Effects of heavy metals on the nitrogen metabolism of the aquatic moss Fontinalis antipyretica L. ex Hedw. A 15N tracer study

The assessment of pollution in aquatic systems necessitates an accurate indication of toxicity of heavy metals for organisms and ecosystems. We used the stable nitrogen isotope 15N to estimate the influence of the heavy metals Cd, Pb and Zn on the synthesis of nitrogen-containing fractions in the aquatic moss Fontinalis antipyretica. This method permits conclusions concerning inhibitory effects of these heavy metals on the assimilation of nitrogen and the biosynthesis of amino acids and proteins. The moss was exposed to metal concentrations of 25-500 microM over a period of 5-10 days. 15N abundance of exposed plants was compared with that of control plants. Similar to a loss of vitality determined using a fluorometric assay, a decrease of the 15N abundance in the N fractions of Fontinalis antipyretica was measured in dependence on the metal concentration. Nevertheless, the individual inhibition by the distinct metals was different, so that the following order of toxicity was derived: Cd > Pb > Zn.