Figure 4

Oxidative stress assessed with DCF assay, where intracellular peroxides can be identified from the cells emitting positive signals. Bars represent responses to four PM doses (15 50, 150 and 300 μg ml^-1) and whiskers show the standard error of the mean (SEM). Asterisks indicate statistically significance significant differences from the control level (Kruskall Wallis; p < 0.05). Numbers refer to a significantly larger response (Dunnett’s C test) compared to the indicated fuel/catalytic converter combination: 1) EN590, 2) EN590 + cat, 3) 30% HVO, 4) 100% HVO, 5) HVO + cat 6) 30% RME, 7) 100% RME and 8) CNG bus.