Combining life-history and toxicokinetic parameters to interpret differences in sensitivity to cadmium between populations of Polycelis tenuis (Platyhelminthes)

Five populations of the planarian Polycelis tenuis, collected from four loc ations in a metal contaminated stream and from one location in an unpollute d tributary stream, were compared for their sensitivity to cadmium by measu ring survival, reproduction, and body size changes during 28 days of exposu re via the mater. Survival data and bioconcentration of cadmium measured at the end of the experiment enabled the use of a kinetic-based toxicity mode l, estimating the lethal body concentration, the uptake rate constant, the elimination rate constant, and the ultimate LC50 as estimated toxicokinetic parameters. Accurate body size selection and a one-month acclimatization p eriod to standardized laboratory conditions mere applied to enhance the com parability between populations. An increased elimination rate constant and a greater ultimate LC50 mere estimated for one of the populations, located downstream from an ancient lead-zinc mine. The cadmium concentration causin g an effect on reproduction varied considerably (a factor of 10) among popu lations but did not differ significantly between populations. For the numbe r of reproducing individuals as a function of cadmium concentration, EC50 a nd steepness of slope of the concentration/effect relationship tended to be correlated positively (P < 0.10), indicating that selection in the field m ay have occurred. Cadmium was found to enhance shrinkage of P. tenuis under conditions of food limitation. (C) 1999 Academic Press.