Phytoremediation of lead and cadmium by thornless honey loccust trees’ (Gleditsia triacanthos L. var. inermis) in contaminated soil near the Tehran-Karaj highway

Phytoremediation is an emerging technology that uses plants to remove pollutants from contaminated sites. The present study examined the absorption of heavy metals by Gleditsia triacanthos L. var. inermis, a tree species planted in the landscape in Tehran-Karaj highway (Iran). This study was arranged in a split plot design with three replications. Experimental treatments included distances of planted trees from highway (30, 65, and 80 m) and three different sampling times (i.e. opening of leaves, late of June, and before the fall). The results showed that with the passage of time and approaching the fall, Pb concentration significantly increased. The highest concentration of Cd was observed in the mid-growth period. With increasing the distance, chlorophyll significantly increased. However, chlorophyll b and total chlorophyll were not influenced by the distance from the highway. The interaction of the distance and sampling time demonstrated that in the nearest distance from the highway, the concentration of chlorophyll decreased with the passage of time, while in the distance of 65 and 80 m from the highway, the concentration of chlorophyll increased in the middle of the growth period. In the nearest distance from the highway, the concentration of Pb significantly increased with the passage of time. By approaching fall, Pb concentration increased in 65 and 80 m from the highway. In the nearest distance from the highway, during mid-growth period, Cd concentration reached its maximum level.