Abstract
Among other things, environmental water pollution results in degradation of plastics into microplastics. The microplastics are composed of toxic pigments, plasticizers, fillers, stabilizers, and flame retardants which leak into the environmental water, thus exposing the humans into drinking contaminated water. Microplastics are also capable of adsorbing toxic heavy metals which are carcinogenic and may affect the reproductive functions of living organisms. Hence, the focus of this research was on the identification and evaluation of microplastics, present in South African waters in tapwater, lakewater from local communities and wasterwater (influent and effluent) from industrial area to raise the awareness and propose the method of dealing with this emerging pollutant in various types of water. The results indicated that influent contains high concentration of microplastics and adsorbed heavy metals.
The microplastics separation from water was carried out using polyvinylidene difluoride (PVDF) and PVDF modified with carbon nano onions (CNOs) membrane. PVDF membrane exhibited the highest flux. Therefore, the application of PDVF exhibited the highest concentration (microplastics per litre) compared to PVDF/CNOs in the influent (140± 1.85 MP/L), effluent (8.8± 2.10 MP/L), tap water (6.5 ± 5.77 MP/L) and lake water (10± 2.65 MP/L). The microplastics were also determined in kitchen plastic utensils such as water bottle, baby bottle, meat wrapper and spice plastic container. The concentrations of microplastics removed from water bottle, baby bottle, meat wrapper and spice bag were 142± 1.55, 120± 2.09, 109 ± 1.77, 94± 1.96 MP/L, respectively.
The presence of microplastics was confirmed by stereo microscope images which displayed the presence of red, blue and black colour plastics. Additionally, the morphological properties were determined using SEM which showed shinny materials which represented microplastics.
The ATR- FTIR equipped with spectrum 10 spectroscopy software established the presence of high-density Polyethylene (50%), Poly (1, 4 butylene terephthalate) (16.6%), Nylon 12 (16.6%) and Cellulose (16.6%) in the influent (wastewater). The FTIR spectra of bottled water and spice packaging confirmed the presence of poly (1,4-cyclohexanedimethylene terephthalate). The spectra of baby milk bottle displayed
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the presence of polypropylene, isotactic while the spectra of meat cover confirmed the existence of polyvinyl chloride.
The quantification of heavy metals extracted from microplastics using digestion method indicated that the concentrations of As (1.759 to 8.699 mg/L), Cu (83.176 mg/L) and Zn (0.610 mg/L) were above the acceptable limits. Therefore, the method of filtering microplastics with PVDF can be applied as an appropriate microplastic analytical monitoring protocol, to ensure adherence to the water quality and management practices in South Africa (SA). Our work will be beneficial in the development of microplastics monitoring system in various municipalities that provide water into households in SA. Water treatment plants may also include the treatment of microplastics in the influent and monitor the effluent before the water is released back into the environment.