Hydrocarbons In Seawater Research Articles

Detection of PAHs in seawater using surface-enhanced Raman scattering (SERS)

The laboratory characterization of a field-operable surface-enhanced Raman scattering sensor (SERS optode) is presented for the detection of aromatic hydrocarbons in seawater. The sensor has been developed for deployment with a robust underwater spectrograph. To meet the demands of the harsh seawater application, sol–gel derived SERS substrates were used. The calibration curves of six PAHs were determined to be of Langmuir adsorption isotherm type with limits of detection ranging from the μg l −1 to ng l −1 level. The experimentally determined adsorption constants varied strongly with the molecular weight of the analytes and correlated with their solubility. A mixture of five PAHs dissolved in seawater was investigated to demonstrate the utility of this method for screening. Emphasis was put on the interference from suspended particulate matter (SPM). The Raman measurement with backscattering configuration was shown to be immune against turbidities up to 1000 NTU. The physico-chemical interference arising from adsorption by the sediment was measured on-line by adding sediment to a PAH-spiked solution. According to the calibration curve, the PAH concentration decrease corresponded to more than 98% of the analyte being scavenged by the sediment.

Determination of polycyclic aromatic hydrocarbons in seawater by high-performance liquid chromatography with fluorescence detection following micelle-mediated preconcentration

In this work, the nonionic surfactant polyoxyethylene-10-lauryl ether has been used for the extraction and preconcentration of 14 polycyclic aromatic hydrocarbons, classified as priority pollutants by the US Environmental Protection Agency, from seawater samples. The cloud-point preconcentration previous separation by HPLC and quantification using fluorimetric detection and wavelength programming allow to determine these pollutants with detection limits ranging from 1.0 to 1.5·10 2 ng/l with RSDs better than 10.4%. The methodology is evaluated using well-established extraction and preconcentration methods and GC–MS.

Depth profiles of volatile halogenated hydrocarbons in seawater in the Bay of Bengal

Measurements were made of bromocarbons (CHBr 3 and CH 2Br 2), iodocarbons (CH 2I 2 and CH 2ClI), and dimethylsulfide (DMS, CH 3SCH 3) in seawater collected from the Bay of Bengal under tropical stratified conditions. These compounds showed different depth profiles, characteristic of each group. CH 2I 2 and CH 2ClI showed very similar depth profiles to chlorophyll- a, suggesting their production by phytoplankton followed by rapid decay in seawater. The CH 2I 2 maximum at a depth a little below the CH 2ClI maximum was consistent with its more significant photolytic decay. The bromocarbons were less localized in their distributions than were the iodocarbons, suggesting their longer residence time in seawater after their release from phytoplankton. Both of these profiles were different from the pattern of DMS, which had its maxima above the chlorophyll- a maximum layer near the surface.

A Mid-Infrared Sensor for Monitoring of Chlorinated Hydrocarbons in the Marine Environment

As part of the European research project SOFIE - “Spectroscopy using Optical Fibres in the Marine Environment”, a portable sensor system for chlorinated hydrocarbons in seawater is being developed. This novel analytical tool for real-time in-situ monitoring of a particularly important class of seawater pollutants consists of a robust, miniaturised FT-IR spectrometer in a sealed aluminium pressure vessel and a fibre optic sensor head. In a laboratory set-up using an ATR-crystal as a simplified sensor head, the effect of potentially interfering substances, both of natural and anthropogenic origin, on the sensor response was tested. It was found that the sensor readings for a specific analyte are not susceptible to aliphatic and aromatic components as well as other chlorinated hydrocarbons up to concentrations well above the average levels to be encountered in the oceans. The same applies for the parameters salinity and turbidity. Consequently, the proposed sensor system should be well suited for real-world sub-sea applications.

Determination of light hydrocarbons dissolved in seawater

A practical method for the on board determination of light (C1–C4) hydrocarbons dissolved in seawater has been developed. The gaseous hydrocarbons in seawater were extracted quickly with a vacuum sparge tower and determined gas chromatographically. By using two cryogenic columns at dry ice–ethanol temperature (−80°C) connected in series, it was possible to completely collect the hydrocarbons. The precision and sensitivity were comparable to that of previous methods. The analysis was completed within 45 min for one sample and the sample volume was 500 ml. The method was successfully applied to the northern North Pacific water collected in summer 1997. The concentrations of C2–C4 hydrocarbons in surface seawater ranged from several to several tens pmol l −1, within the range of concentrations in previous studies.

Measurement of a time-weighted average concentration of polycyclic aromatic hydrocarbons in seawater: An improved procedure of blue rayon hanging technique for monitoring benzo(a)pyrene

We have proposed a time-weighted measurement using blue rayon that selectively adsorbs and concentrates polycyclic aromatic hydrocarbons (PAH), e.g. benzo(a)pyrene (BaP). Though the method was demonstrated to be a convenient way to monitor PAH, the amount adsorbed to the blue rayon depends on the intensity of water stream and the level of PAH. The intensity of water stream was measured by ‘plaster ball’ method, while TWA of PAH in water was measured by a portable sampler using solid phase extraction cartridge. A level of BaP measured by the original blue rayon technique was corrected in this way by the water stream intensity, which correlated well with the TWA of BaP measured by the portable sampler. The improved blue rayon hanging method was applied to several field sites in the Seto Inland Sea of Japan. TWA of BaP ranged from 0.08 to 3.78 ngl −1. These results showed the possibility that the method could be used to evaluate pollution in aquatic environment.

Light nonmethane hydrocarbons in seawater

A database of dissolved C2‐C4 hydrocarbons in the surface water of the oceans is compiled based on more than 1000 measurements. Hydrocarbon emission rates are calculated using a diffusive microlayer approach and climatologic wind data. This database is used to calculate averages and ranges of variation, and an attempt is made to identify the environmental factors which have an impact on the hydrocarbons dissolved in seawater. The paper focuses on data obtained in situ since other techniques generally contain larger uncertainties. Mean concentrations are 134 pmol/L for ethene, 59 pmol/L for propene, and 37 pmol/L for 1‐butene. Alkane concentrations are lower with an average value of 22 pmol/L for ethane and less than 14 pmol/L for the other alkanes and acetylene. Ninety percent of the concentrations of an individual compound generally ranges within an order of magnitude. Ethene concentrations are significantly anticorrelated with the transfer velocities of the sea‐air exchange (r=−0.49; r0.01=0.29). Ethene concentrations are not correlated with the solar radiation, chlorophyll a, and the water temperature. Averaged emissions of C2‐C4 hydrocarbons extrapolated to the global ocean of 2.1 × 1012 g/yr are calculated, with ethene alone contributing about 40% to the total. Thus the oceanic source is on the low side of previous estimates and plays a minor role in global budgets compared to continental sources.

Horizontal and vertical profiles of light hydrocarbons in sea water related to biological, chemical and physical parameters

In situ-measurements of light (C 2 -C 4 ) nonmethane hydrocarbons (NMHC) in sea water were performed during a ship cruise in spring 1991 in the Mediterranean, the Atlantic and the North Sea. The investigated regions were characterized with respect to biological (phytoplankton density, chlorophyll concentration), chemical (concentration of dissolved organic carbon, DOC) and physical parameters (irradiation intensity, wind velocities). These data were analysed for possible correlations with NMHC concentrations. An anticorrelation was found between NMHC concentrations and wind velocity. There were indications of a correlation between alkene concentration and the concentration of photochemically reactive DOC. For regions of low phytoplankton densities, significant positive correlations between biological activity (i.e.. chlorophyll concentration and cell density) and the concentrations of all NMHC except ethane were obtained. In contrast, in regions of an active growing phytoplankton bloom the concentrations of all NMHC except n-butane were inversely related to biological activity. In the vertical profiles, the alkanes often showed pronounced concentration maxima in depths of 1–10% relative light intensity, i.e., at the bottom of the euphotic zone. Alkene concentration maxima occurred in the upper layer of the euphotic zone. During periods of very low wind velocities, i.e., low mixing in the ocean surface layer and low emission rates, the concentrations of alkenes in surface water exhibited a distinct diurnal pattern with the concentrations increasing during day time and remaining constant at night. DOI: 10.1034/j.1600-0889.47.issue5.8.x

The dissolution and photodegradation of Kuwaiti crude oil in seawater. Part 2: A laboratory photodegradation apparatus and photodegradation kinetics of a model seawater soluble hydrocarbon (phenanthrene)

A laboratory photodegradation apparatus, incorporating a calibrated xenon lamp, controlled temperature unit and quartz reaction cells designed to simulate natural irradiation by sunlight, and which is suitable for kinetic studies of hydrocarbon degradation in seawater, is described. The apparatus and experimental method was used to determine the pseudo-first order photodegradation constant (k p) of phenanthrene (a component present in the seawater-soluble fraction of crude oil) in seawater at 25 °C. The k p values determined in duplicate experiments were −0.342 ± 0.003 and −0.317 ± 0.029 h −1 with half-lives ( t 1 2 ) of 2.03 and 2.19 h. Extrapolation to natural sunlight at latitude 30 °N (Florida midday, midsummer assuming 12 h daylight) gave t 1 2 values of 8.6–9.5 h, suggesting that photodegradation is a significantly fast reaction for removal of phenanthrene from seawater under some conditions. Gas chromatography-mass spectrometry (GC-MS) and ultraviolet fluorescence spectrophotometry were both suitable methods for monitoring the degradation, but GC-MS was most suitable for the determination of photoproducts. The identifiable products amounted to some 12% of the total products after 7 h irradiation, and their distribution was consistent with a known mechanism of phenanthrene degradation involving formation of an unstable and reactive 9,10-epoxide. The photolysis method should prove valuable for the determination of k p and t 1 2 values for a wide range of petroleum hydrocarbons in seawater.

Thermogenic hydrocarbons in seawater of the Gippsland Shelf, southeast Australia

An offshore survey measured the concentration of thermogenic hydrocarbons (THCs) in samples extracted from seawater at 718 locations along 22 traverse lines across the Gippsland Shelf, southeast Australia, and recorded compounds typical of subsurface crude oil and natural gas (petroleum) accumulations. Background concentrations of 8 ppm, with isolated peak levels of 20 to 52 ppm, were detected in samples extracted from seawater at depths of 30 to 50 m over distances of 10 km. Two sources have been suggested - seepage of THCs from subsurface accumulations of petroleum, or THCs in waste-water discharged by several offshore petroleum production facilities which are present on the shelf. A waste-water source is favoured because of the transitory nature of the concentrations, and changes in composition consistent with plume drift away from the point(s) of discharge. Overall, however, the concentration of THCs in waters of the Gippsland Shelf compare favourably with levels in waters affected by urban runoff. The concentration of THCs in other coastal waters from urban and onshore sources is low, equivalent to the background concentration in the major oceans of the world.

Development of protective polymer coatings for silver halide fibers and their application as threshold level sensors for chlorinated hydrocarbons in sea water

The stability of silver halide fibers in artificial sea water (ASW) with and without a protective polymer coating and the influence of high salt concentrations on the sensor response was investigated. In contrast to bare silver halide fibers, the polymer coated fibers remain stable in contact with chloride solutions. This enables the application of a recently presented mid-IR fiber evanescent wave spectroscopy (FEWS) sensor system for the quantitative detection of chlorinated hydrocarbons (CHC) also in sea water.

Production mechanism of C2‐C4 hydrocarbons in seawater: Field measurements and experiments

The production mechanism of light nonmethane hydrocarbons (NMHC) in seawater was investigated during the North Atlantic atmospheric chemistry program (NATAC) in April and May 1991 in the European coastal seas and the North Atlantic. A significant alkene production occurred in the presence of light only. Under conditions of negligible NMHC emissions (low wind velocity) increasing hydrocarbon concentrations were observed during daytime, whereas the concentrations remained constant during night. NMHC formation experiments were carried out with seawater filled in quartz glass bottles and showed the same dependence of light. Experiments with differently pretreated seawater samples indicated that the presence of dissolved organic material (DOM) is also necessary for alkene production. We suggest a two‐step production mechanism for alkenes: first DOM is released, probably from algae, then part of this material is photochemically transformed into alkenes. The production rates in the quartz glass bottles were comparable to the production rates in the ocean surface. This indicates that the processes occurring in the experimental setups represent the processes occurring in the field. Since the production ‐ and emission rates were in the same range it can be concluded that the budget of light alkenes in the remote marine environment is determined by the production in seawater as the dominant source and the flux into the atmosphere as the main loss process.

Influence of synthetic and biogenic surfactants on the toxicity of water-soluble fractions of hydrocarbons in sea water determined with the bioluminescence inhibition test

The influence of increasing amounts of surfactants on the toxicity of hydrocarbons was determined using the bioluminescence inhibition test (Microtox test). Three biogenic and three synthetic surfactants were tested against the water-soluble fractions (WSF) of crude and weathered Ekofisk oil, phenol, and naphthalene. Surfactant concentrations below 100 mg litre −1 lowered the toxicity of the WSF, indicating an antagonistic interaction reducing the toxicities of surfactants and hydrocarbons. At concentrations greater than 100 mg litre −1 the toxicity rose again and was higher than the untreated WSF. The point of reversal seemed to be the critical micelle concentration, at which the formation of oil/water emulsions is possible.

Analysis of mixtures of polycyclic aromatic hydrocarbons in sea-water by synchronous fluorescence spectrometry in organized media

The spectrofluorimetric characteristics of chrysene, perylene, dibenz[a,c]anthracene and coronene were studied in aqueous medium and in the presence of cationic, anionic and non-ionic surfactants. The great enhancement of the fluorescence of these polycyclic aromatic hydrocarbons (PAHs) in hexadecyltrimethyl-ammonium bromide and synchronous fluorescence spectrometry were used for the establishment of two methods for the analysis of binary and ternary mixtures of these compounds. The former allows the simultaneous determination of dibenz[a,c]anthracene and coronene using Δλ= 89 nm, with detection limits of 0.20 and 0.22 ng ml–1, respectively. In the latter, three different Δλ values are used for the simultaneous determination of chrysene, perylene and coronene, viz., 41, 3 and 140 nm, respectively. Limits of detection of 0.17 ng ml–1 for chrysene, 0.13 ng ml–1 for perylene and 0.14 ng ml–1 for coronene were obtained. Good recoveries were obtained when both methods were applied to the analysis of binary and ternary mixtures of these PAHs added to sea-water.

Baseline levels of hydrocarbons in seawater of the Southern Ocean: Natural variability and regional patterns

Baseline levels of hydrocarbons in seawater of the Southern Ocean: Natural variability and regional patterns

Hydrocarbons in seawater, sediment, and oyster from the omani coastal waters

Over half of the world crude oil supply is transported from the Arabian Gulf area via tankers through the narrow Strait of Hormuz, which forms the northern boundary of the Sultanate of Oman. Generally, crude oil tanker traffic off the coast of Oman is relatively heavy and all the vessels entering the Gulf to load at various terminals pass by the coastal line of Oman. The present work plays an essential part on the Omani marine monitoring program. The purpose of this program was to establish baseline levels of selected heavy metals, chlorinated and petroleum hydrocarbons in some marine species. This study aims to assess hydrocarbons in seawater, sediment and rocky oysters from the different sites along Omani coastal waters.

Measurements of dissolved nonmethane hydrocarbons in sea water

An automated stripping technique for the measurement of dissolved hydrocarbons in sea water is presented together with some results obtained during a ship cruise from Europe to Brazil. The sea water concentrations of NMHC were determined in a three step process: degassing, preconcentration, and gas chromatographic analysis. In a stripping chamber the dissolved gases were purged from sea water with helium. The stripped hydrocarbons were cryogenically concentrated, and after thermal desorption they were injected into the gas chromatograph. The light fraction (C2–C4) was separated on a packed and the heavy fraction (C5–C10) on a capillary column. All valves were microprocessor controlled in order to achieve an automated process. For the C2–C4 hydrocarbons the stripping efficiencies exceeded 90% except for acetylene (80%), the lower limit of detection was 1 to 4.5 pmol hydrocarbon per liter of sea water and the accuracy of the method was better than 25%, depending on the individual hydrocarbons. Typical oceanic concentrations were in the 10 and 100 pmol/l range. Alkenes were generally more abundant than the corresponding alkanes and within the homologous series the concentrations decreased with increasing number of carbon atoms.

Formation of low molecular weight carbonyl compounds by sensitized photochemical decomposition of aliphatic hydrocarbons in seawater

Anthraquinone has been found to be a compound occuring frequently in seawater. Excited by solar radiation it acts as one of many natural and man-made photosensitizers and can thus be used as a model substance for the study of sensitized photochemical reactions of environmental chemicals. Experimentally it has been shown to mediate the oxidative photochemical decomposition of aliphatic hydrocarbons which, lacking absorption bands in the solar UV range at sea level, are by themselves photochemically inert. Formaldehyde, smaller amounts of acetaldehyde and acetone as well as a still unidentified carbonyl compound are the principal low molecular weight products generated in the anthraquinone-sensitized photooxidation, with natural as well as artificial sunlight, of straight chain saturated hydrocarbons accommodated in high purity water. Qualitatively the same results were obtained in natural seawater as reaction medium from which particles were removed by glass fiber filtration and organic compounds by adsorption on activated charcoal. The concomittant generation of homologous series of methylketones and terminal alkenes suggest a decomposition mechanism involving cyclic electron rearrangement in a 6-membered transition state. Based on HPLC analysis of their 2,4-dinitrophenylhydrazones, the rates of volatile carbonyl generation in the sensitized photo-oxidation of n-tetradecane was determined in the liquid phase. Also determined was the rate of formaldehyde formation in the gas phase from n-tetradecane and from two Brazilian crude oils. The rates of generation of acetaldehyde and acetone could not be determined in the experiments with crude oils because of irregular changes of concentrations with time. The rate of concentration increase of formaldehyde in the vapour phase over the hydrocarbon surface film was similar to that in the water underneath. The artifical light source was a high pressure xenon lamp whose emission spectrum closely resembles that of natural sunlight at sea level. It was calibrated against the intensity of natural sunlight using pnitroacetophenone/pyridine as binary chemical actinometer.

Development of a pulsed-laser, fiber-optic-based fluorimeter: determination of fluorescence decay times of polycyclic aromatic hydrocarbons in sea water

A fiber-optic-based system for remote measurement of time-resolved fluorescence emission spectra is described and characterized. A pulsed nitrogen laser is used to induce fluorescence and a time-gated, one-dimensional photodiode array is used to measure the decay of the fluorescence emission spectra. The results compare favorably with reported values for well characterized compounds having fluorescence decay times in the range 4–50 ns. The potential of using time-resolved fluorimetry (TRF) over fiber-optic cables as a means of improving the specificity of remote fluorescence determinations of spectrally similar polycyclic aromatic hydrocarbons in sea water is demonstrated.

Dissolved/Dispersed Hydrocarbons in Sea Water, Determined by Infrared and Fluorescence Spectroscopy

Abstract Samples of sub-surface (1m) and surface water were collected in the harbour of Las Palmas. These have been analyzed by infrared and by fluorescence spectroscopy in order to provide information on the levels of hydrocarbons generally present in the area. With the infrared method, the absorbance at 2925cm−1 has been measured and the values are given as API mixture equivalents. For the determination of total hydrocarbons by fluorescence spectroscopy, both the single-wavelength excitation fluorescence spectra which were used for the determination of the total concentration and the synchronous excitation spectra which give more structural information were recorded. The concentrations are given as chrysene equivalents. In all cases, high concentration levels of oil were detected. The results obtained from the two methods have been explained based upon the meteorological and oceanographic conditions.