Evaluation of the Cytotoxic Effects of Humid Lightweight Coal Ash derived from the Disposal of Waste on Normal Human Keratinocyte and Endothelial Cell Lines in 2-D and 3-D Culture

The presence of waste in the environment has frequently been indicated as a significant risk to human health. Therefore, landfill sites and the disposal of urban solid and non-hazardous waste by incineration are subject to much environmental monitoring, in addition to the regulations already in place. However, little action has been taken, and consequently no specific legislation exists, in relation to the assessment of the real biological risk of various substances, including chemical mixtures and ashes, derived from the incineration processes. This study assessed the cytotoxic potential of humid lightweight coal ash (LA) derived from incineration processes and waste management, on two cell lines: NCTC 2544 normal human keratinocytes and HECV endothelial cells. To reach this goal and to assess more-realistic methods for animal replacement, we employed different in vitro experimental approaches: acute and longer exposure to LA, by direct and indirect contact (0–2mg/ml and 16mg, respectively), both in 2-D and 3-D cultures. In 2-D HECV cultures, we observed a decrease in the viability index, but only during direct contact with LA doses higher than 0.1mg/ml. Moreover, some striking differences in cytotoxicity were observed between the 2-D and 3-D models. Taken together, these observations indicate that, for studying pollutant toxicity during longer exposure times, 3-D cultures in direct contact with the pollutant seem to offer a more suitable approach — they mimic the in vivo behaviour of cells more realistically and under strictly controlled conditions. Thus, in readiness for possible forthcoming European regulations, we believe that the proposed study, even in its preliminary phase, can provide new advice on the assessment of the toxic and biological potential of particular chemical compounds derived from waste management processes.