Common hydrophytes as bioindicators of nickel, chromium and cadmium pollution

Twelve Mediterranean hydrophyte species collected in Lebanon were evaluated for their potential as bioindicator species for heavy metal pollution in nutrient cultures enriched with 1 ppm Cr, Ni and Cd. These were: Nasturtium officinale R.Br, Apium nodiflorum L., Veronica beccabunga L., Veronica anagallis aquatica L., Veronica lysimachioides L., Veronica anagalloides L., Mentha longifolia L., Mentha aquatica L., Mentha pulegium L., Potentilla reptans L., Mentha sylvestris L., and Cardamine uliginosa L.. Large variability in response to exposure to the heavy metals was observed. Growth rates remained high during the experimental period, indicating that the plants were little affected by the presence of the metal at the experimental concentration. Metal accumulation and bioconcentration varied within at least one order of magnitude, and ranged from less than 10 to over 200. Cr was preferentially accumulated in the roots. All species but M. pulegium, P. reptans and V. anagallis aquatica accumulated and bioconcentrated sufficient Cr to qualify as bioindicator species. Five of the species that accumulated Cr also accumulated Ni, with the same partitioning into the root. These were: N. officinale, C. uliginosa sp., M. longifolia, M. aquatica and M. sylvestris, all of which may also be used as bioindicators of Ni pollution. Only one species, M. aquatica, accumulated Cd significantly, and may, therefore, be used as a bioindicator for all three metals.