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Abstract The occurrence and distributions of selected endocrine-disrupting chemicals (EDCs), along with related environmental factors, were investigated in two rivers and six reservoirs in the Pearl River Delta. The vertical profiles of aqueous 4- tert -octylphenol (OP), 4-nonylphenol (NP), and estrone (E1) were constant, with little change in concentration between the surface and the river bottom, while higher aqueous concentrations of bisphenol A (BPA) were found in the bottom layers of the rivers. OP and NP in suspended particulate matter (SPM) were transferred from the surface to the bed layer, ultimately accumulating in the sediment. However, the particulate profiles of BPA and E1 both featured increases from the surface to the bottom layers and attenuation in the river bed. Dissolved oxygen (DO), water temperature, and pH were negatively correlated with the EDC concentrations, and negative relationships between DO and distribution coefficient (K d) values for OP and NP were found as well. This indicated that these environmental parameters were primarily responsible for the EDC vertical distribution and SPM-water partitioning in the rivers. Positive relationships were observed between chlorophyll a and EDCs in the particulate phase, and the algae/water K d values for EDCs in reservoirs were comparable to the SPM/water and sediment/water K d values from the rivers. These results suggest that algae played an important role in regulating the distribution of EDCs in surface waters. Moreover, relationships between UV absorbance and EDCs revealed that π-π interactions were among the dissolved organic carbon (DOC)-EDC binding mechanisms and that DOC fractions with higher degrees of aromaticity and humification possessed higher affinities towards EDCs. Graphical abstract Image 1 Highlights • Dissolved oxygen, water temperature, and pH were negatively correlated with the EDC concentrations in river water. • Algae regulate the distribution of EDCs in surface waters. • π-π interaction is to important dissolved organic carbon (DOC)-EDC bonding mechanism. • DOC aromaticity and humification could enhance its affinity with EDCs. EDC vertical distributions and transfer mechanisms among various matrices are related with several factors other than organic carbon in aquatic environments. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs) were investigated by GC–NCI–MS in sediments collected from the Pearl River Delta (PRD) and Guiyu town, South China. The concentrations of ∑ 39 PBDEs and BDE 209 were in the ranges of 0.31–38.9 ng g −1 and 12.2–488 ng g −1 in the PRD, and 2.57–21,207 ng g −1 and 7.02–66,573 ng g −1 in Guiyu, respectively. The levels of PBDEs in Dongjiang River (DJ), Zhujiang River (ZJ), and Beijiang River (BJ), and Guiyu (GY) followed the order: GY > DJ > ZJ > BJ. The very high PBDE concentration (87,779 ng g −1 ) was detected at G1 sediment in Guiyu compared with those in sediments from other regions around the world. The PBDE mixtures detected were mainly comprised of penta-, octa-, and deca-BDEs, in which deca-BDE was the dominant constituent. The abundant congeners, excluding BDE-209, were BDE-47, BDE-99, and BDE-183, suggesting the diverse use of commercial products containing these congeners in this region. The concentrations of major congeners were significantly correlated with total organic carbon (TOC) contents ( p  < .01). A good regression between the logarithmic TOC-normalized BDE average concentrations and their log K ow confirmed that the sorption of PBDEs on sediment organic matter governed their spatial distribution, transport, and fate in the sediments. Furthermore, risk quotients (RQs) derived from concentrations of PBDEs in sediments from our study may pose high ecological risks to exposure of benthic organisms. [ABSTRACT FROM AUTHOR]

The desorption kinetics and mechanism were investigated using a Tenax extraction technique on different sediments spiked with radiocarbon-labeled benzo[ a ]pyrene (BaP). Five sedimentary fractions were sequentially fractionated, and the only nonhydrolyzable organic carbon fractions (NHC) were characterized using advanced solid-state 13 C nuclear magnetic resonance spectroscopy (NMR), improved six end-member model, and a CO 2 gas adsorption technique. The sediments contained high percentages of algaenan and/or sporopollenin but low percentages of black carbon and lignin. A first-order, two-compartment kinetics model described the desorption process very well ( R 2 > 0.990). Although some of the organic carbon fractions were significantly related to the desorption kinetics parameters, the NHC fractions showed the highly significant correlation. Moreover, the nanoporosity or specific surface area (SSA) of the NHC fractions was highly related to their OC contents and aliphatic C ( R 2 = 0.960, p < 0.01). The multiple regression equations among the desorption kinetics parameters, structural parameters, and nanoporosity were well established ( R 2 =>0.999). Nanoporosity and aromatic C were the dominant contributors. Furthermore, the enhanced percentages of desorbed BaP at elevated temperatures significantly showed a linear regression with the structure and nanoporosity. To our knowledge, the above evidence demonstrates for the first time that the transfer (or diffusion) of BaP in the nanopores of condensed aromatic components is the dominant mechanism of the desorption kinetics of BaP at organic matter particle scale. [ABSTRACT FROM AUTHOR]

Endocrine disrupting chemicals (EDCs) were seasonally investigated in surface water, suspended particulate matter, and sediments of the Pearl River Delta (PRD), South China. EDC concentrations in the surface water were generally higher in the summer than in winter. The surface water in the investigated rivers was heavily contaminated by the phenolic xenoestrogens. Moreover, the in-situ log K soc and log K poc values and their regression with log K ow in the field experiments suggest that binding mechanisms other than hydrophobic interaction are present for the sedimentary organic carbon and particulate organic carbon (SOC/POC). The log K soc –log K ow and log K poc –log K ow regression analyses imply that higher complexity of nonhydrophobic interactions with EDCs is present on the SOC samples comparing with the POC samples, which is related to their different sources. [ABSTRACT FROM AUTHOR]

To better understand interaction mechanism of sediment organic matter with hydrophobic organic compounds, sorption of phenanthrene (Phen) and nonylphenol (NP) by bulk sediments and their fractions was investigated. Three surface sediments were selectively fractionated into different organic fractions, including the demineralized carbon (DM), lipid free carbon (LF), lipid (LP), and nonhydrolyzable carbon (NHC) fractions. The structure and microporosity of the isolated fractions were characterized by NMR and CO 2 adsorption techniques, and used as sorbents for Phen and NP. The calculated micropore volumes ( V o ) and specific surface area (SSA) values are positively related to the concentrations of aromatic C and char for the DM, LF and NHC fractions, suggesting that aromatic moieties and char component significantly contribute to the microporosity. The LF fractions exhibit greater sorption affinity than the DM fractions do, indicating that the presence of LP could block the accessibility of sorption sites for Phen and NP. Significant and positive correlations among log K′ FOC values for Phen and NP and aromatic carbon and char contents, and V o and SSA values suggest the aromatic moieties and microporosity dominate their sorption of HOCs by sediment organic matter (SOM). As the NHC fractions have much stronger sorption than other fractions do, they dominate the overall sorption by the bulk samples. This study indicated that the important roles of aromatic moieties, accessibility, and microporosity in the sorption of HOCs by SOM. [ABSTRACT FROM AUTHOR]

In this study, the role of organic matter structure and microporosity in the adsorption and degradation of radioactive nonylphenol in sediments treated with potassium ferrate solutions was investigated. The demineralized fractions and acid non-hydrolyzable fractions were isolated and characterized via advanced solid-state 13C nuclear magnetic resonance and CO 2 gas adsorption technology, respectively. Radioactive nonylphenol in the sediments was also fractionated into 14CO 2 , water-soluble residues, extractable residues, and strongly bound residues after treatment with potassium ferrate. A first-order, two-compartment kinetic model well described the mineralization and degradation kinetics of radioactive nonylphenol in the sediment (R 2 > 0.99). The degradation percentages of spiked nonylphenol were highly negatively correlated with aromatic carbon, aliphatic carbon, and microporosity estimated from acid-non-hydrolyzable fractions in the bulk sediments (R 2 > 0.82, p < 0.01). The percentages of adsorbed parent nonylphenol residues were highly positively correlated with aromatic carbon, aliphatic carbon, and microporosity estimated from acid-non-hydrolyzable fractions in the bulk sediments (R 2 > 0.90, p < 0.01). The parent nonylphenol compound desorbed into the aqueous phase and was completely degraded. This study is the first to demonstrate the important role of aromatic carbon, aliphatic carbon, and microporosity in acid non-hydrolyzable fractions on the degradation of nonylphenol during the potassium ferrate oxidation treatment process. [Display omitted] • Stable SOM was an important fraction in the sediments. • Aliphatic C and aromatic C were major structure of the stable SOM. • The stable SOM mainly consisted of sporopollenin, algaenan, and char. • The adsorbed parent NP was protected by the stable SOM. • Structure and micropore of the stable SOM controlled the adsorption and degradation of NP. [ABSTRACT FROM AUTHOR]

Algal samples were fractionated into lipid (LP), lipid free (LF), alkaline nonhydrolyzable carbon (ANHC), and acid nonhydrolyzable carbon (NHC) fractions, and were characterized by the quantitative 13 C multiCP NMR technique. The biosorption isotherms for nonylphenol (NP) were established and compared with previously published data for phenanthrene (Phen). The log K OC values are significantly higher for the field-collected plankton samples than for the commercial algae and cultured algae samples, correlating with their lipid contents and aliphatic carbon structure. As the NHC fraction contains more poly(methylene) carbon, it exhibits a higher biosorption capacity. The sorption capacities are negatively related to the polarity index, COO/N–C=O, polar C and O-alkyl C concentrations, but are positively related to the H/O atomic ratios and poly(methylene) carbon. The higher sorption capacities observed for NP than for Phen on the investigated samples are explained by specific interactions such as hydrogen bonding and π–π interaction. [ABSTRACT FROM AUTHOR]

The recognition of nucleic acids is a general strategy used by the host to detect invading pathogens. Many studies have established that MITA/STING is a central component in the innate immune response to cytosolic DNA and RNA derived from pathogens. MITA can act both as a direct sensor of cyclic dinucleotides (CDNs) and as an adaptor for the recruitment of downstream signaling components. In both roles, MITA is part of signaling cascades that orchestrate innate immune defenses against various pathogens, including viruses, bacteria and parasites. Here, we highlight recent studies that have uncovered the molecular mechanisms of MITA-mediated signal transduction and regulation, and discuss some notable issues that remain elusive. [ABSTRACT FROM AUTHOR]

• A computational procure to quantify the stress field intensity is developed. • A new modified non-proportional hardening factor is established. • The notch effect and the stress concentration can be well characterized by the absolute value of the relative stress gradient. • A multiaxial life prediction model for notched specimens is established. Engineering components with geometric discontinuous structures generally appear notch effect, which might eventually induce fatigue failure. In this study, a novel multiaxial fatigue prediction model is established for notched components by incorporating the notch effect and non-proportional hardening. Firstly, according to the notch effect, a computational procure of damage parameters is presented by combining the notion of stress intensity with finite element simulations based on the critical plane method. Secondly, considering the non-proportional hardening effect of path modes and material properties, a new modified non-proportional hardening factor is proposed. Particularly, the relationship between the relative stress gradient and the fatigue life is investigated under different stress concentration factors. Finally, with the help of the Manson-Coffin equation, a multiaxial fatigue life prediction model is developed subjected to multiaxial proportional/non-proportional loadings. Experimental data of medium steel En8 and GH4169 alloys are utilized to evaluate and validate the proposed model as well as four other classical models (FS model, MSWT model, Yu model and CXH model). The result indicates that the proposed model yields a higher accuracy on multiaxial fatigue life than other four models, and the majority of prediction results are within the ±2 life factor. [ABSTRACT FROM AUTHOR]

• The critical distance is not a constant for different materials under multiaxial stress states. • The non-proportional hardening and stress concentration can deeply influence the fatigue life of notched specimens. • A reliability framework for the analysis of multiaxial fatigue strength of notched specimens is established. • Novel P f - W - N f curves are developed and analyzed under the different survival probabilities. Notch features often raise critical effects on fatigue lives of engineering components, which deserve particular attention for assessing their structural integrity and reliability. In this study, through modifying the strain energy density model, a probabilistic framework for assessing the fatigue life of notched specimens is established under multiaxial loadings. Firstly, the strain energy density is calculated by the finite element method on an arbitrarily material plane is investigated. Secondly, a modified energy-based model is proposed by incorporating the notch effect and size effect, the non-proportional hardening and the stress concentration factors. Finally, combining the modified strain energy density model with the Weibull distribution as well as the theory of critical distance, a new probabilistic fatigue framework is developed to estimate the fatigue life of notched specimens under different survival probabilities. Experimental data of TC4 alloy, Al7050-T7451, GH4196 alloy and medium steel En8 notched specimens are employed to validate the proposed model and other six energy-based models (MSWT model, CXH model, CCB model, VF model, Liu model). The comparison results exhibit that the proposed model yields a higher accuracy than six other models within the ±2 life factor. Meanwhile, novel P f - W - N f curves of multiaxial notched specimens with different survival probabilities are presented and analyzed. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) from riverine and lacustrine water was isolated using a reverse osmosis (RO) system. Solid-state 13C nuclear magnetic resonance (13C NMR) was used to quantitatively evaluate the compositions and constituents of DOM, which are compared with previous investigations on marine DOM. Results indicated that concentration factor (CF) was a key metric controlling yield and sorption of DOM on the RO system. The sorption was likely non-selective, based on the 13C NMR and δ13C analyses. Carbohydrates and lipids accounted for 25.0-41.5% and 30.2-46.3% of the identifiable DOM, followed by proteins (18.2-19.8%) and lignin (7.17-12.8%). The freshwater DOM contained much higher alkyl and aromatic C but lower alkoxyl and carboxyl C than marine DOM. The structural difference was not completely accounted for by using structure of high molecular weight (HMW) DOM, suggesting a size change involved in transformations of DOM during the transport from rivers to oceans. [ABSTRACT FROM AUTHOR]

Highlights: [•] PAHs are relatively higher in marine fish than in freshwater fish. [•] PAHs respectively show significant correlations with DOC, POC, and Chl a. [•] The log K oc for PAHs is one order magnitude higher than the predicted. [•] The logBCF values in fish and their tissues are nonlinear in respect to log K ow. [•] Lipid is related to PAHs in freshwater fish, but not in marine fishes. [Copyright &y& Elsevier]

Highlights: [•] Sediment cores were collected from reservoir sediments of the Pearl River Delta. [•] Cu, Zn, Ag, Cd, and As were significantly accumulated during last three decades. [•] Heavy metals were strongly associated with algal organic matter in the sediments. [•] Principal component analysis was used to assess the enrichment of heavy metals. [•] Sedimentary process of heavy metals was affected by primary productivity. [ABSTRACT FROM AUTHOR]

Shale was thermally treated to obtain a series of kerogen with varied maturation. Their chemical, structural and porous properties were related to the sorption and/or desorption behaviors of phenanthrene and benzene. As the treatment temperature increases, aliphatic and carbonyl carbon of the kerogen samples decrease, while their aromaticity and maturation increase. Meanwhile, the isothermal nonlinearity of phenanthrene and benzene increases whereas the sorption capacity and micropore adsorption volumes (V o,d) initially increase and then decrease. The V o,d of benzene is significantly correlated with, but higher than that of phenanthrene, suggesting similar micropore filling mechanism and molecular sieve effect. The benzene desorption exhibits hysteresis, which is related to the pore deformation of the kerogen and the entrapment of solute in the kerogen matrix. The V o,d of phenanthrene and benzene on the kerogen samples accounts for 23–46% and 36–65% of the maximum sorption volumes, respectively, displaying the importance of the micropore filling. [Copyright &y& Elsevier]

Abstract: Two sediments were demineralized and sequentially fractionated into extracted fractions [free lipid (FL), bound lipid (BL) and lignin (LG)] and residual fractions [free lipid free (FLF), bound lipid free (BLF) and lignin free (LGF)]. The sorption isotherms of phenanthrene (Phen) were examined to evaluate the importance of various fractions on sorption. A lignin extraction procedure was for the first time applied to separate the lignin or degraded lignin fraction from sediment organic matter (SOM). The extracted LG was similar to model lignin in terms of elemental ratios and sorption behavior. FL and LG fractions were quite important, as their contents were much higher than reported values. Phen sorption for the extracted fractions was almost linear, whereas that for the residual fractions was nonlinear, especially for LGF with n 0.56–0.63. As the different organic fractions were removed sequentially, sorption energy distribution on the residual sediment organic matter (SOM) became more heterogeneous. In addition, increasing sorption capacity for the residual fractions, except for BLF with its high polarity, suggested that more sorption sites on the SOM matrix became accessible to Phen. The sorption capacity for LGF was comparable to that of condensed SOM. The residual fraction LGF generally controlled the overall sorption at low Phen concentration, but the extractable fraction FL surpassed the former fraction at high Phen concentration, demonstrating the importance of condensed SOM in the sorption of hydrophobic organic compounds (HOCs) in sediments. [Copyright &y& Elsevier]

Abstract: Prior to the 2008 Wenchuan earthquake (Mw 7.9), Sichuan, China, no earthquake of magnitude larger than M 7.0 had been reported in the historical record for the Longmenshan region. To reveal paleoseismic behaviors in this region, we conducted a paleoseismic study along the 2008 Wenchuan earthquake fault scarp at the town of Yingxiu along the Beichuan–Yingxiu fault. Through a trench investigation, geomorphic analysis and radiocarbon dating, we interpret the occurrence of three paleoseismic events (including the Wenchuan earthquake) within the past 6000years. The cumulative vertical displacement resulting from the three seismic events is ~7.6m. The coseismic uplift for the Wenchuan earthquake is ~2.4m. Integrated with previous paleoseismic results along the fault, the age of the penultimate event is constrained between 3300 and 2300cal BP. We suggest the antepenultimate event occurred later than 5920–5730cal BP. An average vertical slip rate of 0.88–0.91mm/year is calculated from the vertical displacement of U2 since 5940–5730cal BP. We estimate that an average recurrence interval of large earthquakes is at most 3000years. Furthermore, the three paleoseismic events revealed at Yingxiu show similar coseismic vertical displacements. We propose that the strain accumulation and deformation across the Longmenshan fault zone is a relatively stable and continuous process since late Quaternary. [Copyright &y& Elsevier]

Abstract: Three faults were involved in the rupture process of the May 12, 2008 Mw7.9 Wenchuan earthquake, representing a rarely documented case of multiple faults rupturing simultaneously. Distinct from the other two major NE-trending surface ruptures, the ~7km long Xiaoyudong surface rupture is oriented NW340° and shows thrust- and left‐slip faulting. In order to understand what role Xiaoyudong rupture played in the tectonic evolution of Longmenshan thrust system, we conducted a detailed investigation including geomorphic feature observation, coseismic displacement measurement, paleo-rupture event trenching, and fault kinematic estimation of the Xiaoyudong area. Our results not only document an in situ paleoearthquake occurring at 3.2–2.3ka BP, but also present the Xiaoyudong rupturing event as an oblique thrust with minor components of left lateral slip. We also found vertical and sinistral slip rates estimated as 1.1–1.5mm/yr and 0.5–0.7mm/yr, respectively. Finally, we suggest that the Xiaoyudong rupture is not a passive tear fault but an active participator of slip partitioning on multiple faults within the Longmenshan thrust system, and moreover, it gave strong response to both the 2008 and the penultimate earthquake while it kept silence with the antepenultimate event. [Copyright &y& Elsevier]

Abstract: The endocrine-disrupting chemicals (EDCs) was investigated in 28 riverine sediments from the Pearl River system, China and analyzed by an ultrasonication extraction and GC–MS method. The concentrations of 4-tert-octylphenol (OP), 4-nonylphenol (NP), and bisphenol A (BPA) in the sediments were in the ranges of <2.0–210, 107–16198 and <1.7–430ng/g dw, respectively. The steroid estrogens estrone (E1) and 17β-estradiol (E2) in the sediments ranged from <1.3 to 10.9ng/gdw and from <0.9 to 2.6ng/gdw, respectively. The spatial distribution of these chemicals was related to the discharge of domestic and industrial wastewater along the rivers. The positive correlation between EDCs and total organic carbon indicates that sedimentary organic carbon is an important factor in controlling the distributions of EDCs. Compared with other previous studies, the ZR and DR rivers from the PRD were heavily contaminated by APs and BPA. [Copyright &y& Elsevier]

The material sensitivity coefficient of Fatemi-Socie model (FS model) is proved to be not a constant for different materials and the effect of the shear stress on fatigue life is not considered. In this condition, a new multiaxial fatigue prediction model considering the shear stress and material sensitivity is established based on the critical plane method in this paper. Firstly, the material plane with the maximum shear strain amplitude is defined as the critical plane and a calculating method to determine the location of critical plane is presented. Secondly, a calculating method of material sensitivity coefficient k ' is proposed considering the effects of both the stress and strain on the critical plane by investigating the relationship between material sensitivity coefficient and the multiaxial fatigue life. Besides, the effect of the normal strain amplitude on the critical plane is considered because it has a certain impact on multiaxial fatigue life. Finally, four materials, including 45 steel, 316 L stainless steel, GH4169 alloy, and 7075-T651 aluminum alloy, are adopted to verify the feasibility and correctness of the proposed model under the proportional and non-proportional loading condition by comparing the equivalent strain model, the maximum shear strain model, the SWT model, KBM model, and FS model with the experimental result. The comparison results show that the prediction life of the proposed model is only second to the KBM model under multiaxial proportional loadings, but the prediction capability is superior to the other five models and the majority of the prediction results are within the scatter band with factor 3 under non-proportional loadings. • The effects of the shear stress and normal stress on multiaxial fatigue life are discussed. • A new calculating method of the material sensitivity coefficient is established. • The relationship between normal strain amplitude and the fatigue life is studied. • A new multiaxial fatigue life prediction model is established. [ABSTRACT FROM AUTHOR]

The contents of nonhydrolyzable organic matter (NHC) and black carbon (BC) were measured in soils and sediments from the Pearl River Delta, South China. Polycyclic aromatic hydrocarbons (PAHs) were extracted respectively by Soxhlet and an accelerated solvent extraction device (ASE) using different solvents. In addition, sequential aqueous leaching at different temperatures was carried out. The PAH content extracted with the sequential three solvent ASE is two times higher than that using the Soxhlet extraction method. The relationship of the PAH content with the NHC content is very significant. The PAH concentrations measured at various temperature steps fit well to the Van''t Hoff equation and the enthalpy was estimated. The investigation indicates that condensed organic matter such as kerogen carbon, aged organic matter, and BC is relevant for the extraction and distribution of native PAHs in the investigated field soils and sediments. [Copyright &y& Elsevier]

Abstract: We investigated contents, distribution and possible sources of PAHs and organochlorine pesticides (Ops) in 43 surface and subsurface soils around the urban Guangzhou where variable kinds of vegetables are grown. The results indicate that the contents of PAHs (16 US EPA priority PAHs) range from 42 to 3077μg/kg and the pollution extent is classified as a moderate level in comparison with other investigations and soil quality standards. The ratios of methylphenanthrenes to phenanthrene(MP/P), anthracene to anthracene plus phenanthrene (An/178), benz[a]anthracene to benz[a]anthracene plus chrysene (BaA/228), indeno[1,2,3-cd]pyrene to indeno[1,2,3-cd]pyrene plus benzo[ghi]perylene (In/In+BP) suggest that the sources of PAHs in the soil samples are mixed with a dominant contribution from petroleum and combustion of fossil fuel. The correlation analysis shows that the PAHs contents are significantly related to total organic carbon contents (TOC) (R 2 =0.75) and black carbon contents (BC) (R 2 =0.62) in the soil samples. Dichlorodiphenyltrichloroethane and metabolites (DDTs) and hexachlorocyclohexanes and metabolites (HCHs) account largely for the contaminants of OPs. The concentrations of DDTs range from 3.58 to 831μg/kg and the ratios for DDT/(DDD+DDE) are higher than 2 in some soil samples, suggesting that DDT contamination still exists and may be caused by its persistence in soils and/or impurity in the pesticide dicofol. The concentrations of HCHs are 0.19–42.3μg/kg. [Copyright &y& Elsevier]

The distribution and bioconcentration of polycyclic aromatic hydrocarbons (PAHs) in water, suspended particulate material (SPM), algae, and zooplankton samples from the Pearl River Delta (PRD), South China, were investigated. The PAHs in the water and SPM samples is significantly associated with chlorophyll a (Chl a), implying the important role of the aquatic productivity on PAH distribution. PAHs in the water or SPM samples were strongly correlated to dissolved organic carbon (DOC) or algal particulate organic carbon (A-POC). Moreover, the log bioconcentration factor (BCF) values (mL g−1) of PAHs in both the algae and zooplankton samples were linearly related to their log octanol-water coefficient (Kow) values. However, the slopes of these relationships were negatively correlated with Chl a, attributing to the difference in the dominant plankton species or the non-equilibrium exchange between air-water-biota. The above results indicate the important role of trophic levels on the distribution and bioaccumulation of PAHs. Unlabelled Image • The phytoplankton OC contributed 36.7% of POC. • PAHs respectively showed significant correlations with DOC, POC, and Chl a. • Aqueous and particulate PAHs were strongly correlated to DOC or algal POC. • Log BCF values of PAHs in planktons were linearly related to their log K ow values. • Algal biomass played an important role on the partitioning and uptake of PAHs. [ABSTRACT FROM AUTHOR]

Neonicotinoid insecticides have posed a great threat to non-target organisms, yet the mechanisms underlying their toxicity are not well characterized. Major modes of action (MoAs) of imidacloprid were analyzed in an aquatic insect Chironomus dilutus. Lethal and sublethal outcomes were assessed in the midges after 96-h exposure to imidacloprid. Global transcriptomic profiles were determined using de novo RNA-sequencing to more holistically identify toxicity pathways. Transcriptional 10% biological potency values derived from ranked KEGG pathways and GO terms were 0.02 (0.01–0.08) (mean (95% confidence interval) and 0.05 (0.04–0.06) μg L−1, respectively, which were more sensitive than those from phenotypic traits (10% lethal concentration: 0.44 (0.23–0.79) μg L−1; 10% burrowing behavior concentration: 0.30 (0.22–0.43) μg L−1). Major MoAs of imidacloprid in aquatic species were identified as follows: the activation of nicotinic acetylcholine receptors (nAChRs) induced by imidacloprid impaired organisms' nerve system through calcium ion homeostasis imbalance and mitochondrial dysfunction, which posed oxidative stress and DNA damage and eventually caused death of organisms. The current investigation highlighted that imidacloprid affected C. dilutus at environmentally relevant concentrations, and elucidated toxicity pathways derived from gene alteration to individual outcomes, calling for more attention to toxicity of neonicotinoids to aquatic organisms. Image 1 • Additional toxicity pathways of neonicotinoid to midges were identified. • Biological potency distribution curve provided sensitive pathway profiles. • The P path based on toxicogenomics could be a warning threshold for risk assessment. • Imidacloprid posed transcriptomic effect to midges at environment concentrations. Capsule: Transcriptomic analysis provides new insights to toxicity pathways of neonicotinoid insecticides to aquatic organisms and serves as an early warning tool for assessing aquatic risk. [ABSTRACT FROM AUTHOR]

The demineralized fraction (DM), lipid-free fraction (LF), nonhydrolyzable organic carbon fraction (NHC), and black carbon (BC) were isolated from five marine surface sediments, and they were characterized by elemental analysis as well as CO 2 and N 2 adsorption techniques, respectively. The NHC fractions were characterized using advanced solid-state 13C nuclear magnetic resonance (NMR) and x-ray photoelectron spectroscopy (XPS). Then, the sorption isotherms of phenanthrene (Phen) and nonylphenol (NP) on all of the samples were investigated by a batch technique. The CO 2 micropore volumes were corrected for the outer specific surface areas (SSAs) by using the N 2 -SSA. Significant correlations between the micropore-filling volumes of Phen and NP and the micropore volumes suggested that the micropore-filling mechanism dominated the Phen and NP sorption. Meanwhile, the (O + N)/C atomic ratios were negatively and significantly correlated with the sorption capacities of Phen and NP, indicating that the sedimentary organic matter (SOM) polarity also played a significant role in the sorption process. In addition, a strong linear correlation was demonstrated between the aromatic C and the sorption capacity of Phen for the NHC fractions. This study demonstrates the importance of the micropores, polarity, and aromaticity on the sorption processes of Phen and NP in the sediments. Image 1 • Sedimentary organic matter (NOM) was chemically fractionated into five fractions. • Structural and microporous properties were investigated using updated methods. • The sorption mechanism of phenanthrene (Phen) and noylphenol (NP) is expounded. • The sorption on black carbon is much higher for Phen than for NP. • Micropore-filling was the major mechanism for the sorption of Phen and NP. This study demonstrates the importance of the micropores, polarity, and aromaticity on the sorption processes of Phen and NP in marine sediments. [ABSTRACT FROM AUTHOR]

Highlights: [•] The bioconcentration and potential effect of EDCs in the PRD were investigated. [•] The E2 activity equivalents suggest high risks in the investigated water. [•] Occurrence of EDCs in fish bile can reflect that in ambient water. [•] The investigated wild carp and algae can bioaccumulate phenolic EDCs. [Copyright &y& Elsevier]

Phytoplankton productivity (PP) is expected to be impacted by climate change and anthropogenic activity in freshwater ecosystems, but the effects and interactions of these environmental stressors are often complex and not clearly understood. In this research, we investigated the influences of climate change and human activity on changes in PP recorded by sedimentary organic geochemical proxies (including bulk properties, Rock-Eval parameters, n -alkanols, and sterols) in the Pearl River Delta of southern China over the past few decades. Multiple proxies suggested that PP has increased in the mesotrophic Lian'an reservoir (LA) and the eutrophic Liuhuahu lake (LHH) since the 1960s. Phytoplankton sterols revealed that the dominant algal community consisted of dinoflagellates, cyanobacteria, and green algae in LA, while cyanobacteria and green algae were the primary algae groups in LHH. Phytoplankton proxies exhibited significant positive correlation with rising temperature (r > 0.57, p < 0.05) and nutrient loadings (r > 0.80, p < 0.01), suggesting that climate warming and nutrient input have contributed to the variations in PP. Climate change has caused a rise in temperature and changes in precipitation, along with human activity such as agriculture, dam construction, and sewage input, have collectively impacted aquatic environments. The generalized additive model (GAM) was used to quantitatively analyze the impacts of climate change and anthropogenic activity on aquatic ecosystems. Results demonstrated the cumulative and synergistic effects of climate change and anthropogenic activity, and higher climatic influences observed after the 1990s. The synergistic effects led to algal blooms and restricted the growth of aquatic macrophytes, particularly in the eutrophic LHH. This has worsened eutrophication and resulted in an imbalance in aquatic ecosystems. In summary, this research emphasizes the interactions between climate change and anthropogenic activity, and PP variations in aquatic ecosystems and underscores the importance of studying these factors to comprehend the influence of environmental stressors. • The phytoplankton productivity (PP) variations were traced by organic geochemical proxies. • Aquatic PP increased as a result of climate change and anthropogenic activity. • Generalized additive model quantified the climate and human impacts on aquatic ecosystems. • The effects of environmental factors resulted in algal blooms and species imbalance. [ABSTRACT FROM AUTHOR]

• Non-hydrolyzable organic matter (NHOM) was isolated from algae and cyanobacteria-rich phytoplankton. • The aliphatic structure of NHOM (algaenan-like) was observed through advanced NMR techniques. • Cyanobacteria-rich NHOM consisted of long, saturated and unbranched hydrocarbon chains. • Cyanobacteria-rich NHOM showed a high oil-prone potential. Two cultured chlorophyceae algae and two cyanobacteria-rich phytoplankton were separated into five fractions and characterized by 13C cross polarization/total sideband suppression (CP/TOSS) nuclear magnetic resonance spectroscopy (NMR), X-ray photoelectron spectroscopy (XPS), Rock-Eval and closed pyrolysis analyses. The structures of the acid nonhydrolyzable organic matter (NHOM) fractions were similar to those of poly(methylene)-rich aliphatic algaenan. We found that the cyanobacteria-rich phytoplankton contained aliphatic nonhydrolyzable biopolymers. The NMR and Rock-Eval analyses showed that the isolated NHOM exhibited high oil-prone potentials. Pyrolysis analysis of the field-collected NHOM from Liuhuahu Park in Guangzhou (GP_NHOM) indicated that it exhibited high oil-prone potential and comprised a long, saturated and unbranched hydrocarbon chain (up to C 33) structural unit. The maximum oil and gaseous hydrocarbon generation potentials reached 55.9% and 7.2%, respectively and were very close to those derived from 13C CP/TOSS NMR, suggesting that 13C NMR is an effective approach for evaluation of oil and gas production potentials. This investigation is helpful for improving understanding of kerogen formation mechanisms through selective preservation and the generation mechanisms of biocrude oil. [ABSTRACT FROM AUTHOR]

We investigated how the degradation of 7–14C–BaP aged in sediments by H 2 O 2 treatment was influenced by the chemical structures, compositions, and microporosity of sedimentary organic carbon (SOC). Unstable OC (USOC), stable OC (STOC), mineral-protected OC (MOC), and chemically resistant OC (ROC) fractions were fractionated. The chemical structures and microporosity of the ROC fractions were characterized by 13C solid-state nuclear magnetic resonance (NMR) and CO 2 adsorption technique, respectively. A first-order, two-compartment kinetics model described the degradation process very well (R 2 > 0.980). The BaP degradation ratios increased with the increasing USOC contents and decreased with the increasing ROC contents. The BaP parent compound in the aqueous solution was almost completely degraded. The considerable portions of oxidized intermediates were detected in different SOC fractions, which represented either oxidized intermediates or parent compounds. The very good multivariate regressions among the degradation kinetics parameters, SOC structures and micropore volumes demonstrated that ROC-bulk, aliphatic moieties, and microporosity played crucial roles in protecting sorbed BaP from being degraded by H 2 O 2. The results showed that ROC, aliphatic moieties, and microporosity played vital roles in Bap degradation process in sediments during H 2 O 2 treatment, which is reported for the first time in this study. Image 1 • The BaP degradation changed with the USOC and ROC contents in marine sediments. • The BaP fraction in USOC and aromatic C structures was easily degraded by H 2 O 2. • The BaP fraction in ROC and aliphatic C was hardly degraded by H 2 O 2. • The BaP fraction sorbed in nicropores was not readily released and mineralized. [ABSTRACT FROM AUTHOR]

Presenilins 1 and 2 (PS1 and 2) are the catalytic subunits of γ-secretase, a multiprotein protease that cleaves amyloid protein precursor and other type I transmembrane proteins. Previous studies with mouse models or cells have indicated differences in PS1 and PS2 functions. We have recently reported that clinical γ-secretase inhibitors (GSIs), initially developed to manage Alzheimer's disease and now being considered for other therapeutic interventions, are both pharmacologically and functionally distinct. Here, using CRISPR/Cas9-based gene editing, we established human HEK 293T cell lines in which endogenous PS1, PS2, or both have been knocked out. Using these knockout lines to examine differences in PS1- and PS2-mediated cleavage events, we confirmed that PS2 generates more intracellular amyloid β (Aβ) than does PS1. Moreover, we observed subtle differences in PS1- and PS2-mediated cleavages of select substrates. In exploring the question whether differences in activity among clinical GSIs could be attributed to differential inhibition of PS1 or PS2, we noted that select GSIs inhibit PS1 and PS2 activities on specific substrates with slightly different potencies. We also found that endoproteolysis of select PS1 FAD-linked variants in human cells is more efficient than what has been previously reported for mouse cell lines. Overall, these results obtained with HEK293T cells suggest that selective PS1 or PS2 inhibition by a given GSI does not explain the previously observed differences in functional and pharmacological properties among various GSIs. [ABSTRACT FROM AUTHOR]

Black carbon was produced by slow pyrolysis under an oxygen-limited condition at 500 °C, and was modified by some chemical methods (oxidation, hydrolysis, activation, and surface recombination). The modified samples were characterized by using elemental analysis, Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) surface analysis, Boehm titration, cation exchange capacity(CEC)analysis, CO 2 adsorption analysis, and then used to investigate the sorption behavior of phenanthrene. The results showed that the activation of ZnCl 2 gave a maximum nanopore volume of 96.5 μL/g and a specific surface area of 241 m 2 /g, while the oxidation of NaClO gave a minimum nanopore volume of 63.3 μL/g and a specific surface area of 158 m 2 /g. The FTIR, XPS, and Boehm titration analysis showed that the new oxygen-containing functional groups were introduced during the oxidation treatments of H 2 O 2 and NaClO. The sorption of phenanthrene on all samples was typically nonlinear, and the nonlinear factor ( n ) was negatively correlated with V o , especially with V o at 0–1.1 nm. The sorption parameter (log K OC ) was positively correlated with nanopore volume ( V o ) and specific surface area (SSA). Moreover, the model analysis showed that the nanopore filling was the main sorption mechanism, and molecular sieve effect was observed in the sorption of phenanthrene. [ABSTRACT FROM AUTHOR]

Kerogen was isolated from the Maoming shale at different temperatures to understand changes in chemical, structural and porosity characteristics during artificial maturation. Advanced solid-state 13 C nuclear magnetic resonance (NMR) techniques were employed along with Fourier transform infrared (FT-IR), Raman spectroscopy (RS), stable carbon isotopes, and Rock-Eval pyrolysis to characterize the organic matter (OM), whereas the microporosity and surface properties were elucidated using N 2 and CO 2 adsorption techniques. As the temperature increased, the aliphatic and carbonyl carbons of the kerogen samples showed remarkable decreases in abundance together with an increase of non-protonated and protonated aromatic carbons. Moreover, the kerogen became more enriched in 13 C and had a higher degree of crystallization with increasing Ro and T max . The aromaticity ranged from 46.9% to 94.7% and the minimum aromatic cluster size varied from 10 carbons at 350 °C to 38 carbons at 500 °C, which was significantly related to the microporosity ( V o, d-co2 ) of the kerogen samples and their nonlinear sorption of phenanthrene and benzene. The microporosity was extensively affected by the loss of aliphatic carbon and the increase of aromatic fused carbon. When the temperature reached 500 °C, the collapse of aromatic interlayer remarkably reduced the micropore volume in the kerogen, and then resulted in the decreasing adsorption of hydrophobic organic chemicals (HOCs). The above observation confirms the molecular sieve effect in the kerogen samples. In addition, the micro-filling adsorption for HOCs is dominant on the thermally simulated kerogen samples. [ABSTRACT FROM AUTHOR]

Stress gradient effect (SGE) and notch size effect (NSE) have important influences on the fatigue performance of engineering components. In this paper, a new multiaxial fatigue life prediction model is developed by considering the effects of both. Firstly, with the help of the coordinate transformation principle (CTP), the location of the dangerous critical plane is found according to the energy-critical plane (ECP) method, and the equivalent stress gradient factor (SGF) within the fatigue damage zone is calculated by analyzing the equivalent stress distribution on the critical plane. Secondly, considering the size of the notch, the effect of stress concentration at the notch is analyzed. Meanwhile, a size influence factor is introduced to characterize the NSE and construct a new fatigue strength reduction factor. Further, combining with the Manson-Coffin equation (MC equation), a new fatigue life prediction model for multiaxial notched components is proposed by considering SGE and NSE on fatigue damage. Finally, the experimental data of fatigue specimens with different notch sizes processed by En8 and GH4169 materials are used for model validation and comparison with other three classical models, and the results show that the prediction life of the new model for proportional and non-proportional loads is within two-fold dispersion band and the prediction ability is better than the other three classical models. • The location of the dangerous critical plane is found according to the energy-critical plane method. • The equivalent stress gradient factor within the fatigue damage zone is calculated. • A size influence factor is introduced and a new fatigue strength reduction factor is proposed. • A new fatigue life prediction model for multiaxial notched components is proposed. [ABSTRACT FROM AUTHOR]

• Trifluoroacetic acid (TFA) and sodium periodate (SP) fractions isolated from Chlorella alga. • Fractions structurally similar to algaenan. • The n -alkanes of SP and TFA fractions dominated by middle chain-length components. • 13C NMR spectroscopy is an effective approach for evaluating oil-prone potential (OGP) of Chlorella. • SP fraction exhibits high yields and OGP value and good bio-oil quality. Nonhydrolyzable organic carbon (NHC) fractions were isolated from commercial Chlorella using trifluoroacetic acid (TFA), sodium periodate (SP), ball mill (MES), and ball mill-sodium periodate (BSP) methods. The structures and relationships of the fractions with oil and gas production potentials (OGP) were investigated by solid-state 13C Cross Polarization/Total Sideband Suppression (CP/TOSS) NMR spectroscopy techniques and by confined pyrolysis. The results demonstrated that the TFA and SP fractions exhibited the highest polymethylene carbon contents and the lowest proportions of polar materials. Both bulk Chlorella and the NHC fractions had considerable oil and gas generation potential. The hydrogen indices evaluated by Rock-Eval analysis were highly significantly correlated with the OGP values estimated for the NHC fractions from the NMR methods. In addition, the oil and gas generated from the Chlorella sample and its NHC fractions were dominated with primary pyrolysis products. The contents of total n -alkanes (n -C 6–33) of the pyrolysates increased with increasing pyrolysis times. The n -alkanes of the TFA, SP, and BSP fraction pyrolysates were dominated by mid chain-length components (n -C 15 , n -C 17 , and n -C 23). Moreover, the SP fraction exhibited high NHC yield and OGP value, and low contents of nitrogen and oxygen. This study significantly improves our understanding of the bio-oil generation potential of this green alga. [ABSTRACT FROM AUTHOR]

Black carbon (BC) has drawn wide interest due to its important role in the global carbon budget and pollutant sequestration. Its soluble carbonaceous component, dissolved BC, is the key for understanding many geological and environmental processes of BC. In this study, we show that dissolved BC can be readily released in water under stirring from bulk BC produced by the slow pyrolysis of biomass. The chemical and structural properties of bulk, colloidal, and dissolved BC were thoroughly examined using elemental analysis and a variety of spectroscopic techniques. Compared with bulk BC, dissolved BC contained 30–40% more oxygen and more polar functional groups, but lower aromaticity and less condensed aromatic clusters. It is concluded that dissolved BC consists primarily of small aromatic clusters substituted by carboxylic groups, and by phenolic groups to a less extent. Dissolved BC represents an important source for soil and aquatic natural organic matter. The structure of dissolved BC was compared with some well-characterized humic substances. Results obtained from this work would shed new light on the mobility, liability, and reactivity of BC, as well as its impact on the global carbon budget and contaminant transport. [ABSTRACT FROM AUTHOR]

• The multiaxial stress gradient effect is studied by the normalized processing. • A new non-proportional additional strengthening factor is established. • A fatigue life prediction method suitable for notched specimens is established combining with Weibull distribution. • The revised P-S-N curves with a failure probability in the range of 5%-95% are given and analyzed. Based on the von-Mises criterion, the influence of stress gradient and additional strengthening effects on fatigue life are considered and a fatigue life prediction method suitable for notched specimens is established combining with Weibull distribution. Firstly, the maximum shear strain amplitude is defined as the damage parameter to determine the location of the critical plane, which can reflect the mechanism of crack initiation and propagation. Secondly, the equivalent stress gradient factor on the critical plane is obtained and the stress gradient influence index is introduced to characterize the degree of influence of the stress gradient. Finally, considering the effects of stress gradient and non-proportional additional strengthening, a new fatigue life prediction method is proposed based on the von-Mises criterion and the Weibull distribution, which can be used to obtain the fatigue life of multiaxial notched specimens under different failure probabilities. In order to verify the reliability of the proposed model, the prediction life using the proposed method, the SWT model, FS model and Manson-Coffin equation are compared with the experimental life of five materials (GH4169, TC4, Al7050, EN8, C40), and the compared results show that the accuracy of the proposed method is higher than that of the other three methods under proportional and non-proportional loading. Meanwhile, the P -S-N curves of multiaxial notched specimens with different failure probabilities are given and analysed. [ABSTRACT FROM AUTHOR]

• Novel aliphatic biopolymers were successfully isolated from two cyanobacteria. • Their structures were nearly identical to those reported for aliphatic algaenans. • The biopolymers comprised long and saturated hydrocarbon chains (up to C 33). • The biopolymers exhibited high gas-prone and oil-prone potentials. Two cultured cyanobacteria species were divided into three fractions, investigated using Rock-Eval, elemental analysis, and 13C cross polarization/total sideband suppression (CP/TOSS) nuclear magnetic resonance (NMR) to obtain information on the structure, composition, and oil and gas production potential (OGP) of these species. Confined pyrolysis experiments were performed on isolated acid nonhydrolyzable organic matter (NHOM) fractions. The results showed that the NHOM fractions from Oscillatoria sp. (OSC_NHOM) and Calothrix anomala (CAL_NHOM) were similar to the highly aliphatic algaenan in structure and capable of generating gas and oil. Pyrolysis experiments of the OSC_NHOM and CAL_NHOM fractions demonstrated that they contained a saturated and unbranched carbon chain with up to 33 carbon atoms and had high OGP. The maximum oil yield (59% for OSC_NHOM and 47% for CAL_NHOM) derived from the pyrolysis experiments was higher than that from oil-prone carbon (46% for OSC_NHOM and 39% for CAL_NHOM), suggesting that the 13C CP/TOSS NMR method slightly underestimates the oil production potential of cultured cyanobacterial (and possibly algal) biopolymers. Our investigation confirms the presence of algaenan-like biopolymers in a broader suite of cyanobacteria. [ABSTRACT FROM AUTHOR]

Highlights: [•] Algal samples were fractionated into four fractions. [•] Phenanthrene sorption for the nonhydrolyzable (NHC) fractions is nonlinear and for the other fractions is linear. [•] The lipid and NHC fractions have higher sorption capacities for phenanthrene than other fractions do. [•] Polymethylene carbon for the NHC fraction is the higher, the greater is its sorption capacity for phenanthrene. [•] The log K oc values are related to lipid contents and polarity indices for the bulk algae and their fraction samples. [ABSTRACT FROM AUTHOR]

Abstract: The indoor (home and workplace) and outdoor concentrations of the sum of 10 polybrominated diphenyl ethers (PBDEs), designated Σ10PBDEs (-28, -47, -66, -100, -99, -85, -154, -153, -138, -183), and BDE-209 were measured using high-volume air samplers in Guangzhou from October 2004 to April 2005. The Σ10PBDEs and BDE-209 concentration ranges were 125.1–2877 and 39–11,468pgm−3, respectively for home air, 181.3–8315 and 80.1–13,732pgm−3 for office air, 322.1–2437 and 73.1–8194pgm−3 for air in other workplaces, and 203.2–2426 and 1082–49,937pgm−3 for outdoor air. The levels of PBDEs in domestic and workplace environments are similar to those reported in others studies. However, the open-air values reported here are significantly higher than those found elsewhere. The dominant congeners observed in indoor air samples were those associated with penta-BDE and deca-BDE commercial mixtures. Our study also indicates that the primary indoor emission sources for PBDEs in Guangzhou are originated from the relatively old electronic/electrical appliances, especially computers, but not the PUF-containing furniture. The median daily human exposures to Σ10PBDEs and BDE-209 via inhalation in Guangzhou are 12.4 and 15.1ngday−1 person−1, respectively. The human inhalation exposure to Σ10PBDEs is higher than reported in two other studies (6.9 and 2.0ngday−1 person−1) presumably due to the larger number of compounds considered in this study as well as the higher outdoor concentrations of PBDEs. [Copyright &y& Elsevier]

Bioconcentration factor (BCF) is often assumed to be linearly associated with the octanol–water partition coefficient K ow for hydrophobic organic chemicals (HOCs). However, a large amount of data has suggested that the correlation between the logBCF and log K ow is curvilinear for HOCs. Similar curvilinear relationship has also been noticed for sorption of HOCs into poly(dimethyl)siloxane (PDMS), a polymer with cross-linked interior structures. So far no satisfactory explanation has been given to account for the deviation. In this study, we acquired additional experimental data to show that the curvilinear relationship between the log-based PDMS-coated fiber–water partition coefficient (log K f) and log K ow for polychlorinated biphenyls (PCBs) was indeed a reflection of the sorption process occurring in PDMS film other than experimental defects. The physical origin of the nonlinearity was pinpointed based on the theory of phase partitioning for HOCs. The linear relationship is observed if the solute molecule is considerably smaller than the size of a monomer unit of PDMS in that the Gibbs free energy required for cavity formation in PDMS is comparable to that in octanol. Higher free energy of cavity formation is needed to create sufficient free volume if the PCB molecular size is comparable to or larger than the monomer unit of PDMS. On the other hand, the free energy of cavity formation in octanol remains almost constant when this occurs, resulting in the observed curvilinear relationship. The proposed model adequately explains the observed data, as well as sheds lights into the physical origin of the steric interactions of large molecular size solute with the PDMS polymer network. [Copyright &y& Elsevier]

Abstract: Because of its cost and time saving features, solid-phase microextraction (SPME) is a leading candidate as a biomimic technique in assessing the bioavailable fraction of hydrophobic organic contaminants (HOCs) in sediment porewater. However, no predictive modeling framework in which to systematically address the effect of key parameters on SPME performance for this application exists. In this study, we derived two governing equations to predict (1) the minimum sediment volume required to achieve non-depletive conditions, and (2) dissolved phase HOC porewater concentrations (C pw) as functions of HOC- and sediment specific characteristics in a conceptual three compartment system. The resulting model predicted that was independent of HOC concentrations both in sediment and porewater, but did vary with hydrophobicity (characterized by log K ow), the fraction of sediment porewater (f pw), and the volume (V f) of the SPME sorbent phase. Moreover, the effects of these parameters were minimized (i.e., reached plateaus) as log K ow approached 4–5. Model predictions of C pw, a surrogate for SPME-based detection limits in porewater, decreased with increasing sediment volume (V s) at low V s values, but rapidly leveled off as V s increased. A third result suggested that the sediment HOC concentration required for SPME is completely independent of K ow. These results suggest that relatively small sediment volumes participate in exchange equilibria among sediment, porewater and the SPME fiber, and that large sediment HOC reservoirs are not needed to improve the detection sensitivity of SPME-based porewater samplers. The ultimate utility of this modeling framework will be to assist future experimental designs and help predict in situ bioavailability of sediment-associated HOCs. [Copyright &y& Elsevier]