## 3 Results and Discussion
### Minerals and Heavy Metals Composition  
Minerals content of microalgae is highly correlated with the growing environment. It also varies with microalgae species, harvesting time, growth phase and growing site. These minerals are not only essential for their growth but can also be a valuable source of a wide variety of macrominerals and trace elements for humans and animals [8]. The mineral composition as well as the heavy metals concentration of _C. reinhardtii_, _Spirulina_ and _Chlorella_ are shown in Table 3. Phosphorus (P) was the most abundant essential element in both _Chlorella_ and _C. reinhardtii_, while potassium (K+) was the dominant one in _Spirulina_ and the second most abundant in _Chlorella_. _Spirulina_ and _Chlorella_ had higher mineral content than _C. reinhardtii_ for most studied minerals except for calcium (Ca2+), copper (Cu2+) and selenium (Se2+). Table 3 shows that _C. reinhardtii_ had higher concentrations of Mn2+, Cu2+ and Fe3+ than the values reported for some land vegetables such as lettuce, cabbage, carrots, broccoli and spinach [57]. The three studied species contained higher amounts of Fe3+/Fe2+ than spinach, which is regarded as an iron-rich food [56]. Importantly, _Spirulina_ is a very rich source of iron (3.73 mg/g DW), thus in theory, consumption of 2.15 g DW per day covers the daily recommendation of a male adult, while 8.4 g DW and 6 g DW of _C. reinhardtii_ and _Chlorella_ would be required, respectively, assuming all iron is bioavailable for absorption [58]. However, iron bioaccessibility and thus its bioavailability from microalgae generally needs to be further investigated. _C. reinhardtii_ contained 0.01 mg/g DW selenium while _Chlorella_ and _Spirulina_ lacked such essential nutrient. A daily allowance of 55 \(\upmu\)g (0.7 \(\upmu\)mol) is recommended for adult men and women. To cover the daily recommendation of selenium, for example, 5.50 g of _C. reinhardtii_ per day is theoretically adequate. Selenium (Se2+) is important for selenoprotein enzymes, which function as defence antioxidants (glutathione peroxididases (GPx)) [59]. A link between the micronutrient Se2+ deficiency and virulence of some contemporary RNA viruses was reported, and supplementation of Se-deficient virus-infected hosts with dietary Se2+ diminished viral mutation rates and improved immunocomp [60]. It might be worth to note that the current pandemic Covid-19 is among the RNA viruses, and thus the adequate intake of Se2+ might have a positive effect on reducing its mutation rates, too. Figure 3: Pigment concentration of _Chlamydomonas reinhardtii_, _Spirulina_ and _Chlorella_ expressed as mg/g DW. Results are the means of triplicate determinations \(\pm\) SD. Generally, many health benefits are associated with the intake of microalgae, however, there are also concerns to be considered. Microalgae are known for their ability to absorb and accumulate heavy metals, which have detrimental health effects on human and animals [61]. In this study, the amounts of arsenic, cadmium, silver and lead were analysed (Table 3). _Spirulina_ and _Chlorella_ contained higher amounts of cadmium (Cd\({}^{2+}\)), arsenic (As\({}^{2+}\)), lead (Pb\({}^{2+}\)) and silver Ag\({}^{+}\) than _C. reinhardtii_. There are several examples of heavy metals' adverse effects on human health. For instance, arsenic-related cancer, as well as peripheral vascular diseases and renal tubular dysfunction are associated with exposure to cadmium and reduced mental development associated with mercury [61]. Limits for presumed safe intakes of contaminants, known as the provisional tolerable weekly intake (PTWI) for all the heavy metals have been set by the FAO/WHO Joint Expert Committee of Food Additives (JECFA) [62]. PTWI is \"an estimate of the amount of a substance in air, food, soil or drinking water that can be assimilated weekly per unit body weight (bw) over a lifetime without appreciable health risk\" [62].