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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. |
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