Subacute oral toxicity of BDE-15, CDE-15, and HODE-15 in ICR male mice: assessing effects on hepatic oxidative stress and metals status and ascertaining the protective role of vitamin E

The present study examined the effects of oral exposure of 4,4′-dibromodiphenyl ether (BDE-15), 4,4′-dichlorodiphenyl ether (CDE-15), and 4,4′-dihydroxydiphenyl ether (HODE-15) on hepatic oxidative stress (OS) and metal status in Institute of Cancer Research (ICR) male mice. Furthermore, the role of vitamin E in ameliorating potential OS caused by BDE-15, CDE-15, and HODE-15 was investigated. Three groups of mice were exposed to 1.20 mg/kg(body weight)/day of each of the three toxicants for 28 days. Results showed that none of the three toxicants altered growth rates of mice, but significantly increased (P?<?0.05) relative liver weights and decreased relative kidney weights. Pathological changes including cell swelling, inflammation and vacuolization, and hepatocellular hypertrophy in livers were observed. Significant decreases (P?<?0.05 and P?<?0.01) in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activity, and glutathione (GSH) levels, together with increases in malondialdehyde (MDA) content were recorded in all toxicant-treated groups. Hepatic copper levels increased in all toxicant-treated groups. Hepatic zinc levels decreased in the liver of BDE-15-treated mice, whereas they increased in the livers of CDE-15-treated and HODE-15-treated mice. In conclusion, daily exposure to the three toxicants perturbed metal homeostasis and increased OS in mouse liver. Experimental data indicated the hepatic oxidative toxicity of the three toxicants followed the order BDE-15?<?HODE-15?<?CDE-15. Moreover, the study proved that daily supplementation of 50 mg/kg vitamin E is effective to ameliorate the hepatic OS status and metal disturbance in mice.     

Acute oral toxicity and liver oxidant/antioxidant stress of halogenated benzene, phenol, and diphenyl ether in mice: a comparative and mechanism exploration

The lethal doses (LD₅₀s) of fluorinated, chlorinated, brominated, and iodinated benzene, phenol, and diphenyl ether in mice were ascertained respectively under the consistent condition. The acute toxicity of four benzenes orders in fluorobenzene (FB)?<?iodobenzene?<?chlorobenzene≈bromobenzene, that of four phenols orders in 4-iodophenol≈4-bromophenol?<?4-chlorophenol (4-MCP)?<?4-fluorophenol (4-MFP), and that of four diphenyl ethers orders in 4,4′-iododiphenyl ether?<?4,4′-difluorodiphenyl ether?<?4,4′-dichlorodiphenyl ether≈4,4′-dibromodiphenyl ether. General behavior adverse effects were observed, and poisoned mouse were dissected to observe visceral lesions. FB, 4-MCP, and 4-MFP produced toxic faster than other halogenated benzenes and phenols, as they had lower octanol–water partition coefficients. Pathological changes in liver and liver/kidney weight changes were also observed. Hepatic superoxide dismutase, catalase activities, and malondialdehyde level were tested after a 28-day exposure, which reflects a toxicity order basically consistent with that reflected by the LD₅₀s. By theoretical calculation and building models, the toxicity of benzene, phenol, and diphenyl ether were influenced by different structural properties.     

Influence of sediment composition on PAH toxicity using zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes) embryo-larval assays

Due to hydrophobic and persistent properties, polycyclic aromatic hydrocarbons (PAHs) have a high capacity to accumulate in sediment. Sediment quality criteria, for the assessment of habitat quality and risk for aquatic life, include understanding the fate and effects of PAHs. In the context of European regulation (REACH and Water Framework Directive), the first objective was to assess the influence of sediment composition on the toxicity of two model PAHs, benzo[a]pyrene and fluoranthene using 10-day zebrafish embryo-larval assay. This procedure was undertaken with an artificial sediment in order to limit natural sediment variability. A suitable sediment composition might be then validated for zebrafish and proposed in a new OECD guideline for chemicals testing. Second, a comparative study of toxicity responses from this exposure protocol was then performed using another OECD species, the Japanese medaka. The potential toxicity of both PAHs was assessed through lethal (e.g., survival, hatching success) and sublethal endpoints (e.g., abnormalities, PMR, and EROD) measured at different developmental stages, adapted to the embryonic development time of both species. Regarding effects observed for both species, a suitable artificial sediment composition for PAH toxicity testing was set at 92.5 % dry weight (dw) silica of 0.2–0.5-mm grain size, 5 % dw kaolin clay without organic matter for zebrafish, and 2.5 % dw blond peat in more only for Japanese medaka. PAH bioavailability and toxicity were highly dependent on the fraction of organic matter in sediment and of the K _ow coefficients of the tested compounds. The biological responses observed were also dependent of the species under consideration. Japanese medaka embryos appeared more robust than zebrafish embryos for understanding the toxicity of PAHs following a sediment contact test, due to the longer exposure duration and lower sensitivity of sediment physical properties.     

Ligninase-mediated transformation of 4,4′-dibromodiphenyl ether (BDE 15)

The structurally related hydroxylated polybrominated diphenyl ether (PBDE) like hydroxylated 4,4′-dibromodiphenyl ether widely occur in precipitation, surface water, and biotic media. The origins of hydroxylated PBDEs (OH-PBDEs) are of particular interest due to their greater toxic potencies than the corresponding PBDEs. We studied the transformation behavior and products of 4,4′-dibromodiphenyl ether (BDE 15) mediated by lignin peroxidase (LiP), an extracellular enzyme that is produced by certain white rot fungus and is widely present in the natural environment. We found that BDE 15 can be effectively transformed through the reaction mediated by LiP, and two different mono-OH-dibromodiphenyl ethers were identified by using gas chromatography–mass spectrometry (GC-MS) and GC-MS/MS. In particular, we compared the reaction behavior for systems variously containing natural organic matter (NOM) and/or veratryl alcohol (VA), a metabolite that certain fungus produces along with LiP in nature. It was found that the VA’s enhancement effect on LiP performance was impaired by the presence of NOM. The findings in this study provide useful information for better understanding the origins of OH-PBDEs found in the environment.     

Toxicity,uptake, and accumulation of nano and bulk cerium oxide particles in <Emphasis Type="Italic">Artemia salina</Emphasis>

Although the toxicological impact of metal oxide nanoparticles has been studied for the last few decades on aquatic organisms, the exact mechanism of action is still unclear. The fate, behavior, and biological activity of nanoparticles are dependent on physicochemical factors like size, shape, surface area, and stability in the medium. This study deals with the effect of nano and bulk CeO₂ particles on marine microcrustacean, Artemia salina. The primary size was found to be 15 ± 3.5 and 582 ± 50 nm for nano and bulk CeO₂ (TEM), respectively. The colloidal stability and sedimentation assays showed rapid aggregation of bulk particles in seawater. Both the sizes of CeO₂ particles inhibited the hatching rate of brine shrimp cyst. Nano CeO₂ was found to be more toxic to A. salina (48 h LC₅₀ 38.0 mg/L) when compared to bulk CeO₂ (48 h LC₅₀ 92.2 mg/L). Nano CeO₂-treated A. salina showed higher oxidative stress (ROS) than those treated with the bulk form. The reduction in the antioxidant activity indicated an increase in oxidative stress in the cells. Higher acetylcholinesterase activity (AChE) was observed upon exposure to nano and bulk CeO₂ particles. The uptake and accumulation of CeO₂ particles were increased with respect to the concentration and particle size. Thus, the above results revealed that nano CeO₂ was more lethal to A. salina as compared to bulk particles.     

Toxicity of sediment cores from Yangtze River estuary to zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) embryos

Toxicity evaluation is an important segment in sediment quality monitoring in order to protect aquatic organisms and human health. The purpose of this study is to assess the toxicity of sediments from three sediment cores in Yangtze River Estuary, China, using the zebrafish (Danio rerio) embryo tests. Fertilized zebrafish eggs were exposed to both whole sediments and sediment organic extracts prepared from collected sediments, in order to provide a comprehensive and realistic insight into the bioavailable toxicity potential of the sediments. As end points, development parameters (mortality, hatching rate, and abnormality) in the developing embryos were recorded during the 96-h exposure. The results showed that some samples increased mortality, inhibited the hatching of embryos, and induced morphological abnormalities. The embryonic toxicities presented serrated changes and irregular distribution with depth, which may be related to hydrodynamic effect and unstable environmental input. However, lethal and sub-lethal effects were more significant at the sub-surface sediments (10～40 cm), which indicated that the pollution is more serious in recent decades.     

Formetanate toxicity and changes in antioxidant enzyme system of <Emphasis Type="Italic">Apis mellifera</Emphasis> larvae

Substantial percentage of world food production depends on pollinating service of honeybees that directly depends on their health status. Among other factors, the success of bee colonies depends on health of developed larvae. The crucial phase of larval development is the first 6 days after hatching when a worker larva grows exponentially and larvae are potentially exposed to xenobiotics via diet. In the present study, we determined the lethal concentration LC₅₀ (72 h) following single dietary exposure of honeybee larvae to formetanate under laboratory conditions, being also the first report available in scientific literature. Activities of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) were also measured in the homogenates of in vitro reared honeybee larvae after single formetanate exposure. Decreased specific activity of SOD and increased activities of CAT and GST suggest the induction of oxidative stress. Higher levels of thiobarbituric reactive species in all samples supported this fact. Comparing determined larval toxicity (LC₅₀ of 206.01 mg a.i./kg diet) with adult toxicity data, we can suppose that the larvae may be less sensitive to formetanate than the adult bees.     

Median lethal concentration of formaldehyde and its genotoxic potential in bullfrog tadpoles (Lithobates catesbeianus)

In order to avoid that contaminated frog farms animals escaping in the environment and become potential vector of emergent diseases, studies with disinfection protocol are strictly necessary. The formaldehyde is one of the compounds tested in fungal disinfection protocols and also used in aquaculture. This study aimed to determine the median lethal concentration (LC_50–96h) of formaldehyde in bullfrog tadpoles and to evaluate the possible genotoxic effects in acute exposition. Accordingly, the animals were exposed to formaldehyde in the concentrations of 6, 9, 12, 15, and 18 mg L^?1, and after 96 h blood samples were drawn for the micronucleus (MN) test. The LC_50–96h was 10.53 mg L^?1, and the MN frequency increased in proportion to the formaldehyde concentrations, with an estimated frequency in the negative control being 1.35 MN/individual. We concluded that formaldehyde is genotoxic to tadpoles of bullfrogs in the tested concentrations, and the choice of this chemical should be contemplated before its use in animals in captivity.     

Toxicity evaluation of cypermethrin,glyphosate, and malathion,on two indigenous zooplanktonic species

In Aguascalientes, Mexico, there is a special concern about pesticides because of their intensive use on guava production areas, which are located in the vicinity of water reservoirs; thus, non-target organisms could be exposed. Thereafter, the aim of this work was to assess the effect of cypermethrin, Faena® (glyphosate), and malathion, which are the most used pesticides in Aguascalientes’ guava production, on the indigenous freshwater species Alona guttata (cladoceran) and Lecane papuana (rotifer). Acute 48-h toxicity tests were carried out, and LC₅₀ values were calculated. Then, five sublethal concentrations (1/80, 1/40, 1/20, 1/10, and 1/5 of the respective LC₅₀) were selected for the chronic assays: (a) intrinsic growth rate analysis in the rotifer and (b) partial life table analysis in the cladoceran. The results of the acute toxicity tests showed that A. guttata was more sensitive to malathion (LC₅₀ = 5.26 × 10^?3 mg/L) at concentrations found in natural environments with continuous application on guava fields, whereas L. papuana was more sensitive to Faena® (LC₅₀ = 19.89 mg/L). The somatic growth of A. guttata was inhibited for the chronic exposure to cypermethrin. In addition, cypermethrin and Faena® seemed to exert endocrine disruptive effects on A. guttata. Moreover, malathion chronic exposure significantly decreased the survival of A. guttata. Moreover, L. papuana was affected chronically for the three pesticides.     

Developmental toxicity of PAH mixtures in fish early life stages. Part I: adverse effects in rainbow trout

A new gravel-contact assay using rainbow trout, Oncorhynchus mykiss, embryos was developed to assess the toxicity of polycyclic aromatic hydrocarbons (PAHs) and other hydrophobic compounds. Environmentally realistic exposure conditions were mimicked with a direct exposure of eyed rainbow trout embryos incubated onto chemical-spiked gravels until hatching at 10 °C. Several endpoints were recorded including survival, hatching delay, hatching success, biometry, developmental abnormalities, and DNA damage (comet and micronucleus assays). This bioassay was firstly tested with two model PAHs, fluoranthene and benzo[a]pyrene. Then, the method was applied to compare the toxicity of three PAH complex mixtures characterized by different PAH compositions: a pyrolytic extract from a PAH-contaminated sediment (Seine estuary, France) and two petrogenic extracts from Arabian Light and Erika oils, at two environmental concentrations, 3 and 10 μg g^?1 sum of PAHs. The degree and spectrum of toxicity were different according to the extract considered. Acute effects including embryo mortality and decreased hatching success were observed only for Erika oil extract. Arabian Light and pyrolytic extracts induced mainly sublethal effects including reduced larvae size and hemorrhages. Arabian Light and Erika extracts both induced repairable DNA damage as revealed by the comet assay versus the micronucleus assay. The concentration and proportion of methylphenanthrenes and methylanthracenes appeared to drive the toxicity of the three PAH fractions tested, featuring a toxic gradient as follows: pyrolytic?Arabian Light?Erika. The minimal concentration causing developmental defects was as low as 0.7 μg g^?1 sum of PAHs, indicating the high sensitivity of the assay and validating its use for toxicity assessment of particle-bound pollutants.     

Assessment of Jatropha curcas L. biodiesel seed cake toxicity using the zebrafish (Danio rerio) embryo toxicity (ZFET) test

Consequent to the growing demand for alternative sources of energy, the seeds from Jatropha curcas remain to be the favorite for biodiesel production. However, a significant volume of the residual organic mass (seed cake) is produced during the extraction process, which raises concerns on safe waste disposal. In the present study, we assessed the toxicity of J. curcas seed cake using the zebrafish (Danio rerio) embryotoxicity test. Within 1-h post-fertilization (hpf), the fertilized eggs were exposed to five mass concentrations of J. curcas seed cake and were followed through 24, 48, and 72 hpf. Toxicity was evaluated based on lethal endpoints induced on zebrafish embryos namely egg coagulation, non-formation of somites, and non-detachment of tail. The lowest concentration tested, 1 g/L, was not able to elicit toxicity on embryos whereas 100 % mortality (based also on lethal endpoints) was recorded at the highest concentration at 2.15 g/L. The computed LC50 for the J. curcas seed cake was 1.61 g/L. No further increase in mortality was observed in the succeeding time points (48 and 72 hpf) indicating that J. curcas seed cake exerted acute toxicity on zebrafish embryos. Sublethal endpoints (yolk sac and pericardial edema) were noted at 72 hpf in zebrafish embryos exposed to higher concentrations. The observed lethal endpoints induced on zebrafish embryos were discussed in relation to the active principles, notably, phorbol esters that have remained in the seed cake even after extraction.     

Acute toxicity and ecotoxicological risk assessment of rice pesticides to Lithobates catesbeianus tadpoles

The objective of this study was to determine the acute toxicity of some pesticides used in irrigated rice farming to Lithobates catesbeianus tadpoles. The LC_50-96h for commercial formulations containing bentazon, penoxsulam, vegetable oil, permethrin and carbofuran, separately and their mixtures, were determined at the proportions commonly used in the field. The limits of risk concentrations of these products for the studied species were also established. The LC_50-96h for tadpoles was 4,530 mg L^?1 for bentazon; 7.52 mg L^?1 for penoxsulam + 145.66 mg L^?1 of vegetable oil; 81.57 mg L^?1 for vegetable oil; 0.10 mg L^?1 for permethrin; 29.90 mg L^?1 for carbofuran (active ingredients), and 38.79 times the dose used in the field for the mixture of these products. The environmental risk was determined only for permethrin, and care should be taken when using the vegetable oil.     

Long-term disruption of growth,reproduction, and behavior after embryonic exposure of zebrafish to PAH-spiked sediment

A natural sediment spiked with three individual polycyclic aromatic hydrocarbons (PAHs; pyrene, phenanthrene and benzo[a]pyrene) was used to expose zebrafish embryos and larvae during 4 days. The total PAH concentration was 4.4 μg g^?1 which is in the range found in sediment from contaminated areas. Quantification of metabolites in the larvae after exposure confirmed the actual contamination of the larvae and indicated an active metabolism especially for pyrene and benzo[a]pyrene. After a transfer in a clean medium, the larvae were reared to adulthood and evaluated for survival, growth, reproduction, and behavior. Measured endpoints revealed a late disruption of growth (appearing at 5 months) and a trend toward a lower reproductive ability. Adults of embryos exposed to sediment spiked with PAHs displayed lethargic and/or anxiety-like behaviors. This latter behavior was also identified in offspring at larval stage. All together, these effects could have detrimental consequences on fish performances and contribution to recruitment.     

Chronic dietary exposure of zebrafish to PAH mixtures results in carcinogenic but not genotoxic effects

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants that can be present at high levels as mixtures in polluted aquatic environments. Many PAHs are potent mutagens and several are well-known carcinogens. Despite numerous studies on individual compounds, little is known about the toxicity of PAHs mixtures that are encountered in environmental situations. In the present work, zebrafish were continuously fed from 5 days post-fertilisation to 14 months post-fertilisation (mpf) with a diet spiked with fractions of either pyrolytic (PY), petrogenic light oil (LO), or petrogenic heavy oil (HO) origin at three concentrations. A decrease in survival was identified after 3 mpf in fish fed with the highest concentration of HO or LO, but not for PY. All PAH fractions caused preneoplastic and neoplastic disorders in long-term-exposed animals. Target tissues were almost exclusively of epithelial origin, with the bile duct epithelium being the most susceptible to chronic exposure to all PAH fractions, and with germ cells being the second most responsive cells. Significantly higher incidences of neoplasms were observed with increasing PAH concentration and exposure duration. The most severe carcinogenic effects were induced by dietary exposure to HO compared to exposure to LO or PY (45, 30 and 7 %, respectively, after 9 to 10 months of exposure to an intermediate concentration of PAHs). In contrast, earliest carcinogenic effects were detected as soon as 3 mpf after exposure to LO, including the lowest concentration, or to PY. PAH bioactivation and genotoxicity in blood was assessed by ethoxyresorufin-O-deethylase activity quantification and comet and micronuclei assays, respectively, but none of these were positive. Chronic dietary exposure of zebrafish to PAH mixtures results in carcinogenotoxic events that impair survival and physiology of exposed fish.     

Triazole-induced toxicity in developing rare minnow (Gobiocypris rarus) embryos

Using rare minnow (Gobiocypris rarus) at early-life stages as experimental models, the developmental toxicity of five widely used triazole fungicides (myclobutanil, fluconazole, flusilazole, triflumizole, and epoxiconazole) were investigated following exposure to 1–15 mg/L for 72 h. Meanwhile, morphological parameters (body length, body weight, and heart rate), enzyme activities (superoxide dismutase (SOD), glutathione S-transferase (GST), adenosine triphosphatase (ATPase), and acetyl cholinesterase (AChE)), and mRNA levels (hsp70, mstn, mt, apaf1, vezf1, and cyp1a) were also recorded following exposure to 0.2, 1.0, and 5.0 mg/L for 72 h. Results indicated that increased malformation and mortality, decreased body length, body weight, and heart rate provide a concentration-dependent pattern; values of 72 h LC₅₀ (median lethal concentration) and EC₅₀ (median effective concentration) ranged from 3 to 12 mg/L. Most importantly, the results of the present study suggest that even at the lowest concentration, 0.2 mg/L, five triazole fungicides also caused notable changes in enzyme activities and mRNA levels. Overall, the present study points out that those five triazole fungicides are highly toxic to the early development of G. rarus embryos. The information presented in this study will be helpful in better understanding the toxicity induced by triazole fungicides in fish embryos.     

Unexpected toxic interactions in the freshwater amphipod Gammarus pulex (L.) exposed to binary copper and nickel mixtures

To document the toxicity of copper and nickel in binary mixtures, freshwater amphipods Gammarus pulex were exposed to the metals given independently or as mixtures. Toxicity to Cu alone was relatively high: 96-h LC₁₀ and LC₅₀ were found at 91 and 196 μg L^?1, respectively. Toxicity to Ni alone was very low, with 96-h LC₁₀ and LC₅₀ of 44,900 and 79,200 μg L^?1, respectively. Mixture toxicities were calculated from single toxicity data using conventional models. Modeled toxicity was then compared with the measured toxicity of the binary mixture. Two kinds of mixtures were tested. Type I mixtures were designed as combinations of Cu and Ni given at the same effect concentrations, when taken independently, to identify possible interactions between copper and nickel. In type II mixtures, Cu concentrations varied from 0 to 600 μg L^?1 while the nickel concentration was kept constant at 500 μg L^?1 to mimic conditions of industrial wastewater discharges. Ni and Cu showed synergic effects in type I mixtures while type II mixtures revealed antagonistic effects. Low doses of Ni reduced Cu toxicity towards G. pulex. These results show that even for simple binary mixtures of contaminants with known chemistry and toxicity, unexpected interactions between the contaminants may occur. This reduces the reliability of conventional additivity models.     

Study on biodegradation process of lignin by FTIR and DSC

The biodegradation process of lignin by Penicillium simplicissimum was studied to reveal the lignin biodegradation mechanisms. The biodegradation products of lignin were detected using Fourier transform infrared spectroscopy (FTIR), UV–Vis spectrophotometer, different scanning calorimeter (DSC), and stereoscopic microscope. The analysis of FTIR spectrum showed the cleavage of various ether linkages (1,365 and 1,110 cm^?1), oxidation, and demethylation (2,847 cm^?1) by comparing the different peak values in the corresponding curve of each sample. Moreover, the differences (T_m and ΔH_m values) between the DSC curves indirectly verified the FTIR analysis of biodegradation process. In addition, the effects of adding hydrogen peroxide (H₂O₂) to lignin biodegradation process were analyzed, which indicated that H₂O₂ could accelerate the secretion of the MnP and LiP and improve the enzymes activity. What is more, lignin peroxidase and manganese peroxidase catalyzed the lignin degradation effectively only when H₂O₂ was presented.     

The effects of henna (hair dye) on the embryonic development of zebrafish (Danio rerio)

The powder of henna is extensively used as decorative skin paint for nail coloring and as a popular hair dye in Asian countries. Its human health risk is extensive, and it is frequently released as waste into the aquatic environment raising the concerns. Zebrafish (Danio rerio) embryos were employed to study the developmental effects of henna. Normal fertilized zebrafish embryos under standard water were selected for the control and test chambers. Three predetermined sublethal concentrations (100, 200, and 275 μM) of henna in 24-well cell culture plates were tested on 1-h postfertilized embryo (pfe) for 96 h. Observation for rates of survival and mortality was recorded; digital camera was used to image morphological anomalies of embryos with a stereomicroscope; and functional abnormalities at 24, 48, 72, and 96 h were performed. The hatching rates of embryos were reduced significantly when treated with 200 and 275 μM or higher concentrations of henna. Slow blood circulation in the whole body was observed with a median effect on hatching exposed to 200 and 275 μM of henna at 48-h pfe. At 72- and 96-h pfe, blood circulation was ceased in the whole body but still had a heartbeat. At 96-h pfe, pericardial sac edema, yolk sac edema, head deformation, spine crooked malformation, and tail malformation (bent tails or hook-like tails) were observed in the surviving larvae at 100 μM. In summary, exposure to henna at 100, 200, and 275 μM causes some altered morphological and physiological abnormalities including increased mortality, hatching delay, slow blood circulation, pericardial sac edema, yolk sac edema, abnormal body axes, twisted notochord, tail deformation, weak heartbeat, and growth retardation and was also detected in some treated embryos and groups having adverse effects on embryonic development of zebrafish provoking potential human developmental risk studies.     

Sorption-desorption behavior of polybrominated diphenyl ethers in soils

Polybrominated diphenyl ethers (PBDEs) are flame retardants that are commonly found in commercial and household products. These compounds are considered persistent organic pollutants. In this study, we used 4,4′-dibromodiphenyl ether (BDE-15) as a model compound to elucidate the sorption and desorption behavior of PBDEs in soils. The organic carbon-normalized sorption coefficient (K_OC) of BDE-15 was more than three times higher for humin than for bulk soils. However, pronounced desorption hysteresis was obtained mainly for bulk soils. For humin, increasing concentration of sorbed BDE-15 resulted in decreased desorption. Our data illustrate that BDE-15 and probably other PBDEs exhibit high sorption affinity to soils. Moreover, sorption is irreversible and thus PBDEs can potentially accumulate in the topsoil layer. We also suggest that although humin is probably a major sorbent for PBDEs in soils, other humic materials are also responsible for their sequestration.     

Factors affecting degradation of dimethyl sulfoxide (DMSO) by fluidized-bed Fenton process

In this study, the target compound is dimethyl sulfoxide (DMSO), which is used as a photoresist stripping solvent in the semiconductor and thin-film transistor liquid crystal display (TFT-LCD) manufacturing processes. The effects of the operating parameters (pH, Fe²⁺ and H₂O₂ concentrations) on the degradation of DMSO in the fluidized-bed Fenton process were examined. This study used the Box-Behnken design (BBD) to investigate the optimum conditions of DMSO degradation. The highest DMSO removal was 98 % for pH 3, when the H₂O₂ to Fe²⁺ molar ratio was 12. At pH 2 and 4, the highest DMSO removal was 82 %, when the H₂O₂ to Fe²⁺ molar ratio was 6.5. The correlation of DMSO removal showed that the effect of the parameters on DMSO removal followed the order Fe²⁺?>?H₂O₂?>?pH. From the BBD prediction, the optimum conditions were pH 3, 5 mM of Fe²⁺, and 60 mM of H₂O₂. The difference between the experimental value (98 %) and the predicted value (96 %) was not significant. The removal efficiencies of DMSO, chemical oxygen demand (COD), total organic carbon (TOC), and iron in the fluidized-bed Fenton process were higher than those in the traditional Fenton process.