Municipal pipeline networks as preferential vapor intrusion pathways: A review.

Recent reports show a rise in instances where municipal networks, such as sewer lines, serve as pathways for vapor intrusion (VI), enabling volatile organic compounds (VOCs) vapors to travel along these networks. These VOCs pose potential health risks to occupants of buildings connected to these networks. Currently, there's a lack of specific technical or regulatory guidance on identifying and assessing the VI risk associated with sewer as preferential VI pathways. This critical review summarizes key findings from studies and site investigations related to sewer VI pathways. These findings cover background VOCs concentration levels in sewers, updates to site conceptual models, advances in sewer sampling techniques, innovative tools for identifying and characterizing sewer VI, and practices for assessing and mitigating sewer VI risk. While significant improvements have been made towards understanding how municipal pipeline networks act as VI pathways, more research is still needed to develop strategies for investigating sites and assessing risks associated with "pipeline VI pathways". Future research could focus on the development of "pipeline VI pathways" data set, the improvement and validation of investigation tools, and improving the understanding of VOCs transportation mechanisms within these "pipeline VI pathways".

Bisphenol analogues induced social defects and neural impairment in zebrafish.

There is evidence in humans that endocrine disrupting chemicals exposure, such as bisphenol A (BPA), is tied to social behavior impacts when evaluated in early life stage. However, the potential social impact of BPA alternatives and its association with central nervous system (CNS) is poorly understood. Here, we performed behavioral test for zebrafish that are continuously exposed to environmental relevant concentrations (5 and 500 ng/L) of BPA, BPF, and BPAF since embryonic stage. Surprisingly, significant social behavior defects, including increased social distance and decreased contact time, were identified in zebrafish treated by 500 ng/L BPAF and BPA. These behavioral changes were accompanied by apparent histological injury, microglia activation, enhanced apoptosis and neuron loss in brain. The gut-brain transcriptional profile showed that genes involved in neuronal development pathways were up-regulated in all bisphenol analogs treatments, indicating a protective phenotype of CNS; however, these pathways were inhibited in gut. Besides, a variety of key regulators in the gut-brain regulation were identified based on protein interaction prediction, such as rac1-limk1, insrb1 and fosab. These findings implicated that the existence of bisphenol analogues in water would influence the social life of fish, and revealed a potential role of gut-brain transcriptional alteration in mediating this effect.

An Automated Solid-Phase Extraction-UPLC-MS/MS Method for Simultaneous Determination of Sulfonamide Antimicrobials in Environmental Water.

The large-scale use of sulfonamide antimicrobials in human and veterinary medicine has seriously endangered the ecological environment and human health. The objective of this study was to develop and validate a simple and robust method for the simultaneous determination of seventeen sulfonamides in water using ultra-high performance liquid chromatography-tandem mass spectrometry coupled with fully automated solid-phase extraction. Seventeen isotope-labeled internal standards for sulfonamides were used to correct matrix effects. Several parameters affecting extraction efficiency were systematically optimized, and the enrichment factors were up to 982-1033 and only requiring about 60 min per six samples. Under the optimized conditions, this method manifested good linearity (0.05-100 µg/L), high sensitivity (detection limits: 0.01-0.05 ng/L), and satisfactory recoveries (79-118%) with acceptable relative standard deviations (0.3-14.5%, n = 5). The developed method can be successfully utilized for the determination of 17 sulfonamides in pure water, tap water, river water, and seawater. In total, six and seven sulfonamides were detected in river water and seawater, respectively, with a total concentration of 8.157-29.676 ng/L and 1.683-36.955 ng/L, respectively, and sulfamethoxazole was the predominant congener.

Biobased epoxidized natural rubber/sodium carboxymethyl cellulose composites with enhanced strength and healing ability.

Conventional vulcanized rubbers cause a non-negligible waste of resources due to the formation of 3D irreversible covalently cross-linked networks. The introduction of reversible covalent bonds, such as reversible disulfide bonds, into the rubber network, is an available solution to the above problem. However, the mechanical properties of rubber with only reversible disulfide bonds cannot meet most practical applications. In this paper, a strengthened bio-based epoxidized natural rubber (ENR) composite reinforced by sodium carboxymethyl cellulose (SCMC) was prepared. SCMC forms a mass of hydrogen bonds between its hydroxyl groups and the hydrophilic groups of ENR chain, which gives the ENR/2,2'-Dithiodibenzoic acid (DTSA)/SCMC composites an enhanced mechanical performance. With 20 phr SCMC, the tensile strength of the composite increases from 3.0 to 10.4 MPa, which is almost 3.5 times that of the ENR/DTSA composite without SCMC. Simultaneously, DTSA covalently cross-linked ENR with the introduction of reversible disulfide bonds, which enables the cross-linked network to rearrange its topology at low temperatures and thus endows the ENR/DTSA/SCMC composites with healing properties. The ENR/DTSA/SCMC-10 composite has a considerable healing efficiency of about 96 % after healing at 80 °C for 12 h.

Environmentally-relevant concentrations of the antipsychotic drugs sulpiride and clozapine induce abnormal dopamine and serotonin signaling in zebrafish brain.

The presence of drugs in surface and groundwaters adversely affects the physiological function of non-target organisms due special activities that can pose a serious threats to various forms of aquatic life. Psychotropic drugs are one of the most commonly used drugs in the world. Hence, the aim of this study was to investigate the effect of environmentally-relevant concentrations of the antipsychotic drugs, sulpiride and clozapine, on dopaminergic (DAergic) and serotonergic (5-HTergic) neurotransmitter systems in the brain of zebrafish. Adult zebrafish (AB strain) were exposed to the environmentally-relevant concentrations of sulpiride, clozapine, or a mixture of sulpiride and clozapine. The effects of the drugs on the mRNA and protein levels of major functional molecules in DAergic and 5-HTergic systems were then analyzed in the telencephalon and diencephalon. Both drugs induced abnormal mRNA and protein levels of important functional molecules of the DA and 5-HT signaling pathways in both telencephalon and diencephalon, as shown by the abnormal transcriptional levels of TH, DAT, DR D1, DR D2, MAO, TPH, serotonin transporter (SERT), 5-HTR 1AA, 5-HTR 1B, 5-THR 2AA, and 5-HTR 2B, and the abnormal translational levels of DAT, DR D2, SERT, 5-HTR 1A, 5-HTR 1B, and 5-HTR 2B. In addition, we observed a specificity in the adverse effects of these antipsychotic drugs, in terms of doses and brain parts. Compared to their effects alone, the drug mixture had a weaker effect on the DA and 5-HT systems, suggesting an antagonistic interaction between sulpiride and clozapine. Our findings suggest that sulpiride and clozapine interfere with DAergic and 5-HTergic neurotransmitter systems in the telencephalon and diencephalon of zebrafish, resulting in possible effects on brain functions and posing a serious threat to the health of zebrafish.

Determination of quinolone antibiotics in environmental water using automatic solid-phase extraction and isotope dilution ultra-performance liquid chromatography tandem mass spectrometry.

The widespread use of quinolones in humans and animals has become a major threat to public health. In this study, a simple, rapid, sensitive, and high throughput method based on automatic solid-phase extraction and isotope dilution ultra-performance liquid chromatography tandem mass spectrometry was described for the determination of trace quinolones in environmental water. The proposed automated solid-phase extraction method was initially optimized, and the optimum experimental conditions found were 1 L water sample with 0.5 g/L Na2EDTA (pH 3) extracted and enriched by CNW Poly-Sery HLB cartridge at a flow rate of 50 mL/min and eluted by 8 mL of methanol. The linearity of the method ranged from 0.05 to 100 µg/L for 15 quinolones, with correlation coefficients ranging from 0.9993 to 0.9999. The limits of detection were in the low ng/L level, ranging from 0.005 to 0.051 ng/L. Finally, the optimized method was applied for determining trace levels of 15 quinolones in Wahaha pure water, tap water, river water, and seawater samples with good recoveries of 93 %-119 % and satisfactory relative standard deviations of 0.1 %-13.9 %. Fourteen quinolones were detected, and ofloxacin was the predominant congener in river water and seawater.

Database examination, multivariate analysis, and machine learning: Predictions of vapor intrusion attenuation factors.

Traditional soil vapor intrusion (VI) models usually rely on preset conceptual scenarios, simplifying the influences of limiting environmental covariates in determining indoor attenuation factors relative to subsurface sources. This study proposed a technical framework and applied it to predict VI attenuation factors based on site-specific parameters recorded in the United States Environmental Protection Agency (USEPA)'s and the California Environmental Protection Agency (CalEPA)'s VI databases, which can overcome the limitations of traditional VI models. We examined the databases with multivariate analysis of variance to identify effective covariates, which were then employed to develop VI models with three machine learning algorithms. The results of multivariate analysis show that the effective covariates include soil texture, source depth, foundation type, lateral separation, surface cover, and land use. Based on these covariates, the predicted attenuation factors by these new models are generally within one order of magnitude of the observations recorded in the databases. Then the developed models were employed to generate the generic indoor attenuation factors to subsurface vapor (i.e., the 95th percentile of selected dataset), the values of which are different between the USEPA's and CalEPA's databases by one order of magnitude, although comparable to recommendations by the USEPA and literature, respectively. Such a difference may reflect the significant regional disparity in factors such as building structures or operational conditions (e.g., indoor air exchange rates), which necessitates generating generic VI attenuation factors on a state-specific basis. This study provides an alternative for VI risk screens on a site-specific basis, especially in states with a good collection of datasets. Although the proposed technical framework is used for the VI databases, it can be equally applied to other environmental science problems.

Characterization of vapor intrusion sites with a deep learning-based data assimilation method.

Appropriate characterization of site soils is essential for accurate risk assessment of soil vapor intrusion (VI). In this study, we develop a data assimilation method based on deep learning (i.e., ES(DL)) to estimate the distribution of soil properties with limited measurements. Two hypothetical VI scenarios are employed to demonstrate site characterization using the ES(DL) method, followed by validation with a laboratory sandbox experiment and then one practical site application. The results show that the ES(DL) method can provide reasonable estimates of the effective diffusion coefficient distributions and corresponding emission rates (into the building) in all four cases. The spatial heterogeneity of site soils can be characterized by considerably enough measurements (i.e., 15 sampling points in the first hypothetical case); otherwise, layered characterization is recommended at the cost of neglecting horizontal heterogeneity of site soils. This new method provides an alternative to characterize VI sites with relatively fewer sampling efforts.

Environmental level of bisphenol F induced reproductive toxicity toward zebrafish.

Bisphenol F (BPF), as an important bisphenol A substitute, is being increasingly used for industrial production. Here we performed large scale fecundity test for zebrafish that are continuous exposed to environmental levels of BPF (0.5, 5 and 50 µg/L) from embryonic stage, and identified suppressed spawning capacity of females and reduced fertility rate of males in adulthood. Although pathological change is only observed in female gonads, the transcriptional change in the hypothalamic-pituitary-gonad axis genes occurred in the gonads of both female and male fish at 150 days post-exposure. F1 generation embryos showed abnormal developmental outcomes including decreased heart rate, reduced body length, and inhibition of spontaneous movement after parental exposure to BPF. RNA-sequencing showed that the genes involved in skeletal/cardiac muscle development were significantly altered in F1 embryos spawned by BPF-treated zebrafish. The advanced pathway analysis showed that cancer and tumour formation were the most enriched pathways in the offspring of 0.5 and 5.0 µg/L groups; organismal development and cardiovascular system development were mainly affected after parental exposure to 50 µg/L of BPF; these changes were mediated by several involved regulators such as GATA4, MYF6, and MEF2C. These findings confirmed that long-term exposure to BPF at environment relevant concentration would result in reproductive toxicity among zebrafish indicating the urgent demand for the control of BPA substitutes.

Occurrence, bioaccumulation and potential risk of polyhalogenated carbazoles in marine organisms from the East China Sea.

As well-known emergent environmental contaminants, polyhalogenated carbazoles (PHCZs) have recently received increasing attention. In this study, we investigated the concentrations of carbazole (CZ) and PHCZs in 70 marine organisms from the East China Sea (ECS). CZ and 9-11 PHCZs were detected in organisms from the ECS, with concentrations in the range of 0.75-33 ng/g lipid weight, lw and 4.3-113 ng/g lw, respectively. Among the PHCZs, there were 3-4 major components in zooplankton, fish, shrimp, crabs, snails and shellfish, and the sum of these major components accounted for 59% to 67% of ∑PHCZs. The bioaccumulation potentials of 1,3,6,8-tetrachlorocarbazole (1368-CCZ) and 3-chlorocarbazole (3-CCZ) from water were observed. The logarithmic bioaccumulation factor (logBAF) values of the CZ and PHCZs increased significantly with increasing logKOW values (R = 0.449-0.784, p < 0.01). The trophic magnification factor (TMF) values of the CZ, 9 PHCZs and ∑PHCZs were calculated to be 3.32, 1.87-4.06 and 2.36, respectively, indicating the potential biomagnification of the CZ and PHCZs in the zooplankton-shrimp-fish food web. The toxic equivalents (TEQs) of PHCZs in organisms from the ECS were in the range of 0.78-36 pg TEQ/g lw. Overall, for the first time, this study systematically examined the occurrence, bioaccumulation and potential risk of PHCZs in the marine food web of the East China Sea.

Determination of Phthalates in Marine Sediments Using Ultrasonic Extraction Followed by Dispersive Solid-Phase Extraction and Gas Chromatography-Mass Spectrometry.

A simple, rapid and novel method has been developed and validated for determination of 16 phthalates in marine sediment samples by gas chromatography coupled to mass spectrometry. Freeze dried samples were first ultrasonic extraction by n-hexane:methylene chloride (1:1, v/v) and n-hexane:ethyl acetate (1:1, v/v) and followed by dispersive solid-phase extraction cleanup. The linearity of this method ranged from 1 to 1,000 µg/L, with regression coefficients ranging between 0.9993 and 0.9999. The limits of detection were in ng/g level, ranging between 0.1 and 0.25 ng/g (dry weight). The concentration of the total phthalates in marine sediment samples from Waters of Dongji (Zhoushan, China), Yueqing Bay (Wenzhou, China) and Coastal Waters of Yuhuan (Taizhou, China) ranged from 235.4 to 608.7 µg/kg with diisobutyl phthalate, dibutyl phthalate and di(2-ethylhexyl) phthalate being the major species, which constitutes of 94.6 and 98.1% of the total phthalates. The recoveries of spiked 16 phthalates at different concentration levels in sediment sample 3 of Waters of Dongji (Zhoushan, China) and sediment sample 3 of Yueqing bay (Wenzhou, China) were in the range of 78-117% and 83-114%, respectively, with relative standard deviations of 2.4-6.8% and 3.4-7.5% (n = 5), respectively. The performance of the proposed method was also compared with traditional Soxhlet extraction and column chromatography cleanup on the same genuine sediment samples and comparable efficiencies were obtained. It is concluded that this method can be successfully applied for the determination of phthalates in different marine sediment samples.

Spatial distribution, partitioning, and ecological risk of short chain chlorinated paraffins in seawater and sediment from East China Sea.

Short chain chlorinated paraffins (SCCPs) have attracted increasing attention due to their potential risks to the ecosystem and human health. However, there is still a lack of systematic research on their environmental fate in the coastal marine environment. In this study, we collected paired seawater (n = 40) and surface sediment samples (n = 40) from East China Sea, and investigated their spatial distribution, partitioning behaviors and ecological risks. The total SCCP concentrations (∑SCCPs) in seawater and sediment samples were in the range of 12.2-430 ng/L and 89.6-351 ng/g (dry weight), respectively. C10-11 SCCPs and Cl5-7 SCCPs were the predominant homologues in all of the samples. This study first calculated the field-based logKOC values for ∑SCCPs in the marine environment, which ranged from 5.0 to 6.5 (mean 5.5). The logKOC values of SCCP homologues (range 3.6-8.0, mean 5.6) showed a weak correlation with their logKOW (R = 0.214, p < 0.05). A preliminary risk assessment indicated that SCCPs at current levels posed no significant ecological risk. Overall, this study contributes to the further understanding of environmental behaviors of SCCPs in the marine environment.

Spectroscopic characterization of dissolved organic matter from macroalgae Ulva pertusa decomposition and its binding behaviors with Cu(II).

Dissolved organic matter (DOM) from macroalgae is regarded a crucial source of autochthonous DOM in coastal ocean. In the present study, the characteristics of DOM from the macroalgae Ulva pertusa decomposition (U. pertusa-DOM) and its binding behaviors with Cu(II) using multiple spectroscopic techniques and chemometric analyses. The labile U. pertusa-DOM could be consumed and transformed by microorganisms. The absorption spectroscopic descriptors indicate that the hydrophobicity, aromaticity, and molecular weight of the U. pertusa-DOM increase during the 27-day incubation period. Fluorescence excitation-emission matrix spectroscopy combined with parallel factor analysis suggests that the relative abundance of the protein-like component (C1) (96.10-84.96%) sequentially decreases, whereas the humic-like components (C2) (2.16-9.73%) and (C3) (1.75-5.31%) in the U. pertusa-DOM increase with the U. pertusa decomposition. The Cu(II) binding properties of the U. pertusa-DOM are dependent on the decomposition time. The order of the conditional stability constant (logKM) is C2 > C1 > C3. The complexation capacity (f) of C1 is higher than those of C2 and C3 at a specific time. Synchronous fluorescence spectroscopy coupled with two-dimensional correlation spectroscopy reveals that the microbial degradation could accelerate the Cu(II) binding to humic-like fractions in the U. pertusa-DOM. These findings will help us better understand the biogeochemical behaviors of macroalgal DOM and heavy metal in coastal ecosystems.

Development and Validation of a Controlled Pressure Method Test Protocol for Vapor Intrusion Pathway Assessment.

Controlled pressure method (CPM) testing is a building-specific diagnostic tool for vapor intrusion (VI) pathway assessment which offers advantages over traditional pathway assessment approaches. By manipulating the building pressure conditions, the CPM creates the worst-case VI impact and provides rapid insight into the type of vapor source(s). The primary barrier to general acceptance and use of this tool is the need for definitive guidance on test design parameters, such as the indoor-outdoor pressure difference (or exhaust fan flow rate), CPM test duration, exhaust fan location, and air sampling location(s) and conditions. This study focused on a systematic evaluation of each of these factors, which then led to the formulation of proposed CPM testing guidelines. The results suggest that CPM tests should be conducted with both negative and positive pressure indoor-outdoor differentials of about 10-15 Pa, and the tests should last for at least nine indoor air exchanges for negative pressure difference testing and four indoor air exchanges for positive pressure difference testing. Although exhaust fan intake sampling is sufficient to provide critical information to assess impacts during negative pressure testing, adding room-specific indoor air sampling to both negative and positive pressure difference testing can provide insight into vapor entry locations and indoor source contributions.

Temporal variability of chlorinated volatile organic compound vapor concentrations in a residential sewer and land drain system overlying a dilute groundwater plume.

Some subsurface sewer and land drain networks will facilitate the migration of chlorinated volatile organic compounds (CVOCs) from dissolved contaminant groundwater plumes to indoor air. As this vapor intrusion (VI) pathway has only recently been documented, guidance for evaluating it, including recommendations for timing, frequency, duration and location for vapor sampling in subsurface piping networks is non-existent. To address this gap, a three-year investigation of CVOC concentrations from land drains, storm drains, and sanitary sewers was undertaken in a neighborhood overlying a large-scale dissolved chlorinated VOC (CVOC) groundwater plume. Vapor sampling included the collection of grab (time-discrete) samples from up to 277 manholes, hourly grab sampling from three manhole locations, and 24-h duration collection during week-long sampling from 13 land drain and sewer manholes. The spatial distribution of vapor and water concentrations and the temporal variations in the vapor values observed in this study suggest that week-long vapor sampling conducted at different times of the year and with samples collected at manhole locations overlying and outside a dissolved plume might be needed to ensure robust VI pathway assessment at other sites. These findings are expected to be of relevance to regulatory agencies involved in the development of current or future VI pathway assessment guidance.

Characterization of fluorescent dissolved organic matter from green macroalgae (Ulva prolifera)-derived biochar by excitation-emission matrix combined with parallel factor and self-organizing maps analyses.

This study investigated the effects of various pyrolysis temperatures and extraction salinities on the fluorescence features of DOM from Ulva prolifera-derived biochar under aseptic conditions using fluorescence excitation-emission matrix (EEM) spectroscopy with parallel factor (PARAFAC) analysis and self-organizing maps (SOM). Four humic-like substances and one protein-like substance were identified by the PARAFAC model. The contents and compositions of PARAFAC components depended more on the pyrolysis temperature than on the extraction salinity. A high pyrolysis temperature could enhance the release of humic-like DOM from biochar. Coupling PARAFAC and SOM facilitates the visualization and interpretation of the relationship between the pyrolysis temperature and the fluorescence properties of DOM. These results are valuable for understanding the effects and processes of macroalgal biochar in the possible environmental and industrial applications.

Effect of organic carbon to nitrogen ratio in wastewater on growth, nutrient uptake and lipid accumulation of a mixotrophic microalgae Chlorella sp.

This study investigated the biomass/lipid production, nutrient removal and fatty acid composition of an isolated mixotrophic microalga (Chlorella sp. G-9) cultured in simulated wastewater with different TOC/TN ratio. As the TOC/TN ratio of wastewater increased from 0 to 24, the growth rate of Chlorella sp. G-9 increased gradually, but did not increase further at 30. Nutrient removal was related to microalgae growth. In the wastewater with TOC/TN ratio of 24 and 30, 99.58% and 99.61% nitrogen was removed, respectively. In conditions of initial TOC/TN ratios of 24 and 30, Chlorella sp. G-9 could accumulate lipid as high as 35.3% and 36.5%, respectively. The corresponding lipid productivities were 34.2 and 32.6 mg L-1 d-1, respectively, which were 13.7 and 13.0 times higher than those in photoautotrophic condition. Increasing the initial TOC/TN ratio of the wastewater could slightly increase the saturated degree in fatty acid, thereby improving the stability of biodiesel.

Creation of a Sub-slab Soil Gas Cloud by an Indoor Air Source and Its Dissipation Following Source Removal.

It is accepted that indoor sources of volatile organic compounds can confound vapor intrusion (VI) pathway assessment. When they are discovered during pre-sampling inspection, indoor sources are removed and air sampling is delayed, with the assumption that a few hours to a few days are sufficient for indoor source impacts to dissipate. This assumption was tested through the controlled release of SF6 and its monitoring in indoor air and soil gas at a study house over 2 years. Results show that indoor sources generate subsurface soil gas clouds as a result of fluctuating direction in the exchange between soil gas and indoor air and that it may take days to weeks under natural conditions for a soil gas cloud beneath a building to dissipate following indoor source removal. The data also reveal temporal variability in indoor air and soil gas concentrations, long-term seasonal patterns, and dissipation of soil gas clouds over days to weeks following source removal. Preliminary modeling results for similar conditions are consistent field observations. If representative of other sites, these results suggest that a typical 1-3 day waiting period following indoor source removal may not be sufficient to avoid confounding data and erroneous conclusions regarding VI occurrence.

Simultaneous nutrient removal and biomass/lipid production by Chlorella sp. in seafood processing wastewater.

Microalgae cultivation in wastewater has received increasing attention in recent years due to its many advantages. In this work, microalgae were cultured in seafood processing wastewater (SPW) for algal biomass and lipid production as well as nutrient removal. The biomass yield of Chlorella sp. achieved in the batch cultivation was 896 mg L-1, indicating that SPW contains a certain amount of nutrients which can be used for the growth of microalgae. However, the maximum specific growth rate of Chlorella sp. cultured in SPW throughout the whole cultivation period was only 0.040 d-1, suggesting that the growth of algal cells was inhibited during the culture process. High concentration of unionized ammonia in the SPW was found to be a factor inhibiting the growth of Chlorella sp. Aerated SPW (ASPW) and diluted SPW (DSPW) proved to be better culture media than SPW without pretreatment. The maximum specific growth rates of Chlorella sp. cultured in ASPW and DSPW during the culture interval were 0.156 and 0.091 d-1, respectively. Aeration pretreatment of SPW reduced the amount of toxic unionized ammonia, while most of the nutrients were retained in the wastewater. Therefore, higher biomass productivity (77.7 mg L-1 d-1) and higher lipid productivity (20.4 mg L-1 d-1) of microalgae were achieved in ASPW. Additionally, improved nutrient removal rates from ASPW were also achieved due to the faster growth of microalgae. The average nutrient removal rates in ASPW during the whole cultivation period were 4.98 and 1.91 mg L-1 d-1 for nitrogen and phosphorus, respectively.

Sample Pretreatment Method for Determination of Indicator Polychlorinated Biphenyls in Seafood using Ultrasonic Extraction Followed by Dispersive Solid-Phase Extraction and Gas Chromatography - Electron Capture Detection.

A simple, rapid and novel method has been developed and validated for the determination of seven indicator polychlorinated biphenyls (PCBs) in seafood samples by gas chromatography coupled to electron capture detector. Freeze-dried samples were done first ultrasonic extraction by n-hexane:methylene chloride:acetone (3:1:1, v/v), and then one-step clean-up (dispersive solid-phase extraction clean-up) or two-step clean-up (concentrated sulfuric acid purification and dispersive solid-phase extraction clean-up) was selected according to the lipid contents of the samples, if the lipid content was no more than 1%, one-step clean-up was used, otherwise, two-step clean-up was chose. The linearity of this method ranged from 1.25 to 100 µg/L, with regression coefficients ranging between 0.9991 and 0.9998. The limits of detection were in low ng/g level, ranging between 0.005 and 0.0076 ng/g (wet weight). The recoveries of spiked seven PCBs with external calibration method at different concentration levels in Pseudosciaena polyactis, Penaeus vannamei and Sinonovacula constricta were in the range of 78-105%, 73-110% and 75-107%, respectively, and with relative standard deviations of 3.3-5.1%, 3.5-6.3% and 3.4-5.1% (n = 5), respectively. The performance of the proposed method was also compared with traditional soxhlet extraction and column chromatography clean-up on the same real seafood samples and comparable efficiencies were obtained. It is concluded that this method can be successfully applied for the determination of PCBs in different seafood samples.