Abstract
The freshwater flagellate alga Euglena agilis Carter was exposed to the polycyclic aromatic hydrocarbon (PAH) anthracene for 96 h under optimal photosynthetically active radiation (PAR), and responses of growth, photosynthetic pigment production, and photosynthetic efficiency were assessed. Anthracene reduced the growth rate (μ) and levels of chlorophyll a (Chl a), chlorophyll b (Chl b), and total carotenoids. The growth rate was more sensitive than photosynthetic parameters, with a median effective concentration (EC50) of 4.28 mg L−1. Between 5 and 15 mg L−1, anthracene inhibited the maximum quantum yield (Fv/Fm) of photosystem II (PSII) and the maximum photosynthetic electron transport rate through PSII (rETRmax) with EC50 values of 14.88 and 11.8 mg L−1, respectively. At all anthracene concentrations, intracellular reactive oxygen species (ROS) were elevated, indicating increased oxidative stress. Anthracene presumably reduced the PSII efficiency of photochemical energy regulation and altered the photochemistry through intracellular ROS formation. Acute exposure to PAHs may induce severe physiological changes in phytoplankton cells, which may influence vital ecological processes within the aquatic environments. Additionally, growth and Chl a content may serve as sensitive risk assessment parameters of anthracene toxicity in water management since EC50 values for both overlap with anthracene levels (8.3 mg L−1) permitted by the US Environmental Protection Agency (USEPA).
Highlights
The freshwater flagellate alga Euglena agilis Carter was exposed to the polycyclic aromatic hydrocarbon (PAH) anthracene for 96 h under optimal photosynthetically active radiation (PAR), and responses of growth, photosynthetic pigment production, and photosynthetic efficiency were assessed
Any severe reduction in these parameters will be followed by a loss of ecological competence and diminished survival of the entire E. agilis population, which could have a devastating impact on associated food chains
Five principal conclusions derived from this study are: (1) The addition of anthracene resulted in a concentration-dependent reduction in cellular growth which appears to be highly related to a reduction in photosynthesis
Summary
The freshwater flagellate alga Euglena agilis Carter was exposed to the polycyclic aromatic hydrocarbon (PAH) anthracene for 96 h under optimal photosynthetically active radiation (PAR), and responses of growth, photosynthetic pigment production, and photosynthetic efficiency were assessed. Anthracene adversely affects the growth and photosynthesis of natural phytoplankton communities, with a toxicity threshold value less than its aqueous solubility[1] It is one of the most rapidly modified hydrocarbons and is assumed to be a strong photosensitizer[5] that induces intracellular oxidative stress and blockage of the photosynthetic electron transport chain[6] through the formation of ROS. Microalgae are an important group of primary producers in aquatic habitats that play a pivotal role in aquatic ecosystems, forming the food and energy base for all organisms, and powering food webs and biogeochemical cycling They are readily exposed to toxic waterborne contaminants and tend to reach an equilibrium with pollutants rather rapidly because they are small with a proportionally large surface area[9].
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