Twelve Mediterranean hydrophyte species collected inLebanon were evaluated for their potential asbioindicator species for heavy metal pollution innutrient 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., Veronicalysimachioides L., Veronica anagalloides L., Mentha longifolia L., Mentha aquatica L., Mentha pulegium L., Potentilla reptansL., Mentha sylvestris L., and Cardamine uliginosa L.. Large variability in responseto exposure to the heavy metals was observed. Growthrates remained high during the experimental period,indicating that the plants were little affected by thepresence of the metal at the experimentalconcentration. Metal accumulation and bioconcentrationvaried within at least one order of magnitude, andranged from less than 10 to over 200. Cr waspreferentially accumulated in the roots. All speciesbut M. pulegium, P. reptans and V. anagallisaquatica accumulated and bioconcentrated sufficientCr to qualify as bioindicator species. Five of thespecies that accumulated Cr also accumulated Ni, withthe same partitioning into the root. These were: N. officinale, C. uliginosa sp., M. longifolia, M. aquatica and M. sylvestris, all of which mayalso be used as bioindicators of Ni pollution. Onlyone species, M. aquatica, accumulated Cdsignificantly, and may, therefore, be used as abioindicator for all three metals.

Choosing native vascular plants as nutrient and toxic element accumulators for passive biomonitoring of urban river quality is not an easy task in Mediterranean rivers, due to the particular climate determining high variations in river hydrology. To identify potential biomonitors for this area, the roots of seven species (Angelica sylvestris, Apium nodiflorum, Tradescantia fluminensis, Nasturtium officinale, Persicaria lapathifolia, Arctium lappa, Typha latifolia), growing in seven sites along the River Irno (Southern Italy), were collected in July 2010 and analyzed regarding their capability to accumulate Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V, and Zn through atomic absorption spectrometry. Notwithstanding the expected different accumulation degree among the species, they highlighted similar spatial contamination gradients, and all of them appeared suitable, alone or in combination, for river passive biomonitoring. A. nodiflorum, in particular, appeared the best biomonitor for the River Irno, where severe anthropogenic impacts were detected: high Cu and Cd contamination from vine cultivation in the upper stretch, and Pb, Zn, and Mn contamination in the medium stretch from airborne dusts coming from a cast iron foundry.