Improvement of biotic nitrate reduction in constructed photoautotrophic biofilm-soil microbial fuel cells.

The biotic nitrate reduction rate in freshwater ecosystems is typically constrained by the scarcity of carbon sources. In this study, 'two-chambers' - 'two-electrodes' photoautotrophic biofilm-soil microbial fuel cells (P-SMFC) was developed to accelerate nitrate reduction by activating in situ electron donors that originated from the soil organic carbon (SOC). The nitrate reduction rate of P-SMFC (0.1341 d-1) improved by âˆ¼ 1.6 times on the 28th day compared to the control photoautotrophic biofilm. The relative abundance of electroactive bacterium increased in the P-SMFC and this bacterium contributed to obtain electrons from SOC. Biochar amendment decreased the resistivity of P-SMFC, increased the electron transferring efficiency, and mitigated anodic acidification, which continuously facilitated the thriving of putative electroactive bacterium and promoted current generation. The results from physiological and ecological tests revealed that the cathodic photoautotrophic biofilm produced more extracellular protein, increased the relative abundance of Lachnospiraceae, Magnetospirillaceae, Pseudomonadaceae, and Sphingomonadaceae, and improved the activity of nitrate reductase and ATPase. Correspondingly, P-SMFC in the presence of biochar achieved the highest reaction rate constant for nitrate reduction (kobs) (0.2092 d-1) which was 2.4 times higher than the control photoautotrophic biofilm. This study provided a new strategy to vitalize in situ carbon sources in paddy soil for nitrate reduction by the construction of P-SMFC.

The interplay of hematite and photic biofilm triggers the acceleration of biotic nitrate removal.

The soil-water interface is replete with photic biofilm and iron minerals; however, the potential of how iron minerals promote biotic nitrate removal is still unknown. This study investigates the physiological and ecological responses of photic biofilm to hematite (Fe2O3), in order to explore a practically feasible approach for in-situ nitrate removal. The nitrate removal by photic biofilm was significantly higher in the presence of Fe2O3 (92.5%) compared to the control (82.8%). Results show that the presence of Fe2O3 changed the microbial community composition of the photic biofilm, facilitates the thriving of Magnetospirillum and Pseudomonas, and promotes the growth of photic biofilm represented by the extracellular polymeric substance (EPS) and the content of chlorophyll. The presence of Fe2O3 also induces oxidative stress (•O2-) in the photic biofilm, which was demonstrated by electron spin resonance spectrometry. However, the photic biofilm could improve the EPS productivity to prevent the entrance of Fe2O3 to cells in the biofilm matrix and mitigate oxidative stress. The Fe2O3 then promoted the relative abundance of Magnetospirillum and Pseudomonas and the activity of nitrate reductase, which accelerates nitrate reduction by the photic biofilm. This study provides an insight into the interaction between iron minerals and photic biofilm and demonstrates the possibility of combining biotic and abiotic methods to improve the in-situ nitrate removal rate.

Influence of crop residue-induced Fe-DOC complexation on nitrate reduction in paddy soil.

Although complexation between dissolved organic matter (DOM) and ubiquitous Fe is known to have a major influence on electron transferring ability in redoximorphic soil, it was unclear whether and how this complexation affected nitrate reduction and N2O productivity. The nitrate reduction of paddy soil in the presence of crop residues returning under flooding conditions was explored in this study. The rate of nitrate reduction in control soil was 0.0677 d-1, while it improved 1.99 times in treatment soil with Chinese milk vetch (CMV) straw returning. During a 28-day incubation period, N2O productivity decreased 0.08-0.91 ppb in CMV soil and 0.43-0.50 ppb in rice straw soil compared with control. The presence of crop residue increased DOC content and Fe (III) reduction rate, which aided in the formation of Fe (II)-DOC complexation. Meanwhile, the addition of CMV increased the content of DOC by 5.14-78.77 mg/kg and HCl extractable Fe (II) by 35.12-1221.03 mg/kg. Crop residues returning to soil increased the relative abundance of iron reductive and electroactive genera, as well as denitrifying genera with more copies of denitrification genes (Archangiaceae, Gemmatimonadaceae, and Burkholderiaceae). The synergistic effect of Fe-DOC complexation, electroactive genera, and denitrifying genera contributed to up-regulated expression of napA and narG (5.84 × 106 and 3.39 × 107 copies increased in the CMV soil compared to the control) numbers and equally accelerated reduction of nitrate to nitrite, while further nitrite reduction was primarily attributed to the abiotic reaction by Fe (II). From a bio-electrochemical point of view, this work provided new insight into the nitrate reduction of paddy soil impacted by Fe-DOC complexation.

Hormonal and haematological biomarkers as indicators of stress induced by Diuron herbicide toxicity on Clarias gariepinus (Burchell, 1822) sub-adults.

Diuron is a globally used herbicide for weed control but has anti-androgenic effects on androgens (testosterone and androstenedione), antagonist effects on thyroid hormone signaling, and haematological effects due to their biotransformation in fish. Endocrine-disrupting biomarkers such as thyroid hormones, sex hormones, and haematological indices of Clarias gariepinus sub-adults exposed to sub-lethal diuron concentrations were studied over a 28-day period. C. gariepinus (n = 200) sub-adults were exposed to sub-lethal concentrations (0.00, 0.09, 0.18, 0.26, and 0.35 mg/L) of diuron. Changes in the hormonal and haematological profiles of the exposed fish were concentration and exposure duration-dependent. The thyroxine (T4), tri-iodothyronine (T3), and 17ß-estradiol (E2) profiles decreased with an increase in concentration and exposure duration. The haemoglobin, pack cell volume, red blood cell, white blood cell, mean cell volume, and mean corpuscular haemoglobin cell decreased, while the mean corpuscular haemoglobin increased with an increase in concentration and exposure duration. Diuron induced stress and altered the physiological mechanisms of fish, and its application in farmlands should be regulated so as to enable a sustainable aquatic eco-system and fishery resources.

Reduced arsenic availability in paddy soil through Fe-organic ligand complexation mediated by bamboo biochar.

The reuse of arsenic (As)-contaminated paddy fields is a global challenge because long-term flooding would result in As release due to the reductive dissolution of iron minerals. Biochar amendment is a common and effective remediation technique for As-contaminated paddy soil. However, the literature is still lacking in systematic research on the function of biochar in controlling the complexation of released dissolved organic matter (DOM) and iron oxides and its synergistic impact on the availability of As in flooded paddy soil. In the present study, bamboo biochar was prepared at different pyrolysis temperatures (300, 450 and 600 °C), as BB300, BB450 and BB600. Four paddy soil treatments including BB300, BB450, BB600 applications (1% ratio, m/m, respectively) and control (CK, no biochar application) were set and incubated for 60 d in flooding condition. The results showed that As availability represented by adsorbed As species (A-As) was mitigated by BB450 amendment compared with CK. The amendment of BB450 in paddy soil facilitated the complexation of HCl extractable Fe(III)/(II) and DOM and formation of amorphous iron oxides (e.g. complexed Fe species). Moreover, the abundance of Geobacteraceae and Xanthomonadaceae, as common electroactive bacteria, was promoted in the BB450 treated paddy soil in comparison to CK, which assisted to form amorphous iron oxides. The formed amorphous iron oxides then facilitated the formation of ternary complex (As-Fe-DOM) with highly stability, which could be considered as a mechanism for As immobilization after biochar was applied to the flooding paddy soil. Thus, the synergistic effect between amorphous iron oxides and electroactive stains could make main contribution to the passivation of released As in paddy soil under long-term flooding condition. This study provided a new insight for As immobilization via regulating iron-organic ligand complexation amendment with biochar in flooding paddy soil.

Susceptibility of Cd availability in microplastics contaminated paddy soil: Influence of ferric minerals and sulfate reduction.

The combined contamination of cadmium (Cd) and microplastics (MPs) in paddy soil always occurred, while its influence on Cd availability remained unclear. This study investigated the Cd availability in Cd-MPs co-contaminated paddy soil in consideration of both ferric minerals and sulfate reduction under flooding conditions. The presence of MPs resulted in a higher Cd releasing risk, as represented by the increase in the available Cd and decrease in Fe-Mn oxide-bound Cd contents, especially on the 7th and 14th days based on the sequential extraction results. MPs facilitated the formation of Fe-organic ligands, which accelerated the reductive dissolution of iron minerals but decreased the amounts of amorphous iron minerals due to the release of dissolved organic substances into pore water. Furthermore, MPs promoted the relative abundance of sulfate-reducing bacteria (such as Streptomyces and Desulfovibrio genera), thus increasing the contents of reductive S species, which was advantageous to the co-precipitation of Fe, S, and Cd on the surface of MPs based on our experimental and statistical results. Taken together, both iron and sulfate reduction under anaerobic conditions played a critical role in Cd mobilization in Cd-MPs co-contaminated paddy fields.

Spice-Induced Metal Contamination and Microbiological Risk Assessment of Instant Noodles Prepared for Human Consumption.

With the rising worries of potential metal contamination in cooked noodles, this study aimed at unravelling, for the first time, the possible source of metal contamination in cooked noodles. Noodles cooked with full spices (CWFS), cooked with half spices (CWHS), cooked with quarter spices (CWQS), and cooked with no spices (CWNS: control) and their spices were analysed for metals using inductively coupled plasma-atomic emission spectrometry. The microbiological quality of the noodles was also evaluated. Metal concentrations in cooked noodles varied with spice quantity. Noodles CWFS had the highest significant (p < 0.05) concentration of Pb (0.36 ± 0.12 mg/kg), Ni (1.05 ± 0.01 mg/kg), Cd (0.07 ± 0.04 mg/kg), Co (0.02 ± 0.002 mg/kg), and Na (9.45 ± 0.04 mg/kg), compared to the control (CWNS). The mean Pb and Ni of spice and cooked noodles were above the WHO acceptable limits for food and could be harmful to consumers. Pearson's correlation and PCA showed that packed noodle spices introduced metals into the cooked noodles. Although the hazard indices (adults and children) in all noodle's groups were less than 1, children still had the potential to contract cancer from Ni exposure because the carcinogenic risk values of CWQS (2.87 × 10-4), CWHS (3.03 × 10-4), and CWFS (3.21 × 10-4) were greater than 10-4. Microbiological analysis revealed the presence of potential pathogens that showed multidrug resistance and the ability to elaborate protease and amylase enzymes. Given the impending chronic health risks inherent in processed noodles, consistent consumption should be avoided.

Deterioration of the quality of packaged potable water (bottled water) exposed to sunlight for a prolonged period: An implication for public health.

The exposure of bottled water to sunlight leaches heavy metals into the water, thereby deteriorating its quality and this informed the study. Three plastic bottle brands (n = 100 per brand) were exposed to sunlight for different durations. The leaching of contaminants was exposure duration dependent. The following ranges were recorded for temperature (26.67-29.83 °C), pH (4.73-6.12), conductivity (159.00-298.67 µs/cm), turbidity (0.92-1.22 N.T.U), TDS (98.17-192.77 mg/l), hardness (38.12-78.17 mg/l), Fe (0.01-0.57 mg/l), Mn (BDL - 0.46), Cr (BDL - 0.37 mg/l), Al (BDL - 0.53 mg/l), Cd (0.02-0.21 mg/l), Zn (1.18-9.90 mg/l), Pb (0.03-1.68 mg/l), As (BDL - 1.48 mg/l), and Ni (0.05-1.55 mg/l). Health risk evaluation in all bottled water brands revealed possible Cr, Cd, Pb, As, and Ni toxicity. The carcinogenic risk of Cr, As, and, Ni, indicated potential cancer. Arsenic posed the highest non-carcinogenic risk, while Ni posed the highest carcinogenic risk in all brands after 42 days of exposure. The microbial parameters failed to meet the WHO safety limits. The exposure of bottled water to sunlight should be avoided, to ensure a healthy population.

Heavy metal co-resistance with antibiotics amongst bacteria isolates from an open dumpsite soil.

Heavy metal co-resistance with antibiotics appears to be synergistic in bacterial isolates via similar mechanisms. This synergy has the potential to amplify antibiotics resistance genes in the environment which can be transferred into clinical settings. The aim of this study was to assess the co-resistance of heavy metals with antibiotics in bacteria from dumpsite in addition to physicochemical analysis. Sample collection, physicochemical analysis, and enumeration of total heterotrophic bacteria counts (THBC) were all carried out using standard existing protocols. Identified bacteria isolates were subjected to antibiotics sensitivity test using the Kirby Bauer disc diffusion technique and the resulting multidrug resistant (MDR) isolates were subjected to heavy metal tolerance test using agar dilution technique with increasing concentrations (50, 100, 150, 200 and to 250 µg/ml) of our study heavy metals. THBC ranged from 6.68 to 7.92 × 105 cfu/g. Out of the 20 isolates subjected to antibiotics sensitivity, 50% (n = 10) showed multiple drug resistance and these were B. subtilis, B. cereus, C. freundii, P. aeruginosa, Enterobacter sp, and E. coli (n = 5). At the lowest concentration (50 µg/ml), all the MDR isolates tolerated all the heavy metals, but at 250 µg/ml, apart from cadmium and lead, all test isolates were 100% sensitive to chromium, vanadium and cobalt. The control isolate was only resistant to cobalt and chromium at 50 µg/ml, but sensitive to other heavy metals at all concentrations The level of co-resistance shown by these isolates is a call for concern.

Public health threats of heavy metals due to the consumption of Achachatina marginata (African Giant Land Snail) from a partially remediated site in Ikot Ada Udo, Akwa Ibom State, South-South Nigeria.

The risk of oral intake of metals from the ingestion of contaminated Achachatina marginata was carried-out. Snail samples (n = 48) were hand-picked, preserved in ice, then analyzed for zinc (Zn), nickel (Ni), chromium (Cr) using inductively coupled plasma-atomic emission spectrometry (ICP-AES, Yobin Yvon JY-24), then cadmium (Cd), lead (Pb) using graphite furnace atomic absorption spectrometry (GF-AAS, 4110 ZL PerkinElmer). The mean levels of metals in snail from each sampling point were higher compared to the control site. SP 1 had the highest significant levels (p < 0.05) of Pb, Zn, Ni, Cd, while SP 3 had the highest significant levels (p < 0.05) of Cr compared to the control site. The mean heavy metals in the snail were 3.280 ± 0.995 mg/kg (Cd), 8.906 ± 2.079 mg/kg (Zn), 0.896 ± 0.401 mg/kg (Cr), 1.867 ± 0.921 mg/kg (Ni), 1.998 ± 0.781 mg/kg (Pb). The mean Cd, Cr, Ni, and Pb in A. marginata were above WHO acceptable limits for food. Heavy metals level in A. marginata had a decreasing trend of Zn > Cd > Pb > Ni > Cr. The estimated daily intake (EDI) of Cd (5.61 × 10-3 mg/kg/day) was higher than the reference oral dose (RfD) value of 0.001 mg/kg/day. The target hazard quotient (THQ) of Cd (5.61) and the hazard index (HI) of metals (6.80) were greater than 1. The carcinogenic risk (CR) of Ni (5.43 × 10-3) and Cd (2.13 × 10-3) from contaminated snails intake were higher than the safe range of 10-6 to 10-4. The THQ, EDI of Cd, HI of the metals, and the CR values of Ni and Cd in snails from the contaminated site reveals a potential future health challenge to consumers and a possibility of contracting cancer over a 70 year lifetime. Furthermore, the findings revealed that the site requires a thorough clean-up for the total restoration of the environment.