Effects of a combined use of macronutrients nitrate, ammonium, and phosphate on cadmium absorption by Egeria densa Planch. and its phytoremediation applicability

Phosphorus and nitrogen fertilizers represent a source of cadmium (Cd) which may be leached into aquatic systems. Macrophytes accumulate contaminants, and Egeria densa has been shown to grow in aquatic environments polluted with trace elements. In this study, Cd accumulation by E. densa exposed to two Cd treatments (3 and 5 mg L−1) was evaluated under increasing nutrient levels (NP as N–NO3 −, N–NH4 +, and P–PO4 3−, in concentrations 5-, 10- and 100-fold higher (NP5, NP10 and NP100) than in the sampling site) to simulate different levels of eutrophication. Bioaccumulation factors and Cd recovery were calculated and effects on plants were evaluated based on chloroplastidic pigment concentrations (chlorophylls a and b, and carotenoids). We conclude that Cd accumulation by Egeria densa is positively influenced by increasing availability of N and P at the level of around NP10 and probably at a broader concentration range not defined in this study. A further increase in N and P, however, does not generate a significant increase in Cd accumulation. Chloroplastidic pigment concentrations were not linearly correlated with Cd accumulation and the NP10 experiment produced less damage to macrophyte when compared to NP5 and NP100 experiments. Under controlled conditions, it was possible to satisfactorily model Cd bioaccumulation over time, in order to provide essential data for E. densa use in phytoremediation processes. The Cd residence in the macrophyte tissue is increased in eutrophic environments, which puts at risk the whole food chain of the aquatic ecosystem, mainly the primary consumers.