Concentrations and bioaccessibility of polycyclic aromatic hydrocarbons in wastewater-irrigated soil using in vitro gastrointestinal test

BACKGROUND, AIM, AND SCOPE: Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants and contribute to the pollution of soil environment. Soil ingestion is of increasing concern for assessing health risk from PAH-contaminated soils because soil ingestion is one of the potentially important pathways of exposure to environmental pollutants, particularly relevant for children playing at contaminated sites due to their hand-to-mouth activities. In vitro gastro-intestinal tests imitate the human digestive tract, based on the physiology of humans, generally more simple, less time-consuming, and especially more reproducible than animal tests. This study was conducted to investigate the level of PAH contamination and oral bioaccessibility in surface soils, using physiologically based in vitro gastro-intestinal tests regarding both gastric and small intestinal conditions. MATERIALS AND METHODS: Wastewater-irrigated soils were sampled from the metropolitan areas of Beijing and Tianjin, China, which were highly contaminated with PAHs. Reference soil samples were also collected for comparisons. At each site, four soils were sampled in the upper horizon at the depth of 0-20 cm randomly and were bulked together to form one composite sample. PAH concentrations and origin were investigated and a physiologically based in vitro test was conducted using all analytical grade reagents. Linear regression model was used to assess the relationship between total PAH concentrations in soils and soil organic carbon (SOC). RESULTS: A wide range of total PAH concentrations ranging from 1,304 to 3,369 mug kg(-1) in soils collected from different wastewater-irrigated sites in Tianjin, while ranging from 2,687 to 4,916 mug kg(-1) in soils collected from different wastewater-irrigated sites in Beijing, was detected. In general, total PAH concentrations in soils from Beijing sites were significantly higher than those from Tianjin sites, indicating a dominant contribution from both pyrogenic and petrogenic sources. Results indicated that the oral bioaccessibility of PAHs in small intestinal was significantly higher (from P < 0.05 to P < 0.001) than gastric condition. Similarly, the oral bioaccessibility of PAHs in contaminated sites was significantly higher (from P < or = 0.05 to P < 0.001) than in reference sites. Individual PAH ratios (three to six rings), a more accurate and reliable estimation about the emission sources, were used to distinguish the natural and anthropogenic PAH inputs in the soils. Results indicated that PAHs were both pyrogenic and petrogenic in nature. DISCUSSION: The identification of PAH sources and importance of in vitro test for PAH bioaccessibility were emphasized in this study. The oral bioaccessibility of individual PAHs in soils generally decreased with increasing ring numbers of PAHs in both the gastric and small intestinal conditions. However, the ratio of bioaccessibility of individual PAHs in gastric conditions to that in the small intestinal condition generally increased with increasing ring numbers, indicating the relatively pronounced effect of bile extract on improving the bioaccessibility of PAHs with relatively high ring numbers characterized by their high K ( ow ) values. Similarly, total PAH concentrations in soils were strongly correlated with SOC, indicating that SOC was the key factor determining the retention of PAHs in soils. CONCLUSIONS: Soils were contaminated with PAHs due to long-term wastewater irrigation. PAHs with two to six rings showed high concentrations with a significant increase over reference soils. Based on the molecular indices, it was suggested that PAHs in soils had both pyrogenic and petrogenic sources. It was also concluded that the oral bioaccessibility of total PAHs in the small intestinal condition was significantly higher than that in the gastric condition. Furthermore, the bioaccessibility of individual PAHs in soils generally decreased with the increasing ring numbers in both the gastric and small intestinal conditions. RECOMMENDATIONS AND PERSPECTIVES: It is suggested that more care should be given while establishing reliable soil criteria for PAHs, especially concerning the health of children who may ingest a considerable amount of PAH-contaminated soil via outdoor hand-to-mouth activities.     

Historical record and sources of polycyclic aromatic hydrocarbons in core sediments from the Yangtze Estuary, China

Polycyclic aromatic hydrocarbons (PAHs) in a sediment core taken from intertidal flat in the Yangtze Estuary were determined by gas chromatography-mass spectrometry. The results indicate that the total concentration of PAHs ranged from 0.08 to 11.74 microg/g. The concentration levels of total and individual PAHs changed dramatically with depth. The concentrations of PAHs were relatively high above 35 cm depth and remained constantly low below this depth. The historical record of PAHs in the core shows subsurface maximum (one or more peak values), followed by decreased levels to the surface and with depth. And, PAH sediment record in the core profile is in agreement with historically sewage discharge events during the 1980s to 1990s. The distribution of target molecule acenephthene, the fluoranthene/pyrene ratio, the proportion of 2-3-ring and 4-5-ring PAHs, and alkylated naphthalene to parent naphthalene in the core profile show that the sources in this area are characterized by petroleum-derived PAH contamination (mainly sewage discharge and the river runoff) and the incorporation of atmospheric inputs. Studies indicate the PAH profile pattern in this site in comparison with other regions appear to reflect its particular local position (near the sewage outlet). Moreover, physico-chemical conditions and sedimentation rate as well as biodegradation also affect the PAH concentration levels in the core sediments.     

Polynuclear aromatic hydrocarbons in the United Kingdom environment: a preliminary source inventory and budget

This paper presents the first attempt to quantify the production, cycling, storage and loss of PAHs in the UK environment. Over 53 000 tonnes of sigmaPAHs (sum of 12 individual compounds) are estimated to reside in the contemporary UK environment, with soil being the major repository. If soils at contaminated sites are included, this estimate increases dramatically. Emission of PAHs to the UK atmosphere from primary combustion sources are estimated to be greater than 1000 tonnes sigmaPAHs per annum, with over 95% coming from domestic coal combustion, unregulated fires and vehicle emissions. It is estimated that approximately 210 tonnes of sigmaPAH are delivered to terrestrial surfaces each year via atmospheric deposition. Therefore, inputs of PAHs to the UK atmosphere outweigh the outputs by a factor of over 4. This may be explained by enhanced particulate deposition near point sources, PAH degradation in the atmosphere and transport away from the UK with prevailing winds. Disposal of waste residues is estimated to contribute a further 1000 tonnes of sigmaPAH per year to the terrestrial environment. It is illustrated that the use of creosote has the potential to release considerable quantities of PAHs to the UK environment. Temporal trends in PAH cycling are then considered. There is good evidence to suggest that air concentrations and fluxes to the UK surface are now lower than at any time throughout this century. Nonetheless, the UK sigmaPAH burden is still increasing at the present time, principally through retention by soils. However, there are marked differences in the behaviour of individual compounds: there is evidence, for example, that phenanthrene concentrations in soils have declined since the 1960s, although soil concentrations of benzo[a]pyrene and other heavier PAHs have continued to increase through this century. Volatilisation of low molecular weight PAHs accumulated in soils over previous decades may be making an important contribution to the current atmospheric burden. The major uncertainties identified by data on this budget are: (1) the lack of PAH concentrations in some environmental matrices; (2) the possible importance of contaminated soils as a major repository and source of PAHs; (3) the lack of emission data (especially vapour phase releases) for some PAH sources; (4) the importance of biodegradation and volatilisation as loss mechanisms for low molecular weight PAHs in soils; and (5) the importance of creosote use in the PAH cycle.     

The persistence of polynuclear aromatic hydrocarbons (PAHs) in sewage sludge amended agricultural soils

In 1968, five metal enriched sewage sludges containing different concentrations of polynuclear aromatic hydrocarbons (PAHs) were applied to different plots on field soils at two experimental sites, Luddington and Lee Valley, in the UK. This resulted in substantial increases in the total PAH soil concentrations in all plots. Since application, losses have occurred, with the high molecular weight PAHs being more persistent. Calculated half-lives range from under 2 years for naphthalene to over 9 years for benzo[ghi]perylene and coronene. The losses of PAH compounds in these field experiments can be related, in part, to their physico-chemical properties, notably the octanol: water partition coefficient.     

Assessment of the bioaccessibility of polycyclic aromatic hydrocarbons in soils from Beijing using an in vitro test

As an important human exposure pathway of contaminants, soil ingestion is of increasing concern for assessing health risk from polycyclic aromatic hydrocarbons (PAHs) in soils. A wide range of total PAH concentrations ranging from 0.112 microg g(-1) to 27.8 microg g(-1) in soils collected from different public sites, including gas stations, roadsides, bus stops, a kindergarten, primary and middle schools, a university and residential area, was detected. In general, total PAHs concentrations in soils from traffic areas were significantly higher than that from the other sites, indicating a dominant contribution from motor vehicles. Physiologically based in vitro tests were used to evaluate the oral bioaccessibility of PAHs in surface soil under different land uses in Beijing regarding both gastric and small intestinal conditions. It was found that the oral bioaccessibility of total PAHs in small intestinal condition, ranging from 9.2% to 60.5% of total PAHs in soil, was significantly higher than gastric condition, ranging from 3.9% to 54.9%. The bioaccessibility of individual PAHs in soils generally decreased with the increasing ring number of PAHs in both gastric and small intestinal conditions. However, the ratio of bioaccessibility of individual PAHs in gastric condition to that in small intestinal condition, generally increased with increasing ring number, indicating the relatively pronounced effect of bile extract on improving bioaccessibility of PAHs with relatively high ring numbers characterized by their high K(ow) values. The observation that bile extract at a level higher than critical micelle concentration could reduce the surface tension of digestive juice substantially, which may cause PAHs to be available for intestinal absorption, calls for more careful establishment of reliable soil criteria for PAHs, especially concerning the health of children who may ingest a considerable amount of PAH-contaminated soil via outdoor hand-mouth activities.     

Pollution survey of polycyclic aromatic hydrocarbons in surface water of Hangzhou, China

The concentrations of 10 polycyclic aromatic hydrocarbons (PAHs) were simultaneously measured for five times (July and November 1999–2002) in four water bodies of Hangzhou, China. To investigate possible sources of PAH contamination, sediments, soils, runoff water and atmospheric particles of the region were also analyzed for their PAH contents. The maximum levels of PAHs in the water bodies (34.4–67.7 μg/l) were found in July, while significantly lower PAH concentrations (4.7–15.3 μg/l) were measured in November. The contamination is substantial and it may have resulted in acute toxic effects on aquatic organisms. The measured PAH concentrations in sediments and soils (224–4222 ng/g), runoff water (8.3 μg/l) and air particles (2.3 μg/m³) are discussed in relation to concentrations and patterns found in the surface water bodies. Comparison of PAH levels in sediments and soils led to the conclusion that the erosion of soil material does not contribute significantly to the contamination of sediments. The atmospheric PAH deposition to water bodies in the city area of Hangzhou was estimated to be 530 tons/a, while the contribution of surface runoff water was estimated to be 30.7 tons/a. The ratios of selected PAH were then used to illuminate the possible origin of PAHs in the examined samples (petrogenic, pyrogenic).     

Concentrations, sources and spatial distribution of polycyclic aromatic hydrocarbons in soils from Beijing, Tianjin and surrounding areas, North China

The concentrations, profiles, sources and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) were determined in 40 surface soil samples collected from Beijing, Tianjin and surrounding areas, North China in 2007, and all sampling sites were far from industrial areas, roadsides and other pollution sources, and across a range of soil types in remote, rural villages and urban areas. The total concentrations of 16 PAHs ranged from 31.6 to 1475.0 ng/g, with an arithmetic average of 336.4 ng/g. The highest PAH concentrations were measured in urban soils, followed by rural village soils and soils from remote locations. The remote-rural village-urban PAH concentration gradient was related to population density, gross domestic product (GDP), long-range atmospheric transport and different types of land use. In addition, the PAH concentration was well correlated with the total organic carbon (TOC) concentration of the soil. The PAH profile suggested that coal combustion and biomass burning were primary PAH sources.     

Using experimental and forest soils to investigate the uptake of polycyclic aromatic hydrocarbons (PAHs) along an urban-rural gradient

Spatial and temporal variation in the atmospheric deposition of PAHs to soil was examined by deploying experimental soils for approximately 165 days and conducting a survey of forest soils at several sites along an urban-rural transect extending from downtown Toronto to approximately 80 km north of the city. PAH concentrations decreased with distance from the urban centre-by a factor of 2 and 60 for the experimental and forest soils respectively. The large gradient for the forest soils is generally consistent with air concentrations of PAHs measured using high volume and passive air samplers. The smaller gradient for the experimental soils was due to kinetic limitations of PAH accumulation and the relatively short deployment period of approximately 165 days. Mean effective deposition velocities (gas+particle) for the full range of PAHs for the experimental soils at the urban, suburban, and the rural sites were 2, 31 and 26 cm s(-1), respectively. These were incorporated into a dynamic model that was used to assess the long-term uptake of PAHs in forest soils. Model results indicate that lower molecular weight PAHs may achieve equilibrium and become involved in soil-air exchange whereas higher molecular weight PAHs are accumulated for much longer time periods.     

Polychlorinated naphthalenes in urban soils: analysis,concentrations, and relation to other persistent organic pollutants

We determined the concentrations of 35 PCNs, 12 PCBs, and 20 PAHs in 49 urban topsoils under different land use (house garden, roadside grassland, alluvial grassland, park areas, industrial sites, agricultural sites) and in nine rural topsoils. The sums of concentrations of 35 PCNs (sigma35 PCNs) were <0.1-15.4 microg kg(-1) in urban soils and <0.1 to 0.82 microg kg(-1) in rural soils. The PCN, PCB, and PAH concentrations were highest at industrial sites and in house gardens. While rural soils receive PCNs, PCBs, and PAHs by common atmospheric deposition, there are site-specific sources of PCNs, PCBs, and PAHs for urban soils such as deposition of contaminated technogenic materials. The PCN, PCB, and PAH concentrations decreased from the central urban to the rural area. In the same order the contribution of lower chlorinated PCNs and PCBs increased because they are more volatile and subject to increased atmospheric transport. The PCNs 52+60, and 73 were more abundant in soil samples than in Halowax mixtures, indicating that combustion contributed to the PCN contamination of the soils.     

Polycyclic aromatic hydrocarbons in Costa Rican air and soil: A tropical/temperate comparison

Surface soil and passive air samples from a network of 23 sampling sites across Costa Rica were analyzed for polycyclic aromatic hydrocarbons (PAHs), allowing for an evaluation of absolute levels, spatial distribution patterns, air/soil concentration (A/S) ratios and relative composition. Annual mean concentrations of four-ring PAHs in air were low (median of approximately 40 pg m⁻³), except in Costa Rica's densely populated central valley (approximately 650 pg m⁻³). PAH concentrations in soil were also low (median of 5 ng g⁻¹ dry weight) and comparable to those reported for other tropical regions. These low soil concentrations result in A/S ratios of four-ring PAHs in Costa Rica that are higher than the equilibrium air–soil partitioning coefficients and also higher than A/S ratios reported for temperate locations. A series of model calculations of increasing complexity were used to seek an explanation for variable A/S ratios of PAHs under tropical and temperate conditions. Temperature-driven changes in air–soil partitioning and differences in PAH degradability under temperate and tropical conditions are insufficient to explain the higher soil concentrations and lower A/S ratios in temperate regions. However, these can be explained by atmospheric deposition of PAHs during historical periods of much higher emissions and air concentrations and by persistence of PAHs in soils on the order of decades. Low PAH concentrations in tropical soils were found to be consistent with constant or increasing emissions, and in particular, do not require that degradation rates in soil are much faster than in temperate areas. In comparison to temperate soils, soils from Costa Rica and other tropical regions have a higher relative abundance of the lighter PAHs. This likely reflects a higher source contribution from biomass burning in the tropics, as well as the preferential loss of lighter PAHs from temperate soils that experienced high PAH deposition in the past.     

Dissolution and removal of PAHs from a contaminated soil using sunflower oil

This study reports on the feasibility of remediation of polycyclic aromatic hydrocarbon (PAH) contaminated soils using sunflower oil, an environmentally-friendly solvent. Batch experiments were performed to test the influence of oil/soil ratio on the remediation of PAH contaminated soil, and to test the mass transfer behaviors of PAHs from soil to oil. An empirical model was employed to describe the kinetics of PAH dissolution and to predict equilibrium concentrations of PAHs in oil. PAH containing oil was regenerated using active carbon. Results show that dissolution of PAHs from a Manufactured Gas Plant (MGP) soil at oil/soil ratios of one or two were almost the same. Nearly all PAHs (81-100%) could be removed by sunflower oil dissolution. Mass transfer coefficients for low molecular PAHs namely fluoranthene, phenanthrene and anthracene were one or two orders of magnitude higher than those for high molecular PAHs with 4-6 rings. Ninety milliliters of PAH containing oil could be regenerated by 10 g active carbon in a batch reactor. Such a remediation procedure indicates that sunflower oil is a promising agent for the removal of PAHs from MGP soils. However, further research is required before the method can be used for in situ remediation of contaminated sites.     

Dissipation of polycyclic aromatic hydrocarbons (PAHs) in the rhizosphere: Synthesis through meta-analysis

Polycyclic aromatic hydrocarbons (PAHs) are widespread and persistent organic pollutants with high carcinogenic effect and toxicity; their behavior and fate in the soil-plant system have been widely investigated. In the present paper, meta-analysis was used to explore the interaction between plant growth and dissipation of PAHs in soil based on the large body of published literature. Plants have a promoting effect on PAH dissipation in soils. There was no difference in PAH dissipation between soils contaminated with single and mixed PAHs. However, plants had a more obvious effect on PAH dissipation in freshly-spiked soils than in long-term field-polluted soils. Additionally, a positive effect of the number of microbial populations capable of degrading PAHs was observed in the rhizosphere compared with the bulk soil. Our meta-analysis established the importance of the rhizosphere effect on PAH dissipation in variety of the soil-plant systems.     

Measuring the flux at the interface of coal-tar impacted sediment and river water near a former MGP site

Determining water movement through contaminated sediment is critical for characterizing transport of chemicals from the sediment to the overlying water. Field studies to characterize the water flow across the sediment-water interface within a river adjacent to a former manufactured gas plant site were conducted. For this purpose, a new design of an interfacial flow meter was developed and tested. The in situ components of the system consisted of: a cylinder with an interfacial area of 2342 cm2; a dome attached to the cylinder; and a flow tube that allows water to flow from inside the dome to the river at the rate equal to the specific discharge across the sediment-water boundary. A 'heat-pulse' method was used to measure flow by heating the center of the flow tube for a brief time period and measuring the temperature profile within the tube over time. The system was calibrated to measure volumetric flux in the range 1.5-4.0 cm d(-1), however using a flow-addition method, the measurement of lower velocities also was accomplished, and calibration at higher fluxes is possible. From the groundwater flow at the interface of the coal-tar impacted sediment and information on the sediment pore water concentrations of several PAHs (poly-cyclic aromatic hydrocarbons), the mass flux of these PAHs to the river were estimated. Information on PAH mass flux at the sediment-water interface is useful for site assessment, including the evaluation of remediation alternatives and longer term site characterization.     

On the use of PAH molecular diagnostic ratios in sewage sludge for the understanding of the PAH sources. Is this use appropriate?

The concentrations ratios of specific pairs of polycyclic aromatic hydrocarbons (PAHs) are widely used for the qualitative determination of the PAHs sources. These ratios are called PAHs molecular diagnostic ratios and are commonly used for PAHs concentrations in air, soils and sediments. Some scientists have extended the use of these ratios also for sewage sludges, suggesting that calculation of these ratios by individual PAHs concentrations can be as effective as in soils or sediments. This paper describes the reason why the PAH molecular ratios calculated from sewage sludge concentrations should not be used for the understanding of the PAH sources.     

Effect of pH control at the anode for the electrokinetic removal of phenanthrene from kaolin soil

Polycyclic aromatic hydrocarbon (PAH)-contaminated soils exist at numerous sites, and these sites may threaten public health and the environment because many PAH compounds are toxic, mutagenic, and/or carcinogenic. PAHs are also hydrophobic and persistent, so conventional remediation methods are often costly or inefficient, especially when the contaminants are present in low permeability and/or organic soils. An innovative technique, electrokinetically enhanced in situ flushing, has the potential to increase soil-solution-contaminant interaction and PAH removal efficiency for low permeability soils; however, the electrolysis reaction at the anode may adversely affect the remediation of low acid buffering capacity soils, such as kaolin. Therefore, the objective of this study was to improve the remediation of low acid buffering soils by controlling the pH at the anode to counteract the electrolysis reaction. Six bench-scale electrokinetic experiments were conducted, where each test employed one of three different flushing solutions, deionized water, a surfactant, or a cosolvent. For each of these solutions, tests were performed with and without a 0.01 M NaOH solution at the anode to control the pH. The test using deionized water with pH control generated a higher electroosmotic flow than the equivalent test performed without pH control, but the electroosmotic flow difference between the surfactant and cosolvent tests with and without pH control was minor compared to that observed with the deionized water tests. Controlling the pH was beneficial for increasing contaminant solubilization and migration from the soil region adjacent to the anode, but the high contaminant concentrations that resulted in the middle or cathode soil regions indicates that subsequent changes in the soil and/or solution chemistry caused contaminant deposition and low overall contaminant removal efficiency.     

Variations in concentrations and compositions of polycyclic aromatic hydrocarbons (PAHs) in coals related to the coal rank and origin

The release of unburnt coal particles and associated polycyclic aromatic hydrocarbons (PAHs) may cause adverse impacts on the environment. This study assessed variations in the concentration and composition of PAHs in a set of fifty coal samples from eleven coal basins worldwide. The maximum PAH concentrations at high volatile bituminous rank were recorded in samples from a single basin. Considering the entire sample set, the highest PAH concentrations were in fact found outside of this rank range, suggesting that the maceral composition and thus the coal’s origin also influenced PAH concentrations. The examination of the PAH compositions revealed that alkylated 2-3 ring PAHs remain dominant compounds irrespective of coal rank or origin. Multivariate analysis based on PAH and maceral content, bulk and maturity parameters allowed the recognition of seven groups with different rank and origin within the coal sample set.     

Increased retention of polycyclic aromatic hydrocarbons in soils induced by soil treatment with humic substances

The analytical recovery of a mixture of polycyclic aromatic hydrocarbons (PAHs) was determined from a soil before and after oxidation with hydrogen peroxide, and subsequently treated with increasing amounts of an exogenous humic acid and subjected to different incubation periods. The release of PAHs from soil depended on the specific structure and physico-chemical properties of each PAH, and increased with additions of exogenous humic materials for both the oxidized and non-oxidized soil as well as with time of PAH permanence in soil. PAH recoveries were lower in the non-oxidized soil, thereby revealing the importance of native organic matter in increasing PAH retention in soils. This study shows that mobility of PAHs in soils can be controlled by soil conditioning with humic substances.     

Distribution and sources of polycyclic aromatic hydrocarbons from urban to rural soils: a case study in Dalian, China

To estimate the distribution and sources of soil polycyclic aromatic hydrocarbons (PAHs) in metropolitan and adjacent areas, soil samples were collected from urban, suburban and rural locations of Dalian, China, and concentrations of 14 PAHs were determined. The spatial PAH profiles were site-specific and determined by the sources close to the sampling sites. PAH concentrations decreased significantly along the urban-suburban-rural transect. The gradient implied that the fractionation effect influenced PAH distribution. Bivariate plots of selected diagnostic ratios showed general trends of co-variation and allowed to distinguish samples taken from different areas. An improved method, factor analysis (FA) with nonnegative constrains, was used to determine the primary sources and contributions of PAHs in soils. The FA model showed traffic average (74%) and coal related residential emission (26%) were two primary sources to Dalian soils. In addition, the FA model provided reasonable explanations for PAH contributions in soils from different sites. The results suggest that FA with nonnegative constraints is a promising tool for source apportionment of PAHs in soils.     

Lability of polycyclic aromatic hydrocarbons in the rhizosphere

Remediation of soils containing high concentrations of polycyclic aromatic hydrocarbons (PAHs) seldom results in complete removal of contaminants, but residual toxicity often is reduced. In this study, soil from a former manufactured gas plant site was treated for 12 months by phytoremediation and then tested for total PAHs, Tenax-TA extractable ("labile") PAHs, aqueous soluble PAHs (PAH(wp)) , and biotoxicity assessed by earthworms survival, nematode mortality, emergence of lettuce seedlings, and microbial respiration. Prior to phytoremediation, the soil had toxic impacts on all bioassays (except the nematodes), and 12 months of remediation decreased this response. Change in labile PAHs was a predictor for change in total PAH for 3- and 4-ring compounds but not for the 5- and 6-ring. Decreases in labile PAHs were correlated (r(2)>or=0.80) with toxicity in the bioassays except microbial respiration. PAH(wp) was correlated only with nematode toxicity prior to remediation but with none of the tests after remediation. Total PAHs were not correlated with any of the bioassay tests. Tenax-TA appears to have potential for predicting residual toxicity in remediated soils and is superior to total concentrations for that application.     

Contamination by polycyclic aromatic hydrocarbons in the Jiulong River Estuary and Western Xiamen Sea, China

The distribution of 16 polycyclic aromatic hydrocarbons (PAHs) was determined in water, sediment and pore water of the Jiulong River Estuary and Western Xiamen Sea, China. Total PAH concentrations varied from 6.96 to 26.9 microg/l in water, 59-1177 ng/ g dry weight in surficial sediments, and 158-949 microg/l in pore water. The PAHs were present in higher levels in pore water than in surface water, due possibly to higher concentrations of dissolved organic carbon or colloids with which the hydrophobic pollutants were strongly associated. Such a concentration gradient implies a potential flux of pollutants from sediment pore water to overlying water. The levels of PAHs in water and pore water were significantly higher than those found in 1998, suggesting recent inputs of these compounds into the area and re-working of sediment phase. The composition pattern of PAHs in the three phases was dominated by high molecular weight PAHs, in particular 5-ring PAHs. The salinity profile of dissolved PAHs suggested that they all behaved non-conservatively due to deviation from the theoretical dilution line. No correlation was found between PAH concentrations in sediment and those in pore water, and the correlation between the partition coefficients of PAHs and sediment organic carbon content was not significant, suggesting the complexity of the partition behaviour of PAHs. As a result of high PAH concentrations in water and pore water, it is likely that they may have caused mortality to certain exposed organisms.