Chunna Yu

Growth, bioluminescence and shoal behavior hormetic responses to inorganic and/or organic chemicals: A review

A biphasic dose response, termed hormesis, is characterized by beneficial effects of a chemical at a low dose and harmful effects at a high dose. This biphasic dose response phenomenon has the potential to strongly alter toxicology in a broad range. The present review focuses on the progress of research into hormetic responses in terms of growth (in plants, birds, algae and humans), bioluminescence, and shoal behavior as end points. The paper describes how both inorganic and organic chemicals at a low dose show stimulatory responses while at higher doses are inhibitory. The article highlights how factors such as symbiosis, density-dependent factors, time, and contrasting environmental factors (availability of nutrients, temperature, light, etc.) affect both the range and amplitude of hormetic responses. Furthermore, the possible underlying mechanisms are also discussed and we suggest that, for every end point, different hormetic mechanisms may exist. The occurrences of varying interacting receptor systems or receptor systems affecting the assessment of hormesis for each endpoint are discussed. The present review suggests that a hormetic model should be adopted for toxicological evaluations instead of the older threshold and linear non-threshold models.

Risk assessment of heavy metals pollution in agricultural soils of siling reservoir watershed in Zhejiang Province, China.

Presence of heavy metals in agriculture soils above the permissible limit poses threats to public health. In this study, concentrations of seven metals were determined in agricultural soils from Yuhang county, Zhejiang, China. Multivariate statistical approaches were used to study the variation of metals in soils during summer and winter seasons. Contamination of soils was evaluated on the basis of enrichment factor (EF), geoaccumulation index (I geo), contamination factor (C f), and degree of contamination (C deg). Heavy metal concentrations were observed higher in winter as compared to summer season. Cr and Cd revealed random distribution with diverse correlations in both seasons. Principal component analysis and cluster analysis showed significant anthropogenic intrusions of Zn, Cd, Pb, Cr, and Cu in the soils. Enrichment factor revealed significant enrichment (EF > 5) of Zn, Cd, and Pb, whereas geoaccumulation index and contamination factor exhibited moderate to high contamination for Zn, Cr, Cd, and Pb. In light of the studied parameters, permissible limit to very high degree of contamination (C deg > 16) was observed in both seasons.

Hydrodechlorination of polychlorinated biphenyls in contaminated soil from an e-waste recycling area, using nanoscale zerovalent iron and Pd/Fe bimetallic nanoparticles

Soil pollution by polychlorinated biphenyls (PCBs) arising from the crude disposal and recycling of electronic and electrical waste (e-waste) is a serious issue, and effective remediation technologies are urgently needed. Nanoscale zerovalent iron (nZVI) and bimetallic systems have been shown to promote successfully the destruction of halogenated organic compounds. In the present study, nZVI and Pd/Fe bimetallic nanoparticles synthesized by chemical deposition were used to remove 2,2′,4,4′,5,5′-hexachlorobiphenyl from deionized water, and then applied to PCBs contaminated soil collected from an e-waste recycling area. The results indicated that the hydrodechlorination of 2,2′,4,4′,5,5′-hexachlorobiphenyl by nZVI and Pd/Fe bimetallic nanoparticles followed pseudo-first-order kinetics and Pd loading was beneficial to the hydrodechlorination process. It was also found that the removal efficiencies of PCBs from soil achieved using Pd/Fe bimetallic nanoparticles were higher than that achieved using nZVI and that PCBs degradation might be affected by the soil properties. Finally, the potential challenges of nZVI application to in situ remediation were explored.

A novel approach to stimulate the biphenyl-degrading potential of bacterial community from PCBs-contaminated soil of e-waste recycling sites

SRpf, culture supernatants from Micrococcus luteus containing the resuscitation-promoting factor (Rpf), was used to enhance the biphenyl-degrading capability of potential microorganisms. The obtained results suggest that the enrichment culture produced by the addition of SRpf (enrichment culture treatment group, ECT) enhanced the biphenyl degradation efficiency, cell growth and bacterial diversity significantly. Biphenyl at concentration of 1500 mg/L was almost completely degraded in 24 h using SRpf at a dosage of 15% (v/v). Six strains unique to the ECT were isolated in pure cultures. This study provides a new insight into bacterial degradation of biphenyl for PCBs-bioremediation, and could be developed as a novel efficient method for obtaining highly desirable pollutant-degrading microorganisms.

PCB congeners induced mitochondrial dysfunction in Vero cells

Two PCB congeners were assessed for their cytotoxicity on Vero cells, in the attempt to compare their structure-activity relationship and to investigate the role of mitochondria involved in toxicity. Flow cytometry was used to monitor the changes of mitochondrial membrane potential (Δψ(m)), cell size and apoptosis rate. Treatments of Vero cell cultures with both PCB 126 and PCB 153 resulted in loss of cell viability in our experimental conditions. In ortho-substituted PCB 153 treated cells, loss of cell viability was accompanied by decreased Δψ(m) and cell shrinkage. The coplanar congener, PCB 126, had no significant effects on Δψ(m) or cell size in this time period of exposure. These studies showed that PCB 153 is more toxic than coplanar PCB 126 to Vero cells within 24h exposure. The cytotoxicity mechanism caused by coplanar or non-coplanar PCB congener was different, and apoptosis might be the main cell death pathway in PCB 153 treated cells.

Bacterial Communities of Polychlorinated Biphenyls Polluted Soil Around an E-waste Recycling Workshop

Polychlorinated biphenyls (PCBs) contamination that has resulted from the recycling of electronic power capacitors and transformers could lead to deterioration in soil quality and high ecological risk. As microorganisms are generally considered to be the best indicators of soil pollution, the diversity of bacterial communities in the soil around an e-waste recycling workshop in the Taizhou e-waste recycling area of China was studied using denaturing gradient gel electrophoresis (DGGE). The results indicated that the PCBs content in the soil decreased with increasing distance from the recycling workshop. Moreover, a gradual change in soil bacteria diversity along the PCBs pollution gradient was observed. Furthermore, the predominance of Proteobacteria and Bacteroidetes was found on the basis of sequence analysis and some highly similar subsequences of microorganisms were also found to be closely related to the catabolism of PCBs and other organic compounds. In a word, our results indicated that PCBs pollutants had an evident impact on the structure of the soil microbial community and the enriched microbes might serve to decompose PCBs in soil.

Paddy field--a natural sequential anaerobic-aerobic bioreactor for polychlorinated biphenyls transformation.

The environmental pollution and health risks caused by the improper disposal of electric and electronic waste (e-waste) have become urgent issues for the developing countries. One of the typical pollutants, polychlorinated biphenyls (PCBs), is commonly found in farmland in Taizhou, a major hotspot of e-waste recycling in China. This study investigated the amount of PCB residue in local farmlands. Biotransformation of PCBs was further studied under different water management conditions in paddy field with or without rice cultivation, with a special focus on the alternating flooded and drying processes. It was found that paddy field improved the attenuation of PCBs, especially for highly chlorinated congeners. In the microcosm experiment, 40% or more of the initial total PCBs was removed after sequential flood-drying treatments, compared to less than 10% in the sterilized control and 20% in the constant-drying system. Variation in the quantity of PCBs degrading and dechlorinating bacterial groups were closely related to the alteration of anaerobic-aerobic conditions. These results suggested that alternating anoxic-oxic environment in paddy field led to the sequential aerobic-anaerobic transformation of PCBs, which provided a favorable environment for natural PCB attenuation.

Sphingobium fuliginis HC3: A Novel and Robust Isolated Biphenyl- and Polychlorinated Biphenyls-Degrading Bacterium without Dead-End Intermediates Accumulation

Biphenyl and polychlorinated biphenyls (PCBs) are typical environmental pollutants. However, these pollutants are hard to be totally mineralized by environmental microorganisms. One reason for this is the accumulation of dead-end intermediates during biphenyl and PCBs biodegradation, especially benzoate and chlorobenzoates (CBAs). Until now, only a few microorganisms have been reported to have the ability to completely mineralize biphenyl and PCBs. In this research, a novel bacterium HC3, which could degrade biphenyl and PCBs without dead-end intermediates accumulation, was isolated from PCBs-contaminated soil and identified as Sphingobium fuliginis. Benzoate and 3-chlorobenzoate (3-CBA) transformed from biphenyl and 3-chlorobiphenyl (3-CB) could be rapidly degraded by HC3. This strain has strong degradation ability of biphenyl, lower chlorinated (mono-, di- and tri-) PCBs as well as mono-CBAs, and the biphenyl/PCBs catabolic genes of HC3 are cloned on its plasmid. It could degrade 80.7% of 100 mg L −1 biphenyl within 24 h and its biphenyl degradation ability could be enhanced by adding readily available carbon sources such as tryptone and yeast extract. As far as we know, HC3 is the first reported that can degrade biphenyl and 3-CB without accumulation of benzoate and 3-CBA in the genus Sphingobium, which indicates the bacterium has the potential to totally mineralize biphenyl/PCBs and might be a good candidate for restoring biphenyl/PCBs-polluted environments.

Hormetic effects of noncoplanar PCB exposed to human lung fibroblast cells (HELF) and possible role of oxidative stress.

Hormesis, a biphasic dose–response phenomenon, which is characterized by stimulation of an end point at a low‐dose and inhibition at a high‐dose. In the present study we used human lungs fibroblast (HELF) cells as a test model to evaluate the role of oxidative stress (OS) in hormetic effects of non coplanar PCB 101. Results from 3‐(4,5‐dime‐thylthiazol‐2‐yl)‐2,5‐diphenyltetrazo‐lium bromide (MTT) assay indicated that PCB101 at lower concentrations (10−5 to 10−1 μg mL−1) stimulated HELF cell proliferation and inhibited at high concentrations (1, 5, 10, and 20 μg mL−1) in a dose‐ and time‐dependent manner. Reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) (except 48 h) showed a significant increase at higher concentrations of PCB 101 than those at the lower concentrations with the passage of time. Antioxidant enzymes such as glutathione peroxidase (GSH‐Px) exhibited decreasing trends in dose and time dependent manner. Lipid peroxidation assay resulted in a significant increase (P < 0.05) of MDA level in PCB 101‐treated HELF cells compared with controls, suggesting that OS plays a key role in PCB 101‐induced toxicity. Comet assay indicated a significant increase in genotoxicity at higher concentrations of PCB 101 exposure compared to lower concentrations. Overall, we found that HELF cell proliferation was higher at low ROS level and vice versa, which revealed activation of cell signaling‐mediated hormetic mechanisms. The results suggested that PCB 101 has hormetic effects to HELF cells and these were associated with oxidative stress.

Hormetic Responses of Food-Supplied Pcb 31 to Zebrafish (Danio Rerio) Growth

Hormesis is commonly defined as a beneficial or stimulatory effect caused by exposure to low doses of a chemical known to be toxic at high doses. Hormetic responses of food-supplied PCB 31 (2, 4’, 5-Trichlorobiphenyl) was studied by using zebrafish (Danio rerio) growth as an end point. The results in general followed the hormesis hypothesis, PCB 31 at lower concentrations (0.042 μg/g and 0.084 μg/g) exhibited beneficial effects on the growth of zebrafish by weight and length while higher concentrations (10μg/g and 20μg/g) revealed inhibitory effects. The magnitude of stimulatory responses of zebrafish growth by weight and length at lower concentrations (0.01-0.084 μg/g) on days 14 and 21 were in the range 9.09-18.18%; 10-38.09% and 4-14.4%; 6.25-10.93%, respectively as compared to control. Growth and conditions indices also suggested that the zebrafish was healthier at lower concentrations as compared to those at higher concentrations. The results of the present study will elaborate fish toxicological evaluation regarding the hormetic model.