Phototransformation of halobenzoquinones in aqueous solution under the simulate sunlight: Kinetics, mechanism and products.

Halobenzoquinones (HBQs) are a novel family of unregulated disinfection byproducts (DBPs). Little is known about their phototransformation activities in natural water. Here, five HBQs with various halogenated substituent types, numbers, and structures positions were selected to investigate the kinetics of degradation in aqueous solutions at various concentrations and in the presence of common environmental variables (Cl-, NO2-, and humic acid). The results indicated that dichloride and dibromo-substituted HBQs were photolyzed, whereas tetrachloro-substituted HBQs showed little degradation. The photolysis rate constant (k) of HBQs decreased with increasing initial concentration. The presence of NO2- and Cl- promoted the degradation of HBQs mainly through the formation of hydroxyl radical (•OH), which were confirmed by electron paramagnetic resonance (EPR). In contrast, humic acid played a negative role on HBQs transformation due to the adsorption and quenching reactions. Possible conversion pathways for HBQs were proposed based on the identification of two major photodegradation products, hydroxylated HBQs and halogenated-benzenetriol, as well as reactive free radicals. This study provided meaningful insights into the environmental fates and risk assessments of HBQs in natural aquatic system.

Photolysis of dinotefuran in aqueous solution: Kinetics, influencing factors and photodegradation mechanism.

The environmental behaviour of neonicotinoid insecticides (NNIs) is of momentous concern due to their frequent detection in aquatic environment and their biotoxicity for non-target organisms. Phototransformation is one of the most significant transformation processes, which is directly related to NNIs exposure and environmental risks. In this study, the photodegradation of dinotefuran (DIN, 1-Methyl-2-nitro-3-(tetrahydro-3-furanylmethyl)-guanidine), one of the most promising NNIs, was conducted under irritated light in the presence of Cl-, DOM along with the effect of pH and initial concentration. The findings demonstrated that in ultra-pure (UP) water, the photolysis rate constants (k) of DIN rose with increasing initial concentration. Whereas, in tap water, at varied pH levels, and in the presence of Cl-, the outcomes were reversed. At the same time, lower concentration of DOM promoted DIN photolysis processes due to the production of reactive oxygen species, while higher concentrations of DOM inhibited the photolysis by the predominance of light shielding effects. The singlet oxygen (1O2) was produced in the photolysis processes of DIN with Cl- and DOM, which was confirmed by electron spin resonance (EPR) analysis. Four main photolysis products and three intermediates were identified by UPLC-Q-Exactive Orbitrap MS analysis. The possible photodegradation pathways of DIN were proposed including the oxidation by 1O2, reduction and hydrolysis after the removal of nitro group from parent compounds. This study expanding our understanding of transformation behavior and fate of NNIs in the aquatic environment, which is essential for estimating their environmental risks.

Recognition, possible source, and risk assessment of organic pollutants in surface water from the Yongding River Basin by non-target and target screening.

Organic pollutants in aquatic environment could have important implications on pollution stress on aquatic organisms and even on the risk of human exposure. Thus, revealing their occurrence in aquatic environment is essential for water quality monitoring and ecological risk purposes. In this study, a comprehensive two-dimensional gas chromatography connected with time-of-flight mass spectrometry (GC × GC-TOF-MS) was applied, to enable non-target and target analysis of pollutants in the Yongding River Basin. Based on the isotopic patterns, accurate masses and standard substances, certain environmental contaminants were tentatively identified which including polycyclic aromatic hydrocarbon (PAHs), organochlorine pesticides (OCPs), phenols, amines, etc. The compounds with the highest concentration were naphthalene (109.0 ng/L), 2,3-benzofuran (51.5 ng/L) and 1,4-dichlorobenzene (35.9 ng/L) in Guishui River. Wastewater treatment plants (WWTPs) discharges were a main source of pollutants in Yongding River Basin, as the types of compounds screened in the downstream river were relatively similar to those from WWTPs. According to the target analysis, a number of pollutants were selected due to the acute toxicity and cumulative discharge from WWTPs and downstream rivers. Three PAHs (naphthalene, Benzo(b)fluoranthene and pyrene) homologues showed moderate risk to fish and H. Azteca in Yongding River Basin, while the rest of the measured chemicals showed low ecological impact across the entire study area based on the risk assessment. The results are helpful for understanding the necessity of high-throughput screening analysis for assessing water quality of rivers and the discharge emissions of pollutants from WWTPs to the river environment.

The photoactivity of complexation of DOM and copper in aquatic system: Implication on the photodegradation of TBBPA.

The photoactivity of dissolved organic matter (DOM) has a great impact on the photodegradation of organic pollutants in natural waters. In this study, the photodegradation of TBBPA was investigated under simulated sunlight irradiation in the presence of copper ion (Cu2+), dissolved organic matter (DOM) and Cu-DOM complexation (Cu-DOM) to illustrate the effect of Cu2+ on photoactivity of DOM. The rate of photodegradation of TBBPA in the presence of Cu-DOM complex was 3.2 times higher than that in pure water. The effects of Cu2+, DOM and Cu-DOM on the photodegradation of TBBPA were highly pH dependent and hydroxyl radical(·OH) responded for the acceleration effect. Spectral and radical experiments indicated that Cu2+ had high affinity to fluorescence components of DOM, and acted as both the cation bridge and electron shuttle, resulting the aggregation of DOM and increasing of steady-state concentration of ·OH (·OHss). Simultaneously, Cu2+ also inhibited intramolecular energy transfer leading to the decrease of steady-state concentration singlet oxygen (1O2ss) and triplet of DOM (3DOM⁎ss). The interaction between Cu2+ and DOM followed the order of conjugated carbonyl CO, COO- or CO stretching in phenolic groups and carbohydrate or alcoholic CO groups. With these results, a comprehensive investigation on the photodegradation of TBBPA in the presence of Cu-DOM was conducted, and the effect of Cu2+ on the photoactivity of DOM was illustrated. These findings helped to understanding the potential mechanism of interaction among metal cation, DOM and organic pollutants in sunlit surface water, especially for the DOM-induced photodegradation of organic pollutants.

Photochemical reaction of glucocorticoids in aqueous solution: Influencing factors and photolysis products.

Glucocorticoids (GCs), as endocrine disruptors, have attracted widespread attention due to their impacts on organisms' growth, development, and reproduction. In the current study, the photodegradation of budesonide (BD) and clobetasol propionate (CP), as targeted GCs, was investigated including the effects of initial concentrations and typical environmental factors (Cl-, NO2-, Fe3+, and fulvic acid (FA)). The results showed that the degradation rate constants (k) were 0.0060 and 0.0039 min-1 for BD and CP at concentration of 50 µg·L-1, and increased with the initial concentrations. Under the addition of Cl-, NO2-, and Fe3+ to the GCs/water system, the photodegradation rate was decreased with increasing Cl-, NO2-, and Fe3+ concentrations, which were in contrast to the addition of FA. Electron resonance spectroscopy (EPR) analysis and the radical quenching experiments verified that GCs could transition to the triplet excited states of GCs (3GCs*) for direct photolysis under irradiation to undergo, while NO2-, Fe3+, and FA could generate ·OH to induce indirect photolysis. According to HPLC-Q-TOF MS analysis, the structures of the three photodegradation products of BD and CP were elucidated, respectively, and the phototransformation pathways were inferred based on the product structures. These findings help to grasp the fate of synthetic GCs in the environment and contribute to the understanding of their ecological risks.

Identifying trends and driving factors of spatio-temporal water quality variation in Guanting Reservoir Basin, North China.

Assessment of river quality has been attracting a great deal of attention because of its important implications for the living environment of human beings and aquatic organisms. This study investigated the spatial and temporal variation of water quality and its possible driving factors of Guanting Reservoir Basin. For this purpose, water quality was assessed with the Canadian Council of Ministers of the Environment Water Quality Index, together with nutrient inputs and social-economic data which were collected and analyzed during the period 2009-2019. The results showed that the overall water quality in Guanting Reservoir increased over time and was rated as "good" during the studied decade. Spatially, water quality in tributary upstream of Yanghe River and Sanggan River was better than that in Guishui River, resulting in better quality in West Reservoir than in East Reservoir. Among water quality indices, total nitrogen was the main pollutant affecting the water quality of the studied area. In addition, principal component analysis and correlation analysis were applied to evaluate the relationships between the socio-economic factors and water quality variation. Urbanization and industry structure were significantly correlated with the water quality variation in upstream tributaries. The findings provide insightful understanding into the spatio-temporal variations of water quality and the associated driving factors of Guanting Reservoir basin, which would help managers in executing theoretical reference for water quality protection.

Occurrence and distribution characteristics of heavy metals in the surface water of Yongding River Basin, China.

Yongding River is a vital socioeconomic zone in China in providing daily usage for humans, animals, and running of industries and agriculture. This study first provides a comparative assessment for the heavy metal pollution in the surface water from 82 estuarine locations along the basin, including the Guanting Reservoir and seven wastewater treatment plants (WWTPs). The occurrence, distribution, potential sources, and water quality relating to the detected heavy metals were addressed. Eleven typical elements (Pb, Cr, As, Cd, Sb, Ba, V, Ti, Zn, Ni, and Be) were investigated, and the results showed that all the measured concentrations were below the WHO guideline limits. Most heavy metals exhibited higher levels in the middle of Yongding River basin due to the discharge of WWTPs. Pb, Ti, Zn, and Cd in the surface water mainly originated from anthropogenic discharge, while Sb and V were mostly contributed to geogenic sources according to the principal component analysis. Three documented methods, water quality index (WQI), heavy metal pollution (HPI), and Nemerow pollution index (Pn) values, were used to evaluate the contamination monitoring of surface water. All the locations were classified as low and moderate risk except Y12, B2, and Y13 for their Pn values were higher than 1.0. The present study highlights the status of heavy metals in Yongding River basin which is helpful in providing fundamental data for assessment of water quality and the effective protection for Yongding River basin in the future.

Simultaneous determination of vanillin, ethyl vanillin and methyl vanillin in Chinese infant food and other dairy products by LC-MS/MS.

An efficient and simple method for determining vanillin, methyl vanillin and ethyl vanillin in milk and dairy products was developed using a liquid-liquid extraction (LLE) procedure coupled to high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Different extraction procedures were tested and optimised by spiking three vanillin compounds into a blank matrix in which none of any food additives were detected, and the extraction with acetonitrile solution and n-hexane as cleaning sorbent allowed an efficient recovery of 87.6-101.7% with RSDs less than 5%. The limit of detection (LOD) ranged from 6.2 to 20.1 µg/kg. High sensitivity, accuracy and selectivity were found for the in-house validated method, which can eliminate the interferences from complicated matrices effectively, and fulfil the quality criteria for routine laboratory application for real samples. The developed method was then finally applied to screen the three analytes in 65 milk and dairy products including infant formula milk powders from local markets to check for compliance with Chinese Regulation. Concentrations of the total vanillin and ethyl vanillin ranged from 0.0323 to 246.3 mg/kg, which is within the limits of Chinese regulations.

Photoformation of persistent free radicals on a montmorillonite-humic acid complex simulated as particulate organic matter in an aqueous solution.

This study investigates the formation of persistent free radicals (PFRs) on particulate organic matter (POM) under irradiation in water. A montmorillonite-humic acid complex (Mnt-HA complex) was prepared to simulate POM, and the generated PFRs were detected by the electron paramagnetic resonance (EPR) technique. EPR signals with the trend of an initial increase and then a decrease were observed under irradiation for 8 days, and the g factors were in the range of 2.0034-2.0039, which indicated the generation of carbon-centered radicals with electrophilic moieties. Different concentrations and types of halophenols and transition-metal ions were respectively adsorbed on the Mnt-HA complex to probe their influence on the formation of PFRs. The amount of PFRs generated in the Mnt-HA complexes was in the order: 2-bromophenol (2-BP) > 2,4-dibromophenol (2,4-DBP) > 2,4-dichlorophenol (2,4-DCP), which implied that halogen substitution and the number of substituents in the halophenols could affect the generation of PFRs. The effects of transition-metal ions that resulted in the reduction of PFRs when adsorbed on the Mnt-HA complex were as follows: Fe3+ > Zn2+ > Cu2+ > Mn2+, and this is in agreement with their redox capacity. Analyzing the induced generation of reactive oxygen species (ROS) and electrons on POM, it is found that halophenols and transition metal ions also affected this process under irradiation. These findings indicate that the photoformation of PFRs on POM could be a source of PFRs in aqueous environments and requires further attention.

Formation of free radicals by direct photolysis of halogenated phenols (HPs) and effects of DOM: A case study on monobromophenols.

The free radicals play an important role to understand direct/indirect transformation mechanisms of organic pollutants. However, very few efforts have been made to elucidate the radicals produced by direct photolysis. In this study, the short-lived radicals generated under simulated sunlight irradiation from representative halogenated phenols (HPs), monobromophenols, were investigated by electron paramagnetic resonance (EPR). The results showed that three radicals, carbon-centered radical (C), hydrogen radical (H) and hydroxyl radical (OH), were generated from the direct irradiation of HPs. Compared to other substitutions, halogenated atom at para-position led to the highest production of these radicals which is in accordance with the energies calculated by density functional theory. Based on the analyses of the reactive species and corresponding intermediate adducts, the possible reaction pathways for these radicals were tentatively proposed. Dissolved organic matters (DOM) could enhance the photodegradation of HPs by directly affecting the radicals' formation, mainly due to generation of excited triplet DOM (3DOM*). A positive correlation was found between the concentrations of hydrated electron and the steady state 3DOM* from different DOM. Our findings provided insights into environmental photochemical fate of HPs through their direct photolysis and will help more accurately understand their phototransformation mechanisms in the environment.

Photochemical reaction of tricresyl phosphate (TCP) in aqueous solution: Influencing factors and photolysis products.

Organophosphate triesters (OPEs) have caused great concern as a class of emerging environmental contaminants due to their widespread use and their toxicity to organisms. However, the phototransformation behavior of OPE is still not fully understood, which is important for understanding their environmental fate. In the present study, the photodegradation of tricresyl phosphate (TCP), one of the most widely detected OPEs in aqueous environments, was investigated including the direct photolysis and in the presence of several natural water factors, NO2-, Fe3+ and humic acid. The degradation process followed the pseudo-first-order kinetics, with rate constant increasing slightly with increasing initial TCP concentration. The presence of NO2- and Fe3+ was observed to promote the photochemical loss of TCP, while humic acid played a negative role on TCP transformation. Electron spin resonance (EPR) analysis showed that carbon-centered radical was produced in the photolysis process of TCP, and hydroxyl radical contributed to the promotion of rate constant for Fe3+ and NO2-. Four photolysis products were tentatively identified by HPLC-LTQ-Orbitrap MS analysis, and the possible degradation pathways of TCP were proposed. These findings provide a meaningful reference for the fate and transformation of OPEs in natural water.

Measurement and prediction of bioconcentration factors of organophosphate flame retardants in common carp (Cyprinus carpio).

The increase in the production and usage plus the toxicity nature of organophosphate flame retardants (OPFRs) has become a concern. However, limited information is available about the bioaccumulation potential of OPFRs in fish. In this study, we determined the 96 h LC50 s, and evaluated the bioaccumulation potential of six most frequently reported OPFRs in gill, kidney, liver, and muscle tissues of common carp (Cyprinus carpio) for 48 d, and a quantitative structure-activity relationship (QSAR) model was developed to predict bioconcentration factors (BCFs) for the remaining 16 OPFRs. The BCFs and half-lives (t1/2) in the tissues ranged from 6.54 (Tris (2-chloroisopropyl) phosphate, (TCPP)) to 528.15 (Tris (2-ethylhexyl) phosphate (TEHP)), and 2.25-5.78 days, respectively. The tissue-specific concentration and BCFs values followed the order of liver > kidney ≥ intestine >> muscle. The proposed QSAR model with a high cross-validated value (Q2(cum)) of 0.930 and a correlation coefficient of 0.94 was obtained and was able to predict log BCF from parameters related to molar volume and isotropic average static field polarizability. The results show that the model has a high level of accuracy, making the proposed approach a suitable method for predicting the log BCF.

Occurrence and profiles of halogenated phenols, polybrominated diphenyl ethers and hydroxylated polybrominated diphenyl ethers in the effluents of waste water treatment plants around Huang-Bo Sea, North China.

Halogenated organic pollutants (HOPs), as ubiquitous environment contaminants, have attracted increasing concerns due to the potential adverse health impacts on organisms and even humans. Waste water treatment plants (WWTPs) are one source of HOPs to the environment through their discharge of treated effluent. In this study, the presence and profiles of 6 halogenated phenols (HP), 17 polybrominated diphenyl ethers (PBDE) and 11 hydroxylated polybrominated diphenyl ethers (OH-PBDE) were investigated in 12 WWTP effluent samples collected near Huang-Bo Sea in Dalian, China. These targeted organohalogen pollutants were found in all the effluent samples with the total concentrations of ΣHPs, ΣPBDEs and ΣOH-PBDEs ranging from 77.2 to 168.5ng/L, from not-detected to 5.3ng/L and from 0.08 to 0.88ng/L, respectively. The most abundant congeners of HPs and PBDEs in the effluents were pentachlorophenol (PCP), BDE-47 and BDE-99, while for OH-PBDEs, 6-OH-BDE-47 and 5-OH-BDE-47 were the most abundant. In addition, the statistical analysis showed that a significant (p<0.05) positive correlation was observed between BDE-47 and its metabolite 6-OH-BDE-47, indicating that PBDEs may be a source of OH-PBDEs detected in the effluents.

Occurrence and levels of nitrofuran metabolites in sea cucumber from Dalian, China.

The occurrence and levels of nitrofuran metabolites (NFMs) in sea cucumber (SC) from Dalian, China, are reported. Four metabolites including 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ), 3-amino-2-oxazolidinone (AOZ), semicarbazide (SEM) and 1-aminohydantoin (AHD) in different SC products (fresh, instant and dry salted SCs) were measured. The frequency of occurrence for NFMs in all SC samples was 42.7%. The total NFM concentrations ranged from non-detectable to 64.6 ng g-1, with a mean of 3.59 ng g-1. AOZ and SEM were the dominant congeners, accounting for 40.1% and 59.1% of the total NFMs, respectively. The concentrations and patterns varied among different regions. Higher levels of NFMs were found in the fresh SC products, and the order for the average concentration of ∑4NFM was fresh > dry salted > instant.

Influence of salinity and temperature on uptake of perfluorinated carboxylic acids (PFCAs) by hydroponically grown wheat (Triticum aestivum L.).

Perfluoroalkyl substances (PFASs) have recently attracted increasing concerns due to their ubiquitous existence, adverse effects and persistence in environment. This study employed four perfluorinated carboxylic acids (PFCAs) to examine effects of salinity and temperature on the PFAS uptake in wheat, one of the major crops in the North China Plain. Wheat plants were grown in the spiked-PFCA hydroponic culture system at different salinities and temperatures. As expected, salinity and temperature significantly impacted the root uptake and translocation of wheat to four PFCAs, and the concentrations for each of PFCAs in wheat root and shoot increased with increasing salinity and temperature, respectively. PFCA concentrations at high salinity or high temperature were up to thrice those found at low salinity or low temperature. Except for perfluorobutanoic acid, the amount of PFCAs in root was always higher than that in shoot at the ranges of salinity and temperature tested. Additionally salinity and temperature were also capable of influencing the transfer factors (TFs) of four PFCAs, and significant increase was observed in the TFs in response to the increases in salinity and temperature.

Measurement of Temperature Dependence for Vapor Pressures of Seventeen OH-PBDEs and Eleven MeO-PBDEs by Gas Chromatographic Method.

Hydroxylated polybromodiphenyl ethers (OH-PBDEs) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs) are emerging organic pollutants. Supercooled liquid vapor pressures (p L) and enthalpies of vaporization (∆vap H) for seventeen OH-PBDEs and eleven MeO-PBDEs were determined by a gas chromatographic technique. p L at 298 K ranged from 0.0173 Pa for 2'-OH-BDE3 to 2.32 × 10(-7) Pa for 3'-OH-BDE154 and they are approximately one order of magnitude smaller than those determined for the counterpart polybrominated diphenyl ethers (PBDEs). ∆vap H was in the range of 76-121 kJ/mol. The temperature dependence of p L was measured by fitting the experimental data with the log(p L/Pa) = a/(T/K) + b equation, and this corresponds to a 50-265 times higher p L value at 0 versus 30°C. Using fundamental quantum chemical descriptors, two quantitative structure-property relationship models (Q cum > 0.935) were developed to estimate p L at any temperature for the additional OH- and MeO-PBDE congeners.

Monohydroxylated Polybrominated Diphenyl Ethers (OH-PBDEs) and Dihydroxylated Polybrominated Biphenyls (Di-OH-PBBs): Novel Photoproducts of 2,6-Dibromophenol.

Hydroxylated polybromodiphenyl ethers (OH-PBDEs) are emerging aquatic pollutants, but their origins in the environment are not fully understood. There is evidence that OH-PBDEs are formed from bromophenols, but the underlying transformation processes remain unknown. Here, we investigate if the photoformation of OH-PBDEs from 2,6-dibromophenol in aqueous solution involves 2,6-bromophenoxyl radicals. After the UV irradiation of an aqueous 2,6-dibromophenol solution, HPLC-LTQ-Orbitrap MS and GC-MS analysis revealed the formation of a OH-PBDE and a dihydroxylated polybrominated biphenyl (di-OH-PBB). Both dimeric photoproducts were tentatively identified as 4'-OH-BDE73 and 4,4'-di-OH-PBB80. In addition, three debromination products (4-OH-BDE34, 4'-OH-BDE27, and 4,4'-di-OH-PBBs) were observed. Electron paramagnetic resonance spectroscopy revealed the presence of a 2,6-dibromophenoxyl radical with a six-line spectrum (a(H) (2 meta) = 3.45 G, a(H) (1 para) = 1.04 G, g = 2.0046) during irradiation of a 2,6-dibromophenol solution in water. The 2,6-dibromophenoxyl radical had a relatively long half-life (122 ± 5 µs) according to laser flash photolysis experiments. The para-para C-C and O-para-C couplings of these 2,6-dibromophenoxyl radicals are consistent with the observed formation of both dimeric OH-PBDE and di-OH-PBB photoproducts. These findings show that bromophenoxyl radical-mediated phototransformation of bromophenols is a source of OH-PBDEs and di-OH-PBBs in aqueous environments that requires further attention.

Biological uptake and depuration of sulfadiazine and sulfamethoxazole in common carp (Cyprinus carpio).

Sulfonamides, a class of the most commonly used antibiotics, are being increasingly released into the aquatic environment and have recently caused considerable concerns. However, knowledge on their fate and ecotoxicological effects upon aquatic organisms is not understood yet. This work investigated mainly the bioconcentration kinetics (uptake/depuration) of sulfadiazine (SDZ) and sulfamethoxazole (SMZ) in common carp (Cyprinus carpio) by exposure in different concentrations under semi-static conditions for 48 d. The uptake rate (k1), growth-corrected depuration rate (k 2g), and biological half-lives (t1/2) of two sulfonamides in liver and muscle were determined and they were 0.135-9.84 L kg(-1)d(-1), 0.0361-0.838 d(-1), 8.3-19.2d, respectively. With exposure concentrations increasing, the uptake rates in liver and muscle decreased obviously but the depuration rates were not closely related with the exposure concentrations. SDZ exhibited higher uptake but lower excretion rates in almost all the liver and muscle than SMZ, resulting in both higher BCFs and half-lives for SDZ. The growth-corrected bioconcentration factors (BCF kg) were measured to be 1.65-165.73 L kg(-1)ww and their averages were in good consistency with the values predicted by previous models within one log unit. The work presented here was the first to model bioconcentration of SMZ and SDZ from water by laboratory-exposed fish.

Bioaccumulation and elimination kinetics of hydroxylated polybrominated diphenyl ethers (2'-OH-BDE68 and 4-OH-BDE90) and their distribution pattern in common carp (Cyprinus carpio).

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have attracted wide concerns due to their toxicities and universal presence in wildlife and humans. The relatively high Kow values of OH-PBDEs imply these compounds may have a significant bioaccumulation potential, but so far, the existing data provide little information regarding the kinetics of uptake and depuration in any organisms. Here we exposed common carps separately to two OH-PBDEs, 2'-OH-BDE68 and 4-OH-BDE90, for 30 days (d) in a flow-through system, followed by a 60-d depuration period in clean water to investigate compound-specific bioaccumulation and tissue distribution. Two OH-PBDEs could accumulate in common carp, and the high concentration was observed in liver or kidney. The uptake rates (k1) of two OH-PBDEs ranged from 0.15 to 21.3 d(-1) in fish, and the elimination rates (k2) ranged from 0.027 to 0.075 d(-1), which leaded to their BCF values in 4.8-299.2 ranges. Half-lives ranged from 9.2 d to 25.6 d. The exposure concentration significantly affected BCF values but didn't change their relative compositions in liver, kidney and muscle after a long exposure time. To our knowledge, this is the first study to systematically assess uptake, depuration kinetics and tissue distribution for OH-PBDEs via a controlled experimental animal model.

Development of a model for predicting reaction rate constants of organic chemicals with ozone at different temperatures.

To assess the persistence and fate of volatile organic compounds in the troposphere, the rate constants for the reaction with ozone (kO3) are needed. As kO3 values are only available for hundreds of compounds, and experimental determination of kO3 is costly and time-consuming, it is of importance to develop predictive models on kO3. In this study, a total of 379 logkO3 values at different temperatures were used to develop and validate a model for the prediction of kO3, based on quantum chemical descriptors, Dragon descriptors and structural fragments. Molecular descriptors were screened by stepwise multiple linear regression, and the model was constructed by partial least-squares regression. The cross validation coefficient QCUM(2) of the model is 0.836, and the external validation coefficient Qext(2) is 0.811, indicating that the model has high robustness and good predictive performance. The most significant descriptor explaining logkO3 is the BELm2 descriptor with connectivity information weighted atomic masses. kO3 increases with increasing BELm2, and decreases with increasing ionization potential. The applicability domain of the proposed model was visualized by the Williams plot. The developed model can be used to predict kO3 at different temperatures for a wide range of organic chemicals, including alkenes, cycloalkenes, haloalkenes, alkynes, oxygen-containing compounds, nitrogen-containing compounds (except primary amines) and aromatic compounds.