Ecotoxicological impact of naproxen on Eisenia fetida: Unraveling soil contamination risks and the modulating role of microplastics.

Soils represent crucial sinks for pharmaceuticals and microplastics, making them hotspots for pharmaceuticals and plastic pollution. Despite extensive research on the toxicity of pharmaceuticals and microplastics individually, there is limited understanding of their combined effects on soil biota. This study focused on the earthworm Eisenia fetida as test organism to evaluate the biotoxicity and bioaccumulation of the typical pharmaceutical naproxen and microplastics in earthworms. Results demonstrated that high concentrations of naproxen (100 mg kg-1) significantly increased the malondialdehyde (MDA) content, inducing lipid peroxidation. Even though the low exposure of naproxen exhibits no significant influence to Eisenia fetida, the lipid peroxidation caused by higher concentration than environmental relevant concentrations necessitate attention due to temporal and spatial concentration variability found in the soil environment. Meanwhile, microplastics caused oxidative damage to antioxidant enzymes by reducing the superoxide dismutase (SOD) activity and MDA content in earthworms. Metabolome analysis revealed increased lipid metabolism in naproxen-treated group and reduced lipid metabolism in the microplastic-treated group. The co-exposure of naproxen and microplastics exhibited a similar changing trend to the microplastics-treated group, emphasizing the significant influence of microplastics. The detection of numerous including lipids like 17-Hydroxyandrostane-3-glucuronide, lubiprostone, morroniside, and phosphorylcholine, serves to identify potential biomarkers for naproxen and microplastics exposure. Additionally, microplastics increased the concentration of naproxen in earthworms at sub-organ and subcellular level. This study contributes valuable insights into the biotoxicity and distribution of naproxen and microplastics in earthworms, enhancing our understanding of their combined ecological risk to soil biota.

The combined toxicity of silver nanoparticles and typical personal care products in diatom Navicula sp.

Toxicity of silver nanoparticles (AgNPs) at environmentally relevant concentrations has been received an increasing attention, and their influence on the bioavailability of personal care products has been seldom studied. Here, the toxicity of AgNPs in typical diatom Navicula sp. was explored, and their influence on the bioavailability of typical personal care products such as triclosan (TCS) and galaxolide (HHCB) was also investigated. The underlying toxicity mechanisms were explored using liquid chromatography-mass spectrometry (LC-MS)-based metabolomics. Low concentrations of AgNPs (10 and 50 µg L-1) induced no observable responses of Navicula sp., in terms of growth rate, chlorophyll contents, and malondialdehyde accumulation. Furthermore, low doses of AgNPs could attenuate TCS or HHCB toxicity to Navicula sp., which was mainly attributed to the reduced oxidative stress. Metabolomics revealed that the disruption of DNA or RNA synthesis and instability of cytokinin-like substances may be also the reasons for the toxicity of AgNPs and TCS to Navicula sp. The damaged algal photosynthesis exposed to HHCB may be recovered by AgNPs, and the presence of signal chemicals (dehydrophytosphingosine and cardamonin) also showed a recovered algal growth. These results emphasize the potential of metabolomics to reveal toxicity mechanism, providing a new perspective on the aquatic risk assessment of nanoparticles and emerging organic pollutants.

Individual and combined toxicity of silver nanoparticles and triclosan or galaxolide in the freshwater algae Euglena sp.

With the widespread production and usage, silver nanoparticles (AgNPs) can be extensively found in the aquatic environment and co-exist with other pollutants for a prolonged time, leading to a more complex ecological risk in natural waters. In this work, the model freshwater algae Euglena sp. was selected to study the toxicity of AgNPs and explore their influences on the toxicity of two frequently detected personal care products, triclosan (TCS) and galaxolide (HHCB). The LC-MS targeted metabolomics was used to analyze the possible toxicity mechanism at the molecular level. Results showed that AgNPs was toxic to Euglena sp. upon 24 h exposure, but the toxicity decreased gradually as exposure times increased. AgNPs (<100 µg L-1) attenuated TCS and HHCB toxicity to Euglena sp., which could be attributed primarily to the decreased oxidative stress. Metabolomic analysis revealed that AgNPs induced a stress on algal defense system upon TCS exposure, but promoted the algal defense system upon HHCB exposure. Furthermore, DNA or RNA biosynthesis was accelerated in algae exposed to TCS or HHCB after the addition of AgNPs, implying that AgNPs may mitigate the genetic toxicity of TCS or HHCB in Euglena sp. These results emphasize the potential of metabolomics to reveal toxicity mechanism and provide new perspectives on the aquatic risk assessment of personal care products in the presence of AgNPs.

Size-dependent effect of microplastics on toxicity and fate of diclofenac in two algae.

Microplastics (MPs) are frequently detected in natural waters and usually acted as vectors for other pollutants, leading to possible threats to aquatic organisms. This study investigated the impact of polystyrene MPs (PS MPs) with different diameters on two algae Phaeodactylum tricornutum and Euglena sp., and the combined toxicity of PS MPs and diclofenac (DCF) in two algae was also studied. Significant inhibition of P. tricornutum was observed after 1 d exposure of 0.03 µm MPs at 1 mg L-1, whereas the decreased growth rate of Euglena sp. was recovered after 2 d exposure. However, their toxicity decreased in the presence of MPs with larger diameters. The oxidative stress contributed a major for the size-dependent toxicity of PS MPs in P. tricornutum, while in Euglena sp. the toxicity was mainly caused by a combination of oxidative damage and hetero-aggregation. Also, PS MPs alleviated the toxicity of DCF in P. tricornutum and the DCF toxicity continually decreased as their diameter increased, whereas the DCF at environmentally concentration could weaken the toxicity of MPs in Euglena sp. Moreover, the Euglena sp. revealed a higher removal for DCF, especially in the presence of MPs, but the higher accumulation and bioaccumulation factors (BCFs) indicated a possible ecological risk in natural waters. The present study explored discrepancy on the size-dependent toxicity and removal of MPs associated with DCF in two algae, providing valuable data for risk assessment and pollution control of MPs associated with DCF.

Bioaccumulation, internal distribution and toxicity of bisphenol S in the earthworm Eisenia fetida.

Due to the strict rules and restrictions on the utilization of bisphenol A (BPA) around the world, an emerging endocrine disrupting chemical, bisphenol S (BPS) has been widely utilized as a substitute and frequently detected in the environment, even in the human body. Although it has been widely studied in the aquatic systems, the fate and toxicological effect of BPS in soil invertebrates are poorly known. This study presented a comprehensive exploration into the attenuation, bioaccumulation, and physiological distribution of BPS in an ecologically significant soil invertebrate, as well as its subsequent ecotoxicological effect to earthworm for the first time. The E. fetida could promote the BPS attenuation in soil, with degradation rates of 92.8 ± 1.6 % and 98.6 ± 1.1 % at dosage of 1.0 mg/kg dry weight soil (DWS) and 0.1 mg/kg DWS, respectively. The bioaccumulation of BPS in the earthworm was up to 111.6 ± 6.0 mg/kg lipid and 12.9 ± 2.9 mg/kg lipid with the initial dosage of 1.0 mg/kg DWS and 0.1 mg/kg DWS, respectively. Furthermore, BPS could induce oxidative stress and the process of antioxidant defense in earthworm cells at relatively high dose (1.0 mg/kg DWS and 10.0 mg/kg DWS), suggesting potential risks of BPS to the soil environment. This study could contribute to a more in-depth understanding of the fate of BPS in soil-earthworm system, and indicate a necessity for better understanding the environmental fate and ecological risks of BPA substitutes in the future.

Phytotoxicity and accumulation of BPS to Pistia stratiotes under the influence of microplastics.

Bisphenol S (BPS) is a contaminant of emerging concern, its exposure and phytotoxicity towards plants, however, is scarce. This study aimed at revealing the BPS translocation in plants and phytotoxicity in the presence of Polystyrene (PS) microplastics. Results found that BPS and PS showed no effect on plant growth, indicating the tolerance of plants towards BPS and PS co-contamination. In addition, plants enriched BPS from soil, and a major part of absorbed BPS was accumulated in roots, as supported by the higher BCF value in roots compared with leaves. Besides, the low TF (<1) suggested the capacity of plants to accumulate BPS in roots, and less translocation to leaves. PS negatively affected the translocation of BPS in plants. PS with large size (5 µm) also increased the distribution of BPS in organelles. Exposure risk assessment suggested low concern of BPS carried in plants to human health. This study underlines the bioaccumulation of BPS in plants, and the effects of PS in the translocation process.

Distribution profiles of bisphenols in school supplies and implications for human exposure.

Bisphenol compounds (BPs) are usually applied in the production of school supplies, however, little is known on the occurrence of BPs in school supplies. In this study, 15 BPs were detected in 121 samples of school supplies collected from commercial market. Among all compounds studied, BPA, BPF, and BPS were the dominant compounds in school supplies with the detection frequency of 93.15 %, 85.62 % and 82.53 %, respectively, and at median concentrations of 161, 23.64 and 14.11 ng g-1 dw. The total concentrations of BPs varied among types of school supplies in the following order: paper (median: 1347 ng g-1 dw) > fabric (521.4 ng g-1 dw) > plastic (472.7 ng g-1 dw) > rubber (352.4 ng g-1 dw). Risk assessment of BPs in school supplies was evaluated by the estimated daily intake (EDI) via dermal absorption, and the median EDIs of ∑15 BPs were 156.78 ng d-1 (11.27-37,042.37 ng d-1) and 432.75 ng d-1 (32.44-91,624.22 ng d-1) for general and occupational people, respectively.

Biological responses of alga Euglena gracilis to triclosan and galaxolide and the regulation of humic acid.

Although the toxicity of triclosan (TCS) and galaxolide (HHCB) in freshwater has been reported, little study is shed light on their molecular toxicity mechanism and the regulation of humic acid (HA). In this work, freshwater algae E. gracilis was selected to explore these processes, and the molecular toxicity mechanism was analyzed by metabolomics. TCS was more toxic to E. gracilis than HHCB at 1 d exposure with the EC50 value of 0.76 mg L-1, but HHCB showed a higher toxicity as the exposure time prolonged. HA could alleviate the toxicity of TCS and HHCB, mainly due to the inhibition of TCS uptake and oxidative stress, respectively. The perturbations on a number of antioxidant defense-related metabolites in response to TCS or HHCB also indicated oxidative stress was a main toxicity mechanism. However, the exposure to HHCB resulted in more pronounced perturbations in the purine metabolism than TCS, implying that HHCB may pose a genetic toxicity on algae. It may explain the higher toxicity of HHCB to algae as the exposure time increased. These findings provide a comprehensive understanding on the ecological risks of TCS or HHCB in natural waters.

Bisphenol S degradation in soil and the dynamics of microbial community associated with degradation.

Bisphenol S (BPS) has been widely applied as a replacement for BPA in industrial application, leading to the frequent detection in the environment. However, its impact on soil microbial communities has not been well reported. Here, effects of BPS exposure on soil microbial communities in the presence of polystyrene (PS) microplastics were revealed. Rapid degradation of BPS occurred with a degradation rate of up to 98.9 ± 0.001 % at 32 d. The presence of BPS reduced the diversity of soil microbial communities, and changed community structures. After BPS treatment, Proteobacteria, and its members Methylobacillus, Rhodobacteraceae and Mesorhizobium became dominant, and were considered as potential biomarkers indicating BPS contamination. Co-occurrence network analysis revealed the increased relationships of certain groups of microbes after BPS treatment. The resultant low stability and resilience towards environment disturbance of microbial community networks implied the biotoxicity of BPS towards soil ecosystems. The degradation and biotoxicity of BPS (p > 0.05) in soil was not affected by the presence of PS. Our findings showed that exposure to BPS could reshape soil microbial communities and impair the robustness of microbial co-occurrence networks.

Microplastics altered contaminant behavior and toxicity in natural waters.

Microplastics (MPs) have received an increasing attention because of their ubiquitous presence and aquatic toxicity associated with MPs and MP-bound contaminants in the natural water. This review is to critically examine the chemical additives leached from MPs, the altered contaminant behaviors and the resulting changes in their aquatic ecotoxicity. Available data suggest that heavy metals Zn, Cr, Pb, and Cd regulated and present in plastics at the sub-mg g-1 to mg g-1 level can leach a significant amount depending on MPs size, aging, pH, and salinity conditions. MP-bound organic contaminants are primarily additive-derived (e.g., brominated diphenyl ethers, nonylphenol, and bisphenol A) at the µg g-1 to mg g-1 level, and secondarily pyrogenic and legacy origins (e.g., PAHs and PCBs) in the range of ng g-1 and mg g-1. MPs tend to have higher but more variable sorption capacities for organic compounds than metals (1.77 ± 2.34 vs. 0.82 ± 0.94 mg g-1). MPs alter the behavior of heavy metals through the electrostatic interactions and surface complexation, while the transport of additive derived organic compounds are altered primarily through hydrophobic effect as supported by a positive correlation (R2 = 0.71) between the logarithmic MPs-adsorbed concentrations and octanol/water partition coefficients (KOW) of organic compounds. MPs constitute less than 0.01% of the total mass of aquatic particulates in typical waters, but play a discernible role in the local partitioning and long-distance movement of contaminants. MPs alone exert higher toxicity to invertebrates than algae; however, when MPs co-occur with pollutants, both synergistic and antagonistic toxicities are observed depending mainly on the ingestibility of MPs, the extent of sorption, MPs as a transport vector or a sink to scavenge pollutants. We finally suggest several key areas of future research directions and needed data concerning the role of MPs in mitigating pollutant leaching, transport and risk under conditions mimicking natural and polluted waters.

Sorption of diclofenac by polystyrene microplastics: Kinetics, isotherms and particle size effects.

Diclofenac (DCF) is a common pharmaceutical that widely distributed in natural waters, and has been received an increasing attention because of its potential toxicity. Additionally, microplastics are also ubiquitous pollutants in natural waters, but little information is available on their interactions. In this study, the sorption of DCF on polystyrene microplastics (PS MPs) with different particle sizes was investigated, and the influence of environmental factors was also explored. Results indicated that the pseudo-second-order kinetic model was suitable to describe the sorption process. The sorption capacity increased with the increase in particle size. The isotherms data for the sorption of DCF on 0.5 and 1 µm PS MPs were best fitted with the Dubinine-Radushkevich model, but the Freundlich and Langmuir models could best describe the sorption of DCF 5 and 20 µm PS MPs, respectively. It is suggested that the sorption was a chemisorption, which is also verified by Fourier transform infrared spectroscopy (FTIR) results. Furthermore, the sorption capacity decreased as pH increased, and increased as ionic strength increased. These findings give a new perspective that the microplastics with larger sizes hold promise for the treatment of DCF-contaminated water.

Toxic effect of fluorene-9-bisphenol to green algae Chlorella vulgaris and its metabolic fate.

Fluorene-9-bisphenol (BHPF), a bisphenol A (BPA) alternative, has recently attracted attention due to its wide use and potential toxicity. However, the toxic effects and fate of BHPF in freshwater algae remains to be elucidated. In this study, the impact of BHPF on Chlorella vulgaris was explored and the removal and bioaccumulation of BHPF by Chlorella vulgaris were investigated. Results showed that C. vulgaris was sensitive to BHPF at the concentration of >1 mg L-1, and lipid peroxidation was significantly increased under the exposure of >0.1 mg BHPF L-1. An oxidative stress was caused by BHPF, as the activities of superoxide dismutase (SOD) were significantly decreased in algal cells by >0.5 mg BHPF L-1. The removal rate of BHPF was significantly enhanced by the addition of algae. In addition, the increasing accumulation of BHPF in algae at concentrations ranging from 0.5 to 5 mg L-1 was observed and may contribute for the increased toxicity of BHPF to C. vulgaris. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) results demonstrated that three metabolites of BHPF were identified in algal cells, which may pose an unexpected effect in aquatic environment.

Comparative study on the toxicity and removal of bisphenol S in two typical freshwater algae.

Bisphenol S (BPS), one of the most widely used bisphenol A substitutes, has recently received more attention because of its high detection in water and potential toxicity. In the present study, the toxicity and removal of BPS in typical freshwater algae Navicula sp. were investigated under laboratory conditions and the comparative study with Chlorella vulgaris was also explored. BPS was more toxic to Navicula sp. than C. vulgaris with their 120-h EC50 values of 3.89 and 25.19 mg/L, respectively. It may be mainly ascribed to the high tolerance of C. vulgaris to BPS. For instance, the superoxide dismutase (SOD) and catalase (CAT) activities of C. vulgaris were increased under the exposure of 20 mg BPS/L, whereas they were increased in Navicula sp. at 1 mg BPS/L. It is implied that the detoxification mechanism of C. vulgaris was activated until BPS concentration reach to 20 mg L-1. Moreover, the results had demonstrated that both algae had promoted the removal of BPS at 0.5 mg/L, but the removal could be inhibited as BPS concentration increased. Navicula sp. presented a better removal of BPS because of their higher accumulation, implying that they may be good materials for the removal of BPS. In addition, the sharp increase of BCF value at 72 h in Navicula sp. under the exposure of environmental-related BPS concentration (0.5 mg/L) may indicate a high risk of BPS to aquatic ecosystem. These findings will provide a reference for the risk assessment of BPS in natural waters.

Occurrence and removal of bisphenol analogues in wastewater treatment plants and activated sludge bioreactor.

The occurrence and removal of ten bisphenol analogues (BPs) in municipal wastewater treatment plants (WWTPs) and laboratory scale activated sludge bioreactor (ASBR) were studied. All targeted BPs except for tetrachlorobisphenol A (TCBPA) were detected in the four WWTPs (W1, W2, W3 and W4) in the ng/L and ng/g dry weight range in wastewater and activated sludge, respectively, indicating that in addition to BPA, the BPA substitutes were widely used in our daily life and industrial production. Discrepant results regarding the removal efficiencies of BPs by different wastewater treatment processes were obtained. The removal rates were 55.6%, 24.4%, -10.1%, 71.4%, 38.9%, 58.0%, 39.1% and 6.4% in W1, 65.4%, 32.8%, 44.7, -13.5%, 20.1%, -29.6%, -25.1% and 99.4% in W2, 11.6%, 48.8%, 38.9%, 22.0%, 99.0%, -29.2%, -56.5% and 32.6% in W3, 33.9%, 30.5%, 17.4%, -47.6%, 62.9%, 83.0%, 4.4% and -4.3% in W4, for BPA, BPB, BPE, BPF, BPS, BPZ, BPAF and BPAP, respectively. The removal of ten targeted BPs in lab-scale continuous flow conventional ASBR and the key factors were investigated. The simulated laboratory-scale ASBR were highly effective in removing BPA, BPB, BPE, BPF, BPM and BPS with removal efficiencies of >94.3%, while BPZ, BPAP, BPAF and TCBPA were recalcitrant to elimination in the stimulated bioreactor with removal efficiencies of 71.3 ± 13.7%, 55.1 ± 21.2%, 47.4 ± 9.5% and 45.3 ± 16.6%, respectively. Protonation, hydrophobicity and molecular features of BPs were critical for their elimination in wastewater.

Toxicity and biotransformation of bisphenol S in freshwater green alga Chlorella vulgaris.

Safety and environmental behavior of bisphenol A (BPA) alternatives have attracted considerable attention because of their wide use. In the present study, toxicity and biotransformation of bisphenol S (BPS), a primary alternative to BPA, in Chlorella vulgaris were investigated. BPS had a significant inhibition on the growth rate of C. vulgaris with an inhibition rate of 41.6%, 103.7% and 238.4% under exposure of 1, 10 and 100 mg L-1 BPS, respectively. BPS (2 d EC50: 3.16 mg L-1) had a higher acute toxicity to C. vulgaris than BPA (2 d EC50: 41.43 mg L-1), but its toxicity was gradually lower than BPA as the exposure time increased. BPS underwent rapid degradation and was more recalcitrant to degradation by C. vulgaris than BPA at 5 and 10 mg L-1. BPS was less accumulated in algal cells than BPA (p < 0.05), suggesting that it may pose less risk than BPA on the aquatic algophagous organisms and other high-trophic-level predators through the food chain. In addition, six new metabolites of BPS were identified in algal cells using high-resolution mass spectrometry. This is the first time that degradation pathway for BPS in algae is described, and these results represent a significant advance in understanding the fate of BPS and other BPA substitutes in the aquatic environment.

Degradation of Carbendazim in Soil: Effect of Sewage Sludge-Derived Biochars.

Application of biochar in soils can affect the soil properties and, in turn, the fate of pesticides. Batch experiments were conducted to investigate the effect of sewage sludge-derived biochars on the dissipation of a fungicide carbendazim in soil, and the transformation of carbendazim in soil was also studied. Results showed that the dissipation of carbendazim was fastest in a loamy soil SD with a half-life of 11.0 d among the three kinds of soils tested in this study. A dual effect (both acceleration and inhibition) of sewage sludge-derived biochars on carbendazim degradation in soil was reported. The addition of 10% biochars produced at 700 °C (BC 700) in soil could accelerate the carbendazim degradation, but an inhibitory effect was observed for 10% BC 300 or BC 500. Degradation of carbendazim was significantly inhibited when 0.5 or 5% BC 700 was added in soil but accelerated when the amendment ratio of BC 700 was increased to 10%. Such complex effects of the sewage sludge biochar should be taken into consideration in risk assessment of pesticides and the biochar effects on soil remediation. Eight metabolites of carbendazim were characterized, seven of which were reported in unamended soil for the first time. The metabolic pathways of carbendazim in soil are proposed.

Phytotransformation and Metabolic Pathways of 14C-Carbamazepine in Carrot and Celery.

Carbamazepine (CBZ) is an anticonvulsant pharmaceutical compound of environmental concern due to its persistence, bioactive toxicity, and teratogenic effects. Studies on the kinetics and metabolic pathways of CBZ in plant tissues are still limited. In the present study, the phytotransformation of 14C-CBZ was explored. The 14C detected in bound residues was lower than in extractable residues (>85% of the uptaken 14C radioactivity) in plant tissues. CBZ underwent appreciable transformation in plants. A large portion of accumulated 14C radioactivity (80.3 ± 6.4%) in the cells was distributed in the cell water-soluble fraction. A total of nine radioactive transformation products of CBZ were identified, three of which were generated in vivo due to the contraction of the heterocycle ring. The proposed metabolic pathways revealed that conjugation with glutathione or phenylacetic acid was the major transformation pathway of CBZ in plants, with the contribution of epoxidation, hydroxylation, methoxylation, methylation, amination, and sulfonation.

Biosolids inhibit uptake and translocation of 14C-carbamazepine by edible vegetables in soil.

Biosolids are regarded as a major source of pharmaceutically active compounds (PhACs) in soil and may lead to their accumulation in plants and potential human risks through dietary intake. Using 14C labeling, we explored the effect of biosolids on the uptake and tissue distribution of carbamazepine (CAB) by three ready-to-eat vegetables (i.e., carrot, celery, and pak choi) under greenhouse conditions. The 14C-CAB was consistently detected in vegetables and plant tissues with bioconcentration factors in a range of 1.28-37.69, and it was easily translocated from root to leaf and/or stem with translocation factors > 1. The inhibition on the uptake and accumulation of 14C-labeled carbamazepine from soil by the addition of biosolids was consistently observed, and such inhibitory effect was related to the biosolid amendment rates, the category of vegetable, and the plant growth stages. The influence of biosolids on behavior of CAB and other emerging pollutants in the soil-plant system should be considered in their environmental risk assessment.

Biological removal of pharmaceuticals by Navicula sp. and biotransformation of bezafibrate.

Pharmaceutically active compounds are of great concern due to their detection frequency in the environment and the unexpected risks. In this study, the simultaneous removal of mixed pharmaceuticals by microalgae was explored using a typical freshwater diatom Navicula sp. Results showed that Navicula sp. could efficiently remove atenolol, carbamazepine, ibuprofen and naproxen with the efficiencies of >90% after 21 d of exposure. As compared to the removal efficiencies of each pharmaceutical in the individual pharmaceutical treatments, the degradation of sulfamethoxazole, bezafibrate, and naproxen was improved in the mixed treatment, whereas the removal efficiencies of carbamazepine and atenolol decreased. Additionally, the presence of hydrophobic pharmaceuticals (i.e., ibuprofen and naproxen) accelerated the degradation of carbamazepine and sulfamethoxazole and inhibited the removal of atenolol in the mixture with the combination of six pharmaceuticals, while the addition of other pharmaceuticals show no significant effect on the removal of ibuprofen and naproxen. The bioaccumulation of pharmaceuticals in Navicula sp. increased as their log KOW values decreased. Four bezafibrate metabolites were identified and the degradation pathways of bezafibrate in diatom were proposed. It is the first report on the metabolism of BEZ in diatom, and further studies on the environmental risk of the metabolites should be investigated.

Algal toxicity, accumulation and metabolic pathways of galaxolide.

Galaxolide (HHCB) is known to be persistent during wastewater treatment and has raised increasing concern due to its high detection frequency in the environment and potentially negative effects. However, little information is available on the degradation of HHCB by algae, the degradation mechanisms and the toxicity of HHCB on algae. In the present study, HHCB was found to be toxic to Navicula sp. and Scenedesmus quadricauda, with a 3 d EC50 of 0.050 and 0.336 mg L-1, respectively. Both microalgae showed high removal efficiency (72.9-100%) for HHCB. S. quadricauda showed a more satisfactory effect in the bioremediation of HHCB than Navicula sp. A total of four metabolites were found in the biotransformation processes of HHCB, and its possible metabolic pathways were proposed. Hydroxylation, methoxylation, methylation, ketonization, demethylation, and oxaloacetate conjunction contributed to the metabolism of HHCB in algal cells.