Ran Tao

Contamination profiles of antibiotic resistance genes in the sediments at a catchment scale

The aim of this study was to investigate the contamination profiles of tetracycline, sulfonamide, and macrolide resistance genes, as well as integrons in sediments of Dongjiang River basin of South China by real time quantitative polymerase chain reaction. sul2 was the most abundant resistance gene, with the average concentration of 6.97×10(8) copies/g and 1.00×10(8) copies/g in the dry and wet seasons, respectively, followed by ermF, sul3, sul1, intI1, tetA, ermB, tetX, tetM, tetQ, tetO, tetW, tetS, ermC, and tetB. The abundance of intI2 gene was the lowest in the sediment samples. Significant correlations existed between the ARGs and sediment properties as well as metals (Cu and Zn) and corresponding antibiotic classes, suggesting that the contamination of ARGs is related to chemical pollution of the sediments in the river basin. Principal component analysis showed distinct groupings of the sampling sites, reflecting that human activities are the key player in the dissemination of ARGs in the catchment environment.

Use of Fe-Impregnated Biochar To Efficiently Sorb Chlorpyrifos, Reduce Uptake by Allium fistulosum L., and Enhance Microbial Community Diversity

Fe-impregnated biochar was assessed as a method to remove the pesticide pollutant chlorpyrifos, utilizing biochar/FeOx composite synthesized via chemical coprecipitation of Fe3+/Fe2+ onto Cyperus alternifolius biochar. Fe-impregnated biochar exhibited a higher sorption capacity than pristine biochar, resulting in more efficient removal of chlorpyrifos from water. Soil was dosed with pristine or Fe-impregnated biochar at 0.1 or 1.0% w/w, to evaluate chlorpyrifos uptake in Allium fistulosum L. (Welsh onion). The results showed that the average concentration of chlorpyrifos and its degradation product, 3,5,6-trichloro-2-pyridinol (TCP), decreased in A.xa0fistulosum L. with increased levels of pristine biochar and Fe-biochar. Fe-biochar was found to be more effective in reducing the uptake of chlorpyrifos by improving the sorption ability and increasing plant root iron plaque. Bioavailability of chlorpyrifos is reduced with both biochar and Fe-biochar soil dosing; however, the greatest persistence of chlorpyrifos residues was observed with 1.0% pristine biochar. Microbial community analysis showed Fe-biochar to have a positive impact on the efficiency of chlorpyrifos degradation in soils, possibly by altering microbial communities.

Transformation of chlorpyrifos in integrated recirculating constructed wetlands (IRCWs) as revealed by compound-specific stable isotope (CSIA) and microbial community structure analysis

Carbon isotope analysis and 454 pyrosequencing methods were used to investigate in situ biodegradation of chlorpyrifos during its transport through three model integrated recirculating constructed wetlands (IRCWs). Results show that plant and Fe-impregnated biochar promoted degradation of chlorpyrifos and its metabolite 3,5,6-trichloro-2-pyridinol (TCP). Carbon isotope ratios in the IRCWs shifted to -31.24±0.58‰ (IRCW1, plant free), -26.82±0.60‰ (IRCW2, with plant) and -24.76±0.94‰ (IRCW3, with plant and Fe-biochar). The enrichment factors (Ɛbulk,c) were determined as -0.69±0.06‰ (IRCW1), -0.91±0.07‰ (IRCW2) and -1.03±0.09‰ (IRCW3). Microbial community analysis showed that IRCW3 was dominated by members of Bacillus, which can utilize and degrade chlorpyrifos. These results reveal that plant and Fe-biochar can induce carbon isotope fractionation and have a positive impact on the chlorpyrifos degradation efficiency by influencing the development of beneficial microbial communities.

Fate of mixed pesticides in an integrated recirculating constructed wetland (IRCW).

In this study, three model integrated recirculating constructed wetlands (IRCWs) planted with and without Cyperus alternifolius were used to investigate their ability to remove four pesticides (chlorpyrifos, endosulfan, fenvalerate, diuron). Iron (Fe)-impregnated biochar produced by Cyperus alternifolius was added as a primary substrate. Results showed that all four pesticides were efficiently removed in the three IRCWs. The highest pesticide removals were achieved when Fe-impregnated biochar was added to the IRCW (99%), followed by the planted (64-99%) and plant-free IRCW (45-99%). The removal of pesticides in IRCWs followed first-order kinetics, with half-lives of 1.5-11.6h. A mass balance study revealed that sorption (32.2-98.6%) and microbial degradation (1.3-52.8%) were the main removal processes in all IRCWs. This study suggests that the IRCW is a promising system to treat pesticide-contaminated water, and plant and Fe-impregnated biochar can enhance pesticide removal.

Biogenic manganese oxides generated by green algae Desmodesmus sp. WR1 to improve bisphenol A removal

Biogenic manganese oxides (BioMnOx) have attracted considerable attention as active oxidants, adsorbents, and catalysts. This study investigated the characteristics of algae-generated BioMnOx and determined its oxidative activity towards bisphenol A (BPA), an endocrine disrupter. Amorphous nanoparticles with a primary Mn valency of +3 were found in BioMnOx produced by Desmodesmus sp. WR1. The mechanism might be that algal growth created conditions favorable to Mn oxidation through increasing DO and pH. Initial Mn2+ concentrations of 6, 30, and 50mgL-1 produced a maximum of 5, 13, and 11mgL-1 of BioMnOx, respectively. Mn2+-enriched cultures exhibited the highest BPA removal efficiency (∼78%), while controls only reached about 27%. BioMnOx may significantly promote BPA oxidation in algae culture, enhancing the accumulation of substrates for glycosylation. Moreover, continuous BioMnOx increase and Mn2+ decrease during BPA oxidation confirmed Mn oxide regeneration. In conclusion, Mn oxide formation by microalgae has the potential to be used for environmental remediation.

Assessment of rhizosphere processes for removing water-borne macrolide antibiotics in constructed wetlands

AimsLimited information is available on plant rhizosphere processes for removing antibiotics in antibiotic-contaminated waters. This study identifies rhizosphere processes and evaluates their relative contributions for the macrolides (ML) removal in aquatic plant systems.MethodsA flask-scale experiment (100 and 300xa0μg/L ML) incorporating Juncus effuses and Canna indica was used to identify the root adsorption, rhizobacterial influences, and plant uptake responsible for the ML (i.e., anhydroerythromycin A, roxithromycin, clarithromycin and tilmicosin) removal.ResultsTotal ML removal rates due to rhizosphere processes were respectively 43.7–67.6% and 44.3–82.2% at 100 and 300xa0μg/L ML. J. effuses removed ML more effectively than C. indica (Pxa0<xa00.05). The relative contribution of rhizospheric pathways to remove all ML followed the order: root sorption > rhizobacterial influence > plant uptake (Pxa0<xa00.01). Sorption and rhizobacterial activity were important removal pathways in wetland plant microcosms, accounting for 36.5–72.8% and 20.5–54.2% of the total rhizosphere associated removal of ML, respectively.ConclusionsRoot sorption and rhizobacterial influence were the main rhizospheric pathways of ML removal in aquatic plant systems. Fe plaque on the root surface, rhizobacterial number and bacterial activity play significant roles in the removal of target pollutants.

Improved DNA purification with quality assurance for evaluation of the microbial genetic content of constructed wetlands

Efficient isolation of target DNA is a crucial first step of DNA-based metagenomic analyses of environmental samples. Insufficient quantity and purity of DNA isolated using commercial kits result in missing genetic information, especially for large-diameter substrates in constructed wetlands (CWs). Here, we addressed this problem by devising a cost-effective calcium chloride lysozyme-sodium dodecyl sulfate (SDS) method (CCLS), with key improvements in the steps of humic acid removal and cell lysis. The buffer comprising Tris, EDTA, Na2O2P7 and PVPP (TENP), and skim milk, could reduce adsorption between microorganisms and substrates, and calcium chloride precipitated and removed over 94% of humic acid. This humic acid removal step, when compared to the PowerSoil DNA kit (MO BIO Laboratories Inc.) (MBKIT), significantly enhanced the DNA purity (A260/230) from 0.68 to 1.63 (pxa0<xa00.01). When gentle and extended cell lysis in CCLS replaced the short but violent bead-beating in the MBKIT, DNA yield and the amount of lysed bacteria detected by quantitative real-time polymerase chain reaction (qPCR) on average increased by 2 and 4 folds, respectively, compared to that obtained using the MBKIT (pxa0<xa00.01). Furthermore, the full-length bacterial 16S rRNA gene and nirK gene from denitrifying microorganisms were successfully amplified from CCLS-generated DNA. Additionally, bacterial diversity indices of richness, Shannon, and evenness examined by denaturing gradient gel electrophoresis (DGGE) increased by 75, 30, and 7%, respectively, by CCLS compared to that using the MBKIT. Hence, the CCLS method enables improved evaluation of microbial density and diversity in CW systems.

Removal of chlorpyrifos in recirculating vertical flow constructed wetlands with five wetland plant species

The removal efficiency of the pesticide chlorpyrifos (50 and 500u202fμgu202fL-1) by five wetland plant species (Cyperus alternifolius, Canna indica, Iris pseudacorus, Juncus effusus and Typha orientalis) was studied in recirculating vertical flow constructed wetland systems (RVFCWs). Results reveal that for chlorpyrifos at different concentrations, good removal efficiencies (94-98%) were observed using the same plant systems, while no significant differences in removal efficiencies were seen between the different plant systems. In addition, the chlorpyrifos removal efficiency of the planted systems increased significantly compared with the unplanted controls. The chlorpyrifos removal efficiency for wetland systems over time fit to the first-order kinetic model, with the first-order kinetic constant (k) ranging from 0.045 to 0.065 h-1. The half-life of chlorpyrifos in the systems ranged from 10.66-15.43u202fh. The shortest chlorpyrifos half-life was detected in the wetland system containing C.xa0indica, followed by that with C.xa0alternifolius and I.xa0pseudacorus. The main pathways to remove chlorpyrifos in these wetland systems were sorption (accounting for 64.6-86.4% of the total removal efficiency) and biodegradation (8.1-33.7%). Plants can enhance chlorpyrifos removal through enhanced biodegradation in the system. Plants with high biomass and transpiration were able to accelerate the removal of chlorpyrifos and conventional pollutants. Hence, C.xa0indica, C.xa0alternifolius and I.xa0pseudacorus could be used as optimal plants for pesticide removal in wetland systems.

Removal of acidic pharmaceuticals by small-scale constructed wetlands using different design configurations

To better understand the performance of constructed wetlands (CWs) to remove acidic pharmaceuticals (APs) in wastewaters in subtropical areas and to optimize CW design criteria, six small-scale CWs under different design configurations were operated. The factors (environmental parameters, water quality, and seasonality) influencing the APs removal were also analyzed to illustrate the removal mechanisms. The results indicated that the best performances of CWs were up to 80-90%. Subsurface flow (SSF) CWs showed high removal efficiency for ibuprofen, gemfibrozil and naproxen, but surface flow (SF) CWs performed better for ketoprofen and diclofenac. The positive relationship between the removal efficiencies of ibuprofen, gemfibrozil, and naproxen with dissolved oxygen and ammonia nitrogen reveals that SSF CWs under aerobic conditions benefit the biodegradation, while the favorable conditions created by SF CWs for receiving solar radiation promote the effective photolysis of ketoprofen and diclofenac. Planted SSF CWs had significantly higher removal efficiencies of ibuprofen and gemfibrozil than the unplanted controls had in all seasons. The removal of all APs was higher in summer and autumn than those in winter. Furthermore, an inverse relationship between removal efficiency and the distribution coefficient (logDow) was observed in SF CWs. Overall, CWs that provide aerobic degradation and photolysis would benefit APs removal in subtropical areas in the south of China.

Differential bioaccumulation of mercury by zooplankton taxa in a mercury-contaminated reservoir Guizhou China

Mercury (Hg) contamination in aquatic systems remains a global concern with the biomagnification of methylmercury (MeHg) through primary consumers (zooplankton) to fish and humans. In this study, total mercury (THg) and MeHg concentrations were analyzed in zooplankton collected from Baihua reservoir (Guizhou Province, China). Our results demonstrated that THg and MeHg concentrations were strongly correlated to zooplankton community and biomass composition. The THg concentration was significantly higher in micro-zooplankton compared to meso-zooplankton and macro-zooplankton, and MeHg concentration increased significantly as body size increased. Hg increases in zooplankton were influenced by the numbers of calanoid copepods and Daphnia present relative to phytoplankton and zooplankton biomass. Many zooplankton taxa in the three size-fractions were affected by THg exposure. The biomasses of Bosmina longirostris, Thermocyclops brevifurcatus, Asplanchna priodonta and Cyclops vicinus vicinus were positively correlated with Hg accumulation, while Daphnia hyalina, and Phyllodiaptomus tunguidus had a negative association. THg and MeHg bioaccumulation factors were correlated with phosphorus and total nitrogen concentration, zooplankton biomass, and chlorophyll-a concentration. Phosphorus loading was associated with increased THg and MeHg accumulation in the zooplankton highlighting biomagification with eutrophication. Chlorophyll-a levels were not correlated to THg and MeHg accumulation in zooplankton when phytoplankton densities were >107u202fcells L-1 and chlorophyll-a concentrations <9 μgL-1. This finding contradicts the idea of MeHg biodilution with increased algae biomass. However, changes in the phytoplankton species and biomass altered the availability of food for zooplankton, particularly micro-zooplankton and macro-zooplankton. Ultimately, the bioaccumulation of MeHg and THg across lower trophic levels was based more on the availability of preferred food resources than on total biological productivity.