The Uptake Of Heavy Metals By Emerging Macrophytes

An assessment as to the potential of Phragmites and Typha to accumulate lead and zinc into aerial tissue sections was carried out during the summer of 1993 under greenhouse conditions. Seven double skin tanks were established for each species using washed and trimmed rhizomes collected locally. These plants were maintained in nutrient solution for six weeks to allow the establishment of aerial growth prior to the commencement of metal dosing. Treatments were assigned randomly to the established tanks and included a control three lead doses and three zinc doses. Stock metal solutions of zinc nitrate (Zn 50,000 mg.dm-3) and lead nitrate (Pb 10,000 mg.dm-3) were used to supplement the nutrient solution to give treatments of 10, 100, 500 mg.dm-3 zinc and 5, 20, 100 mg.dm-3 lead. The nutrient solution was replaced weekly and adjusted for evapotranspiration twice weekly with un-amended nutrient solution making the liquid volume back up to the 12 dm3 mark.The uptake of lead by Typha and Phragmites was found to be minimal. Aerial samples generally contained under 10 mg.kg-1 and the highest recorded value of 33 mg.kg-1 was recorded in a Typha sample that had been dosed at 100 mg.dm-3 for only two weeks These two species do accumulate zinc but in a quite different way with Phragmites accumulating zinc both more rapidly and to a much greater extent than Typha. The accumulation of zinc by Phragmites in this experiment, whilst considerable, is less than that reported by others.. The system used in this work was designed with the important aim of minimising any substrate interaction but was never expected to totally eliminate it.