Preliminary evidence of nanoparticle occurrence in water from different regions of Delhi (India)

The objective of this study was to obtain preliminary evidence of metal-based nanoparticle (NP) occurrence in Delhi (India). Six sampling locations (inlets and outlets of two different municipal wastewater treatment plants (WWTPs), groundwater, and river water) were collected in three independent sampling events. Microscopic analysis (TEM) found majority (40%) of the particles ranged between 150 and 200 nm followed by particles of size 100-150 nm (22%) at the inlet of WWTP, while at outlet, 90% of the particles were < 100 nm. Compared with the outlet of the WWTPs, particles at the inlet were found to be greater than 40%. Intensity-based particle size distribution (PSD) revealed particle size at influent in the range of 210 nm, while at effluent, particle size for both WWTPs ranged < 100 nm. Particles of size between 100 and 200 nm were found to get removed from both the treatment plants and thus making it evident that NP gets settled or adsorbed in sludge. Spectral analysis (EDX) further confirmed the presence of metals such as Al, As, Ag, Mn, Fe, Ti, and Zn at different weight percentages. Overall, findings of this study confirmed the presence of metal-based engineered NPs (ENPs) from anthropogenic sources and it cannot also be ruled out the possible formation of NPs within the wastewater from natural minerals. Moreover, to solve definitive clues for ascertaining the sources of NPs in complex samples, more sophisticated research techniques, such as inductively coupled plasma-mass spectrometry (ICP-MS) in combination with field flow fractionation, single-particle ICP-MS, and radio-labeling in combination or in single should be considered.