Testing particulate matter toxicity via in vitro methods: what should be tested?

Unlike other toxic substances, usually of a known chemical formula, air particulate matter (PM) is a mixture of solid and liquid particles. The most frequently used tests are in vitro in nature and examine ‘cell viability’ following 24-hour exposure to PM. In most cases, PM induces sub-toxic viability responses but other key cell functions are not detected. The aim of this study was to compare the toxicity profiles of engineered NPs: zinc oxide (ZnO), crystalline form of silicon oxide (SiO2), and nickel (Ni), which are frequently present in ambient air pollution. Three different assays (acellular and cellular) were chosen to test PM biological targets: (1) plasmid scission assay – detecting DNA damage (indicative of the ability to produce reactive oxygen species; ROS; Figure 1); (2) haemolysis assay – informing about red blood cells (RBCs) membranes integrity; (3) proliferation assay inspected on HUVEC (human umbilical vein endothelial cells) at 24, 48 and 72 hours post-exposure to NPs.