Based on the characteristics of atom types

Hall’s electrotopological state indices（En） were calculated for 122 nonionic organic compounds.On the basis of the characteristics of substituents and conjugated matrix

a novel molecular conjugated parameter（B） was defined and calculated for 122 molecules in this paper.En and B show good structural selectivity for organic molecules.A satisfactory relationship between bioconcentration factor（BCF） and En

B is expressed as: lgBCF=-0.076+1.006B+0.077E38+ 0.274E9+0.111E39（n′=122

R=0.966

F=408.35

S=0.401）

which could provide estimation and prediction for the BCF of nonionic organic chemicals.Furthermore

the model is examined to validate overall robustness with Jackknife tests.The four structural parameters are used as the input neurons of artificial neural network

and a 4∶10∶1 network architecture is employed.A good model can be constructed with the back-propagation algorithm

the correlation coefficient R and the standard error s are 0.990 and 0.216

respectively.This shows that the artificial neural network model for the bioconcentration factor appears to be more reliable than the multivariate regression model.The results show that the new parameter B and electrotopological state index have good rationality and efficiency for the bioconcentration factors of organic compounds.