N-15 metabolic test for the determination of phytotoxic effects of chemicals and contaminated environmental samples

A stable isotope N-15-nitrogen test (ESIMA = Ecotoxicological Stable Isotop e Metabolic Assay) was developed to assess biological effects and the poten tial toxicological hazard of chemicals and contaminated environmental sampl es on plant metabolism. The assay measures the effect of toxicants on the i ncorporation of a N-15 labelled tracer into the total nitrogen fraction (bo th the nonprotein and protein fraction) of plants. Segments of Pisum arvens e epicotyls are used as test substrates because of their high metabolic act ivity. The plant material is incubated under standardised conditions for tw o hours; subsequently N-15 incorporation is analysed by determining the N-1 5 abundance (N-15 atom-%) in the epicotyl segments. The effects of toxicants are evaluated by comparing the N-15 incorporation rates of control tissue and epicotyl segments exposed to individual chemica ls or complex environmental samples. The specificity and sensitivity of eff ects as indicated by ESIMA were compared with effects as measured by two es tablished ecotoxicological bioassays, the pollen tube growth test using pol len of Nicotiana sylvestris and the bacterial luminescence inhibition test using pollen of Photobacterium phosphoreum. The results of the study clearl y indicate the suitability of ESIMA for assessing toxic impacts on plant ni trogen metabolism.