THE OCCURRENCE AND DISTRIBUTION OF TRACE-METALS IN HALOPHYTES

Sediments and selected halophytic plants from two salt marshes in Essex (UK) were analysed for the occurrence of a variety of metals including arsenic (As), calcium (Ca), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), nickel (Ni), lead (Pb), selenium (Se) and zinc (Zn). The majority of metals occurred in the sediments at concentrations lower than or approaching the shale standard. This, however, was not the case for Cd, Hg and Pb at Two Tree Island salt marsh which is situated on the Thames Estuary. At this more industrialized site these non essential elements were enriched in the sediments and halophytic plants but at concentrations that did not appear to affect the well being of the plants. Only Zn concentrations in plant material reflected levels within the sediment. The occurrence and distribution of metals within different halophytic species was compared by analysing roots and aerial parts from Salicornia spp., Spartina spp., Aster tripolium and Atriplex portulacoides (Halimione portulacoides syn.). In general, the metals accumulated mainly in the roots and were not transported to the aerial parts with the exception of the chemically mobile elements; Cd, Mn and Zn which were more evenly distributed. The halophytes chosen in this study did not reflect the concentration of metals within the surficial sediments and are, therefore, not suitable as indicators for sediment pollution.