4. Conclusions
In this study, the toxicity of extracts of sewage sludge, bottom
ashes from woodchip gasification and sludge/woodchip co-gasification on human cells was investigated. The results show that both
the sewage sludge extract and bottom ashes from gasification exhibit
toxic effects on the human HepG2 and MRC-5 cells, at high concentrations
in the culture medium. As a result, cell viability
decreased significantly associated with abnormal cell morphology
was observed. The toxicity effect may become greater or slighter
with increased exposure durations, depending on the cell type
and source of toxicity. In order to investigate the causes of their
cytotoxicity, the effects of pH value, heavy metals, ionic strength
and PAHs were evaluated. After eliminating the influence of highly
basic environment by neutralization, ionic strength was found to
play a more important role in the observed toxicity than heavy
metals, while the contribution from PAHs was insignificant. A further
study (including animal models) on the gas emissions from
the gasifier and other types of human cells will provide a more
complete picture of potential health effects arising from the gasifi-
cation processes.