Release of TiO2 – (Nano) particles from construction and demolition landfills

Abstract

A large fraction of engineered nanomaterials (ENM) will be deposited in landfills and it is assumed that ENM are securely locked in landfill sites and cannot leach into the environment (e.g. surface waters). However, experimental evidence supporting this assumption is lacking, as current production volumes of ENM are still too small and/or analytical techniques not sensitive enough to allow for the detection and quantification of ENM in landfill leachates. TiO2 particles are currently used in large quantities, for example in construction materials such as paints and renders as white pigments and their sizes extend into the nano-size range. We, therefore, selected TiO2 particles as a surrogate to assess the potential release of ENM from construction and demolition (C&D) landfill sites. We collected leachate samples from a landfill over one year and used complementary analytical techniques, including inductively coupled plasma (ICP) – optical emission spectroscopy (OES), automated scanning electron microscopy (auto SEM), transmission electron microscopy (TEM) and single particle ICP - mass spectrometry (spICPMS) to quantify TiO2 particles in landfill leachates. Total elemental Ti contents were mostly around a few tens of μgL−1 and were strongly correlated with total suspended solids. Based on the volumetric discharge of the landfill leachate water from the landfill, we estimate a total amount of ~0.5kg of TiO2 particles that are released annually from the landfill. Ti concentrations derived from ICP-OES measurements were in good agreement with quantifications based on TiO2 particles detected by auto SEM analyses. spICPMS measurements indicated a number concentration of Ti-containing particles in the order of 105mL−1 and TEM analyses dominantly revealed nanoscale TiO2 particles with a spherical shape typically observed for TiO2 particles used as white pigments. In addition, angular TiO2 particles with a well-defined crystal habitus were detected, suggesting that also natural TiO2 particles of comparable sizes are present in the landfill leachates.The results from this study indicate that (nanoscale) TiO2 particles are released from C&D landfill sites (~5g/year). Although the amount of TiO2 particles released from C&D landfill sites may still be rather low, these particles may serve as proxy for assessing the future release of ENM from C&D landfill sites, which may become relevant as an increasing use of ENM is predicted for construction materials in general.