**4. Transformation and detoxification of PBDEs in plants**

While PBDEs in the atmosphere are photolytically transformed by hydroxylation und subsequent transformation to lower brominated congeners or ring closure to the corresponding dibenzofurans [41, 42] and PBDEs in soil and sediments are mainly mineralized by stepwise debromination or detoxified by hydroxylation (OH-BDE) or methoxylation reactions (MeO-BDE) in the rhizosphere, strongly affected by the degree of bromination, concentration of oxygen, organic matter and microorganisms [43], intrinsic PBDEs in plants can be transformed by the same three transformation pathways. Exemplarily, transformation of BDE-28 and BDE-47 in maize was analyzed in detail by Wang et al. [44]. BDE-47 (Br4) was dominantly converted to 6-MeO-BDE-47 (275 ng∙g−1 DM) in the root phase, followed by 5-MeO-BDE-47 (40 ng∙g−1 DM), ∑Br2-BDEs (23 ng∙g−1 DM), ∑Br3-BDEs (20 ng∙g−1

DM), and small quantities of two unidentified hydroxylated BDEs (8 ng∙g−1 DM) with continued decrease over time, similar to the transformation behavior against BDE-28 (Br3). Similar results were observed in plants of pumpkins, rice, wheat and soybean for BDE-47 and BDE-99 with formation of 5-OH-BDE-47, 6-OH-BDE-47, 4'-OH-BDE-49, 4'-OH-BDE-42, 4-MeO-BDE-42, and BDE-28 in case of BDE-47 as parent congener, and with formation of 4-OH-BDE-99 and 4-MeO-BDE-99 in case of BDE-99 as soil contaminant [45, 46]. The total PBDE levels clearly dropped in all studies. In liver cells, transformation of both low and moderate brominated BDEs was shown by cytochrome P450 monooxygenases and glutathione-S-transferase, two enzyme complexes also found in plants, where they can potentially catalyze the same reactions. However, both enzyme sets were induced by BDE-209, but this congener was not converted [47]. In difference, various study showed comparable PBDE patterns both in soil and plant tissues at almost unchanged concentration levels over time, underlining negligible metabolism of PBDEs in plants [6]. In summary, PBDEs might be transformed in plants by debromination, hydroxylation and methoxylation reactions, but transformation behavior strongly depends on the plant species and the established microbial consortium in the rhizosphere [48].
