UPTAKE OF ARSENIC BY ESTUARINE PLANTS AND INTERACTIONS WITH PHOSPHATE, IN THE FIELD (RHINE ESTUARY) AND UNDER OUTDOOR EXPERIMENTAL CONDITIONS

Soil and plants [Urtica dioica L. and Phragmites australis (Cav.) Trin. ex. Steud.] from the flood plains of the former Rhine estuary were analysed for arsenic and phosphorus. Concentrations of arsenic in roots and shoots of P. australis were not correlated with concentrations of arsenic and phosphorus in the soil. Arsenic concentrations in the roots of U. dioica were negatively correlated with concentrations of arsenic in the soil and positively correlated with phosphorus in the soil. In outdoor experiments, arsenic added to the soil as sodium cacodylate was found to inhibit the growth of U. dioica more than lead arsenate. The growth of P. australis was not affected by high arsenic concentrations in the soil. Both species took up increasing amounts of arsenic with increasing arsenic concentrations in the soil. Loss of phosphorus from the soil indicated that arsenic mobilizes phosphorus and that this process also depends on the plant species growing in the soil. U. dioica grown in soil containing 1 μmol As g-1 dry soil was found to take up more arsenic with increasing phosphate additions to the soil. The results indicate that phosphorus is an important factor determining the uptake of arsenic by some plant species. Effects of arsenic on plants will therefore depend on the amount of phosphorus available in the soil. © 1990.