LOW-MOLECULAR-WEIGHT METAL-COMPLEXES IN THE FRESH-WATER MOSS RHYNCHOSTEGIUM-RIPARIOIDES EXPOSED TO ELEVATED CONCENTRATIONS OF ZN, CU, CD AND PB IN THE LABORATORY AND FIELD

The possible occurrence of low molecular weight, soluble ligands binding copper, zinc, cadmium and lead was investigated in Rhynchostegium riparioides, a widespread moss in flowing waters, which occurs at sites influenced by "heavy" metal contamination as well as ones free of contamination. In order to identify metal complexes with any such ligands, Rhynchostegium plants from an uncontaminated site were first incubated for 48 hr in medium including the metal (10 or 100-mu-M) in question. Fractionation of cell extracts of this material by gel permeation HPLC revealed the presence of complexes with a similar retention time to poly(gamma-glutamylcysteinyl)glycine metal complexes extracted from cell suspension cultures of Datura innoxia. However, the peaks corresponding to metal associated with these complexes in HPLC profiles of extracts from Rhynchostegium were low, so an acetone precipitation step was introduced to concentrate the bound metal. The estimated yield of Cu associated with low M(r) ligands following acetone precipitation was 65% for Rhynchostegium and 106% for D. innoxia; the equivalent values for Cd were 25 and 40%, respectively. A Zn complex with a different apparent retention time was also present; the possibility that this might be an artifact associated with the extraction procedure is discussed. There was no evidence for intracellular binding of Pb by low M(r) ligands. Estimates of the amount of Cu and Cd associated with low M(r) ligands increased following incubation of Rhynchostegium from an uncontaminated site in media containing increasing concentrations (10, 50, 100-mu-M) of metal. Similar complexes were also detected in populations of the same species taken directly from a contaminated site, i.e. without laboratory incubation in the presence of metal. Estimates of the proportions of Cu and Cd in Rhynchostegium from contaminated sites which were bound by these complexes, expressed as a percentage of the total metal accumulated by the moss, ranged from 0.06 to 0.65% for Cu and 0.24 to 2.08% for Cd.