Tissue-specific accumulation, depuration and histopathological effects of 3,6-dichlorocarbazole and 2,7-dibromocarbazole in adult zebrafish (Danio rerio).

Although polyhalogenated carbazoles have been detected with increasing frequency in aquatic ecosystems, their bioaccumulation in fish and corresponding pathological effects related to bioaccumulation are still unclear. Here, we investigated the tissue-specific accumulation, depuration, and histopathological effects of two typical PHCZs, 3,6-dichlorocarbazole (36-CCZ) and 2,7-dibromocarbazole (27-BCZ), in adult zebrafish at three levels (0, 0.15 µg/L (5 × environmentally relevant level), and 50 µg/L (1/10 LC50). The lowest concentrations of 36-CCZ (1.2 µg/g ww) and 27-BCZ (1.4 µg/g ww) were observed in muscle, and the greatest concentrations of 36-CCZ (3.6 µg/g ww) and 27-BCZ (4 µg/g ww) were detected in intestine among the tested tissues. BCFww of 36-CCZ and 27-BCZ in zebrafish ranged from 172.9 (muscle) to 606.6 (intestine) and 285.2 (muscle) to 987.5 (intestine), respectively, indicating that both 36-CCZ and 27-BCZ have high potential of bioaccumulation in aquatic system. The 0.15 µg/L level of 36-CCZ or 27-BCZ caused lipid accumulation in liver, while 50 µg/L of 36-CCZ or 27-BCZ induced liver lesions such as fibrous septa, cytolysis, and nuclear dissolution. Brain damage such as multinucleated cells and nuclear solidification were only observed at 50 µg/L of 27-BCZ. This study provided valuable information in assessing the health and ecological risks of 36-CCZ and 27-BCZ.

Comparison of hematite-facilitated anaerobic digestion of acetate and beef extract.

The effect of hematite with different specific surface areas (SSA) on anaerobic methanogenic process was investigated in this study using two different carbon sources (acetate or beef extract). Comparative analyses showed that methane generation rate, microbial growth and the starting-up duration were all significantly enhanced by hematite. The reduction rate of high SSA hematite was 2.5-3.5 times greater than that of low SSA hematite. This work indicated that low SSA hematite was superior to high SSA hematite in facilitating methanogenesis which was partially attributed to the lower affinity for the iron-reduction bacteria.

[Effect of natural and hydrothermal synthetic goethite on the release of methane in the anaerobic decomposition process of organic matter].

The effects of natural goethite (NGt) and synthetic goethite (SGt) on the release of methane in the anaerobic biochemical system consisted of dissimilatory iron-reducing bacteria (DIRB) and methane-producing bacteria (MPB) were investigated through batch tests with sodium acetate as the carbon source. To explore the effects and mechanisms of both mineral materials on the release of methane in the anaerobic decomposition process of organic matter in the presence of DIRB, the main gas components and total organic carbon (TOC) , total inorganic carbon (TIC), and Fe2+ in the aqueous phase of the experimental process were determined and XRD analyses were conducted for the solid-phase product. Moreover, the minerals were analyzed by specific surface area (BET), X-ray diffraction (XRD), X-ray fluorescence (XRF). Modified Gompertz equation was used to fit the cumulative methane and carbon dioxide. Results showed that the maximum cumulative production of methane was brought forward by 60-78 days by the addition of goethite and CO2 was effectively reduced by 30% - 67% compared with the control samples. SGt was more effective than NGt in promoting the release of CH4 and reducing the CO, emission. Furthermore, the analysis of the solid product showed that the addition of goethite can fix part of CO2 by the formation of siderite.