Bioaccumulation and physiological responses of the Coontail, Ceratophyllum demersum exposed to copper, zinc and in combination.

Ceratophyllum demersum is a submerged aquatic angiosperm which is fast growing in contaminated water. This plant has no roots and so takes up nutrients from the water column without the complicating factor of differential shoot/root uptake of nutrients. 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 and integrating sphere spectrometer were applied to detect copper and zinc toxicity effects on the light reactions of photosynthesis C. demersum is an aquatic plant that could be a good accumulator of Cu and Zn in actual solution in the water column. Additionally, RGR (relative growth rate) and chlorophyll content of C. demersum show that toxic effects of Cu or Zn increased over time. 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), biochemical (chlorophyll content) and from measurements of photosynthesis using Pulse Amplitude Modulation (PAM) fluorometry. Moreover, the combination of Cu and Zn caused more toxic effect than either Cu or Zn separately. Whole plant scans using an integrating sphere spectrophotometer showed that Cu, Zn and Zn + Cu toxicity effects could be identified from spectral scans but were not specific enough for Cu, Zn and Zn + Cu toxicity to be distinguished from one another.