Use of lichen biomass to monitor dissolved metals in natural waters

Concentrations of 9 dissolved metals were monitored at 10 sampling stations along the Bayou d'Inde by suspending perforated tubes containing 5 g of the lichen Parmelia oraesorediosa in the water for 2 weeks. Atomic absorption spectrophotometry of the dried digested lichen material showed that the distribution of zinc, copper, chromium and nickel resembled that observed previously in periphyton and surface sediments, with concentrations increasing from the bayou mouth to reach a maximum at the station located inside an industrial ditch, and then declining further upstream. The maximal concentration of mercury occurred at the same sampling station indicating mobilization of mercury trapped in the heavily contaminated sediments. Chromium concentrations were highest in lichen material near the same upstream industrial ditch, while the maximal iron and manganese concentrations were recorded at the bayou mouth which was affected by ship and barge traffic and sewage effluents. Lichen material had a powerful metal-accumulating ability, and could be a useful biomonitor of dissolved metals in natural waters.