Biosorption mechanism of wild celery, Vallisneria natans towards lead and its effect on the chlorophyll content

Abstract

Vallisneria natans is a variety of the Vallisneria americana species and is commonly found in freshwaters. In this study, Vallisneria natans (wild celery) was used as an accumulator in water solutions containing high levels of lead. Vallisneria natans also called Vallisneria americana Var. natans, is a genus within the family of frog bite plants Hydrocharitaceae. The Vallisneria natans samples were exposed to different lead concentrations: 100 ppm, 300 ppm, 500 ppm, and 0 ppm for 15 days without prior acclimatization. The uptake of the plant in different concentrations was determined by AAS analysis. The uptake mechanism of lead on V. natans was also investigated through the determination of the different lead ion concentrations adsorbed (supernatant), and absorbed (residue) by the macrophyte. The extent of V. natans to phytoremediate lead was also assessed by determining the percentage of lead ions accumulated by the plant. Furthermore, examination of its photosynthetic activity at different lead concentrations was also done by double-beam UV-Vis spectrophotometry to determine the general effect of lead ions to V. natans. The concentration of chlorophyll a and b was also determined to compare the effect of lead contamination on chlorophyll a and chlorophyll b. The percentage of loss in chlorophyll a and b in varying lead concentrations was also measured for clearer depiction of the effect of lead on chlorophyll content of V. natans.

Results have shown that V. natans favors adsorption in biosorbing lead ions and that V. natans proved to be effective in adsorbing high levels of lead even in treatments without acclimatization. Results have also shown that the photosynthetic activity of V. natans was appreciably affected by the presence of lead ions. Thus, the use of V. natans as a biosorbent in the field of bioremediation was proven to be a promising and efficient approach for the removal of lead ions up to 500 ppm as observed in this study. In immediate bioremediation, V. natans still proved to be effective as it is capable of adsorbing high levels of lead even in treatments without acclimatizing the plant. The percentage uptake of residue samples have decreased as the concentration of lead is increased which means that the ability of V. natans to absorb lead ions is weakened by the increasing presence of lead ions. Also, comparison of the mean lead uptake of V. natans in supernatant and residue samples at all lead treatments has shown that the macrophyte is more capable of sequestering lead ions via adsorption. Results obtained have also shown that the photosynthetic activity of V. natans was appreciably affected by the presence of lead ions. Chlorophyll a content of the macrophyte has decreased as lead concentration was increased. Chlorophyll b content has increased as lead concentration was increased from 0 ppm to 100 ppm and then decreased as lead concentration was increased from 100 ppm to 300 ppm, and then to 500 ppm.