Xiaofeng Cao

Developmental toxicity and endocrine disruption of naphthenic acids on the early life stage of zebrafish (Danio rerio)

Oil sands process‐affected water (OSPW) has been reported to exhibit adverse effects on the environment and wildlife. Although the compounds responsible are unknown, naphthenic acids (NAs) have been considered to be implicated. The current study was designed to investigate whether NAs might cause developmental toxicity and endocrine disruption on the early life stage of zebrafish (Danio rerio). The success of embryo hatch was inhibited by 2.5 mg l–1 oil sands NAs (OS‐NAs) exposure, and both OSPW NAs and commercial NAs (C‐NAs) exposure resulted in a variety of developmental lesions in the fish larvae, such as yolk sac edema, pericardial edema and spinal malformation. The transcription of genes involved cytochrome P450 aromatase (CYP19a and CYP19b), estrogen receptors (ERα, ERβ1 and ERβ2), and vitellogenin (VTG) was analyzed to evaluate the endocrine disrupting effects of NAs. Significant up‐regulated gene expressions of CYP19b, ERα and VTG were observed in both OS‐NAs and C‐NAs groups, which indicated the deleteriously estrogenic potential of NAs. These results confirmed that NAs derived from crude petroleum could negatively impact the development and endocrine function of zebrafish, and be primarily responsible for the toxicity of OSPW. Copyright

Transcriptional responses of earthworm (Eisenia fetida) exposed to naphthenic acids in soil

In this study, earthworms (Eisenia fetida) were exposed to commercial NAs contaminated soil, and changes in the levels of reactive oxygen species (ROS) and gene expressions of their defense system were monitored. The effects on the gene expression involved in reproduction and carcinogenesis were also evaluated. Significant increases in ROS levels was observed in NAs exposure groups, and the superoxide dismutase (SOD) and catalase (CAT) genes were both up-regulated at low and medium exposure doses, which implied NAs might exert toxicity by oxidative stress. The transcription of CRT and HSP70 coincided with oxidative stress, which implied both chaperones perform important functions in the protection against oxidative toxicity. The upregulation of TCTP gene indicated a potential adverse effect of NAs to terrestrial organisms through induction of carcinogenesis, and the downregulation of ANN gene indicated that NAs might potentially result in deleterious reproduction effects.

The importance of neutral and niche processes for bacterial community assembly differs between habitat generalists and specialists

The mechanisms of community assembly are a central focus in the field of microbial ecology. However, to what extent these mechanisms differ in importance by traits of groups is poorly understood. Here we quantified the importance of neutral and niche processes in community assembly for bacteria, habitat specialists and generalists in 21 plateau lakes of China. Results showed that both neutral and niche processes played a critical role in the assembly of entire bacterial communities, shaping a unique biogeographical pattern. A few habitat generalists and many specialists were identified. Interestingly, habitat specialists were only governed by niche process, with seven significant environmental variables-salinity, dissolved oxygen, water transparency, total phosphorus, ammonium-nitrogen, temperature and total nitrogen-independently explaining 40.3% of the biological variation. By contrast, habitat generalists were strongly driven by neutral process, with 50.9% of the variation of detection frequency explained in neutral community model. Only three environmental variables-salinity, total nitrogen and dissolved oxygen-significantly affected the distribution of habitat generalists, independently explaining 13.6% of the variation. Governed by different assembly mechanisms, habitat specialists and generalists presented disparate biogeographical patterns. Our result emphasizes the importance of investigating the bacterial community assembly at more refined levels than entire communities.

Research status and trends in limnology journals: a bibliometric analysis based on SCI database

An effective bibliometric analysis was applied in this work to evaluate global scientific production of the subject category of “limnology” from 2001 to 2010. Data was based on the Science Citation Index compiled by Institute for Scientific Information (ISI), Philadelphia, USA. The h-index and NetDraw were designed to characterize the limnology publications. The results showed that the limnology research constantly increased over the past decade. The researchers paid most attention to “diatoms”, “eutrophication” and “phosphorus”. Moreover, the keywords plus of “growth”, “model”, “dynamic”, offered a thorough description for the limnology research. Among the research institutes interested in limnologic research, the US Geological Survey was the flagship while the USA attained a dominant position in the global research in the field.

Quantification and characterization of naphthenic acids in soils from oil exploration areas in China by GC/MS

Naphthenic acids (NAs) are a toxic complex mixture of carboxylic acids occurring naturally in petroleum. Due to the serious potential risks of NAs towards terrestrial ecology during crude oil exploration and production processes, and the lack of efficient methodologies for extraction and analysis of these compounds, the goal of this study is to detail the development of a routine method for extraction, and quantitative and qualitative analysis of NAs in oil contaminated soils. Solid phase extraction using a MAX cartridge was employed in combination with GC/MS. Ethyl acetate with 2% formic acid used as an elution solvent showed the best recoveries of NAs (98.36–112.35%). The total NA concentration and NA profiles of oil contaminated soil samples from 4 oil fields in China were examined. High concentrations of NAs (maximum, 132.91 mg kg−1) were detected in soils, which implied toxic and estrogenic risks for human and terrestrial organisms. Different profiles of NA mixtures were observed in soils from 4 different oil fields, and evaporation and biodegradation could influence the compounds of NAs. The authors present the first feasible method for analysis of NAs in soil.

Bacterioplankton community responses to key environmental variables in plateau freshwater lake ecosystems: A structural equation modeling and change point analysis

Elevated environmental pressures negatively affect the bacterial community structure. However, little knowledge about the nonlinear responses of spatially related environmental variable across multiple plateau lake ecosystems on bacterioplankton communities has been gathered. Here, we used 454 pyrosequencing of 16S rRNA genes to study the associations of bacterial communities in terms of environmental characteristics as well as the potentially ecological threshold-inducing shifts of the bacterial community structure along the key environmental variables based on hypothesized structural equation models and the SEGMENTED method in 21 plateau lakes. Our results showed that water transparency was the major driving force and that total nitrogen was more significant than total phosphorus in determining the taxon composition of the bacterioplankton community. Significant community threshold estimates for bacterioplankton were observed at 7.36 for pH and 25.6% for the percentage of the agricultural area, while the remarkable change point of the cyanobacteria community structure responding to pH was at 7.74. Furthermore, the findings indicated that increasing nutrient loads can induce a distinct shift in dominance from Proteobacteria to Cyanobacteria, as well as a sharp decrease and adjacent increase when crossing the change point for Actinobacteria and Bacteroidetes along the gradient of the agricultural area.

Cyanobacteria in lakes on Yungui Plateau, China are assembled via niche processes driven by water physicochemical property, lake morphology and watershed land-use

Plateau lakes are important ecosystems with diverse ecological functions. Cyanobacteria play a key role in plateau lakes as primary producers. However, they are threatening when dense blooms occur. Identifying cyanobacteiral biogeography and the mechanism of assembly processes shaping the distribution of cyanobacteria in plateau lakes is critical for understanding cyanobacterial ecology and applying it to lake management. In the present study, the biogeographic pattern and importance of neutral and niche processes in assembly of cyanobacteria in 21 lakes on Yungui Plateau, China were examined. Results showed that cyanobacteria exhibit unique biogeographic pattern, and most of them have a narrow habitat preference in plateau lakes. They were assembled via niche processes driven by water physicochemical property, lake morphology and watershed land-use, which explained 62.4% of the biological variation. Neutral processes were not at play. Water physicochemical property (key variables - dissolved oxygen, salinity, trophic status and pH) was the most dominant driver shaping its unique biogeographic pattern. Watershed land-use especially urban land, water body and agricultural land also exhibited a strong impact on cyanobacterial distribution, followed by lake morphology. As most of the cyanobacteiral genus detected in these plateau lakes were potential toxin-producers, this study indicated that in order to protect waters from toxic-bloom in the future, reducing nutrient loading and land-use practices are two practical approaches in plateau lake management.

Oxidative damage of naphthenic acids on the Eisenia fetida earthworm.

Naphthenic acids (NAs) have been gaining recognition in recent years as potentially harmful environmental contaminants. Few studies have focused on the potential ecotoxicity of NAs to terrestrial environment. In this study, the responses of antioxidant system and lipid peroxidation and DNA damage were investigated after exposing Eisenia fetida to soil contaminated with NAs. The results indicated that NAs induced a significant increase (p < 0.05) in superoxide dismutase and catalase enzyme activities. The glutathione peroxidase enzyme activities were significantly inhibited (p < 0.05) in the medium and high dose treatments. An increase in malondialidehyde indicated that NAs could cause cellular lipid peroxidation in the tested earthworms. The percentage of DNA in the tail of comet assay of coelomocytes as an indication of DNA damage increased after treatment with different doses of NAs, and a dose‐dependent DNA damage of coelomocytes was found. In conclusion, oxidative stress caused by NAs exposure induces physiological responses and genotoxicity on earthworms.

Disruption of endocrine function in H295R cell in vitro and in zebrafish in vivo by naphthenic acids.

Oil sands process-affected water (OSPW) have been reported to exhibit endocrine disrupting effects on aquatic organisms. Although the responsible compounds are unknown, naphthenic acids (NAs) have been considered to be implicated. The current study was designed to investigate the endocrine disruption of OSPW extracted NAs (OS-NAs) and commercial NAs (C-NAs) using a combination of in vitro and in vivo assays. The effects of OS-NAs and C-NAs on steroidogenesis were assessed both at hormone levels and expression levels of hormone-related genes in the H295R cells. The transcriptions of biomarker genes involved in endocrine systems in zebrafish larvae were investigated to detect the effects of OS-NAs and C-NAs on endocrine function in vivo. Exposure to OS-NAs and C-NAs significantly increased production of 17β-estradiol (E2) and progesterone (P4), and decreased production of testosterone (T). Both OS-NAs and C-NAs significantly induced the expression of several genes involved in steroidogenesis. The abundances of transcripts of biomarker gene CYP19b, ERα, and VTG were significantly up-regulated in zebrafish larvae exposed to OS-NAs and C-NAs, which indicated that NAs had negative effects on estrogen-responsive gene transcription in vivo. These results indicated that NAs should be partly responsible for the endocrine disrupting effects of OSPW.