Response surface methodology based optimization of cadmium and lead remediation from aqueous solution by water hyacinth (Eichhornia crassipes [Mart.] Solms) and its anatomical study

Abstract

This experiment was performed to optimize the response surface methodology (RSM) based reduction of cadmium (Cd²⁺) and lead (Pb²⁺) from the aqueous solution and to study anatomical effects of Cd²⁺ and Pb²⁺ stress on stomata of water hyacinth (Eichhornia crassipes [Mart.] Solms) during phytoremediation. Laboratory experiments were carried out to grow E. crassipes plants in six treatments of Cd²⁺ and Pb²⁺ viz., 0 mgL^-1 (Control), 2 mgL^-1, 4 mgL^-1, 6 mgL^-1, 8 mgL^-1 and 10 mgL^-1 in 25 liter capacity glass aquariums. A 2-factor central composite design (CCD) with total 25 experimental runs and the predictor regression model equation was applied to optimize the prime conditions for the Cd²⁺ and Pb²⁺ reduction. Different plant growth attributes viz., translocation factor; kinetic plant growth rate, fresh plant biomass and total chlorophyll content were also found highest up to 4 mgL^-1 concentration of Cd²⁺ and Pb²⁺. Structural damage in the stomata of E. crassipes was evaluated under microscopic view and found that above 4 mgL^-1 concentration of Cd²⁺ and Pb²⁺ in the medium, significant structural damage to the stomata of leaves of the E. crassipes occurred. The results of this study concluded that E. crassipes can remediate Cd²⁺ and Pb²⁺ from the medium more efficiently at 1.22 mgL^-1 concentration and the developed model can be used to navigate the design space. Furthermore, the different plant growth attributes were also affected above 4 mgL^-1 concentration of Cd²⁺ and Pb²⁺ in the medium.