Fu-Qiang Peng

Biotransformation of progesterone and norgestrel by two freshwater microalgae (Scenedesmus obliquus and Chlorella pyrenoidosa): transformation kinetics and products identification.

Natural and synthetic steroid hormones such as progesterone and norgestrel in the aquatic environment may cause adverse effects on aquatic organisms. This study investigated the biotransformation of progesterone and norgestrel in aqueous solutions by two freshwater microalgae Scenedesmus obliquus and Chlorella pyrenoidosa and elucidated their transformation mechanisms. More than 95% of progesterone was transformed by the two microalgae within 5d. For norgestrel, almost complete transformation by S. obliquus was observed after 5 d, but nearly 40% was remained when incubated with C. pyrenoidosa. The results also showed that these two compounds were not accumulated in the algal cells. Biotransformation was found to be the main mechanism for their loss in the aqueous solutions, and it followed the first-order kinetic model. For progesterone, three main transformation products, i.e. 3β-hydroxy-5α-pregnan-20-one, 3,20-allopregnanedione and 1,4-pregnadiene-3,20-dione, and six minor androgens were identified. For norgestrel, only two transformation products, 4,5-dihydronorgestrel and 6,7-dehydronorgestrel, were identified for the first time. Hydroxylation, reduction and oxidation are proposed to be the main transformation pathways. Among the two microalgae species, S. obliquus was found more efficient in the transformation of the two target compounds than C. pyrenoidosa. The results clearly demonstrated the capability of the two microalgae to transform the two progestogens. The biotransformation and products could have significant environmental implications in the fate and effects of the two steroids.

Ferrate(VI) oxidation of tetrabromobisphenol A in comparison with bisphenol A

Ferrate(VI) (Fe(VI)) oxidative removal of various organic micropollutants mainly depends on the reactivity of Fe(VI) to target micropollutants and coexisting constituents present in source water. This study evaluated the potential of Fe(VI) oxidation of the brominated flame retardant tetrabromobisphenol A (TBBPA) by using reaction kinetics, products identification and toxicity evaluation, and investigated the influencing effects of humic acid and clay particles on Fe(VI) removal of TBBPA in comparison with bisphenol A (BPA). The obtained apparent second-order rate constants (k(app)) for Fe(VI) reaction with TBBPA ranged from 7.9(±0.3) × 10(3) M(-1) s(-1) to 3.3(±0.1) × 10(1) M(-1) s(-1) with the half-life (t1/2) ranging from 1.7 s to 419.3 s at pH 7.0-10 for an Fe(VI) concentration of 10 mg L(-1). Easier oxidation by Fe(VI) was observed for TBBPA than for BPA. Fe(VI) can destroy and transform the TBBPA molecule through β-scission reaction, yielding the chemical species of low bromine-substituted products. More importantly, the oxidation of TBBPA by Fe(VI) led to the loss of its multiple hormonal activities (androgenic, antiestrogenic and antiandrogenic activities). The organic component humic acid decreased the TBBPA and BPA reactions with Fe(VI), while the inorganic component montmorillonite had no effect on their removal within the tested concentrations. Increasing the Fe(VI) dosage can reduce the effects of soluble organic matter and clay particles present in source waters on the degradation process, leading to the complete removal of target micropollutants.

Cellular responses and bioremoval of nonylphenol and octylphenol in the freshwater green microalga Scenedesmus obliquus.

The removal of nonylphenol (NP) and octylphenol (OP) by the freshwater green microalga Scenedesmus obliquus was studied in cultures exposed to different concentrations of NP and OP for 5 days. In most cases, low NP and OP concentrations (<1 mg/L) did not affect the growth, fluorescence transient (F(v)/F(m)), photosynthetic pigments and cell ultrastructure of S. obliquus, whereas high NP and OP concentrations (>1 mg/L) suppressed algal growth, decreased F(v)/F(m) and photosynthetic pigments, and destroyed algal ultrastructure. S. obliquus had a rapid and high ability to remove NP and OP. After 5 days of culturing, >89 percent NP and >58 percent OP were removed by this alga, with the highest removal efficiency being near 100 percent. The removal of NP and OP was mainly caused by algal degradation. Extracellular NP contents of S. obliquus were lower than intracellular NP contents, with the ratios changing from 0 to 0.74. However, most of extracellular OP contents of S. obliquus were higher than intracellular OP contents, with the ratios changing from 0.74 to 2.15. The two alkylphenols exhibited a high bioconcentration potential, with one-day bioconcentration factors (BCF) of NP and OP varying between 3393 to 13262 and 949 to 3227, respectively. After 5 days of culturing, high BCF values were still recorded when NP and OP initial concentrations were higher than 0.5 mg/L. These results demonstrated potential application of this algal species in the removal of organic contaminants including alkylphenols in addition to nutrients and metals.

Biotransformation of the flame retardant tetrabromobisphenol-A (TBBPA) by freshwater microalgae

Tetrabromobisphenol-A (TBBPA) is the most widely used brominated flame retardant. However, little is known about its biotransformation by algae in aquatic environments. The authors investigated transformations of TBBPA by 6 freshwater green microalgae and identified its transformation products. Transformation experiments were conducted under axenic conditions in a laboratory for 10 d. The results showed that TBBPA could be transformed by the selected microalgae, with nearly complete removal by Scenedesmus quadricauda and Coelastrum sphaericum following 10-d incubation. Five transformation products were positively identified by mass spectrometry: TBBPA sulfate, TBBPA glucoside, sulfated TBBPA glucoside, TBBPA monomethyl ether, and tribromobisphenol-A. The mechanisms involved in the biotransformation of TBBPA include sulfation, glucosylation, O-methylation, and debromination, which could be an important step for its further degradation. This suggests that microalgae can play an important role in the fate of TBBPA in aquatic environments. The present study is the first report on algal transformation of TBBPA, and the proposed transformation products could have significant environmental implications.

Degradation of Norgestrel by Bacteria from Activated Sludge: Comparison to Progesterone

Natural and synthetic progestagens in the environment have become a concern due to their adverse effects on aquatic organisms. Laboratory studies were performed to investigate aerobic biodegradation of norgestrel by bacteria from activated sludge in comparison with progesterone, and to identify their degradation products and biotransformation pathways. The degradation of norgestrel followed first order reaction kinetics (T1/2 = 12.5 d), while progesterone followed zero order reaction kinetics (T1/2 = 4.3 h). Four and eight degradation products were identified for norgestrel and progesterone, respectively. Six norgestrel-degrading bacterial strains (Enterobacter ludwigii, Aeromonas hydrophila subsp. dhakensis, Pseudomonas monteilii, Comamonas testosteroni, Exiguobacterium acetylicum, and Chryseobacterium indologenes) and one progesterone-degrading bacterial strain (Comamonas testosteroni) were successfully isolated from the enrichment culture inoculated with aerobic activated sludge. To our best knowledge, this is the first report on the biodegradation products and degrading bacteria for norgestrel under aerobic conditions.