PHYTOREMEDIATION: ASSESSING TOLERANCE OF TREE SPECIES AGAINST HEAVY METAL (PB AND CD) TOXICITY

Abstract

The toxicity effects of heavy metals (lead and cadmium) on germination, root length and dry biomass of tree species viz., Thespesia populneoides, Leucaena leucocephala and Delonex regia were evaluated. Cadmium was found to be more toxic than lead. The results further showed that dose response of heavy metals were inversely proportional to germination, root growth and dry biomass. The percentage germination and higher % DFC values showed that the seeds of L. leucocephala were least affected by lead and cadmium toxicity while scoring the best germination response among the three tree species. Exposure to high concentration (125ppm) of Cd decreased the root size of L. leucocephala, T. populneoides and D. regia by 89.79, 71.8 and 62.26% respectively. However, at the same concentration, lead inhibited the root growth (39.62%) in case of D. regia while much higher reduction was observed for L. leucocephala and T. populneoides around 62.7%. Furthermore, the % phytotoxicity and tolerance index confirmed that D. regia appeared to be the most tolerant species whereas, T. populneoides and L. leucocephala were moderately tolerant and less tolerant species respectively against the Pb and Cd treatment. This study gives an insight to the possible mechanism of hypertolerance, signifying that trees can be successfully used for phytoremediation.