｆｎｉｔｒｏｇｅｎａｎｐｈｏｓｐｈｏｒｕｓｐｏｌｌｕｔｉｏｎｈａ…     

Heavy metal concentrations in edible bivalves and gastropods available in major markets of the Pearl River Delta

ＩｎｔｒｏｄｕｃｔｉｏｎＩｔｉｓｉｎｃｒｅａｓｉｎｇｌｙｄｉｆｆｉｃｕｌｔｔｏｃｏｎｓｉｄｅｒｍａｒｉｎｅｐｏｌｌｕｔｉｏｎｉｎＨｏｎｇＫｏｎｇｗｉｔｈｏｕｔｒｅｆｅｒｅｎｃｅｔｏＧｕａｎｇｄｏｎｇＰｒｏｖｉｎｃｅｏｒｔｈｅｅｎｔｉｒｅＰｅａｒｌＲｉｖｅｒＤｅｌｔａ.ＴｈｅＰｅａｒｌＲｉｖｅｒＤｅｌｔａｉｓｎｏｔｏｎｌｙａｇｅｏｍｏｒｐｈｉｃａｌｕｎｉｔｂｕｔａｌｓｏａｇｅｏｇｒａｐｈｉｃａｌｕｎｉｔａｎｄｔｈｅｓｃｏｐｅｏｆｔｈｅＰｅａｒｌＲｉｖｅｒＤｅｌｔａｓｈｏｕｌｄｉｎｃｌｕｄｅｍａｊｏ…     

Model calculating annual mean atmospheric dispersion factor for coastal site of nuclear power plant

ＩｎｔｒｏｄｕｃｔｉｏｎＡｎａｔｍｏｓｐｈｅｒｅｄｉｓｐｅｒｓｉｏｎｆｉｅｌｄｅｘｐｅｒｉｍｅｎｔｗａｓｄｏｎｅｏｎｔｈｅｃｏａｓｔａｌｓｉｔｅｏｆｎｕｃｌｅａｒｐｏｗｅｒｐｌａｎｔ (ＮＰＰ)ｉｎｔｈｅｅａｓｔｐａｒｔｏｆＣｈｉｎａｄｕｒｉｎｇ 1995— 1996 Ｔｈｅｃｏｎｔｅｎｔｏｆｔｈｉｓｅｘｐｅｒｉｍｅｎｔｉｎｃｌｕｄｅｓ:ｈｏｕｒｌｙｏｂｓｅｒｖａｔｉｏｎｏｆｗｉｎｄａｎｄｔｅｍｐｅｒａｔｕｒｅｏｎｔｈｅｔｏｗｅｒｏｆ10 0ｍ ;Ｏｂｓｅｒｖａｔｉｏｎｏｆｓｕｒｆａｃｅｗｉｎｄａｎｄｓｅｅａｎｄｌ…