*Article* **Effects of the Ionic Liquid [BMIM]Cl on the Baltic Microphytobenthic Communities**

**Zuzanna Sylwestrzak, Aleksandra Zgrundo \* and Filip Pniewski**

Faculty of Oceanography and Geography, University of Gda ´nsk, Al. Piłsudskiego 46, 81-378 Gdynia, Poland

**\*** Correspondence: aleksandra.zgrundo@ug.edu.pl

**Abstract:** Ionic liquids (IL) are regarded as the solution to the modern world's need to create and use compounds that exhibit a range of desirable properties while having a low environmental impact. However, recent reports are shattering the image of ionic liquids as environmentally friendly substances, especially in relation to the aquatic environment, revealing their potentially toxic effects. To assess the potential environmental impact of ILs, we conducted an experiment involving 1-butyl-3 methylimidazolium chloride ([BMIM]Cl), a substance considered to be the least hazardous among the imidazolium chloride ILs, on Baltic microphytobenthic communities. Microphytobenthos collected from the environment was tested under controlled laboratory conditions, and both the cell counts and the chloroplast condition were used as endpoints. It was shown that [BMIM]Cl at concentrations of 10−<sup>3</sup> and 10<sup>−</sup>2, considered safe based on a cumulative impact assessment, has a negative effect on the condition of the microalgal cells and causes a reduction in population size. Although, under the influence of [BMIM]Cl, only a small proportion of the species was eliminated from the communities, only two species among those important to the communities showed resistance to this compound and eventually began to dominate the communities.

**Keywords:** ionic liquid; IL; [BMIM]Cl; microphytobenthos; microalgal communities; microphytobenthic communities; toxic effect; ecotoxicological test; environmental pollution
