Impact of organic pollutants on metal and As uptake by helophyte species and consequences for constructed wetlands design and management.

Various industrial processes and anthropogenic activities in urban areas induce a release of metals, metalloids and organic pollutants. Phytoremediation of co-contaminated waters in constructed wetlands is a promising solution for reducing the impact on natural environments. In order to improve the design and management of constructed wetlands, more knowledge is needed concerning the effect of organic pollutants on plant metal and metalloid uptake. In this study, the effects of a mixture of organic pollutants commonly found in industrial effluents (hydrocarbons, polycyclic aromatic hydrocarbons, anionic detergent) on the uptake of ten metals and metalloids (MM), i.e. Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn, by five helophytes having a wide European distribution were studied. Main effects of plant species and pollutant conditions on metal uptake and interactions between factors were determined by a statistical treatment of a microcosm experiment. Overall, the order of element uptake in plants was Fe > Al > Mn > Cr, Ni, Zn, > Cu > As, Cd, Pb, which was consistent with relative concentrations in the rhizosphere environment of microcosms. Larger amounts of metals were retained in belowground biomass of plants than in aboveground parts. Statistical analysis showed that organic pollutants enhanced the accumulation of Mn in whole plants and the retention of Fe in belowground parts, while they reduced the accumulation of Cd, Ni, and Zn in whole plants and the retention of Cu in belowground parts. For the other MM (Al, As, Cr, Pb), effects were variable, depending on the plant species. Among the five plants tested, Carex cuprina generally removed the highest quantities of MM, which was the result of both a high metal accumulation capacity and high biomass production. Nevertheless, no significant proportion of the MM total loading could be removed in plants' aboveground parts.