Determination of heavy metal contents of some microalgae by atomic absorption spectrometry

In this thesis study, the concentrations of Cu, Ni, Co, Mn, Fe, Pb, and Cr present in the structure of selected microalgae were determined using atomic absorption spectrometry. The microalgae Chlorella vulgaris, Scenedesmus obliquus, and Arthrospira platensis used in the study were freeze-dried and subsequently ground into a fine powder using an agate mortar. From the ground biomass, 0.5 g samples were weighed into Teflon vessels, and sequentially treated with 80% (v/v) HNO3, an 8 mL concentrated HNO3: 2 mL concentrated HCl mixture, and an 8 mL concentrated HCl : 2 mL concentrated HNO3 mixture. The samples were then subjected to microwave-assisted digestion to achieve complete dissolution and homogeneity. Following digestion, the samples were diluted with ultrapure water and analyzed by atomic absorption spectrometry to determine the metal concentrations in the microalgae. When Scenedesmus obliquus and Arthrospira platensis were digested with 80% (v/v) HNO3, higher metal concentrations were obtained, whereas for Chlorella vulgaris, higher metal concentrations were observed when digestion was carried out using the concentrated HNO3: concentrated HCl mixture. In Arthrospira platensis and Chlorella vulgaris, the most abundant metal was Fe (225.00 × 10⁻² mg metal/g dry algae and 66.00 × 10⁻² mg metal/g dry algae, respectively), while the least abundant metal was Ni (0.41 × 10⁻² mg metal/g dry algae and 0.25 × 10⁻² mg metal/g dry algae, respectively). Similarly, in Scenedesmus obliquus, Fe was the most abundant metal (121.00 × 10⁻² mg metal/g dry algae), whereas Co exhibited the lowest concentration (0.41 × 10⁻² mg metal/g dry algae). When the metal concentrations detected in the microalgae were compared with the permissible limit values for heavy metals in cosmetic products, all measured values were found to be below the regulatory thresholds. This outcome indicates that microalgae present a viable and compliant raw material option for cosmetic applications.