Quantitative aspects of enhanced liver tumour formation in CF-1 mice by dieldrin

The dose-response characteristics of dieldrin-mediated enhancementof liver tumour formation in CF-1 mice were analysed, usingexisting tumour data from chronic feeding studies at six levelsof continuous exposure, involving a total of > 1500 animals.The dose-response relationship can be expressed as: D_x x T_x= D₀ x T₀ = constant, where T₀ = the median liver tumour inductionperiod in control CF-1 mice, T_x = the median liver tumour inductionperiod in dieldrin-treated mice at a dose level D_x, D₀ = thebackground dose equivalent for the induction of ‘spontaneous’liver tumours, D_x = the sum of background dose (D₀) and actualdieldrin dose (_x). The relationship, which is a Druckrey equation(D x Tⁿ = constant) where n = 1, indicates that: (i) the velocityof liver tumour development is proportional to the daily doselevel (D_x), (ii) the total tumourigenic dose is constant acrossall doses, (iii) the effects of dieldrin on the neo-plasticprocess in mouse liver are essentially irreversible and cumulative,and (iv) there is no evidence for a threshold level. However,when _x «D₀, the actual contribution of dieldrin to tumourformation is expected to be negligible.