Myriophyllum alterniflorum DC. Effect of low concentrations of copper and cadmium on somatic and photosynthetic endpoints: A chemometric approach

Aquatic plants can be a sensitive and cost effective route to understanding the effects of contaminants and assessing ecosystem health. Among the aquatic macrophytes, watermilfoil genus Myriophyllum could be used in ecological surveys as in situ biomonitors of water quality due to its ability to concentrate pollutants in their tissues and reflect the environmental pollution. The objectives of the present study were to evaluate the phytotoxicity of two heavy metals, Cu (essential micronutrient) and Cd (non-essential metal) alone or in mixture at realistic (low) concentration levels to a common European watermilfoil, Myriophyllum alterniflorum. ANOVA Kruskall-Wallis data indicate that effect of pH and mixture on copper or cadmium amounts in plants was statistically non significant. Correlation between variables was assessed using Spearman's rank order correlation. The main correlations were between: (i) time and node length, (ii) fresh mass and dry mass, (iii) chlorophyll A and carotenoids, and (iv) copper and cadmium in the mixture study. In addition to the Spearman correlations, data were analysed using the factor analysis. High positive loadings of mass (fresh weight and dry weight) along the factor 1 axis and high loadings (positive for copper and cadmium treatment, negative for the mixture) of plant growth (time, node length) along the factor 2 axis are evident. In conclusion, statistical estimate of the data revealed no strong significant relationships between the treatment (copper and cadmium in M. alterniflorum) and the somatic or photosynthetic endpoints studied. This lack of significant results could be explained by the low metal concentrations tested and this study failed to reproduce our first conclusions about the correlation between cadmium, chlorophyll A and carotenoids.