Are the existing guideline values adequate to protect soil health from inorganic mercury contamination?

© 2018 Elsevier Ltd Currently, data that guide safe concentration ranges for inorganic mercury in the soil are lacking and subsequently, threaten soil health. In the present study, a species sensitivity distribution (SSD) approach was applied to estimate critical mercury concentration that has little (HC 5 ) or no effect (PNEC) on soil biota. Recently published terrestrial toxicity data were incorporated in the approach. Considering total mercury content in soils, the estimated HC 5 was 0.6 mg/kg, and the PNEC was 0.12–0.6 mg/kg. Whereas, when only water-soluble mercury fractions were considered, these values were 0.04 mg/kg and 0.008–0.04 mg/kg, respectively

Effect of Nitrogen Rates and Foliar Spray of Micronutrients on Growth and Yield of Sesame (Sesamum indicum L.)

To find out optimum nitrogen (N) and micronutrients (MNs) doses for the growth and yield of sesame the experiment was undertaken at Sher-e-Bangla Agricultural University Research field, Dhaka, during April to July 2013 with three replications in a randomized complete block design (RCBD). Three different N levels viz. N0= without N, N1= 60 kg h-1, N2=120 kg h-1 and four micronutrients (MNs) levels viz. M0= without MNs, M1= 50 ppm MNs, M2= 100 ppm and M3= 150 ppm MNs. The N significantly increased morphological characters - plant height, number of  leaves plant-1, branch number plant-1, fresh and dry weight of shoot and root; yield contributing characters-  number of pod plant-1, pod diameter, pod length, seed weight plant-1, seed weight plot-1 compared to control (N0). The rate of application of N 60 kg ha-1 produced the highest seed yield (1.21 t ha-1) which is consisting with most of the vegetative growth of sesame. Foliar application of different concentration of micronutrients also improved the morphological characters and seed yield of sesame as N. Interestingly 1000-seed weight did not show any significant differences with both  N and micronutrients. The maximum number of pod plant-1, pod diameter, pod length, seed weight plant-1, seed yield (1.14 tha-1) significantly increased with 150 ppm micronutrients. Therefore, this experimental results suggest that the use of 60 kg Nha-1 and 150 ppm micronutrients have produced highest seed yield of sesame by adjusting in plant morphological characters and yield contributing characters of sesame

Bioremediation of mercury: not properly exploited in contaminated soils!

© 2017, Springer-Verlag Berlin Heidelberg. Contamination of land and water caused by heavy metal mercury (Hg) poses a serious threat to biota worldwide. The seriousness of toxicity of this neurotoxin is characterized by its ability to augment in food chains and bind to thiol groups in living tissue. Therefore, different remediation approaches have been implemented to rehabilitate Hg-contaminated sites. Bioremediation is considered as cheaper and greener technology than the conventional physico-chemical means. Large-scale use of Hg-volatilizing bacteria are used to clean up Hg-contaminated waters, but there is no such approach to remediate Hg-contaminated soils. This review focuses on recent uses of Hg-resistant bacteria in bioremediation of mercury-contaminated sites, limitation and advantages of this approach, and identifies the gaps in existing research

A simple spectrophotometric method for rapid quantitative screening of arsenic bio-transforming bacteria

© 2020 A simple spectrophotometric technique for inorganic arsenic speciation of known total arsenic has been developed for application in quantitative screening of arsenite-oxidizing and arsenate-reducing bacteria from the wide range of environmental isolates. The technique is based on the spectrophotometric absorbance measurement of the color intensity in the arsenic and potassium permanganate mixture. Since arsenate does not react with potassium permanganate, the intensity of color decreases proportionately with the increasing concentration of arsenite in the total arsenic. The speciation method can be used over a pH range of 4–9. The validity of the results obtained from this spectrophotometric method was confirmed with the Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry (LC-ICP-MS). This method has great potential for the screening of arsenite-oxidizing bacteria

As(V) removal from aqueous solution using a low-cost adsorbent coir pith ash: Equilibrium and kinetic study

© 2017 Elsevier B.V. In this study, the adsorptive removal of As(V) from aqueous solution by using a low-cost adsorbent coir pith ash (CPA) was analysed in a batch system. The adsorption capacity of CPA was investigated under different process parameters, these being pH, adsorbent dose, initial As(V) concentration and contact time. The CPA was found to adsorb As(V) over the initial solution pH range of 2–12, and the best adsorbent dose was 5 g/L. Adsorption kinetics data were best fitted to the pseudo-second-order kinetic model. The Langmuir and Dubinin–Radushkevich (D–R) isotherms represented the adsorption equilibrium data very well. The maximum adsorption capacity was 36.5 mg/g as per Langmuir isotherm at room temperature (25 °C). The mean free energy (8.64 kJ/mol) obtained from the D–R isotherm model revealed that the type of adsorption depends on the ion-exchange mechanism. The results showed that adsorbent CPA has great potential for removing As(V) from contaminated water

Long-lasting effect of mercury contamination on the soil microbiota and its co-selection of antibiotic resistance.

Antibiotic resistance genes (ARGs) in the environment are an exposure risk to humans and animals and is emerging as a global public health concern. In this study, mercury (Hg) driven co-selection of ARGs was investigated under controlled conditions in two Australian non-agricultural soils with differing pH. Soils were spiked with increasing concentrations of inorganic Hg and left to age for 5 years. Both soils contained ARGs conferring resistance to tetracycline (tetA, tetB), sulphonamides (sul1), trimethoprim (dfrA1) and the ARG indicator class 1 integron-integrase gene, intI1, as measured by qPCR. The last resort antibiotic vancomycin resistance gene, vanB and quinolone resistance gene, qnrS were not detected. Hg driven co-selection of several ARGs namely intI1, tetA and tetB were observed in the alkaline soil within the tested Hg concentrations. No co-selection of the experimental ARGs was observed in the neutral pH soil. 16S rRNA sequencing revealed proliferation of Proteobacteria and Bacteriodetes in Hg contaminated neutral and alkaline soils respectively. Multivariate analyses revealed a strong effect of Hg, soil pH and organic carbon content on the co-selection of ARGs in the experimental soils. Additionally, although aging caused a significant reduction in Hg content, agriculturally important bacterial phyla such as Nitrospirae did not regrow in the contaminated soils. The results suggest that mercury can drive co-selection of ARGs in contaminated non-agricultural soils over five years of aging which is linked to soil microbiota shift and metal chemistry in the soil

Protozoal food vacuoles enhance transformation in Vibrio cholerae through SOS-regulated DNA integration.

Vibrio cholerae, the bacterial pathogen responsible for the diarrheal disease cholera, resides in the aquatic environment between outbreaks. For bacteria, genetic variation by lateral gene transfer (LGT) is important for survival and adaptation. In the aquatic environment, V. cholerae is predominantly found in biofilms associated with chitinous organisms or with chitin "rain". Chitin induces competency in V. cholerae, which can lead to LGT. In the environment, V. cholerae is also subjected to predation pressure by protist. Here we investigated whether protozoal predation affected LGT using the integron as a model. Integrons facilitate the integration of mobile DNA (gene cassettes) into the bacterial chromosome. We report that protozoal predation enhances transformation of a gene cassette by as much as 405-fold. We show that oxidative radicals produced in the protozoal phagosome induces the universal SOS response, which in turn upregulates the integron-integrase, the recombinase that facilitates cassette integration. Additionally, we show that during predation, V. cholerae requires the type VI secretion system to acquire the gene cassette from Escherichia coli. These results show that protozoal predation enhances LGT thus producing genetic variants that may have increased capacity to survive grazing. Additionally, the conditions in the food vacuole may make it a "hot spot" for LGT by accumulating diverse bacteria and inducing the SOS response helping drive genetic diversification and evolution