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Herein, the synthesis of a biocompatible silver nanoparticles (AgNPs), for colorimetric detection of toxic mercury (II) ion (Hg2+), is reported. Phenolic-rich fraction of Asystasia gangetica leaf was extracted and used as a reductant of silver salt, all within the hydrophilic konjac glucomannan (KgM) solution as stabilizer, at room temperature (RT). The bioactive components of Asystasia gangetica phenolic extract (AGPE), as elucidated with a (UHPLC-MS-QTOF-MS), revealed plethora of phenolic compounds, which can facilitate the reduction of silver salt at ambient conditions. Sparkling yellow colloidal solution of KgM-AgNPs was realized within 1 h, at RT, having a UV–vis maximum at 420 nm. KgM-AgNPs was characterized using UV–vis, Raman and (FTIR), TEM, SEM, EDS, XRD, TGA/DTG. TEM and FESEM images showed that KgM-AgNPs were spherical, with particle size distribution around 10–15 nm from TEM. The KgM-AgNPs biocompatibility was investigated on mouse L929 fibrobroblast and rat erythrocytes, without any harmful damages on the tested cells. In aqueous environment, KgM-AgNPs demonstrated good detection capacity toward Hg2+, in a Hg2+ concentration dependent fashion, within 3 min. Absorbance ratios (A360/A408) was linear with Hg2+ concentrations from 0.010–10.0 to 10.0–60.0 µM, with an estimated (LOD) of 3.25 nM. The probe was applied in lake water sample, with satisfactory accuracy.

An imbalance in the environment's composition leads to significant effect on human activities such as farming. Of importance are heavy metals which are introduced anthropogenically or naturally. This calls for environmental monitoring and subsequent remediation if needed. An environmental monitoring exercise was conducted on Ikwo soils of Ebonyi State, eastern Nigeria with the aim of determining concentration levels for possible remediation. A total of 18 soil composite samples taken at 0-50 cm below soil surface from fallowed and cultivated soils not fertilized were subjected to heavy metal analyses and fertility indices like: organic matter (OM), cation exchange capacity (CEC), % total nitrogen (%TN), organic carbon (OC), and salinity. A correlation at 95% confidence level between geo-accumulations (I) of the various heavy metals with salinity, OM, and CEC of the sampled soils reveals that I could be a contributing factor to the fertility status of the soils. With the aid of inductively coupled plasma atomic emission spectrophotometer (ICP-AES), the distribution pattern was determined as Mn> Fe> Zn>Cu> Mo> Cd> V>Hg>Ti> Ni>Bi> Pb> Co>Ag>Au> Cr>Pd>Pt. The I of the heavy metals in the study area varied from heavily to extremely contaminated levels. A remediation exercise was recommended on Ikwo soils due to their high salinity level and low CEC.

The use of cyanidin as a metallochromic agent in analyses of heavy metal is reported. Cyanidin is a ligand that was extracted from Gmelina arborea fruit and characterized. The cyanidin was used to form complexes with metals in five fish samples for the quantitative determination of Cu, Zn, Ca and Mg. The optimum pH for absorbances of the cyanidin-metal complexes was observed at 5. Experimental results obtained using cyanidin were compared with analyses results obtained by Atomic absorption spectrophotometry (AAS) and both methods were evaluated using paired T-test to ascertain the suitability of cyanidin as metallochromic agent for the quantitative determination of heavy metals in fish samples. A null hypothesis that cyanidin method is a good alternative to AAS was accepted for the analyses of Cu and Zn (p > 0.05). The paired T-test, however rejected the null hypothesis for the determination of Ca and Mg (p < 0.05). This study has provided a cheap, sensitive, rapid, simple and easy method for metal determination in analytical samples.

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