Toxicity potential assessment of silicon dioxide (SiO2) and zinc oxide (ZnO) on green microalgae Chlamydomonas sp. strain GO1.

Abstract

Due to the variety of applications for nanomaterials (NMs) and ultrafine solids, their amounts released into the environment is constantly increasing, and their impact on ecosystems and organisms has led to remarkable problems. However, extensive studies on the effects of dispersed ultrafine inorganic metal oxides on algal growth at cellular and genomic levels still need to be performed. We assessed the potential toxicity of two commercial ultrafine inorganic metal oxides, silicon dioxide (SiO₂) and zinc oxide (ZnO), using the single-celled green microalgae Chlamydomonas sp. strain GO1 as a eukaryotic model. The cell response to commercial inorganic oxides was evaluated at physiological, biochemical, and molecular levels. An estimation of population growth inhibition levels was made. After 72 h of exposure, the IC₅₀ of SiO₂ and ZnO were 14.50 ± 2.98 mg/L and 56.80 ± 8.3 mg/L, respectively. Genotoxic effects of the studied materials were evaluated by acridine orange staining method and showed DNA fragmentation and morphological changes, including cell shrinkage and chromatin condensation on microalgae cells treated with both oxide materials. In addition, generated cytotoxic effects were evaluated. An inhibition of microalgae growth and a decrease in cell viability were observed. Antioxidant defense mechanisms, including enzymatic and non-enzymatic, were activated in response to materials exposure. We have also proven an overexpression of genes involved in carbohydrate biosynthesis and apoptosis. Infrared investigation suggested surface chemical interaction between algal cells and commercial ultrafine inorganic oxides.