Measuring TiO2 Engineered Particle Concentrations in Surface Waters with Multi-Element sp-ICP-MS

Sewage spills are a major source of titanium dioxide Engineered (nano)-particles into the environment

Loosli, F.; Wang, J.; Rothenberg, S.;  Bizimis, M.; Winkler, C.; Borovinskaya, O.; Flamigni, L.; Baalousha, M.
Environmental Science: Nano
DOI: 10.1039/c8en01376d

TiO₂ engineered nano- and micro-particles are used in paints, coatings, plastic, paper, food, cosmetics, sun blocks and various other products, with 6.1 million metric tons consumed in 2016. The toxicity of TiO₂ engineered nanoparticles has been demonstrated in numerous studies. Eg. engineered nanomaterials (ENM) can induce cytotoxic, genotoxic, and inflammatory effects, and oxidative stress. Therefore, ENM must be strictly managed to minimize their exposure to humans. Lack of suitable analytical tools to quantitatively detect engineered nanomaterials in complex natural environments makes needed exposure assessment difficult.

Predicted no effect concentrations (PNEC) for ENM are based on theoretical fate models with little support from experimental data. These theoretical models do not take into account points of discharge of nanomaterials into the environment – “hot spots” that otherwise would help to better parameterize and validate them.

In this study, the authors use multi-element single particle inductively coupled plasma mass spectrometry (ME-sp-ICP-MS) conducted on a TOFWERK icpTOF mass spectrometer to detect and quantify the amount of engineered TiO₂ particles released during sanitary sewer overflow spills.

Multiple techniques are applied in this challenging study to quantify the fraction of engineered released TiO₂ particles in the high background of natural Ti-containing particles. With its capability of simultaneous detection, the icpTOF helps to differentiate engineered TiO₂ from natural Ti-containing particles based on elemental fingerprinting of individual particles. Although ME-sp-ICP-MS does not provide reliable quantitative results on particle number concentration due to the inability to detect TiO₂ particles < 40 nm (detection limit), it does help to identify Nb as a reliable tracer for natural particles. This is turn is used to determine the total concentration of TiO₂ engineered particles by bulk techniques. Besides engineered particles, the icpTOF enables the study of natural minerals on a much smaller scale. In the study river samples, elemental ratios of Ti to various other elements in individual particles were in agreement with average riverine particulate and/or crustal material element ratios.

This is the first time, to the best of our knowledge, that these elemental associations and ratios of Ti to natural elemental tracers have been identified and quantified on an individual particle basis. These findings are indicative of the considerable advantages offered by ME-SP-ICP-MS in identifying natural tracers of natural particles, which will be extended to other types of particles in the future.