RELATION BETWEEN HEAVY-METAL CONCENTRATIONS IN SALT-MARSH PLANTS AND SOIL

The aim of the research reported here was to investigate the relation between heavy metal concentrations in salt marsh plants, extractabilit y of the metals from soil and some soil characteristics. In April 1987 , Spartina anglica and Aster tripolium plants and soil were collected from four salt marshes along the Dutch coast. The redox potential of t he soil between the roots of the plants and at bare sites was measured . Soil samples were oven-dried and analyzed for chloride concentration , pH, fraction of soil particles smaller than 63 mum (f < 63 mum), los s on ignition (LOI) and ammonium acetate and hydrochloric acid extract able Cd, Cu and Zn concentrations. The roots and shoots of the plants were analyzed for Cd, Cu and Zn. Because drying of the soil prior to c hemical analysis might have changed the chemical speciation of the met als, and therefore the outcome of the ammonium acetate extraction, a s econd survey was performed in October 1990. In this survey A. tripoliu m plants and soil were collected from two salt marshes. Fresh and matc hed oven-dried soil samples were analyzed for water, ammonium acetate and diethylene triaminepentaacetic acid (DTPA) extractable Cd, Cu and Zn concentrations. The soil samples were also analyzed for f < 63 mum, LOI and total (HNO3/HCl digestion) metal concentrations. Soil metal c oncentrations were correlated with LOI. Drying prior to analysis of th e soil had a significant effect on the extractability of the metals wi th water, ammonium acetate or DTPA. Plant metal concentrations signifi cantly correlated only with some extractable metal concentrations dete rmined in dried soil samples. However, these correlations were not con sistently better than with total metal concentrations in the soil. It was concluded that extractions of metals from soil with water, ammoniu m acetate or DTPA are not better predictors for metal concentrations i n salt marsh plants than total metal concentrations, and that a major part of the variation in metal concentrations in the plants cannot be explained by variation in soil composition.