Treatment of tannery waste contaminated soil through phytoremediation

Abstract

Tannery effluent contains high concentrations of heavy metals, thus reducing soil fertility and depleting nutrients. Due to various anthropogenic (industrial) activities and natural processes, the accumulation of heavy metals in soil has rapidly grown. Due to their inability to biodegrade, heavy metals persist in the environment, risk getting into the food chain through crop plants, and eventually may build up inside humans due to biomagnification. Heavy metal poisoning poses a significant threat to both human health and the ecosystem because of its carcinogenic nature. This study evaluated the uptake of heavy metals from soil contaminated by tanneries by two hyperaccumulating plants, Salvia splendens (Morog ful) and Cathranthus roseus (Noyon tara), which are readily found in Dhaka. An initial analysis revealed elevated levels of chromium, lead, nickel, copper, and zinc in the soil samples collected from an area adjacent to of the tannery estate waste dumping site in Savar, Dhaka. These concentrations exceeded the standard values established by several countries and organizations. The study determined that chromium, lead, nickel, copper, and zinc concentrations of soil were 265 mg/kg, 69 mg/kg, 2.8 mg/kg, 40 mg/kg, and 166 mg/kg, respectively. Salvia splendens and Cathranthus roseus were found to uptake heavy metals from contaminated soil in various plant sections. Despite this, both plants could sustain a growth rate of over 90% compared to plants grown in non-contaminated soil. The results showed that Salvia splendens rapidly extracted heavy metals during its first growth phase, while Cathranthus roseus exhibited quick extraction of heavy metals during its final growth phase. The Salvia splendens plant (density-1) accumulated 278.4 mg/kg, 77.7 mg/kg, 37.3 mg/kg, 108.2 mg/kg, and 739.1 mg/kg of total chromium, lead, nickel, copper, and zinc, respectively, in 10 weeks. The concentrations of the same heavy metals absorbed by Cathranthus roseus (density-1) in 12 weeks were measured to be 87.6 mg/kg, 50.4 mg/kg, 22.3 mg/kg, 87.6 mg/kg, and 424 mg/kg, respectively. Salvia splendens exhibited superior uptake efficiency for all the heavy metals examined in this study compared to Cathranthus roseus. Therefore, both plants can be utilized in an eco-friendly manner to treat soils contaminated with heavy metals.