Use of nonlinear regression techniques for describing concentration-response relationships of plant species exposed to contaminated site soils

The objectives of this study were to examine the effects of two contaminate d site soils on seedling emergence and growth, compare the responses of dif ferent endpoints and species sensitivity, and develop appropriate statistic al methods for the analysis of concentration-response curves. Plants were e xposed to field-collected soils contaminated with amines or condensate. We reparameterized three nonlinear models (logistic, logistic with hormesis, a nd exponential) to determine any inhibiting concentration for a specified p ercent effect and confidence interval using regression analysis. Weighting procedures were applied, when necessary, to accommodate heteroscedasticity. This nonlinear regression approach was very satisfactory when used with da ta sets, each with 11 treatments, and produced an accurate, easily interpre ted, and quantitative description of the data, which also provided qualitat ive information. The IC50s ranged from 2 to 96% contamination for condensat e-contaminated soil and from 3 to 38% contamination for amine-contaminated soil. The responses were specific to species, endpoint, and soil. Mass meas urements were generally more sensitive and precise than length measurements . Definitive tests were more sensitive than acute tests for endpoints other than emergence.