Photodegradation of fluorene in aqueous solution: Identification and biological activity testing of degradation products

• Degradation of fluorene under UV–vis irradiation in water was investigated.
• Twenty six photoproducts were characterized using GC–MS coupling.
• Competing photodegradation pathways of fluorene under UV–vis irradiation have been suggested.
• Some photoproducts of fluorene are biologically much more active than the parent compound.

Degradation of fluorene under UV–vis irradiation in water was investigated and structural elucidation of the main photoproducts was achieved using gas chromatography coupled with mass spectrometry. Twenty-six photoproducts were structurally identified, mainly on the basis of electron ionization mass spectra interpretation. The main generated transformation products are hydroxy derivatives. Some secondary photoproducts including fluorenone, hydroxy fluorenone, 2-biphenyl carboxylic acid, biphenylene, methanol fluorene congeners and hydroxy fluorene dimers were also observed. A photodegradation pathway was suggested on the basis of the chemical structures of photoproducts. Fluorene as well as its main photoproducts for which chemical standards were commercially available were tested for their ability to elicit cytotoxic, estrogenic and dioxin-like activity by using in vitro cell-based bioassays. None of the tested compounds was cytotoxic at concentrations up to 100 μM. However, 2-hydroxyfluorene and 3-hydroxyfluorene exerted significant estrogenic and dioxin-like activity on a concentration range of 3–30 μM, while fluorene and 9-hydroxyfluorene were weakly or not active, respectively, in our assays. This supports the view that photodegradation processes can generate by-products of higher toxicological concern than the parent compound and strengthens the need to further identify transformation products in the aquatic environment.