Toxicity Effects Of Four Alkyl Phenolic Compounds On Zebrafish (Brachydanio Rerio)

The adult zebrafish (Brachydanio rerio) were exposed to o-cresol, m-cresol, p-cresol, and 2,4-di-ter-butylphenol and their toxic effects were assessed by the individual toxicity test (including acute toxicity in 96h, accumulation toxicity, subacute toxicity in 40 days), and combination toxicity one.The results of acute toxicity test showed that these four compounds had moderate toxicity. The 96h median lethal concentrations and 95% confidence intervals were 26.300 [24.266, 28.510] mg/L for p-cresol, 26.607 [23.227,30.479] mg/L for o-cresol, 29.854 [27.669, 32.211] mg/L for m-cresol, and 1.800[1.542, 2.104] mg/L for 2,4-di-ter-butylphenol, respectively. Their toxicity order was 2,4-di-ter-butylphenol> p-cresol>o-cresol>m-cresol. Furthermore, the safe concentrations were 0.263mg/L for p-cresol, 0.266mg/L for o-cresol, 0.299mg/L for m-cresol, and 0.018mg/L for 2,4-di-ter-butylphenol.In the accumulation toxicity test, Kcum was used as an evaluation index, showing that the degree of accumulation for o-cresol, m-cresol, p-cresol 2,4-di-ter-butylphenol were all slight. Their accumulation toxicity order was o-cresol>2,4-di-ter-butylphenol≥p-cresol>m-cresol.The results of subacute toxicity test showed that these four compounds affected dramatically the absolute growth of weight or length and instantaneous growth rate of the fish. These effects were most distinct during the period of from 30th to 40th day. When the concentration of p-cresol, m-cresol, and 2,4-di-ter-butylphenol were 13.150 mg/L, 14.927 mg/L, and 0.900 mg/L, the conclusions of T test between trial groups and the comparision groups were P<0.05 on 30th days. By contrast, the conclusions were P<0.01 on 40th days, when the concentration of m-cresol was 4.976mg/L, p-cresol was 13.150mg/L and 6.575mg/L, 2,4-di-ter-butylphenol was 0.900mg/L and 0.300mg/L, respectively.Toxic unit analysis, toxic unit illustration and additive index were adopted to evaluate combination toxicity. The compounds in mixture conformed to equal toxicity. The results revealed that the combination toxicity of p-cresol and o-cresol was synergistic effect at 24h, additive effect at 48h, followed synergistic effect was observed from 72h to 96h, the same effect also was found in the mixture of p-cresol and m-cresol. P-cresol and 2,4-di-ter-butylphenol displayed independent or antagonistic effect from 24h to 96h. At last, o-cresol, p-cresol, and m-cresol exhibited antagonistic effect at 24h, then synergistic effect from 72h to 96h.