Spirulina was grown in the presence of polyethylene glycol-coated gold nanoparticles 5 nm diameter that were supplemented to cultivation medium in concentration range from 1.0 to 20.0 μM. Therefore, we conducted a life cycle assessment in the presence of gold nanoparticles (AuNPs), in particular applied on the first day of cultivation, on the 3rd day, corresponding to the beginning of the exponential growth phase, and on the 5th day, which refers to the stationary growth phase. The involvement of gold nanoparticles in the biosynthetic activity of spirulina was accompanied by the accumulation of free radicals, the presence of which was demonstrated on the basis of the amount of malondialdehyde (MDA) as a final product of lipid peroxidation (Figure 1).figureFig. 1. MDA content (abs) in spirulina biomass by introducing AuNPs into culture medium on the first day of cultivation, on the 3rd day of cultivation, and on the 5th day of cultivation. In the experimental variant with the introduction of Au nanoparticles on the first day of cultivation, measurement of MDA contents showed a nonlinear trend, the correlation with AuNPs concentrations being strong, r=0.731. The MDA content in spirulina biomass doubled after exposure to nanoparticles compared to control values. Adding concentrations of 15 - 20 μM AuNPs generated an increase in MDA content of more than 150%. The oxidative degradation of lipids led to cellular overproduction of reactive oxygen species as a result of excessive activity of Au nanoparticles. In the experimental variant with the introduction of AuNPs on the 3rd day of cultivation, MDA content increased by 45 - 70% in samples with 10 - 20 μM AuNPs, the correlation being strong linear, r=0.868. The MDA values determined in the culture supplemented with AuNPs on the 3rd day of cultivation were lower compared to the values obtained with the addition of nanoparticles on the first day of the cultivation cycle. In the experimental variant with the introduction of nanoparticles on the 5th day of cultivation, changes in MDA content showed a nonlinear trend. No significant change in MDA content (a slight increase by 18 %) was observed in spirulina biomass under all applied concentrations of nanoparticles. During the stationary growth phase, the biosynthetic activity of spirulina was reduced, which did not favor the involvement of nanoparticles in this process.