Name: Sudeshna Mondal.
Guide: Prof. Chandramouli Subramaniam
Topic of research: Spectro-electrochemical studies of nanomaterials for applications in
sensors and energy storage
Description of research work:
Detection of emerging contaminants in bottled water
Origin of problem: Plastics, or synthetic organic polymers, have turned out to be one of the most useful inventions of the last century. The seamless integration of plastics into society, along with the wide-range of applications they cater to, have been a primary reason behind their ubiquitous existence. In spite of their vital role in advancement of society, one of the major and pertinent problems in handling plastics has been their long lifetime and non-biodegradability. This is further compounded by the fact that nearly 60% of the total worldwide production of plastics (totaling to 8300 million metric tons in 2017) is discarded either as landfills or into water bodies.1 Such large-scale dumping of plastics is thought to leach toxic xenobiotic contaminants into water bodies and human food sources leading to irreversible effects on ecosystem and human health. Chemicals such as Bisphenol A (BPA); a commonly used additive during production of PET (polyethylene terephthalate) based plastic bottles causes reproductive defects in children, infertility and breast cancer in humans, when exposed above the threshold limit of 0.6 ppm according to European Union Migration limit.2
Societal context: Our study attempted to understand the thermal stability of PET that is commonly used for storage and handling of water and food products. This assumes greater significance in the Indian context when ambient temperature reach 45oC in summer. Currently, very few tools exist for detection of such harmful xenobiotics, owing to their particularly low concentration (sub-ppm) in daily used products. Further, the organic nature of the contaminants demands very specialized and cumbersome techniques such as mass-spectrometry that are often limited to laboratory conditions and trained technicians.
Science behind the detection: Attempting to provide a viable solution to this problem, we have come up with a spectroscopic platform for detection of such xenobiotics. This work, recently published in ACS Sustainable Chemistry &Engineering,3 utilizes a technique called Surface Enhanced Raman Spectroscopy (SERS) for real-time detection of these contaminants. It is based on the Raman effect of inelastic scattering of light by molecules. The frequency of scattering is a characteristic fingerprint of the molecule. The intensity of scattering signal is enhanced by 106 – 108 times when the molecule is located on the surface of metallic nanoparticles. This enables detection of molecules at ultra-high sensitivity extending up to single molecules. Further, analyzing the vibrational modes helps in pinpointing the molecule with very high specificity. Utilizing this concept, we employ thermal field as a parameter to engineer interaction of Ag/Au nanoparticles and direct them to form well-ordered assemblies. Such nanoparticles assemblies (termed Soret colloids) provide ultra-high sensitivity and spectroscopic specificity – a unique combination of mutually exclusive properties.
Results: The real-time studies were carried out by subjecting PET plastics containing water to temperatures of 40ºC, 50ºC and 65ºC for 12 hours under laboratory conditions. Upon examining the water samples, definitive evidence of BPA in the water samples were observed through SERS. Disturbingly, we could detect BPA concentrations ranging from 0.17 ppm to 0.32 ppm in all these samples. The leaching of BPA from plastics has also been confirmed from complimentary techniques such as mass spectrometry and atomic-force microscopy. The identification of xenobiotic chemicals such as BPA in drinking water samples at such concentrations raises very important and pertinent questions about the safety of drinking water especially those stored and transported in PET based containers. This study presents a conclusive evidence for the dangers of storing and transporting food material in an unregulated manner in PET based containers.
Implications to society: Water bottles and food packaging is one of the largest consumers of plastics. While their use in inevitable, there is lack of guidelines on handling, transport and storage of such products. Temperatures between 40 – 65oC are regularly encountered during the transport and storage of distilled water in PET containers. Therefore, the dangers posed by the findings of this study are real and relevant for tropical countries like India. In this context, this spectroscopic platform is of particular importance as it opens up transformative opportunities for analytical qualitative and quantitative environmental monitoring. Further, this study also highlights the need for stricter governmental regulations to tackle dangers of such emerging contaminants of water and food produces.
Geyer, R., Jambeck, J. R., Law, K. L., Science Advances, 2017,3(7), e1700782.
Lin, P. Y.; Hsieh, C. W.; Hsieh, S., Sci Rep 2017,7 (1), 16698.
Mondal, S.; Subramaniam, C., ACS Sustainable Chemistry & Engineering2020, 8, 7639.
Figure: Detection of xenobiotics in bottled water