Effects of sodium pentaborate pentahydrate exposure on Chlorella vulgaris growth, chlorophyll content, and enzyme activities

• Sodium pentaborate pentahydrate (SPP) was synthesized from a rapid and simple method.
• The effects of synthetic SPP on superoxide dismutase and catalase activities in C. vulgaris had been observed.
• The detrimental effects of synthetic SPP on C. vulgaris was no long-term or irreversible damage.

Sodium pentaborate pentahydrate (SPP) is a rare mineral. In this study, SPP was synthesized from boric acid and borax through low-temperature crystallization, and its effects on the growth of the alga, Chlorella vulgaris (C. vulgaris) were assessed. The newly synthesized SPP was characterized by chemical analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and differential thermal analysis. The changes in C. vulgaris growth, chlorophyll content, and enzyme activities upon exposure to SPP for 168 h were evaluated. Results showed that SPP treatment was detrimental to C. vulgaris growth during the first 24–120 h of exposure. The harmful effects, however, diminished over time (168 h), even at an effective medium concentration of 226.37 mg B L−1 (the concentration of boron applied per liter of culture medium). A similar trend was observed for chlorophyll content (chlorophyll a and b) and indicated that the photosynthesis of C. vulgaris was not affected and that high levels of SPP may even promote chlorophyll synthesis. Superoxide dismutase and catalase activities of C. vulgaris increased during 24–120 h exposure to SPP, but these activities gradually decreased as culture time progressed. In other words, the initial detrimental effects of synthetic SPP on C. vulgaris were temporary and reversible. This research provides a scientific basis for applications of SPP in the environment.