Mercury and lead: assessing the toxic effects on growth and metal accumulation by Lemna minor.

Lemna minor L. was used to investigate the toxic effects of Pb and Hg either alone or in various binary mixtures under the static test conditions. A full-strength Jacob culture medium was used for the long-term cultivation of duckweeds and the experiments. Tests were run for 4 and 7 days. The EC(50) values for Pb was estimated as 6.8 ± 0.2 mg L(-1) and 5.5 ± 0.1 mg L(-1) for a 4 and a 7-day test periods, respectively. Hg was much more toxic than Pb with the EC(50) of 0.64 ± 0.03 mg L(-1) (4 days) and 0.48 ± 0.02 mg L(-1) (7 days). The amounts of Pb uptake by the plants were determined by atomic absorption spectrometer (AAS). The cold vapor AAS-technique (CV-AAS) was used for Hg determination. The interactive effect between Pb and Hg on growth was evaluated as additive on the basis of statistical data analysis. However, an antagonistic interaction was observed on the metal accumulation efficiency.

Speciation of chromium in the presence of copper and zinc and their combined toxicity.

Speciation of chromium has attracted a great deal of interest in view of the toxic properties of Cr(6+) compared with the much less toxic Cr(3+). A freshwater plant, duckweed which is uniquely suitable for aquatic toxicity tests is utilized to study the growth responses and accumulation of chromium in the presence of copper and zinc. Speciation analysis was carried out by using differently activated alumina. Metal ion concentrations in the plant were determined by FAA spectrometry. Results of the present study revealed that the oxidation state of chromium as well as its concentration in media controlled the growth and the metal accumulation in duckweed. Regarding this, Lemna minor (common duckweed species) accumulated Cr(3+) in smaller quantities and it resulted in relatively larger growth responses, whereas Cr(6+) was accumulated in larger quantities and it yielded relatively smaller growth responses. Different types of metal interactions among chromium, copper, and zinc ions were evident. These interactions were classified as synergistic, antagonistic, and additive and they were strictly dependent on the oxidation state of the chromium ion.