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A green synthetic approach to synthesize silver nanoparticles (AgNPs) using the stem extract of Piper chaudocanum for highly sensitive colorimetric detection of Hg2+ with a low limit of detection of 23 nM and easy colorimetric read-out has been reported. In addition, the biosynthesized AgNPs demonstrated efficient antibacterial activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. The morphology and structure of the as-synthesized AgNPs were examined using SEM, TEM, EDX, XRD and FT-IR analyses. The XRD and TEM results confirm the formation of AgNPs with an average particle size of 8–12 nm. The TLC, CC and HPLC revealed that four main compounds, pentacosanoic acid (1), piperine (2), β-sitosterol (3), and campesterol glucoside (4), isolated from P. chaudocanum extract act as reducing and stabilizing agents for AgNP formation, and piperine plays a vital role in green synthesis. The chemical structures of these compounds were determined by ESI MS, FTIR, and 1D, 2D NMR spectroscopic data analysis. This approach is an efficient, green, cost-effective, eco-friendly and promising technique for synthesizing AgNPs with applications in the colorimetric detection of Hg2+ and antibacterial activity.

Red mud modifying by rice husk char (HM105) was sucessfully fabricated through activation of red mud slurry (RM) by rice husk char (RH). HM105 was then characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction and employed as an adsorbent for the removal of methylene blue (MB) from aqueous solutions. Some impact parameters on the adsorption of MB as contact time and initial concentration were studied. The results showed that the removal of MB on HM105 was the highest at 90 min and initial concentration of 200 ppm and adsorption data well fitted with Langmuir adorption isotherm model with the maximum adsorption capacity of HM105 was 220.26 mg/g. It demonstrated that HM105 was potential adsobent for treatment of MB as well as other dyes in wastewater.

Antibiotics are contaminants at low concentrations and found in water with the range of ng/L. Determination of antibiotics at trace concentrations requires modern and high accuracy equipment. Liquid chromatography mass tandem spectrometry (LC-MS/MS) able to determine contaminants at ppt and ppb levels, which is suitable for quantification of the macrolide and tetracycline group in water. The Analytical method using Agilent Triple Quard 6460 LC-MS/MS system with positive ion mode. Agilent XDB C18 column (1.8 µm × 2.1 × 100 mm) and Agilent Eclipse SDB C18 pre-column (2.1 × 5 mm × 1.8 µm) were used. Mobile phase was acetonitrile and HCOOH 0.1%. Samples were cleaned with Oasis PRiME HLB 3cc SPE column (150 mg). The method was evaluated based on specificity, recovery, repeatability and estimation of the uncertainty. The method detection limit (MDL) for the analytes is 0.03 µg/L. Recovery ranges from 85.23 -117.70%; repeatability (RSDr) is between 2.20% and 12.45%.

This study investigates the impacts of wastewater and biosolids application on cultivated Vietnamese Fluvisols and Acrisols. Chemical impacts, i.e. enrichment of macronutrients (N, P, K) and trace metals (mainly Cu, Zn, Cd, Pb), and solubility and mobility of trace metals were examined. Experiments were carried out in peri-urban vegetable and/or rice-dominated farming systems of Hanoi, Ha Tay, Vinh Phuc and Nam Dinh cities. Batch studies were performed in order to measure metal solubility in soil solution, and multi-surface models including the soil sorption surfaces, i.e. iron hydroxides (DLM), organic matter (SHM and NICA-Donnan model), and phyllosilicate clay (Gaines-Thomas) were tested for describing metal binding. A multi-surface model was used to run various scenarios including (i) changing metal loading (Cd, Cu, Zn) up to the present Vietnamese maximum acceptable soil concentration (MAC), and (ii) varying soil organic matter (SOM) content and (iii) soil pH within the ranges found in the national soil inventory of Acrisols and Fluvisols, respectively. These soil types represent 73% of agricultural soils in Vietnam. Field balance calculations revealed macronutrient and trace metal (Cu, Zn) accumulation in intensive peri-urban vegetable systems in Hanoi City. The N surplus ranged from 85-882 kg ha-1 yr-1, while P and K surpluses were 109-196 and 20-306 kg ha-1 yr-1, respectively. For Cu and Zn surpluses varied from 0.2-2.7 and 0.6-7.7 kg ha-1 yr-1, respectively, wastewater and biosolids being the major sources accounting for 75-98 and 62-94% of the total Cu and Zn input. Application of biosolids significantly increased the ‘total’ (reverse aqua regia-extractable) soil Zn concentration, whereas concentrations of Cd and Pb were not significantly different from the control. However, there were positive relationships between EDTA-extractable Cd, Cu and Zn and biosolids application rates. For total dissolved Cd, Cu and Zn the multi-surface models provided very good model fits for all soils and thus these can be used to describe their binding and solubility in tropical Fluvisols and Acrisols. Scenario simulations identified the potential risk of metal losses to the environment (i.e. Cd and Zn), as influenced by loading up to MAC, soil acidification and decreasing soil organic matter content, especially for Acrisols. Assuming the same metal input rate as at present, it was roughly estimated to take 20-325 and 40-450 years to reach the MAC for Cu and Zn, respectively. It was concluded that wastewater and biosolids can be major nutrient sources in peri-urban agricultural production systems. However, they can also contribute to substantial trace metal inputs and represent a potential threat to soil quality, water environment and human health. Soil organic matter is a major sorbent for Cd, Cu, and Zn in tropical Acrisols and Fluvisols, and pH is the main factor controlling the solubility of metals in these soils. Regarding Pb, modelling was not successful and further refinements of the models will be required.