Ecotoxicological assessment of copper and zinc in a common aquatic plant Ceratophyllum demersum: Physiological effects and biomarker responses

Utilizing and discharging chemical products containing trace metals lead to widespread contamination in the aquatic environment. Although copper (Cu) and zinc (Zn) are essential plant micronutrients, excessive concentrations may induce stress and mortality. This study investigated the physiological responses of a common aquatic plant, Ceratophyllum demersum, exposed to Cu (0, 2, 5, 10, and 50 μM) or Zn (0, 50, 100, 500, and 1000 μM) for 3 days. Both Cu and Zn were accumulated in plant tissues. Cu exposure led to severe phytotoxicity effects, manifested as a rapid decrease in photosynthetic efficiency (Fv/Fm and ՓPSII), a significant reduction in pigments and an increase in oxidative stress markers. In contrast, minor effects were observed in Zn-treated plants. In addition, Cu exposure suppressed the expression of D1, rubisco large subunit, and alpha-tubulin proteins but did not affect the PSI-B core subunit of PSI. Our study suggested that Cu is a potent phytotoxin by disturbing the principal reactions of photosynthesis and inducing oxidative stress and protein degradation. The overall health status of C. demersum was assessed by adopting the biomarker response index (BRI) approach. The effects of Cu were categorized as moderate in 2 μM and severe in 5, 10, and 50 μM whereas the effects of Zn were categorized as slight in 50 μM, negligible in 100 μM and major in 500 and 1000 μM. BRI effectively substantiates data interpretation of complex plant responses to trace metals and should be further adapted into biomonitoring suites in aquatic systems.