Investigation on the relationship between critical body residue and bioconcentration in zebrafish based on bio-uptake kinetics for five nitro-aromatics.

It is well known that the critical body residue (CBR) can be estimated via bioconcentration factor (BCF). However, the relationship between CBR and BCF in zebrafish has not been carried out based on bio-uptake kinetics for nitro-aromatics. In this paper, the time-variable concentrations and CBRs in zebrafish were determined for five nitro substituted benzenes. The result shows that CBR values can well be calculated from the BCF and external critical concentrations (LC50 ). Although CBRs measured from 5 h exposure period are greater than the CBRs obtained from 96 h for the five nitro-aromatics, no significant difference was observed, indicating that the CBR approach is a truer measure of chemical levels in exposed organisms and an ideal indicator to reflect the toxicity of a chemical. The bio-uptake can well be described by first-order kinetics and reach steady-state within 48 h. Almost same BCF values are obtained from the ratio of concentration in the fish (Cf ) and in the water (Cw ) at apparent steady-state and the ratio of the rate constants of uptake (k1 ) and depuration (k2 ) assuming first-order kinetics. The toxicity ratio (TR) can reflect the difference of internal critical concentrations and be used to identify mode of action.