Bioaccessibility and reliable human health risk assessment of heavy metals in typical abandoned industrial sites of southeastern China.

Heavy metal pollution caused by a large number of abandoned industrial sites cannot be underestimated, but its human health risks have not been accurately assessed. This study investigated the pollution of heavy metals in soils of the typical abandoned industrial sites in southeastern China. Based on the bioaccessibility of different heavy metals (Pb, Ni, Cu, Zn, Cd, Cr) in the industrial soils, the human health risks were accurately evaluated, and the controlling factors were quantitatively assessed. The results showed that the heavy metals in each typical abandoned industrial sites had a high degree of spatial heterogeneity. Among them, Cd was the most susceptible to relevant discrete input from external factors such as human activities, followed by Zn, Pb, Cr, Ni and Cu. The bioaccessible concentration of heavy metals by the physiological-based extraction test (PBET) had a good correlation (R2 = 0.58 ∼ 0.86) with its bioavailable concentration by diethylenetriaminepentaacetic acid (DTPA) extraction. The regression model based on soil parameters had great potential to predict the bioaccessibility of heavy metals in abandoned industrial sites (R2 = 0.49 ∼ 0.95). The total concentration of heavy metals, Fe, soil texture and pH were the controlling factors of the metal bioaccessibility. Compared with the total concentration, the hazard index (HI) and carcinogenic risk (CR) values calculated based on gastrointestinal bioaccessibility were decreased by 39.0∼77.9% and 68.2∼79.9% in adults, and 45.3∼88.0% and 73.9∼83.5% in children, respectively. This work provides a feasible theoretical basis for reliable assessment of the human health risks of heavy metals in the abandoned industrial sites in the future.

Disturbance and restoration of soil microbial communities after in-situ thermal desorption in a chlorinated hydrocarbon contaminated site.

Thermal desorption technology has been widely used for the remediation of organic contaminated soil, but the heating process may alter the soil properties and its safety reutilization. After thermal remediation, the target pollutants including chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,2,3-trichloropropane and vinyl chloride in the chlorinated hydrocarbon contaminated site were reduced significantly. The soil microbial α-diversity was also reduced by more than half. Notably, the relative abundance of Chloroflexi decreased by 9.0%, while Firmicutes had a 9.0% increase after thermal remediation. By water regulation and exogenous microorganism addition, the soil microbial community could not be restored to its initial state before thermal remediation in a relatively short time (30 days). The relative abundance of Proteobacteria increased from 25.4% to 41.7% and 51.0% by water regulation and exogenous microorganism addition, respectively. The modularity of the microbial co-occurrence network was strengthened after microbial restoration, but the interaction among microorganisms was weakened. Thermal remediation might be conducive to the C- and N-cycle related processes, but severely weakened the sulfide oxidation processes. Notably, microbial restoration would benefit the recovery of the S-cycle functional groups. These results provided a new perspective for the safety reutilization of soil after thermal remediation.

The prevalence of potential pathogens in ballast water and sediments of oceangoing vessels and implications for management.

Ballast water and sediments can serve as prominent vectors for the widespread dispersal of pathogens between geographically distant areas. However, information regarding the diversity and distribution of the bacterial pathogens in ballast water and sediments is highly limited. In this study, using high-throughput sequencing and quantitative PCR, we investigated the composition and abundance of potential pathogens, and their associations with indicator microorganisms. We accordingly detected 48 potential bacterial pathogens in the assessed ballast water and sediments, among which there were significant differences in the compositions and abundances of pathogenic bacterial communities characterizing ballast water and sediments. Rhodococcus erythropolis, Bacteroides vulgatus, and Vibrio campbellii were identified as predominant pathogens in ballast water, whereas Pseudomonas stutzeri, Mycobacterium paragordonae, and Bacillus anthracis predominated in ballast sediments. Bacteroidetes, Vibrio alginolyticus, Vibrio parahaemolyticus, and Escherichia coli were generally detected with median values of 8.54 × 103-1.22 × 107 gene copies (GC)/100 mL and 1.16 × 107-3.97 × 109 GC/100 g in ballast water and sediments, respectively. Notably, the concentrations of Shigella sp., Staphylococcus aureus, and V. alginolyticus were significantly higher in ballast sediments than in the water. In addition, our findings tend to confirm that the indicator species specified by the International Maritime Organization (IMO) might underestimate the pathogen risk in the ballast water and sediments, as these bacteria were unable to predict some potential pathogens assessed in this study. In summary, this study provides a comprehensive insight into the spectrum of the potential pathogens that transferred by ship ballast tanks and emphasizes the need for the implementation of IMO convention on ballast sediment management.

Deciphering the characterization, ecological function and assembly processes of bacterial communities in ship ballast water and sediments.

Various microorganisms are transported worldwide via the water and sediments inside ship ballast tanks. Nevertheless, the ecological functions and assembly processes of bacterial communities in ballast water and sediments remain poorly understood. Here, we investigated the bacterial composition, community assembly processes, and putative functions through analyses of 70 ballast water and sediment samples obtained from various ships. The results showed that the ballast sediments contained a higher diversity of bacterial communities, whereas the ballast water was characterized by the dominance of Proteobacteria. Both the composition and potential function structures of bacterial communities were clearly different between the ballast water and sediment samples. The ballast water exhibited an abundance of microorganisms that involved in sulfur oxidation, whereas the bacterial species associated with nitrogen metabolism were abundant in the sediments. Co-occurrence network analysis revealed that the communities in ballast sediment samples possessed more complex network structures with higher modularity and positive associations among bacterial populations. Stochastic processes, especially the dispersal limitation process played the most important influence in the assembly of the communities in ballast water. Meanwhile, the bacterial communities in the ballast sediments were primarily governed by the homogeneous selection of determinacy. The results from this study will help us understand the ecological processes related to the bacterial communities in the ballast tanks and provide a foundation for the management of ballast water and sediments.

In Vitro Bioaccessibility and Health Risk Assessment of Arsenic and Zinc Contaminated Soil Stabilized by Ferrous Sulfate: Effect of Different Dietary Components.

Iron-based materials have good stability in reducing the mobility and toxicity of heavy metals, but the behavior and human health risks of heavy metals could be affected by dietary components. This study investigated the effect of typical diets (lettuce, cooked rice and apples) on the bioaccessibility and morphological changes of arsenic (As) and zinc (Zn) in contaminated site after stabilization by ferrous sulfate (FeSO4). The results showed that the bioaccessibility of As and Zn were increased in a co-digestion system of food. The augmented effect on As bioaccessibility mainly occurred in the gastric phase: apple > lettuce > cooked rice (p < 0.05), while the augmented effect on Zn bioaccessibility mainly occurred in the intestinal phase: lettuce > apple > cooked rice (p < 0.05). FeSO4 weakened the dissolution effect of dietary components on As bioaccessibility, and reduced As bioaccessibility in the gastric and intestinal phases by 34.0% and 37.9% (p < 0.05), respectively. Dietary components and Fe fractions influenced the speciation and distribution of As and Zn. FeSO4 reduced the hazard quotient (HQ) and carcinogenic risk (CR) values of the contaminated soil by 33.97% and 33.59%, respectively. This study provides a reference for a better understanding of more realistic strategies to modulate exposure risks of heavy metal-contaminated sites.

Transfer of antibiotic-resistant bacteria via ballast water with a special focus on multiple antibiotic-resistant bacteria: A survey from an inland port in the Yangtze River.

Ship ballast water can transfer harmful organisms, including antibiotic-resistant bacteria (ARB), among geographically isolated waters. In this study, the presence and composition of ARB and multiple ARB (MARB) were investigated in the ballast waters of 30 vessels sailing to the Port of Jiangyin (Jiangsu Province, China). ARB were detected in 83.3% of the ship's ballast water samples. Moreover, penicillin- and cephalothin-resistant bacteria were the most and least prevalent ARB in the ballast waters, respectively. Oxytetracycline-, chloramphenicol-, tetracycline-, and vancomycin-resistant bacteria were also detected at high concentrations. The multiple antibiotic resistance index demonstrated the presence of MARB, which exceeded 200% in the ballast waters of five ships. Furthermore, 15 species, including the human opportunistic pathogens Vibrio alginolyticus and Serratia nematodiphila, were resistant to at least three antibiotics. Therefore, the potential ecological risk of ARB warrants further attention because of their effective invasion by ballast water.

Elucidating the role of earthworms in N2O emission and production pathway during vermicomposting of sewage sludge and rice straw.

Vermicomposting is a sustainable option for the recycling of biodegradable organic waste. However, it also produces nitrous oxide (N2O), which is a highly potent greenhouse gas. In this study, the N2O stable isotope and functional genes for nitrogen cycling were determined to investigate the sources of N2O during vermicomposting. The results showed that vermicomposting promoted the organic degradation and nitrogen nitrification, and the presence of earthworms increased the emission of N2O during vermicomposting compared to that during the control treatment with no earthworms. The site preference analysis of N2O stable isotope showed that both nitrification and denitrification were present during the early stages of vermicomposting, while nitrification was the dominant contributor to N2O production in the later stages. Moreover, earthworms increased the gene copies of amoA, and stimulated the nitrifying bacteria, and hence, increased the N2O emission via nitrification. In addition, the activity of earthworms reduced the gene number of nosZ during vermicomposting, while the denitrification was the main source of N2O in the earthworm gut, as the conditions inside the gut inhibited nosZ. Overall, nitrification was the major pathway (55.8-88.7 %) for N2O production, which was promoted by the introduction of earthworms through nitrification.

Vessel transport of antibiotic resistance genes across oceans and its implications for ballast water management.

The emergence and spread of antibiotic resistance are major threats to ecosystems and human health. Transoceanic channels (e.g., ship ballast water) can transfer harmful aquatic organisms across geographically isolated waters. However, the occurrence of antibiotic resistance genes (ARGs) in ship ballast water and their relationship with microbial communities and environmental factors remain unknown. In this study, ballast water from 28 vessels sailing to Shanghai and Jiangyin (China) were collected, and the ARGs in these water samples were investigated. Considerable levels of ARGs and integrase of the class-I integrons (intI1) were detected in all ballast water samples. sul1 and tetQ were the most and least abundant ARGs in ballast water samples, respectively. The ARGs were strongly correlated with those of the 16S rRNA and intI1 genes. Ballast water exchange can reduce the absolute abundance of some kinds of ARGs while increasing the relative abundance of several ARGs (e.g., mefA, mexF, strB, sul1, and tetQ). Moreover, the bacterial hosts of ARGs were generally different in the unexchanged ballast water (UEBW) and exchanged ballast water (EBW). In particular, Leisingera and unclassified_Erythrobacteraceae were the main ARGs-associated genera in the EBW, while Pseudohongiella, Cycloclasticus, OM43_clade, norank_f_Rhodospirillaceae, and norank_f_Rhodobacteraceae were the dominant ARGs hosts in the UEBW. Overall, ship ballast water is an effective moving carrier for the global transference of ARGs, and its sufficient management is required for mitigating ARGs propagation across oceans.

Effects of earthworms on nitrogen transformation and the correspond genes (amoA and nirS) in vermicomposting of sewage sludge and rice straw.

The effects of earthworms on nitrogen transformation and the responsible functional genes during disposal of sewage sludge and rice straw were investigated in this study. Vermicomposting resulted in the lower pH and total organic carbon (TOC) compared to the control treatment without earthworms. Moreover, the presence of earthworms could promote the nitrogen mineralization and nitrification process in vermicomposting. Earthworms increased the activity of ammonia monooxygenase and abundance of amoA-nitrifier and reduced its diversity, whereas they reduced the density of nirS-denitrifying bacteria but enhanced its diversity. Nitrosospira was the dominant amoA-nitrifier and earthworms stimulated its growth in the vermicomposting. The presence of earthworms could also affect the community composition of nirS-denitrifying bacteria despite most of the nirS-denitrifier was not be classified at the genus level. In conclusion, the presence of earthworms had significant influence on the diversity and abundances of amoA and nirS genes and affect the nitrogen bio-transformation in vermicomposting.

Effects of C/N ratio and earthworms on greenhouse gas emissions during vermicomposting of sewage sludge.

The emissions of greenhouse gases (CO2, CH4, and N2O) during bio-stabilization of sewage sludge under different C/N ratios with/without Eisenia fetida were evaluated in this study. Vermicomposting led to the more significant reductions of pH, TOC and C/N ratio compared to the control treatment without earthworms. C/N ratio had a significant effect on the emission of N2O, whereas its influences on CO2 or CH4 emission were not obvious. Earthworms reduced the CH4 emission greatly, although the CO2 emission was not affected by earthworms. Furthermore, a higher emission of N2O was observed in vermicomposting compared to the control. Both the C/N ratios and earthworms exerted statistically significant effects on the total GHG emission. Vermicomposting could enhance the degradation of organics and accelerate the mineralization process of nitrogen, whereas the increase in the C/N ratio could reduce GHG emission during vermicomposting of sewage sludge.

Abundances and profiles of antibiotic resistance genes as well as co-occurrences with human bacterial pathogens in ship ballast tank sediments from a shipyard in Jiangsu Province, China.

Ship ballasting operations may transfer harmful aquatic organisms across global ocean. This study aims to reveal the occurrences and abundances of antibiotic resistance genes (ARGs) and human bacterial pathogens (HBPs) in ballast tank sediments. Nine samples were collected and respectively analyzed by real-time quantitative PCR and high-throughput sequencing technologies. Ten ARGs (aadA1, blaCTX-M, blaTEM, ermB, mefA, strB, sul1, sul2, tetM, and tetQ) and the Class-I integron gene (intI1) were highly prevalent (105-109 gene copies/g) in ballast tank sediments. The sul1 was the most abundant ARG with the concentration of 108-109 copies/g and intI1 was much more abundant than the ARGs in ballast tank sediments. The strong positive correlations between intI1 and ARGs (blaCTX-M, sul1, sul2 and tetM) indicated the potential spread of ARGs via horizontal gene transfer. In ballast tank sediments, 44 bacterial species were identified as HBPs and accounted for 0.13-21.46% of the total bacterial population although the three indicator pathogenic microbes (Vibrio cholerae, Escherichia coli, and Enterococci) proposed by the International Maritime Organization were not detected. Pseudomonas pseudoalcaligenes, Enterococcus hirae, Shigella sonnei and Bacillus anthracis were the dominant pathogens in ballast tank sediments. Zn and P in sediments had positive effects on the ARGs. Network analysis results indicated that sul1 and sul2 genes existed in several bacterial pathogens. Ballast tank sediments could be regarded as a carrier for the migration of ARGs. It is important to manage ballast tank sediments reasonably in order to prevent the dissemination of ARGs and bacterial pathogens.

Composition and influencing factors of bacterial communities in ballast tank sediments: Implications for ballast water and sediment management.

This study aims to reveal the composition and influencing factors of bacterial communities in ballast tank sediments. Nine samples were collected and their 16S rRNA gene sequences were analyzed by high-throughput sequencing. The analysis results showed the Shannon index in ballast tank sediments was in the range of 5.27-6.35, which was significantly higher than that in ballast water. Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi and Proteobacteria were the dominant phyla and accounted for approximately 80% of all 16S rRNA gene sequences of the samples. Besides, the high contents of sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria were detected in sediments, indicating that the corrosion of metal caused by SRB might occur in ballast tank. In addition, the trace of human fecal bacteria and candidate pathogens were also detected in ballast tank sediments, and these undesirable microbes reduced the effect of ballast water exchange. Furthermore, C and N had significant effects on the bacterial community composition in ballast tank sediments. In conclusion, our findings suggest that the proper management and disposal of the ballast tank sediments should be considered in order to reduce the negative impact and ecological risks related to ballast water and sediments.

[Primary study on contents of sulfate reducing bacteria (SRB) and organic matter from intertidal zone at Chongming Dongtan].

Collected soil samples from different tidal flats and elevation in Chongming Dongtan wetland, then conducted sulfate-reducing bacteria (SRB) based on MPN method, determined organic matter content and calculated SO4(2-)/Cl- molar ratio, for the research on the distribution of SRB, relevance to soil organic matter content as well as influence of plant rhizosphere environment on SRB growth. The results show the distribution of SRB is ranked as middle flat > climax flat > bald flat. The same tidal flats at different depths, the SRB levels are shown as 51-52 cm > 21-22 cm > 81-82 cm, therefore 51-52 cm soil depth of Dongtan wetland is the suitable area for SRB to grow. However, in different tidal and depth, the distribution of organic matter content presents climax flat > middle flat > bald flat. From 21-51 cm, as the depth increasing, the organic matter content decreases while the amount of SRB significantly increasing, which indicates SRB utilizes the soil organic matter to carry out reduction reaction. The SO4(2-)/Cl- molar ratios of all soil samples are less than 0.05, indicating that SRB are actively engaged in sulfate reduction. The concentration of SRB in reed rhizosphere soil is the highest, showing that Phragmites australis rhizosphere environment in Dongtan wetland could enhance SRB growth, while the number of SRB in Spartina alterniflora rhizosphere environment is relatively lower than the non-rhizosphere environment, indicating that the rhizosphere effect has different effects on SRB in Dongtan tidal flats.