Uptake and Toxicity of Arsenic, Copper, and Silicon in Azolla caroliniana and Lemna minor

Abstract

Here we report on the analysis of two aquatic plant species, Azolla caroliniana and Lemna minor, with respect to tolerance and uptake of co-occurring arsenic, copper, and silicon for use in engineered wetlands. Plants were cultured in nutrient solution that was amended with arsenic (0 or 20 μM), copper (2 or 78 μM), and silicon (0 or 1.8 mM) either singly or in combination. We hypothesized that arsenic and copper would negatively affect the uptake of metals, growth, and pigmentation and that silicon would mitigate those stresses. Tolerance was assessed by measuring growth of biomass and concentrations of chlorophyll and anthocyanins. Both plant species accumulated arsenic, copper, and silicon; L. minor generally had higher levels on a per biomass basis. Arsenic negatively impacted A. caroliniana, causing a 30% decrease in biomass production and an increase in the concentration of anthocyanin. Copper negatively impacted L. minor, causing a 60% decrease in biomass production and a 45% decrease in chlorophyll content. Silicon augmented the impact of arsenic on biomass production in A. caroliniana but mitigated the effect of copper on L. minor. Our results suggest that mixtures of plant species may be needed to maximize uptake of multiple contaminants in engineered wetlands.

KEY WORDS:

• arsenic
• copper
• silicon
• phytoremediation
• mixed contaminants
• chlorophyll
• anthocyanins

ACKNOWLEDGMENTS

We would like to acknowledge the United States Department of Agriculture (Grant No. 2006-38894-03732) for funding; Jonathan Frantz, Defne Apul, Alison Spongberg, and Michael Weintraub for suggestions during preparation of the manuscript; and Doug Sturtz for operation of the ICP-OES.