A regional approach for health risk assessment of toxicants in plastic food containers.

Plastic food containers are being used popularly, generating a waste of about 115 million tons in Vietnam. Such waste is causing environmental and health issues. This study conducted a field survey with 250 local people and selected 59 samples out of 135 plastic food containers collected in Go Vap district, Vietnam. Collected plastic samples identified compositions were PET 13.6%, PP 28.8%, PS 16.9%, and 40.7% undefined plastics. Collected plastic samples were classified based on the plastic type using recycling code and quantitatively analyzed with X-ray fluorescence spectroscopy method to assess concentrations of Cd, Sb, Pb, Hg, Sn, Cr, Br, Cl, and S. Most of these collected plastic samples (91.5%) were found to contain 8/9 hazardous substances and most elements contained in these plastics were below their standard thresholds. These elements in plastic samples could be divided as the result into three hazard groups: (1) high hazard group (Sb, Cl, and S); (2) medium hazard group (Cr, Br and Hg); and (3) low hazard groups (Cd, Pb and Sn). Among substances in the high hazard group, element Sb was assessed for its migration because only Sb is regulated in Vietnam in QCVN 12-1: 2011/BYT. Substances of Cl, S, Cr, Br, and Hg (group 1, 2) do not have regulations related to the method of decontamination. Thus, additional health risks need to be assessed using the USEtox model. Finally, this study proposed a screening process to assess the risk of toxicity of elements contained in plastic food containers through ISO 31000:2018. Supplementary Information: The online version contains supplementary material available at 10.1007/s43188-023-00194-0.

Sono-oxidation treatment of hazardous ABS/PC surface for its selective separation from ESR styrene plastics.

This study reports the selective hydrophilization of the ABS/PC blend surface using the peroxide-sonochemical system and then its selective separation by froth flotation technique from other ABS-based plastics (ABS, ABS/PMMA) and PS/HIPS in electronic shredder residue (ESR). FT-IR and XPS measurements confirm that the hydrophilic moiety development on the ABS/PC surface led to increasing the wettability of ABS/PC and then decreased its floatability. The confocal scanning results also support the enhancement of microscale roughness of the treated ABS/PC surface. The enhanced surface roughness is attributed to the oxidative process which degrades hydrophobic moieties and promotes hydrophilic functional groups on the ABS/PC surface using commercial oxidant peroxide and ultrasound. This study also investigated removal of Br-containing compounds on the ABS/PC surface. The optimum conditions for selectively ABS/PC separation are peroxide concentration 2%, power cycle 70%, treatment time 5 min, temperature 50 °C, floating agent concentration 0.4 mg/L, flotation time 2 min, and airflow rate 0.5 L/min. ABS/PC was selectively separated from ESR styrene plastics with high recovery and purity of 98.9% and 99.8%, respectively. Hence, the developed novel surface treatments having removal of hazardous Br chemicals and none-formation of secondary pollutants should be applied for upgrading plastic recycling quality.

Sustainable hydrophilization to separate hazardous chlorine PVC from plastic wastes using H2O2/ultrasonic irrigation.

Polyvinyl chloride (PVC) products comprise a large portion of plastic wastes and cause severe environmental burdens in thermal recycling such as toxic release and disposal difficulties. Selective separation methods for PVC containing hazardous chlorine are required for the development of suitable disposal or material recycling processes. However, separating PVC selectively from municipal plastic waste mixtures is difficult due to their similar hydrophobic surface and appearance densities. This study presents a one-step, selective separation technique for PVC using H2O2 solution under ultrasonic irrigation to promote the selective development of hydrophilicity only on the PVC surface. The combined treatment helped to decrease air bubbles attached on the PVC surface because of increased wettability, which allowed the treated PVC to settle on the bottom of the flotation reactor. However, the remaining plastic wastes were easily floated off because they maintained their hydrophobicity. The combined treatment with a low concentration of 3% H2O2 and ultrasonic irrigation for 30 min afforded 100% purity and recovery of the PVC separated from the municipal plastic waste mixture. This proposed treatment is therefore a promising and inexpensive way to improve plastic recycling quality through selective PVC separation by the selective development of hydrophilicity on its surface.

The superior photocatalytic activity of Nb doped TiO2/g-C3N4 direct Z-scheme system for efficient conversion of CO2 into valuable fuels.

In this study, we firstly aimed to use Nb as dopant to dope into the TiO2 lattice in order to narrow band gap energy or enhance photocatalytic activity of the Nb-TiO2. Then, the prepared Nb-TiO2 was combined with g-C3N4 to establish Nb-TiO2/g-C3N4 direct Z-scheme system for superior reduction of CO2 into valuable fuels even under visible light. The obtained results indicated that the band gap energy of the Nb-TiO2 (2.91 eV) was lower than that of the TiO2 (3.2 eV). In the successfully established Nb-TiO2/g-C3N4 direct Z-scheme system, the photo-excited e- in the CB of the Nb-TiO2 combined with the photo-excited h+ in the VB of the g-C3N4 preserving the existence of e- in the CB of the g-C3N4 and h+ in the VB of Nb-TiO2, and thereby, the system produced numerous amount of available e-/h+ pairs for the reduction of CO2 into various valuable fuels. In addition, the produced e- of the Nb-TiO2/g-C3N4 existing in the CB of the g-C3N4, which the potential energy is approximately -1.2 V, would be strong enough for the reduction of CO2 to generate not only CH4 and CO but also HCOOH. Among established Nb-TiO2/g-C3N4 materials, the 50Nb-TiO2/50 g-C3N4 material was the best material for the CO2 reduction.

Selective separation of ABS/PC containing BFRs from ABSs mixture of WEEE by developing hydrophilicity with ZnO coating under microwave treatment.

This study reports a simple and facile method to separate plastic wastes of acrylonitrile-butadiene-styrene (ABS) and ABS-based plastics (blends of ABS) in waste electronic and electrical equipment (WEEE) by froth flotation after inducing hydrophilization by ZnO coating under microwave treatment. ABS-based plastics containing brominated flame retardants (BFRs) can release hazardous substances, such as hydrogen bromide and brominated dioxins, during disposal or recycling activities. ABS and ABS-based plastics are typical styrene plastics with similar properties and it is, therefore, difficult to separate them selectively for recycling. We used 2-min microwave treatment to rearrange and change the molecular mobility on the surface of the ZnO-coated ABS with increased hydrophilic surfaces, which eased the selective separation of the ABS/polycarbonate (PC) blend containing BFRs from the remaining plastics. Therefore, the combined ZnO coating and microwave treatments can facilitate the selective separation of ABS/PC blend plastics with a recovery and purity of 100% and 91.7%, respectively, in a short flotation time of 2min. Based on these findings, the combination of ZnO coating-microwave treatment and froth flotation can be applied for the selective separation of ABS-based plastics, leading to improved plastic recycling quality.

Development of hydrophobicity and selective separation of hazardous chlorinated plastics by mild heat treatment after PAC coating and froth flotation.

Polyvinyl chloride (PVC) containing chlorine can release highly toxic materials and persistent organic pollutants if improperly disposed of. The combined technique of powder activated carbon (PAC) coating and mild heat treatment has been found to selectively change the surface hydrophobicity of PVC, enhancing its wettability and thereby promoting its separation from heavy plastic mixtures included polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS) and acrylonitrile butadiene styrene (ABS) by means of froth flotation. The combined treatments helped to rearrange the surface components and make PVC more hydrophobic, while the remaining plastics became more hydrophilic. After the treatments at 150°C for 80s the contact angle of the PVC was greatly increased from 90.5 to 97.9°. The SEM and AFM reveal that the surface morphology and roughness changes on the PVC surface. XPS and FT-IR results further confirmed an increase of hydrophobic functional groups on the PVC surface. At the optimized froth flotation and subsequent mixing at 150rpm, 100% of PVC was recovered from the remaining plastic mixture with 93.8% purity. The combined technique can provide a simple and effective method for the selective separation of PVC from heavy plastics mixtures to facilitate easy industrial recycling.

Sustainable and Selective Separation of PVC and ABS from a WEEE Plastic Mixture Using Microwave and/or Mild-Heat Treatment with Froth Flotation.

This study reports simple, selective, and sustainable separation of chlorinated plastic (polyvinyl chloride, PVC) and acrylonitrile butadiene styrene (ABS) containing brominated flame retardants (BFRs) from mixed waste electrical and electronic equipment (WEEE) plastics using microwave and/or mild-heat treatment. Microwave treatment after plastic coating with powdered activated carbon (PAC) selectively increased the hydrophilicity of the PVC surface, which facilitated PVC separation (100% recovery and purity) from the WEEE plastic mixture under the optimum flotation conditions. A further mild-heat treatment for 100 s facilitated selective separation with the highest recovery and purity (100%) of PAC-coated ABS containing BFRs from the remaining plastic mixture due to selective formation of a twisted structure with a lower density than water and the untreated ABS. Mild-heat treatment only of PAC-coated WEEE plastic mixture resulted in successful recovery of (100%) the ABS and PVC. However, the recovered PVC had slightly reduced purity (96.8%) as compared to that obtained using the combined heat and microwave treatments. The combination of both treatments with flotation facilitated selective and sustainable separation of PVC and ABS from WEEE plastics to improve their recycling quality.