Relationship among the acute toxicity, critical body residue, and bioconcentration of ortho-dinitrobenzene in zebrafish (Danio rerio) based on toxicokinetics

The internal critical concentration represented by the critical body residue (CBR) is an ideal indicator for reflecting the toxicity of a chemical. Although some authors have realized that the CBR 50 can be calculated from the LC 50 via the bioconcentration factor (BCF), the effects of exposure time and exposure concentration on the relationship between the LC 50 and CBR 50 have not been investigated to date. In this paper, the LC 50 and CBR 50 of ortho-dinitrobenzene in zebrafish were experimentally determined and their relationship was investigated. The results showed that ortho-dinitrobenzene exhibited excess toxicity and cannot completely be identified as a reactive compound based on toxic ratio. Comparison of the measured CBR 50 and the CBR 50 calculated from the LC 50 via the BCF showed that there was a 0.46 log unit difference. Investigation of the relationship between the concentration in fish calculated by the toxicokinetic model and exposure time showed that the bio-uptake of fish was fast and reached a steady state in the toxicity test, indicating that the difference in CBR 50 values could not be attributed to the different exposure times used in toxicity and BCF assays. On the other hand, investigation of the measured bioconcentration ratio (BCR) showed that the BCR (or BCF app ) decreased with increasing exposure concentration. Compared with the CBR 50 calculated from the LC 50 via the BCF, the CBR 50 calculated from the LC 50 via the BCF app is close to the measured CBR 50 , suggesting that the difference in CBR 50 values is attributed to the different exposure concentrations used in the BCF and toxicity assays.