Toward a better extraction of titanium dioxide engineered nanomaterials from complex environmental matrices

Abstract

Detection, characterization, and quantification of engineered nanomaterials (ENMs) in aquatic systems is a topic of high interest because ENMs are being released increasingly into the environment. In the natural environment, ENMs form heteroaggregates with natural particles which complicates their characterization and quantification. This study investigates the influence of sodium pyrophosphate (NaPP) and sodium oxalate (NaOx) on TiO2 ENM stability in the presence of montmorillonite, natural organic matter (Suwannee River humic acids, SRHA), and CaCl2 with the aim to propose a fundamental protocol for the extraction of ENMs from natural waters. NaPP, not only prevents aggregation, but also rapidly induces TiO2 ENM disaggregation and release from TiO2-clay heteroaggregates -previously formed in presence of CaCl2 and SRHA- in the form of individual particles, or small aggregates. The recovery of TiO2 ENMs in a montmorillonite dispersion in presence of SRHA and CaCl2 was >90% for the <100 nm size fraction, independent of the CaCl2 concentration. In contrast, without NaPP treatment, no TiO2 ENMs smaller than 100 nm were recovered in presence of divalent cations without SRHA, and <15% TiO2 ENMs were recovered in the <100 nm fraction in the presence of divalent cations and SRHA. NaOx did not affect the stability of TiO2 ENMs in the absence of electrolytes and did not stabilize TiO2 ENMs in presence of divalent electrolyte. These findings provide a proof-of-concept for the application of NaPP for the extraction of TiO2 ENMs, and potentially other ENMs, from ENM-natural particle heteroaggregates. Release of ENMs in the form of individual particles, or small aggregates is essential to facilitate ENM characterization and quantification in complex environmental media.