Simultaneous Measurement of Trace Levels of Hg, As, Sb, and Bi in Coastal Seawater with a Multichannel Chemical Vapor Generation Atomic Fluorescence Spectrometer.

Trace levels of Hg, As, Sb, and Bi in coastal seawater have been simultaneously detected by a laboratory-built multichannel chemical vapor generation coupled to an atomic fluorescence spectrometer. The system was configured with a built-in electrochemical H2 generator as the fuel supplier to replace chemical H2 produced by the oxidation of potassium borohydride under acidic conditions in traditional instruments. The electrochemical H2 generator not only isolated the atomization process from the chemical vapor injection process but also improved the stability of atomization, excitation, and fluorescence emission in the hydrogen flame, making it easier to optimize conditions for CVG while introducing evaporating multielement vapors. Calibrations were obtained using a mixed standard solution of Hg(II), As(III), Sb(III), and Bi(III). The addition of KBr to a 3% (v/v) HCl solution was selected as the preservative to ensure the stability of 0.10 µg/L Hg(II) in a multielement standard solution for at least 15 days while also preserving µg/L levels of As(III), Sb(III), and Bi(III) stable. The method detection limits (LOD, 3σ) were 0.001, 0.015, 0.010, and 0.005 µg/L for Hg, As, Sb, and Bi, respectively. The relative standard deviations (RSD, n = 7) of the standard spiked seawater samples were 3.2% (0.020 µg/L Hg), 1.2% (0.50 µg/L As), 1.0% (0.50 µg/L Sb), and 3.5% (0.050 µg/L Bi), respectively. The recoveries of seawater samples spiked with different salinities were in the range of 84.5%(Sb)-114%(Hg). The system has been successfully applied to the simultaneous analysis of the four elements in the seawater samples collected from Xiamen Bay, Southeast China.

Automated Determination of Dissolved Reactive Phosphorus at Nanomolar to Micromolar Levels in Natural Waters Using a Portable Flow Analyzer.

Automated in-field methods for measuring dissolved reactive phosphorus (DRP) over a large concentration range are in high demand for the purpose of better understanding the biogeochemistry of phosphorus in the river-estuary-coast continuum to the open ocean. Here, an automated portable and robust analyzer was described for the determination of nanomolar to micromolar levels of DRP in natural waters. The quantification of DRP was based on classic phosphomolybdenum blue (PMB) chemistry. All the components of the analyzer were computer-controlled using LabVIEW-based laboratory-programmed software. When equipped with a 3 cm Z-type flow cell, the system demonstrated linearity with concentrations up to 12 µmol L-1, a sampling rate of 20 h-1, a limit of detection of 0.11 µmol L-1, and relative standard deviations (RSDs) of 0.4-4.6% (n = 11-576). When a solid-phase extraction cartridge was combined with the analyzer, the PMB formed from the sample was automatically concentrated on the hydrophilic-lipophilic balanced sorbent. The concentrated PMB compound was eluted with NaOH solution and measured in the spectrophotometric system. Under optimal conditions, the nanomolar-level mode afforded a sampling rate of 8 h-1, a limit of detection of 1.7 nmol L-1, and RSDs of 3.0-5.7% (n = 11-120). The system exhibited advantages that included a wide linear range, high sensitivity and reproducibility, low reagent consumption, and insignificant interference from salinity, silicate, arsenate, and other P-containing compounds. The system was successfully applied for discrete sample analysis, fixed site online monitoring, and the real-time underway measurement of DRP in riverine-estuarine-coastal waters.

Application of an Isotope Binary Mixing Model for Determination of Precise Mercury Isotopic Composition in Samples with Low Mercury Concentration.

An isotope binary mixing model was applied for high precision measurement of mercury isotope ratios in samples with low mercury concentrations by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Standard addition was used to evaluate the precision and accuracy of the isotope composition calculations resulting from the isotope binary mixing model. A high, steady 202Hg signal of approximately 2.13 V was achieved, with the mercury concentration reaching 3 ng/mL. The isotopic composition of three standards (NIST SRM 1646a; NIST SRM 1575a; BCR 482) and natural samples were precisely determined. The standards and natural samples were diluted to low mercury concentrations (low to 0.90 ng/mL) and mixed with standard solutions (NIST SRM 3133) with high mercury concentrations (50 ng/mL); the isotopic compositions of low mercury concentration samples were calculated using an isotope binary mixing model after the isotopic compositions of the mixing solutions were measured. The results showed that the uncertainty of the calculated mercury isotopic compositions was in an acceptable range and the calculation isotope data were in good agreement with direct measurements. Our method allows the precise determination of mercury isotope composition in mercury solutions of concentrations (0.90 ng/mL) below the detection limit of the current system (3.00 ng/mL).

A Novel Active Sampler Coupling Osmotic Pump and Solid Phase Extraction for in Situ Sampling of Organic Pollutants in Surface Water.

Active samplers for ambient monitoring of trace contaminants in surface water are highly desirable, but their use is often constrained by power supply. Here, we proposed a novel solution by coupling an improved osmotic pump (OP) with a solid-phase extraction (SPE) cartridge to construct a power-free active sampler for organic contaminants. The OP simply consisted of two cylindrical chambers separated by a reverse osmosis membrane. We, for the first time, added ion-exchange resins into the OP inlet chamber and successfully constructed OPs with a smooth and constant flow. In the OP-SPE sampler, water was continuously drawn through the SPE cartridge at a constant flow, and time-weighted average concentration over the sampling course may be easily calculated from the amount of target analytes retained on the SPE cartridge and water collected in the sampler. The OP-SPE samplers were deployed in a river to detect herbicides, and the measured concentrations were largely in agreement with the average of 11 daily spot samples. Given that a wide range of SPE cartridges are available for different classes of organic contaminants, this approach is versatile and may find widespread applications for in situ sampling of surface water under different conditions, including poorly accessible locations.

Development of an Integrated Syringe-Pump-Based Environmental-Water Analyzer ( iSEA) and Application of It for Fully Automated Real-Time Determination of Ammonium in Fresh Water.

The development of a multipurpose integrated syringe-pump-based environmental-water analyzer ( iSEA) and its application for spectrophotometric determination of ammonium is presented. The iSEA consists of a mini-syringe pump equipped with a selection valve and laboratory-programmed software written by LabVIEW. The chemistry is based on a modified indophenol method using o-phenylphenol. The effect of reagent concentrations and sample temperatures was evaluated. This fully automated analyzer had a detection limit of 0.12 µM with sample throughput of 12 h-1. Relative standard deviations at different concentrations (0-20 µM) were 0.23-3.36% ( n = 3-11) and 1.0% ( n = 144, in 24 h of continuous measurement, ∼5 µM). Calibration curves were linear ( R2 = 0.9998) over the range of 0-20 and 0-70 µM for the detection at 700 and 600 nm, respectively. The iSEA was applied in continuous real-time monitoring of ammonium variations in a river for 24 h and 14 days. A total of 1802 samples were measured, and only 0.4% was outlier data (≥3 sigma residuals). Measurements of reference materials and different aqueous samples ( n = 26) showed no significant difference between results obtained by reference and present methods. The system is compact (18 cm × 22 cm × 24 cm), portable (4.8 kg), and robust (high-resolution real-time monitoring in harsh environments) and consumes a small amount of chemicals (20-30 µL/run) and sample/standards (2.9 mL/run).

Real-time redox speciation of iron in estuarine and coastal surface waters.

An automated, shipboard-use system was developed for real-time speciation of iron in coastal surface waters. It comprised a towed Fish underway sampler and a modified reverse flow injection analysis system with a liquid waveguide capillary flow cell-spectrophotometric detection device. The detection was based on the reaction between ferrozine and Fe(II). The detection limits of 0.3 and 0.7 nM were achieved for Fe(II) and Fe(II+III), together with their respective dynamic linear ranges of 0.5-250 and 0.9-250 nM. The system was successfully deployed and run consecutively for about 1 week during a cruise in August 2009 to the East China Sea off the Changjiang Estuary. The distribution of operationally defined field dissolvable Fe(II) and Fe(II+III) (expressed as Fea(II) and Fea(II+III)) in these areas was obtained, which showed that both Fea(II) and Fea(II+III) concentrations decreased with salinity when there were relatively high Fea(II) concentrations (up to about 120 nM) near shore. A distinct distribution of Fea(II) to Fea(II+III) ratios was also revealed, with a ratio of 0.58 in the water off Changjiang Estuary and 0.19 in the open ocean.

Determination of benzimidazole anthelmintics in milk and honey by monolithic fiber-based solid-phase microextraction combined with high-performance liquid chromatography-diode array detection.

A porous poly(methacrylic acid-co-ethylene dimethacrylate) monolithic fiber (MEMF) for solid-phase microextraction (SPME) of five benzimidazole anthelmintics was prepared by in-situ polymerization. The effect of polymerization conditions on SPME of the target analytes was studied thoroughly. The physicochemical properties of the monolith were characterized by infrared spectroscopy, elemental analysis, scanning electron microscopy, and mercury intrusion porosimetry. Several conditions affecting the extraction efficiency were investigated and, under the optimized conditions, a simple and sensitive method for the determination of trace benzimidazoles residues in milk and honey was established by coupling MEMF-SPME with high-performance liquid chromatography-diode array detection (MEMF-SPME-HPLC-DAD). Under the optimum experimental conditions, the limits of detection (S/N = 3) of the method were 0.11-0.30 µg L(-1) for milk and 0.086-0.28 µg L(-1) for honey. Evaluation of intra-day and inter-day precision showed reproducibility was satisfactory-relative standard deviations (RSD) for both were <10 %. Finally, the method was successfully used for determination of benzimidazole residues in milk and honey. Recoveries obtained for determination of benzimidazole anthelmintics in spiked samples ranged from 72.3 to 121 %, with RSD always <11 %.

Effect of environmental factors on the complexation of iron and humic acid.

A method of size exclusion chromatography coupled with ultraviolet spectrophotometry and off-line graphite furnace atomic absorption spectrometry was developed to assess the complexation properties of iron (Fe) and humic acid (HA) in a water environment. The factors affecting the complexation of Fe and HA, such as ionic strength, pH, temperature and UV radiation, were investigated. The Fe-HA complex residence time was also studied. Experimental results showed that pH could influence the deprotonation of HA and hydrolysis of Fe, and thus affected the complexation of Fe and HA. The complexation was greatly disrupted by the presence of NaCl. Temperature had some influence on the complexation. The yield of Fe-HA complexes showed a small decrease at high levels of UV radiation, but the effect of UV radiation on Fe-HA complex formation at natural levels could be neglected. It took about 10 hr for the complexation to reach equilibrium, and the Fe-HA complex residence time was about 20 hr. Complexation of Fe and HA reached a maximum level under the conditions of pH 6, very low ionic strength, in the dark and at a water temperature of about 25°C, for 10 hr. It was suggested that the Fe-HA complex could form mainly in freshwater bodies and reach high levels in the warm season with mild sunlight radiation. With changing environmental parameters, such as at lower temperature in winter or higher pH and ionic strength in an estuary, the concentration of the Fe-HA complex would decrease.

Preparation of monolithic fibers for the solid-phase microextraction of chlorophenols in water samples.

Monolithic fibers were synthesized and applied for the solid-phase microextraction and determination of chlorophenols in environmental water samples by coupling with HPLC. The fibers were prepared by copolymerization of vinylimidazole and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The effect of the preparation conditions of monolithic fibers on the extraction efficiencies was investigated in detail. Several characteristic techniques, such as elemental analysis, infrared spectroscopy, mercury-intrusion porosimetry, and SEM were used to characterize the monolithic material. The effect of the extraction parameters, including desorption solvent, extraction and desorption time, pH values, and ionic strength in sample matrix on the extraction performance was investigated thoroughly. Under the improved extraction conditions, the linear ranges of 2-chlorophenol, 2,4-dichlorophenol and pentachlorophenol were 1.0-200 µg/L and 2.0-200 µg/L for 2,4,6-trichlorophenol. The detection limits (S/N = 3) were in the range of 0.16-0.45 µg/L, the RSDs for intraday and interday precisions were <7.0%. Finally, the proposed method was successfully used to detect different environmental water samples. The recoveries of spiked water samples were ranged from 90.0 to 115%. At the same time, satisfactory repeatability was achieved with RSDs < 9.0%.

Flow injection analysis of trace chromium (VI) in drinking water with a liquid waveguide capillary cell and spectrophotometric detection.

Hexavalent chromium (Cr(VI)) is an acknowledged hazardous material in drinking waters. As such, effective monitoring and assessment of the risks posed by Cr(VI) are important analytical objectives for both human health and environmental science. However, because of the lack of highly sensitive, rapid, and simple procedures, a relatively limited number of studies have been carried out in this field. Here we report a simple and sensitive analytical procedure of flow injection analysis (FIA) for sub-nanomolar Cr(VI) in drinking water samples with a liquid core waveguide capillary cell (LWCC). The procedure is based on a highly selective reaction between 1, 5-diphenylcarbazide and Cr(VI) under acidic conditions. The optimized experimental parameters included reagent concentrations, injection volume, length of mixing coil, and flow rate. Measurements at 540 nm, and a 650-nm reference wavelength, produced a 0.12-nM detection limit. Relative standard deviations for 1, 2, and 10 nM samples were 5.6, 3.6, and 0.72 % (n = 9), and the analysis time was <2 min sample(-1). The effects of salinity and interfering ions, especially Fe(III), were evaluated. Using the FIA-LWCC method, different sources of bottled waters and tap waters were examined. The Cr(VI) concentrations of the bottled waters ranged from the detection limit to ∼20 nM, and tap waters collected from the same community supply had Cr(VI) concentration around 14 nM.

In-situ measurement of dissolved sulfide in surface sediment porewater using diffusive gradients in thin films (DGT) coupled with digital imaging.

Dissolved sulfide in sediment porewater significantly influences aquatic ecosystems. Conventionally, sulfide determination in sediment porewater relies on ex-situ analytical methods, susceptible to measurement errors due to sulfide oxidation and volatilization during sample analysis. In this study, we introduced an innovative in-situ method for assessing dissolved sulfide in surface sediment porewater, leveraging the integration of diffusive gradients in thin films (DGT) with digital imaging. The DGT device effectively concentrates sulfide in sediment porewater, inducing observable color changes in the binding gel. Recordings of these changes, captured by imaging equipment, facilitated the establishment of calibration curves correlating grayscale value alterations in the binding gel to sulfide concentrations. Under optimal conditions, the developed method demonstrated a linear detection range of 3.0-200 µmol L-1 at 20 °C, particularly when the exposure time exceeded 180 min. The developed method is insensitive to salinity and suitable for measuring sulfide concentrations in various natural water environments. Compared to traditional ex-situ methods, our approach circumvents challenges linked to intricate pre-treatment, prolonged analysis duration, and significant systemic errors. This proposed method presents a real-time solution for sulfide concentration assessment in surface sediment porewater, empowering researchers with an efficient means to monitor and study dynamic sulfide levels.

On-site monitoring of dissolved Sb species in natural waters by an automatic system using flow injection coupled with hydride generation atomic fluorescence spectrometer.

Antimony (Sb) is a toxic and potentially carcinogenic element in the environment. The toxicity of Sb(III) is ten times that of Sb(V). Therefore, on-site monitoring technique for dissolved Sb species is crucial for the study of Sb environmental processes. In this study, an automated, portable, and cost-effective system was developed for field simultaneous analysis of Sb(III) and Sb(III + V) in natural waters. The system comprised a portable atomic fluorescence spectrometer equipped with a built-in electrochemical H2 generator to reduce the consumption of acid/borohydride solution and make the atomizer more stable for on-site analysis. Flow injection technique was also used to achieve on-line pretreatment of water samples, including filtration, acidification, pre-reduction, and hydride generation procedures. Under the optimal conditions, the limits of detection (3σ, n = 11) of the developed method were 0.015 µg/L and the linear ranges were 0.05-5.0 µg/L for both Sb(III) and Sb(III + V). The relative standard deviations (n = 11) of the spiked samples of Sb(V) were 3.2% (0.05 µg/L), 3.3% (0.2 µg/L), and 1.7% (0.5 µg/L), respectively. The spiked recoveries of lake water, treated wastewater, and seawater ranged from 97.0% to 108.5%. The novel system of flow injection coupled with hydride generation atomic fluorescence spectrometer (FI-HG-AFS) was applied to carry out an 18-h fixed-point monitoring at a secondary settling tank of a wastewater treatment facility in Xiamen University, and a 6-h real-time underway analysis in the surface seawater of Dongshan Bay, China, proving that the system was capable of long-term monitoring in the field.

Automated spectrophotometric analyzer for rapid single-point titration of seawater total alkalinity.

An automated analyzer was developed to achieve fast, precise, and accurate measurements of seawater total alkalinity (AT) based on single-point titration and spectrophotometric pH detection. The single-point titration was carried out in a circulating loop, which allowed the titrant (hydrochloric acid and bromocresol green solution) and a seawater sample to mix at a constant volume ratio. The dissolved CO2 in the sample-titrant mixture was efficiently removed by an inline CO2 remover, which consists of a gas-permeable tubing (Teflon AF2400) submerged in a sodium hydroxide (NaOH) solution. The pH of the mixture was then measured with a custom-made spectrophotometric detection system. The analyzer was calibrated against multiple certified reference materials (CRMs) with different AT values. The analyzer features a sample throughput time of 6.5 min with high precision (±0.33-0.36 µmol kg(-1); n = 48) and accuracy (-0.33 ± 0.99 µmol kg(-1); n = 10). Intercomparison to a traditional open-cell AT titrator showed overall good agreement of 0.88 ± 2.03 µmol kg(-1) (n = 22). The analyzer achieved excellent stability without recalibration over 11 days, during which time 320 measurements were made with a total running time of over 40 h. Because of its small size, low power consumption requirements, and its ability to be automated, the new analyzer can be adapted for underway and in situ measurements.

Development of monolith-based stir bar sorptive extraction and liquid chromatography tandem mass spectrometry method for sensitive determination of ten sulfonamides in pork and chicken samples.

A highly sensitive method was developed for the simultaneous determination of ten sulfonamides in pork and chicken samples by monolith-based stir bar sorptive extraction (SBSE) coupled to high-performance liquid chromatography tandem mass spectrometry. The samples were freeze-dried and extracted by acetonitrile, then enriched and further extracted by SBSE which was based on poly(vinylphthalimide-co-N,N-methylenebisacrylamide) monolith (SBSE-VPMB) as coating. To achieve optimum extraction performance of SBSE for sulfonamides, several parameters, including pH value and ionic strength in the sample matrix and extraction and desorption time, were investigated in detail. Under the optimal conditions, the limits of detection (S/N = 3) for target sulfonamides were 1.2-6.1 ng/kg in pork and 2.0-14.6 ng/kg in chicken, respectively. Real samples spiked at the concentration of 0.5 and 5.0 µg/kg showed recoveries above 55% and relative standard deviations below 12%. At the same time, the extraction performances of target sulfonamides on SBSE-VPMB were compared with other SBSE based on porous monolith and commercial SBSE.

Sensitive determination of organic acid preservatives in juices and soft drinks treated by monolith-based stir cake sorptive extraction and liquid chromatography analysis.

A simple, efficient, and sensitive method for simultaneous determination of sorbic acid (SA), benzoic acid (BA), and cinnamic acid (CA) in juices and soft drinks was developed by stir cake sorptive extraction (SCSE) coupling to high-performance liquid chromatography with diode array detection. The SCSE based on polymeric ionic liquid-based monolith (PILM) as extractive medium was used to concentrate these three organic acid preservatives. Because hydrophobic and ion-exchange interactions co-contributed to the extraction, the PILM-SCSE exhibited a high extractive capability towards analytes. To obtain optimum extraction performance, several SCSE parameters were investigated and discussed, including desorption solvent, pH value, ionic strength in the sample matrix, and the extraction and desorption time. Under the optimized extraction conditions, limits of detection of 0.16, 1.08, and 0.18 µg/L (S/N=3) and quantification limits of 0.52, 3.42, and 0.61 (S/N=10) were obtained for SA, BA, and CA, respectively. The method also showed good linearity and reproducibility, as well as advantages such as simplicity, low cost, and high feasibility. Finally, the proposed method was successfully applied to the determination of SA, BA, and CA in real juices and soft drinks, and the recoveries ranged from 63.0 to 107 %.

New monolithic stir-cake-sorptive extraction for the determination of polar phenols by HPLC.

A novel porous monolith has been prepared and used as a sorbent in stir-cake-sorptive extraction (SCSE). The monolithic material was prepared by in-situ copolymerization of allyl thiourea (AT) and divinylbenzene (DB) in the presence of dimethylformamide as a porogen solvent. To optimize the polymerization conditions, different monoliths with different ratios of functional monomer to porogenic solvent were prepared, and their extraction efficiency was investigated in detail. The monolith was characterized by elemental analysis, scanning electron microscopy, mercury intrusion porosimetry, and infrared spectroscopy. Analysis of polar phenols in environmental water samples by a combination of ATDB-SCSE and HPLC with diode-array detection was selected as a model for the practical application of the new sorbent. Several extraction conditions, including extraction and desorption time, pH, and ionic strength of the sample matrix were optimized. The results showed that the new monolith had high affinity for polar phenols and could be used to extract them effectively. Under the optimum conditions, low detection (S/N = 3) and quantification (S/N = 10) limits were achieved for the phenols, within the ranges 0.18-0.90 and 0.59-2.97 µg L(-1), respectively. The linearity of the method was good, and the method enabled simple, practical, and low-cost extraction of these analytes. The distribution coefficients between ATDB and water (K(ATDB/W)) were calculated for the phenolic compounds and compared with K(O/W). Finally, the proposed method was successfully applied to the determination of the compounds in three environmental water samples, with acceptable recovery and satisfactory repeatability.

Preparation of magnetic poly(vinylimidazole-co-divinylbenzene) nanoparticles and their application in the trace analysis of fluoroquinolones in environmental water samples.

Nanosized spherical magnetic poly(vinylimidazole-co-divinylbenzene) particles were synthesized and used as a sorbent for the enrichment of trace fluoroquinolones (FQs) from environmental water samples. A suspension polymerization procedure was used to prepare the sorbent. The magnetic sorbent was characterized by SEM, transmission electron microscopy, elemental analysis, and FTIR spectroscopy. Analysis of enrofloxacin, marbofloxacin, fleroxacin, lomefloxacin, and sparfloxacin in environmental water samples by the combination of the magnetic sorbent and HPLC with diode array detection was selected as a paradigm for the practical application of the new adsorbent. Several extraction conditions, including desorption solvent, extraction and desorption time, pH value, and ionic strength in sample matrix, were optimized. Results showed that the new sorbent had high affinity for FQs and could be used to extract them effectively. Under the optimum conditions, low detection (S/N = 3) and quantification (S/N = 10) limits were achieved for the target analytes, within the ranges of 0.20-1.46 and 0.68-4.84 µg/L, respectively. Method repeatability was achieved in terms of intra- and interday precisions, indicated by the RSDs, which were both <10.0%. The method also showed good linearity, simplicity, practicality, and environmental friendliness for the extraction of FQs. Finally, the developed method was successfully applied to the determination of FQs in lake water, surface water, and reservoir water samples. Acceptable recoveries of spiked target compounds in these water samples were in the range of 52.1-104.5%.

Sensitive monitoring of penicillin antibiotics in milk and honey treated by stir bar sorptive extraction based on monolith and LC-electrospray MS detection.

In the present study, a convenient and sensitive method for determination of six penicillin antibiotics (amoxicillin, ampicillin, penicillin G, oxacillin, cloxacillin, and dicloxacillin) in milk and honey samples was developed. Milk and honey samples were diluted with water, then directly treated by stir bar sorptive extraction based on poly (vinylimidazole-divinylbenzene) monolithic material as coating. The analytes were analyzed by LC/ESI- MS/MS. Several extraction parameters including extraction and desorption time, pH value, and ionic strength in sample matrix were investigated in detail. Under the optimized extraction conditions, the calculated detection limits for the target compounds were as low as 0.23-2.66 ng/kg in milk and 0.18-1.42 ng/kg in honey, respectively. Good linearity was obtained for analytes with the correlation coefficients (R(2)) above 0.997. Excellent method reproducibility was achieved in terms of intraday and interday precisions, indicated by the RSDs of <5.0 and <10.0%, respectively. Finally, the proposed method was successfully applied to the determination of penicillin antibiotics residues in different milk and honey samples.

Vertical distribution of total mercury and methylmercury in sediment of the Fugong mangrove area at Jiulong River Estuary, Fujian, China.

The concentrations and vertical distributions of total mercury (Hg) and methylmercury (methyl Hg) in the sediment of the Fugong mangrove area, located at the Jiulong River Estuary, Fujian, China, were investigated. The concentrations of total mercury were between 0.12-0.17 and 0.11-40.14 microg/g, while concentrations of methylmercury were between 0.15-1.8 and 0.081-0.58 ng/g (as mercury), in the dry and rainy seasons, respectively. The total mercury concentration was not correlated with the sampling depth. As the depth increased, methylmercury concentrations first increased to their maximum level at a depth of 10-25 cm, and then decreased; this was similar to the vertical distribution characteristics of methylmercury/total mercury ratios. The mangrove ecosystem was considered as a source of methylmercury for adjacent areas, due to the higher average methylmercury concentration in the mangrove sediment than other sediments nearby. Statistically significant logarithmic correlations, conic correlations, and negative correlations were observed for methylmercury and sulfide concentration, sediment organic matter, and sediment pH, respectively.

Quantification, morphology and source of humic acid, kerogen and black carbon in offshore marine sediments from Xiamen Gulf, China.

Three types of macromolecular organic matters (MOMs), i.e. humic acid (HA), kerogen+black carbon (KB), and black carbon (BC) were extracted from marine sediments of Xiamen Gulf, southeast of China. The chemical composition, morphological property and source of the three extractions were characterized by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) and scanning electron microscope (SEM). The results showed that KB was the predominant fraction in MOMs, which accounted for 61.79%-89.15% of the total organic content (TOC), while HA consisted less than 5%. The relative high contents of kerogen and BC, and low contents of HA in the samples indicated that anthropogenic input might be the major source of organic matter in marine sediments near the industrial regions. The characterization of SEM, not only revealed morphological properties of the three fractions, but also allowed a better understanding of the source of MOMs. The delta13C values of the three fractions suggested that materials from terrestrial C3 plants were predominant. Furthermore, the anthropogenic activities, such as the discharge of sewage, coal and biomass combustion from industry nearby and agricultural practices within drainage basin of the Jiulong River, were remarkably contributed to the variations in delta13C values of MOMs in the offshore marine sediments.