Physiological and biochemical responses of a marine diatom Phaeodactylum tricornutum exposed to 1-octyl-3-methylimidazolium bromide

The marine diatom Phaeodactylum tricornutum is an important basal resource in the marine food chain and is used as a standard test organism in toxicological studies. In this study, in vivo experiments were performed to analyze the effects of 1-octyl-3-methylimidazolium bromide ([C8mim]Br) on the growth, photosynthetic activity, and antioxidant enzymes of P. tricornutum using 96 h growth tests in a batch-culture system. The results showed that [C8mim]Br significantly inhibited the growth of P. tricornutum, with a 96 h EC50 of 8.89 mg l-1, and likely restricts PSII electron transfer and light use efficiency of the diatom. With increasing [C8mim]Br concentrations, the soluble protein content in the diatom increased by 35.9, 58.5, 123.3, 197.7, and 207.0% in 5, 10, 20, 40, and 80 l-1 [C8mim]Br treatments relative to the controls, respectively. Concentrations of [C8mim]Br ≤10 mg l-1 caused a slight increase of superoxide dismutase (SOD) activity (from 16.37 to 23.04 U g-1 protein) in the diatom, but inhibited its activity at concentrations above 10 mg l-1. These observations indicate that moderate [C8mim]Br stress (about 10 mg l-1) likely stimulates the synthesis of proteins and free radical quenching. The general increase in malondialdehyde (MDA) content suggests that the physiological effects of [C8mim]Br were caused by free radical generation. Thus, potential risks exist if [C8mim]Br is accidentally released into the aquatic environment