Abstract
Contamination of aquatic ecosystems linked to anthropogenic activity is currently a major concern; therefore, ecotoxicological studies are needed to assess its effect on organisms. The main objective of this study was to investigate the effects of different pollutants on microalgae in search of sensitive biomarkers that can promote a common cytotoxic response regardless of the contaminant. Cultures of the freshwater microalga Chlamydomonas reinhardtii were exposed for 24 h to four chemicals, three emerging pollutants (benzophenone-3, bisphenol A and oxytetracycline) and one priority substance (atrazine). A cytometric panel was carried out to assess toxicity biomarkers including cellular growth, inherent cell properties, viability, vitality, cytoplasmic membrane potential and ROS levels. Lipid peroxidation, photosynthetic efficiency and transcriptional responses of photosynthesis- and oxidative stress-related genes using RT-qPCR were also studied. Some toxicity responses showed a similar pattern; a decrease in growth rate, vitality and photosynthetic efficiency and an increase in autofluorescence and in the number of cells with depolarised cytoplasmic membrane and were found for all chemicals tested. However, ATZ and OTC provoked a decrease in cell size, whereas BP-3 and BPA caused an increase in cell size, intracellular complexity and ROS levels and a decrease in cell viability. Assayed pollutants generally promoted an overexpression of genes related to cellular antioxidant defence system and a subexpression of photosynthesis-related genes. In addition to the traditional growth endpoint, cell vitality, autofluorescence and gene expression of catalase, glutathione peroxidase and Fe-superoxide dismutase were significantly affected for all chemicals tested, showing a common cytotoxic response. Among the tested substances, BP-3 provoked the strongest cytotoxic alterations on this microalga, pointing out that some emerging contaminants could be more harmful to organisms than priority pollutants.
Highlights
Water pollution and its effect on aquatic ecosystems are currently serious environmental issues to be faced
The European Union (EU) established a framework for Community action in the field of water policy attaching a list of priority substances, which included heavy metals, hydrocarbons or pesticides, whose pres ence in the environment was regulated by law (European Commission, 2000)
The malondialdehyde (MDA), reacts with thiobarbituric acid (TBA), yielding a pink coloured species (Ersan et al, 2006). 45 mL of C. reinhardtii cultures were centrifuged; cells were resuspended in 1 mL of phosphate buffered saline (PBS) and disrupted in a Mini-Beadbeater, with a mixture of glass and zirconium beads and with sonication. 400 μL of supernatant were mixed with 500 μL of 10% trichloroacetic acid (TCA) (w/v) and 250 μL of 0.67% thiobarbituric acid (TBA) (w/v)
Summary
Water pollution and its effect on aquatic ecosystems are currently serious environmental issues to be faced. The European Union (EU) established a framework for Community action in the field of water policy attaching a list of priority substances, which included heavy metals, hydrocarbons or pesticides, whose pres ence in the environment was regulated by law (European Commission, 2000). Atrazine (ATZ), an herbicide widely used in agriculture throughout the world, was included in that list. It acts on photosystem II (PSII), blocking the electron transport chain, inhibiting photosynthesis (Rutherford and Krieger-Liszkay, 2001). Previous studies have reported the negative effects of atrazine on aquatic ecosystems (Esperanza et al, 2017; Graymore et al, 2001; Kabra et al, 2014; Sjollema et al, 2014).
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