Endocrine Disrupting Compounds (EDCs) have emerged as a new class of organic micro-pollutants imposing detrimental effects on living beings. Minimisation of these pollutants from water bodies is essential for aquatic ecology as well as humans. In this context, nanomaterials are gaining immense importance for scavenging and degradation of these EDCs.
The accessibility of sufficient pure water in terms of both quantity and quality is vital for human existence. Unfortunately, our hydric resources have become seriously polluted due to the continuous expansion of industries and urbanisation. Recently, EDCs have emerged as a new class of organic micro-pollutants. Once EDCs enter into the water supply system, they impose detrimental effects on living beings. EDCs can alter the hormonal balance in humans thereby contributing to numerous adverse health outcomes like abnormalities in sex organs, alterations in sperm quality and fertility, endometriosis, early puberty, altered nervous system, and immune function, certain cancers, respiratory problems, metabolic issues, diabetes, obesity, cardiovascular problems, growth, neurological, etc. The EDCs are known to exert these adverse effects by affecting the transport and metabolism of hormones and interrupting cellular signaling pathways. They can disturb and impede the activity of enzymes involved in steroidogenesis, thereby severely affecting the metabolism of estrogens.
On the basis of their occurrence and origin, these micro-pollutants can be classified into two different categories: Natural and Synthetic. Natural EDCs include steroids, antibiotics, hormones, and phytoestrogen, while synthetic EDCs includes Bisphenol A (BPA), dioxins, perchlorate, phthalates, vinclozolin, Diethylstilbestrol (DES) compounds, Polychlorinated Biphenyls (PCB) etc. The main sources of these micropollutants are human excretion (sewage), improper disposal of hospital waste, leaching from landfills, drain water, and effluents of pharmaceutical and healthcare industries. According to several reports, higher concentrations of EDCs are found in various freshwater as well as sea water fishes by the process of bioaccumulation. Thus, EDCs may enter the food chain through fishes. Therefore, an effective strategy to eliminate these hazardous water contaminants is essential for both the humans and aquatic ecology.
Nanotechnology-based approaches have recently taken a major stride in order to scavenge these water pollutants. A number of research groups across the world are actively involved in the development of nanomaterials for the aqueous phase removal of EDCs. Various nanomaterials like silver, titanium oxide, and iron oxide Nanoparticles (NPs), nanoparticles/biochar composite, and palladium/iron bimetallic nanocomposite have been extensively used. Prof Nikhil R. Jana from the Centre for advanced materials, Kolkata, India has demonstrated complete degradation of BPA by gold NPs-reduced graphene nano-complex under visible solar light. It was anticipated that visible light-induced the generation of hydroxyl radical which can degrade BPA into smaller organic fragments such as phenol derivatives and aliphatic aldehydes/ketones. Another research group has developed a reactive bed by using alginate, activated carbon, and MnO2 which showed astonishing potential for tylosin removal. Most of these nanomaterials were synthesized through chemical synthesis methods that involve toxic and volatile reagents which are in turn responsible for the secondary pollution.
Recently, sustainable and green technologies have drawn the attention of researchers to eliminate water pollutants. The government regulations are becoming more and more stringent towards the subrogation of synthetic and toxic chemical compounds due to the concept of environmental stewardship. In this context, biologically synthesized nanomaterials have gained widespread recognition due to their eco-friendly nature. These nanoparticles are synthesized from the cellular extract of plants, fungi, algae, and bacteria which function as reducing and stabilizing agents. The cellular extract of living organisms is a rich source of several active biomolecules, phytochemicals, vitamins, enzymes, amino acids, and other natural reducing agents. These biomolecules add different functional groups over the surface of nanoparticles which actively confiscate pollutant molecules by forming different chemical bonds. Different parts of the plants including leaf, root, stem, seed, pod, peel, and fruit have been used to synthesize almost all sorts of metallic nanoparticles like iron, zinc, copper, gold, silver, palladium, and manganese. Various bacterial, fungal, and algal species have also been utilised to produce bio-engineered nanoparticles. The important advantage of this green synthesis method is its sustainable nature and economic viability. Moreover, the reusability of these nanomaterials has also been found satisfactory. As per the research work conducted worldwide, it is observed that biologically developed nanomaterials can be recycled without any noticeable loss in their removal efficiency. The nanomaterials synthesized by using the biogenic route have proven their efficacy as an adsorbent and catalyst for the aqueous phase removal of EDCs. The successful applications of these environmentally benign nanomaterials are reported both on a laboratory scale and in the treatment of real wastewater. These nanoparticles can easily be incorporated or coupled with some other treatment technologies in order to enhance their treatment ability. Researchers are using biologically produced nanomaterials in membrane reactors, filtration units, and other separation devices in order to study the synergistic effects for the treatment of effluent and drinking water-bearing EDCs. Willy Verstraete and their research group from the Faculty of Biosciences Engineering, Ghent University developed biogenic manganese oxide and palladium nanoparticles and applied them in a membrane-based bioreactor for the treatment of STP effluent. A number of EDCs present in the sewage effluent were effectively eliminated. Biogenic nanoparticles have been found equally effective for natural and synthetic EDCs. In this context, Prof. Duan from Jinan University, China produced biogenic manganese oxides generated by green algae Desmodesmus sp. WR1 to improve BPA removal. Similarly, successful removal of natural EDCs such as 17-α-estradiol, 17-β-estradiol and estrogens from wastewater has also been reported. Prof. Ines A. C. Pereira from Universidade Nova de Lisboa, Portugal is actively engaged in developing biogenic nanoparticles for the removal of antibiotics and other EDCs from water and wastewater. The application of biogenic nanoparticles in modern wastewater treatment facilities may be revolutionary because of the low-cost, high efficiency, and environmental acceptability.