Toxicity of ozone generated from different combinations of ozone concentration (C) and exposure time (T): a comparison of the relative effect of C and T on hatch rates of Penaeus (Marsupenaeus) japonicus embryos

The toxicities of several CT values generated from different combinations of ozone concentration (C) and exposure time (T) were evaluated using hatch rates of Penaeus (Marsupenaeus) japonicus embryos as a measure of ozone toxicity. Embryo hatch rates were investigated at five different CT values (0.5, 1, 2, 4 and 8), produced from different combinations of C (0.5, 1 and 2 ppm) and T (0.5, 1, 2, 4 and 8 min). The experiment was conducted at 16, 120 and 480 min post-spawning for two P. japonicus families. The effect of C on embryo hatch rate when treated at different CT values varied between post-spawning treatment times and families. Where differences in hatch rates were found between C treatments at a single CT value, hatch rates decreased with increasing C. These results indicate that CT values generated by higher C and shorter T values are more toxic to P. japonicus embryos than CT values generated by lower C and longer T values. Our findings indicate that ozone dose cannot be prescribed solely by the CT value, but must also be qualified by describing the C and T values used to generate the CT value. These results have significant implications for designing treatment protocols that aim to use ozonation as a disinfection agent for cultured organisms.