Toxicity of single steroid hormones and their mixtures toward the cyanobacterium Microcystis aeruginosa

Several compounds, such as hormones, are released uncontrolled into the aquatic environment, and some of these pollutants have an adverse effect on endocrine systems of humans and other organisms. However, there is insufficient information about the effect of natural and synthetic hormones on non-target organisms, such as cyanobacteria. Therefore, in this study, the adverse effects of hormones, singly and in combination, on Microcystis aeruginosa were explored for the first time. Chronic toxicity was evaluated based on biomass and chlorophyll a measurements during 14 days of exposure. Growth of cyanobacteria after exposure to 0.1-100 mg L-1 of hormones was inhibited in a concentration-dependent manner. In most cases, a low concentration of hormones (0.1-1 mg L-1) did not affect the growth of cyanobacteria, but a higher concentration (> 10 mg L-1) inhibited the growth. The obtained 14-day EC50 values were 88.92-355.15 mg L-1. According to these values, the decreasing order of the toxicity of the eight hormones to tested cyanobacteria was 17-alpha-ethinylestradiol > progesterone > 17 beta-estradiol > 5-pregnen-3 beta-ol-20-one > testosterone> estrone > levonorgestrel > estriol. Moreover, data show that mixed hormones were more toxic than single compounds and more than additive effect was observed. The achieved 14-day EC50 values for mixed hormones were 56.66-166.83 mg L-1. Simultaneous presence of several hormones in the aquatic environment may lead to increased toxicity (more than additive effect) and cause serious ecological effects, more harmful than expected.