The Seed Germination Test as a Valuable Tool for the Short-Term Phytotoxicity Screening of Water-Soluble Polyamidoamines.

Six differently charged amphoteric polyamidoamines, synthesized by the polyaddition of N , N '-methylenebisacrylamide to alanine, leucine, serine, arginine (M-ARG), glutamic acid (M-GLU) and a glycine/cystine mixture, were screened for their short-term phytotoxicity using a seed germination test. Lepidium sativum L. seeds were incubated in polyamidoamine water solutions with concentrations ranging from 0.156 to 2.5 mg mL -1 at 25 ± 1 °C for 120 h. The seed germination percentage ( SG %), an indicator of acute toxicity, and both root and shoot elongation, related to plant maturation, were the considered endpoints. The germination index ( GI ) was calculated as the product of relative seed germination times relative radical growth. The SG % values were in all cases comparable to those obtained in water, indicating no detectable acute phytotoxicity of the polyamidoamines. In the short term, the predominantly positively charged M-ARG proved to be phytotoxic at all concentrations ( GI < 0.8), whereas the predominantly negatively charged M-GLU proved to be biostimulating at intermediate concentrations ( GI > 1) and slightly inhibitory at 2.5 mg mL -1 (0.8 < GI < 1). Overall, polyamidoamine phytotoxicity could be correlated to charge distribution, demonstrating the potential of the test for predicting and interpreting the eco-toxicological behavior of water-soluble polyelectrolytes.