Polymer Supported Calix[4]Arene Derivatives for the Extraction of Metals and Dichromate Anions

Three newly synthesized polymer supported calix[4]arene ionophores (7–9) were synthesized, and their ion binding properties toward selected alkali (Li⁺, Na⁺, K⁺, Cs⁺) and transition metal (Hg²⁺, Ni²⁺, Cu²⁺, Co²⁺, Cd²⁺, and Pb²⁺) cations were investigated. It has been observed that these ionophores are not selective toward a particular metal cation but show better ion binding property as compared to monomeric calixarene derivatives (2 and 6). Ionophore 6 and its supported polymer were also employed in dichromate anion extraction experiments. The polymeric ionophore (9) was found an effective extractant for dichromate anion even at pH 7.     

Preconcentration and determination of lead and cadmium levels in blood samples of adolescent workers consuming smokeless tobacco products in Pakistan

The present study was aimed to evaluate the cadmium (Cd) and lead (Pb) levels in the blood samples of adolescent boys, chewing different smokeless tobacco (SLT) products in Pakistan. For comparative purpose, boys of the same age group (12–15 years), not consumed any SLT products were selected as referents. To determine trace levels of Cd and Pb in blood samples, a preconcentration method, vortex-assisted liquid–liquid microextraction (VLLME) has been developed, prior to analysis by flame atomic absorption spectrometry. The hydrophobic chelates of Cd and Pb with ammonium pyrrolidinedithiocarbamate were extracted into the fine droplets of ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate, while nonionic surfactant, Triton X-114 was used as a dispersing medium. The main factors affecting the recoveries of Cd and Pb, such as concentration of APDC, centrifugation time, volume of IL and TX-114, were investigated in detail. It was also observed that adolescent boys who consumed different SLT products have 2- to 3-fold higher levels of Cd and Pb in their blood samples as compared to referent boys (p?<?0.001).     

Label-free colorimetric nanosensor with improved sensitivity for Pb2+ in water by using a truncated 8–17 DNAzyme

• Unmodified-AuNP based, colorimetric nanosensor was constructed for Pb²⁺ detection. • 5-nucleotide truncation in DNAzyme made complete substrate detachment upon Pb²⁺. • Ultrasensitive and selective detection of Lead (II) was achieved with 0.2×10^-9 mol/L LOD. Water pollution accidents, such as the Flint water crisis in the United States, caused by lead contamination have raised concern on the safety of drinking water distribution systems. Thus, the routine monitoring of lead in water is highly required and demands efficient, sensitive, cost-effective, and reliable lead detection methods. This study reports a label-free colorimetric nanosensor that uses unmodified gold nanoparticles (AuNPs) as indicators to enable rapid and ultra-sensitive detection of lead in environmental water. The 8–17 DNAzyme was truncated in this study to facilitate the detachment of single-stranded DNA fragments after substrate cleavage in the presence of Pb²⁺. The detached fragments were adsorbed over AuNPs and protected against salt concentration-induced aggregation. Accordingly, high Pb²⁺ would result in rapid color change from blue to pink. The established sensing principle achieved a sensitive limit of detection of 0.2×10^-9 mol/L Pb²⁺, with a linear working range of two orders of magnitude from 0.5×10^-9 mol/L to 5×10^-9 mol/L. The selectivity of the nanosensor was demonstrated by evaluating the interfering metal ions. The developed nanosensor can serve as a substitute for the rapid analysis and monitoring of trace lead levels under the drinking water distribution system and even other environmental water samples.     

Integrated solid waste management based on the 3R approach

Integrated solid waste management (ISWM) based on the 3R approach (reduce, reuse, and recycle) is aimed at optimizing the management of solid waste from all the waste-generating sectors (municipal, construction and demolition, industrial, urban agriculture, and healthcare facilities) and involving all the stakeholders (waste generators, service providers, regulators, government, and community/neighborhoods). This article discusses the concept of solid waste management (SWM). Initially, SWM was aimed at reducing the risks to public health, and later the environmental aspect also became an important focus of SWM. Recently, another dimension is becoming a critical factor for SWM, i.e., resource conservation and resource recovery. Hence, the 3R approach is becoming a guiding factor for SWM. On the one hand, 3R helps to minimize the amount of waste from generation to disposal, thus managing the waste more effectively and minimizing the public health and environmental risks associated with it. On the other hand, resource recovery is maximized at all stages of SWM. Lately, the new concept of ISWM has been introduced to streamline all the stages of waste management, i.e., source separation, collection and transportation, transfer stations and material recovery, treatment and resource recovery, and final disposal. It was originally targeted at municipal solid waste management (MSWM), but now the United Nations Environment Programme (UNEP) is promoting this concept to cover all waste generating sectors to optimize the level of material and resource recovery for recycling as well as to improve the efficiency of waste management services. The ISWM concept is being transformed into ISWM systems to replace conventional SWM systems. This article further discusses the implementation process for ISWM. The process includes a baseline study on the characterization and quantification of waste for all waste generating sectors within a city, assessment of current waste management systems and practices, target setting for ISWM, identification of issues of concern and suggestions from stakeholders, development of a draft ISWM plan, preparation of an implementation strategy, and establishment of a monitoring and feedback system. UNEP is assisting member countries and their cities to develop an ISWM plan covering all the waste generating sectors within a specific geographical or administrative area such as a city or municipality. This umbrella approach is useful to generate sufficient volumes of recycling materials required to make recycling industries feasible. This is also helpful for efficient reallocation of resources for SWM such as collection vehicles, transfer stations, treatment plants, and disposal sites. UNEP is assisting cities to develop and implement ISWM based on the 3R approach. These experiences could be useful for other countries to develop and implement ISWM to achieve improved public health, better environmental protection, and resource conservation and resource recovery.     

Synthesis and Extraction Study of Calix[4]arene Dinitrile Derivatives Incorporated in a Polymeric Backbone with Bisphenol-A

Two new copolymers containing pendant calix[4]arene units with nitrile functionalities at their lower rim have been synthesized via nucleophilic substitution reactions involving 5,11,17,23-tetra-tert-butyl-25,27-bis(cyanomethoxy)-26,28-dihydroxy-calix[4]arene (3) or 25,27-bis(cyanometh oxy)-26,28-dihydroxy-calix[4]arene (4) with 1,5-dibromopentane and bisphenol-A. The phase transfer studies were performed by using liquid–liquid extraction procedures. It has been deduced from the observations that both copolymers show a good phase transfer affinity toward selected alkali, alkaline earth, and transition metal cations, unlike their precursor (3).     

EDTA-enhanced phytoremediation of contaminated calcareous soils: heavy metal bioavailability,extractability, and uptake by maize and sesbania

Natural and chemically enhanced phytoextraction potentials of maize (Zea mays L.) and sesbania (Sesbania aculeata Willd.) were explored by growing them on two soils contaminated with heavy metals. The soils, Gujranwala (fine, loamy, mixed, hyperthermic Udic Haplustalf) and Pacca (fine, mixed, hyperthermic Ustollic Camborthid), were amended with varying amounts of ethylenediaminetetraacetic acid (EDTA) chelating agent, at 0, 1.25, 2.5, and 5.0 mM kg^?1 soil to enhance metal solubility. The EDTA was applied in two split applications at 46 and 60 days after sowing (DAS). The plants were harvested at 75 DAS. Addition of EDTA significantly increased the lead (Pb) and cadmium (Cd) concentrations in roots and shoots, uptake, bioconcentration factor, and phytoextraction rate over the control. Furthermore, addition of EDTA also significantly increased the soluble fractions of Pb and Cd in soil over the controls; the maximum increase of Pb and Cd was 13.1-fold and 3.1-fold, respectively, with addition of 5.0 mM EDTA kg^?1soil. Similarly, the maximum Pb and Cd root and shoot concentrations, translocation, bioconcentration, and phytoextraction efficiency were observed at 5.0 mM EDTA kg^?1 soil. The results suggest that both crops can successfully be used for phytoremediation of metal-contaminated calcareous soils.