The authors investigated the effect of preincubation of environmental waters amended with inorganic nutrients (nitr-gen, phosphorus, and traces of iron and magnesium) on the kinetics of the microbial transformation of phenol, propanil, propyl ester of (2,4-dichlorophenoxy) acetic acid, methyl parathion, Ronnel, and methoxychlor in pond and river waters. No effect on the second-order rate constants for these compounds was observed, although there was an increase in the bacterial populations and the pseudo-first-order rate constants. The use of nutrient-amended waters could be a useful tool for estimating second-order rate constants for an expanded number of compounds. This technique would provide a larger data base for predicting the behavior of xenobiotic compounds in the environment by using currently available mathematical models. (Copyright (c) 1986, American Society for Microbiology).