David M. Johnson

Swimming and Recovery Abilities of Juvenile Chinese Sturgeon Acipenser sinensis

AbstractBreeding populations of the Chinese Sturgeon Acipenser sinensis are endemic to the Yangtze River in China, but other wild populations have been extirpated, and the species is critically endangered. The swimming performance of juvenile Chinese Sturgeon was tested in a flume-type respirometer using a three-phase test: a constant velocity endurance test, followed by a 30-min recovery period, and then a stepped velocity test to determine the critical swimming speed (Ucrit). Swimming endurance (at 19 ± 1°C) was tested at five constant speeds: 3.0, 3.5, 4.0, 4.5, and 5.0 body lengths per second (BL/s) (groups 1–5). A control group (group 0) was used to determine Ucrit for fish that had not been subjected to the endurance test. The Ucrit of the control group (U′) was 4.32 ± 0.30 BL/s (mean ± SE) and after fish had completed the endurance test the Ucrit ranged from 2.88 ± 0.15 BL/s in group 1 to 3.64 ± 0.28 BL/s in group 5, with corresponding recovery ratios (Ucrit/U′) of 66.7 ± 3.4% and 84.3 ± 6.4%. Endu...

Bioaccumulation of heavy metals in the lotus root of rural ponds in the middle reaches of the Yangtze River

PurposeThe subject of this study is the sediment and wild lotus plants in unmanaged ponds, near Yichang City, contaminated by heavy metals. The objective is to determine the extent and frequency of heavy metal accumulation by lotus root in the ponds of rural areas and its significance to food safety and human health.Materials and methodsThe study area is located in the middle reaches of Yangtze River. The 11 sampling sites selected (Z1–Z11) were unmanaged ponds, and the lotus root samples were from wild plants. The lotus root and soil samples were processed using wet digestion, according to the national standard method; we tested concentration of heavy metal (Pb, Cd, Cr, As, Cu, and Zn). Both a single-factor index and an integrated pollution index were used to assess the heavy metal pollution of soil and wild lotus root. Correlation was used to examine the relationship of lotus root concentration to sediment concentration for each heavy metal.Results and discussionCadmium (Cd) and arsenic (As) in both soil and pond sediment exceeded standards. The maximum single pollution index (SPI) for Cd and As was 1.16 and 1.15, respectively. The maximum integrated pollution index (IPI) for heavy metals was 2.17 for soil and 2.10 for sediment (moderate pollution). The heavy metal content in some samples of lotus root exceeded the national food standard and pose a health risk. The significant correlations of heavy metal concentrations (Pb, Cd, and As) in pond sediment with those in the surrounding soil show that the ponds act as sinks for agricultural nonpoint source pollution (NPS). The heavy metal concentrations in the peel of the edible tuber were 1.3∼9.0 times higher than those in the inner flesh.ConclusionsWhile Cd, Pb, and As concentrations in the sediment did not violate soil standards, concentrations in the lotus root did violate food standards. This species could be proposed as a suitable heavy metal bioindicator for the early stages of pollution from agricultural NPS.

BiOBr photocatalyzed decarboxylation of glutamic acid: reaction rates, intermediates and mechanism

The degradation of glutamic acid by BiOBr under both UV and visible irradiation was investigated and compared with degradation by TiO2/UV. Analysis of the reaction rates and the distribution of intermediates was used to show that both BiOBr systems, unlike the TiO2 system, catalyze direct substrate oxidation by valance band holes.

Complex Formation via Hydrogen bonding between Rhodamine B and Montmorillonite in Aqueous Solution

This study investigates the adsorption mechanism differences among four nitrogenous dyes, sulforhodamine G (SRG), uncharged/deprotonated rhodamine B (RhB), orange II (Or II) and methyl blue (MB) by montmorillonite (MMT). MMT adsorption capacity for cationic MB was three times that of uncharged RhB and anionic SRG, while anionic Or II was not absorbed. Colloidal MMT particles have two types of surfaces, basal and edge, that interact with nitrogenous dyes very differently. The surface acidity of MMT was characterized with the pyridine adsorption method using in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS). Adsorption of cationic MB was compared with the adsorption of RhB. In-situ attenuated total reflectance Fourier transform infrared (in-situ ATR-FTIR) spectroscopy indicated that a nitrogen atom on RhB complexes with a metal hydroxyl on an MMT edge through a water bridge. The highly polar edge hydroxyl is important to hydrogen bond formation. Cation ion exchange and washing experiments, as well as studies on the effect of temperature, pH and ionic strength on adsorption further clarified the adsorption mechanism. Our results provide insights into the effects of molecular structure on the adsorption of nitrogenous dyes by clay and the role of edge surfaces in the adsorption process.

Brönsted Catalyzed Hydrolysis of Microcystin-LR by Siderite

Six naturally occurring minerals were employed to catalyze the hydrolysis of microcystin-LR (MC-LR) in water. After preliminary screening experiments, siderite stood out among these minerals due to its higher activity and selectivity. In comparison with kaolinite, which is known to act as a Lewis acid catalyst, siderite was found to act primarily as a Brönsted acid catalyst in the hydrolysis of MC-LR. More interestingly, we found that the presence of humic acid significantly inhibited catalytic efficiency of kaolinite, while the efficiency of siderite remained high (∼98%). Reaction intermediates detected by LC-ESI/MS were used to indicate cleavage points in the macrocyclic ring of MC-LR, and XPS was used to characterize siderite interaction with MC-LR. Detailed analysis of the in situ ATR-FTIR absorption spectra of MC-LR indicated hydrogen bonding at the siderite-water-MC-LR interface. A metastable ring, involving hydrogen bonding, between surface bicarbonate of siderite and an amide of MC-LR was proposed to explain the higher activity and selectivity toward MC-LR. Furthermore, siderite was found to reduce the toxicity of MC-LR to mice by hydrolyzing MC-LR peptide bonds. The study demonstrates the potential of siderite, an earth-abundant and biocompatible mineral, for removing MC-LR from water.

Se enhanced phytoremediation of diesel in soil by Trifolium repens

A pot-culture experiment was conducted to assess the effects of selenium (Se) (0.5 mg kg-1) on Trifolium repens exposed to various levels of diesel (0, 15, 20, 25 g kg-1) for 30 days and 60 days. Exposure to diesel for 60 day led to concentration-dependent decreases in root morphogenesis, chlorophyll content and CAT activity, and to dose-dependent increases in MDA content and SOD activity. The residual diesel concentration in soil increased and the removal efficiency decreased with soil diesel concentration. The chlorophyll content and residual diesel concentration after were slightly higher at 30 days than at 60days. Application of Se to soil increased Trifolium repens tolerance to diesel and significantly increased the phytoremediation effect at 60 days, with a removal rate of 36 ± 8%, compared to 28 ± 7% in the control. These results contribute to the ongoing effort to develop an effective phytoremediation system for soils highly contaminated by diesel.