MICROALGA CHLORELLA VULGARIS AS A MONITORING SYSTEM OF MICRONUTRIENS AND HEAVY METALS CONTAMINATION

The management of solid wastes and compost products in agro-ecosystems involves the accumulation and spread of micronutrients and heavy metals in soil and water due to leaching and run-off processes. These metals can reach the water table, accumulate in excessive amounts and be rejected in groundwater and rivers, with significant impact and environmental risks. The treatment and removal of these inorganic pollutants is of special importance, since metals as copper (Cu), manganese (Mn) or zinc (Zn) are non-biodegradable and persist in the environment posing a threat to the biota and the environment. Due to their photosynthetic ability and fast growth rates, autotrophic microorganisms such as the microalgae appear to be particularly effective in the interaction and metabolization of these compounds. Despite the relative simplicity of these microorganisms, many of the mechanisms underlying absorption and/or removal of micronutrients and heavy metals are still unknown. Conversely,in order to use these living forms in biomonitoring and management of inorganic pollutants in the environment, it is necessary to know their potentiality in terms of tolerance/resistance to concentration thresholds and toxicity effects. For this purpose, at laboratory scale the microalgae Chlorella vulgaris has been used to remove and/or detoxify from micronutrients that can also be toxic metals, Cu, Mn, Zn in a controlled growth system. Different concentrations and treatments, each in three replicates, were tested in microcosms consisting in Pyrex flasks inoculated with the algae colonies in TAP medium (control) and TAP enriched with Cu, Mn and Zn. The algae cultures were weekly monitored during a three weeksperiod, by measuring the photosynthetic pigments, the chlorophyll fluorescence and Cu, Mn and Zn contents in algal dry biomass and in the growth medium by Inductively Coupled Plasma-Optical Emission Spectrometry. A significant decrease in Zn and Cu was observed in the growth medium associated with an increase of their concentration in the dry biomass, suggesting a good ability of C. vulgaris in removing these metals from polluted waters. The relative concentrations of Cu, Mn and Zn in the medium and inside the alga, together with the physiological performance of this microorganism, are discussed in order to evaluate the possible applications in commercial stage of biomonitoring and bioremediation technologies.