Detection of nanoplastics and their uptake of lead in aqueous environmental media
Nanoplastics and microplastics can be widely found in the environment due to mechanical or chemical degradation of larger plastics. They are of recent concern because of their wide distribution and potentially harmful effects for the environment. These fragments can act as vector for other pollutants, such as heavy metals, which can be adsorbed or entrapped inside the nanoplastics. Reliable detection and quantification of these nanoplastics from environmental matrices are necessary to understand the fate and transport of the particles. Also, the uptake of pollutants is necessary to better estimate their potential hazards. However, existing detection and quantification techniques of nanoplastics have disadvantages such as size resolution issues and limitations in producing mass concentration data. Likewise, better separation and selective detection are important to assess the adsorption of heavy metals on to nanoplastics in natural waters. This thesis aims to develop and apply advanced methods to efficiently separate, detect, quantify, and characterize nanoplastics in complex environmental matrices by hyphenating asymmetric flow field – flow fractionation (AF4) with various online detectors. First, AF4 is hyphenated with a total organic carbon (TOC) detector to provide an efficient separation via AF4 and selectively quantify the mass concentrations of polystyrene nanoplastics across a range of diameters (50 nm to 500 nm) in an aqueous matrix of organic and inorganic colloids. This research further couples AF4 with inductively coupled plasma – mass spectrometry (ICP-MS) to investigate heavy metal (lead) uptake onto the polystyrene nanoplastics as a function of the surface functional groups on the nanoplastics, and natural organic matter and salts in the aqueous background matrix. Compared to conventional batch methods (solution depletion) to evaluate lead uptake, the hyphenated AF4-ICP-MS method enabled a direct assessment of the lead adsorption onto the nanoplastics without matrix interferences and was critical to detect low levels of adsorbed lead and to confidently distinguish lead uptake in different matrices.