Friday, June 26, 2009

Selection of plants for phytoremediation of sites contaminated with several metals

Phytoremediation refers to the use of higher plants to rehabilitate contaminated sites without the need to excavate the contaminant material and dispose of it elsewhere. The use of plants capable of taking up high amounts of metals has been proven effective in the rehabilitation of metal-contaminated soils. Plants are grown for a certain period of time and are then harvested and subjected to composting, compaction, incineration, ashing, pyrolysis, direct disposal or liquid extraction. In principle, the best plants for the purpose are those that can tolerate the polluted soil condition, can absorb high amounts of the contaminants, and have economic value (e.g. flowering plants) so that they can also be a source of income. Thus, selection of the suitable plant species is crucial to the success of any phytoremediation program.

In a recent study by HY Lai of MingDao University and and ZS Chen of National Taiwan University published in the International Journal of Phytoremediation, 33 flowering plant species were tested on a 1.3-ha field in central Taiwan. The site is contaminated with multiple metals (As, Cr, Ni, Cu and Zn) due to the continuous irrigation of wastewater from surrounding chemical plants in the last decade. The study used three models for the selection of suitable species: 1) a relative percentage weighting of the growth condition and the metal accumulation capacity of 80% and 20%, respectively; 2) a relative percentage weighting of the growth condition and the metal accumulation capacity of 50% and 50%, respectively; and 3) a relative percentage weighting of the growth condition and the metal accumulation capacity of 0% and 100%, respectively.

The 33 plants included bougainvillea (Bougainvillea spp.), rainbow pink (Dianthus chinensis), serissa (Serissa japonica), French marigold (Tagetes patula), rose of Sharon (Hibiscus syriacus), water willow (Salix warburgu), Chinese ixora (Ixora chinensis), sunflower (Helianthus annuus), Chinese hibiscus (Hibiscus rosasinensis), gold dewdrop (Duranta repens), kalanchoe (Kalanchoe blossfeldiana), creeping trilobata (Wedelia trilobata), garden canna (Canna generalis), garden verbena (Verbena hybrida), Malabar chestnut (Pachira macrocarpa), purslane (Portulaca oloraua), common lantana (Lantana camara), fancy leaf caladium (Caladium xhortulanun), coleus (Coleus blumei), golden trumpet (Allamanda cathartica), common melastoma (Melastoma candidum), Carland flower (Hedychium coronarium), Manaca raintree (Brunfelsia uniflora), yellow cosmos (Cosmos sulphureus), silver apricot (Ginkgo biloba), temple tree (Plumeria acutifolia), orchid tree (Aglaia odorata), star cluster (Pentas lanceolata), blue daza (Evolvulus nuttallianus), cockscomb (Celosia cristata), scandent scheffera umbrella tree (Schefflera arboricola), Bojers spurge (Euphorbia splendens), and croton (Codialum variegatum).

Some of the highlights of the study: Twelve (12) plants out of the 33 tested were selected based on two key factors: 1) ability to tolerate the toxicity of metals (i.e. good growth of the plant) and 2) ability to accumulate high concentrations of metals in the shoot. Using equal weighting (meaning 50% to 50%) of good growth condition (factor No. 1) and of accumulated metal concentrations (factor No. 2), six (6) woody and six (6) herbaceous plant species showed the best potential for phytoremediation of the contaminated site and thus were selected for further testing. These included the following plant species: purslane, garden canna, Bojers spurge, Chinese ixora, croton, kalanchoe, serissa, garden verbena, rainbow pink, French marigold, scandent scheffera umbrella tree, Chinese hibiscus, and sunflower.

The study also revealed that the herbaceous species accumulated higher concentrations of metals and thus have higher “bioconcentration factor” (ratio of metal concentration in shoots to that of the soils) compared to the woody species. The increase of metal concentrations for the herbaceous species were 9.4-fold for Cu, 5.1-fold for Cr, and 8.9-fold for Zn while for the woody species they were 3.1-fold for Cu, 2.5-fold for Cr, and 4.3-fold for Zn.


Lai HY and ZS Chen. 2009. In-situ selection of suitable plants for the phytoremediation of multi-metals contaminated sites in central Taiwan. International Journal of Phytoremediation 11: 235-250.

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