Maturity index values reflect life history characteristics often inferred by morphology. We tested the hypothesis that Acrobeloides and Aphelenchus are sensitive to chemical pollutants, opposite of what their colonizer-persister (CP) value of 2 suggests. Acrobeloides and Aphelenchus were reared at 19 degrees C and provided diets of Escherichia coli and Rhizoctonia solani, respectively. LC50 values for Aphelenchus exposed to copper or benzo(a)pyrene (BaP) are greater than Acrobeloides. Copper impedes growth of Acrobeloides at 10 microg/g, and results in 100% mortality at 20 microg/g. In contrast, Aphelenchus is more resilient, with no visible impact at 20 microg/g. Acrobeloides and Aphelenchus were sensitive to much lower concentrations of BaP than copper, i.e., 0.5 microg/g inhibited development of Acrobeloides and 2 microg/g for Aphelenchus. Egg size and hatch were unaffected at 15 microg/g copper. In contrast, 0.5 microg/g BaP reduced both egg size and hatch for Aphelenchus but not Acrobeloides. Survival of Acrobeloides and reproduction of Aphelenchus responded differently to copper and BaP, implying the relationship between this classification and their sensitivity to short-term effects may be less straightforward than presumed. Refinement of index values based on empirical evidence can be used to improve sensitivity and interpretation of nematode community indices for environmental monitoring.