Bioaccumulation and physiological responses of coontail, ceratophyllum demersum exposed to copper, zinc and their combination

Abstract

Ceratophyllum demersum is a submerged aquatic angiosperm which is fast growing in contaminated water. This plant has no roots and so takes up nutrients slowly from the water column. This study aimed to compare the bioaccumulative capacities of Cu, Zn and their combination by C. demersum and physiological responses (growth, chlorophyll content, and photosynthetic rate) of C. demersum to Cu and Zn. Additionally, pulse amplitude modulation (PAM) technology was applied to detect copper and zinc toxicity effects on the light reactions of photosynthesis. Cu and Zn are essential trace elements for plant growth, development, and generally higher plants take up Cu in the form Cu2+ to around 10 μg/g in dry plant tissue. Increases of Cu in aquatic ecosystems is a consequence of various anthropogenic sources such as Cu mine drainage, Cu -based pesticides, industrial and domestic wastes and antifouling paints. It is commonly found in treated wastewaters. Toxicity of Cu causes oxidative stress, and the ions themselves could directly initiate oxidative breakdown of polyunsaturated lipids by two readily interconvertible oxidation states and it can catalyze the formation of free radicals through the Haber-Wiss reaction. Zinc is an essential element for the normal growth and metabolism which playsan important role in enzyme activation and is also involved in the biosynthesis of some enzymes and growth hormones of plants. Excess Zn has clearly visible effects (causes chlorosis) with inhibition of growth and decrease in biomass production; severe toxicity can also be fatal. Zinc toxicity is involved with metabolism through competitive inhibition of other essential ions, inactivation of enzymes, and displacement of essentialcofactor elements from functional sites of enzymes. Like Cu it is commonly found in domestic wastewaters. There are many techniques used to remove contaminants from contaminated water. However, phytoremidiation is the best solution to remove the low contaminants from waste water. C. demersum is an aquatic plant that could be a good accumulator for Cu and Zn while they were together in solution. Additionally, RGR (relative growth rate), chlorophyll content of C. demersumshow that acute toxic effects when exposed to Cu or Zn increased overtime. It was found that Cu and Zn effects manifested themselves more slowly than expected: at least 5 to 10 d were needed for noticeable effects both macroscopically (physical appearance), microscopically (Chloroplast morphology and numbers) and from measurements of photosynthesis using Pulse Amplitude Modulation (PAM) fluorometry. Moreover, the combination of Cu and Zn in the highest concentration was a higher toxic effect more than Cu or Zn in all parameters measured in this study.