In-situ reactivation and reuse of micronsized sulfidated zero-valent iron using SRB-enriched culture: A sustainable PRB technology.

Sulfidated zero-valent iron (S-ZVI) is an attractive material of permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. However, S-ZVI is prone to be passivated due to the oxidation of reactive and conductive iron sulfide (FeSx) shell and the formation of inactive and non-conductive ferric (hydr)oxides, which serve as electron transfer barriers to hinder the electron flow from Fe° core to contaminants. This study thus proposed a novel approach for in-situ reactivation and reuse of micronsized S-ZVI (S-mZVI) in PRB using sulfate-reducing bacteria (SRB) enriched culture to realize long-lasting remediation of Cr(VI)-contaminated groundwater. S-mZVI were passivated after reactions with Cr(VI) due to the formation of electron transfer barriers (mainly inactive and non-conductive Fe(III) (hyd)oxides, which increased the polarization resistance from 16.38 to 27.38 kΩ cm2 and hindered the electron transfer from the Fe° core. Interestingly, the passivated S-mZVI was efficiently reactivated by providing the SRB-enriched culture and organic carbon within 12 h, and the Cr(VI) removal capacity of S-mZVI in the three use cycles increased to 37.4 mg Cr/g, which was 2.1 times higher than that of the virgin S-mZVI. After biological reactivation, the Rp of reactivated S-mZVI decreased to 12.30 kΩ cm2. SRB-mediated reactivation removed the electron transfer barriers via biotic and abiotic reduction of Fe(III) (hyd)oxides. Especially, the microbial Fe(III) reduction mediated by FmnA-dmkA-fmnB-pplA-ndh2-eetAB-dmkB protein family enhanced the Fe2+ release from the surface and the subsequent re-formation of reactive and conductive FeSx shell. A long-term PRB column test further demonstrated the feasibility of in-situ biological reactivation and reuse of S-mZVI for enhanced Cr(VI)-contaminated groundwater remediation. Within 64 days, the Cr(VI) removal capacity of S-mZVI in the four use cycles increased by 3.2 times, compared to the virgin one. The bio-reactivation using the SRB-enriched culture and sulfate locally-available in groundwater will reduce the chemical and maintenance costs associated with the frequent replacement of reactive ZVI-based materials. The PRB technology based on the bio-renewable S-mZVI can be a sustainable alternative to the conventional PRBs for the long-lasting and low-cost remediation of groundwater contaminated by oxidative pollutants.

The effect of a soft diet on molar dentin formation during the occlusal establishment period.

OBJECTIVE: This study intends to investigate the effect of a soft food diet on molar dentin formation during the occlusal establishment period. It can provide dietary guidance for infants to strengthen their dental structure. DESIGN: 60 BALB/c mice were used to obtain mandibles during lactation (P0.5, P7.5, P15.5, P21.5) and occlusal establishment (P27.5, P33.5, P60.5). The mice were randomly divided into soft or hard diet groups after weaning at day 21.5. Hematoxylin-eosin and aniline blue staining were used to observe the morphology and number of odontoblasts and the amount of molar dentin formation. Immunohistochemistry was performed to observe the proliferation and apoptosis of odontoblasts. The in vivo fluorescence double-labeling was applied to evaluate the rate of molar dentin formation. RESULTS: The soft diet group had poorer periodontal membrane development but more cervical dentin deposition. Alterations in morphology and the number of odontoblasts showed a stronger correlation with age rather than food hardness. There are no significant differences in proliferative and apoptotic behavior of dentin-forming cells between the two groups. Rather, it affected the rate of dentin deposition. The rate of dentin deposition was high in the soft diet group from P21.5 to P27.5, but it was surpassed by the hard diet group within P27.5-P33.5, and the difference between the two groups disappeared at P33.5-P60.5. CONCLUSIONS: A soft diet promotes molar early cervical dentin formation. This advantage is caused by an enhanced odontoblast secretion rate rather than affecting the morphology, number, proliferation, or apoptosis of odontoblasts.

Adaptability of sulfur-disproportionating bacteria for mine water remediation under the pressures of heavy metal ions and high sulfate content.

Biological sulfide production processes mediated by sulfate/sulfur reduction have gained attention for metal removal from industrial wastewater (e.g., mine water (MW) and metallurgical wastewater) via forming insoluble metal sulfides. However, these processes often necessitate the addition of external organic compounds as electron donors, which poses a constraint on the broad application of this technology. A recent proof of concept study reported that microbial sulfur disproportionation (SD) produced sulfide with no demand for organics, which could achieve more cost-benefit MW treatment against the above-mentioned processes. However, the resistance of SD bioprocess to different metals and high sulfate content in MW remains mysterious, which may substantially affect the practical applicability of such process. In this study, the sulfur-disproportionating bacteria (SDB)-dominated consortium was enriched from a previously established SD-driven bioreactor, in which Dissulfurimicrobium sp. with a relative abundance of 39.9 % was the predominated SDB. When exposed to the real pretreated acidic MW after the pretreatment process of pH amelioration, the sulfur-disproportionating activity remained active, and metals were effectively removed from the MW. Metal tolerance assays further demonstrated that the consortium had a good tolerance to different metal ions (i.e., Pb2+, Cu2+, Ni2+, Mn2+, Zn2+), especially for Mn2+ with a concentration of approximately 20 mg/L. It suggested the robustness of Dissulfurimicrobium sp. likely due to the presence of genes encoding for the enzymes associated with metal(loid) resistance/uptake. Additionally, although high sulfate content resulted in a slight inhibition on the sulfur-disproportionating activity, the consortium still achieved sulfide production rates of 27.3 mg S/g VSS-d on average under an environmentally relevant sulfate level (i.e., 1100 mg S/L), which is comparable to those reported in sulfate reduction. Taken together, these findings imply that SDB could ensure sustainable MW treatment in a more cost-effective and organic-free way.

Obstructive sleep apnea and serum total testosterone: a system review and meta-analysis.

PURPOSE: Testosterone deficiency (TD) negatively affects male sexuality, reproduction, general health, and quality of life. In recent years, decreased serum testosterone levels have been reported to be caused by obstructive sleep apnea (OSA). However, these results are controversial and lack the support of a large number of high-quality studies. Hence, we performed a meta-analysis to assess the association between OSA and serum testosterone levels. METHODS: To identify eligible studies, we conducted a systematic retrieval in the electronic databases (PubMed, Web of Science, the Cochrane Library, EMBASE) from their inception to September 2021. We chose studies with definitive diagnoses of OSA, including effects of OSA on testosterone level. Random effect model was used for analysis. RESULTS: This meta-analysis included 24 case-control studies with 1389 patients (1268 male patients) and 845 controls (745 male control). The serum testosterone levels in the male OSA group were significantly lower than that of control group [SMD = - 0.97, 95% CI (- 1.47, - 0.47)], while there was no difference in female patients with OSA and control [SMD = 0.06, 95% CI (- 0.22, 0.33)]. Subgroup analysis showed that race, age, body mass index (BMI), and detection method were the reason for high heterogeneity (I2 = 94.9%). CONCLUSIONS: The results indicated that OSA is significantly correlated with the decrease in serum testosterone levels in men. Male patients with OSA should be alerted to secondary diseases caused by low testosterone levels.

Formation of halogenated disinfection byproducts in chlorinated real water during making hot beverage: Effect of sugar addition.

Chlorine disinfection is widely applied in drinking water treatment plant to inactivate pathogens in drinking water, but it unintentionally reacts with organic matter present in source waters and generates halogenated disinfection byproducts (DBPs). Sugar is one of the most commonly used seasoning in our diet. The addition of sugar could significantly improve the taste of the beverages; however, the effects of sugar on DBP formation and transformation remain unknown. In this study, the effects of sugar type and dose on the halogenated DBP formation in chlorinated boiled real tap water were evaluated during making hot beverages. We found that sugar can react with chlorine residual in tap water and generate halogenated DBPs. As the most commonly used table sugar, the addition of sucrose in the water sample at 100 or 500 mg/L as C could increase the level of total organic halogen (TOX) by ∼35%, when compared with the boiled tap water sample without sugar addition. In addition, fifteen reported and new polar brominated and chlorinated DBPs were detected and proposed from the reaction between chlorine and sucrose; accordingly, the corresponding transformation pathways were also proposed. Moreover, the DBP formation in the chlorinated boiled real tap water samples with the addition of xylose, glucose, sucrose, maltose and lactose were also investigated. By comparing with the TOX levels in the water samples with different sugar addition and their calculated TOX risk indexes, it was suggested that applying xylose as a sweetener in beverages could not only obtain a relatively high sweetness but also minimize the adverse effect inducing by halogenated DBPs during making hot beverages.

Human exposure to phthalate esters associated with e-waste dismantling: Exposure levels, sources, and risk assessment.

Phthalate esters (PAEs) can be released into the environment during the dismantling of electronic waste (e-waste), but urinary levels of PAE metabolites (mPAEs) in humans living in e-waste sites have not been documented. In this study, 11 mPAEs were determined in urine samples collected from participants living in e-waste dismantling sites and a reference area in Southern China. The total urinary concentrations of the 11 mPAEs (∑mPAEs) in the e-waste sites (range: 11.1 ng/mL to 3380 ng/mL) were dominated by mono-(2-isobutyl) phthalate and mono-n-butyl phthalate. Participants living in the e-waste sites had significantly higher (p < 0.05) urinary concentrations of ∑mPAEs (and 5 individual mPAEs) than those in the reference area. Hence, e-waste dismantling activities contributed to human exposure to PAEs. The exposure doses of di-n-butyl phthalate, di(2-ethylhexyl)phthalate, di-iso-butyl phthalate, dimethyl phthalate, and diethyl phthalate were 3.41, 3.04, 1.37, 0.25, and 0.20 µg/kg bw/day, respectively. Furthermore, the health risk assessment in terms of hazard quotient and hazard index showed that approximately 22% of the participants living in the e-waste sites had HI values exceeding 1; importantly, 68% of them were non-adults (i.e., 0-18 years old). In the e-waste sites, 8 of the 11 mPAEs in urine samples had significantly positively associations (r = 0.185-0.358, p < 0.05) with the urinary concentration of 8-hydroxy-2'-deoxyguanosine, a marker of DNA oxidative stress. Therefore, people living in e-waste dismantling areas may have a potential health risk caused by PAE exposure. To the best of our knowledge, this study is the first to measure urinary mPAE levels in people living in e-waste dismantling areas.