CCD study on the ecophysiological effects of heavy metals on Lemna gibba

A Central Composite Design (CCD) of response surface methodology was applied to predict the ecophysiological effects of a mixture of heavy metals on a Lemnaceae (Lemna gibba). Specifically, the effect of Cd, Cr, Cu, Zn, Ni cations on L. gibba growth and the respective changes in the amounts of photosynthetic pigments, were studied, and the results were statistically analyzed using JMP 9.0.2 (SAS Institute) software. The analysis aimed at determining the most harmful heavy metals and their combined interaction with other metals. All duckweed samples were finally, analyzed by FT-IR for examining the effect of heavy metals on their molecular structure. Each metal had a distinct effect on the L. gibba physiology. Important interactions were also, observed for two combinations of heavy metals: Cd2+/Cr6+, and Cr6+/Cu2+. High correlation was found between the experimental and predicted results, reflected by R2 (coefficient of determination). The FT-IR results showed that the biomass presented a number of functional groups capable to bind with heavy metals ions such as carboxyl, phosphate, amides and hydroxide groups.