Polycyclic aromatic hydrocarbons in the sediments of Xiangjiang River in south-central China: occurrence and sources

The Xiangjiang River (XR), located in Hunan province in south-central China, is the second largest tributary of the Yangtze River. The occurrence, and sources of the polycyclic aromatic hydrocarbons (PAHs) in the 20 surface sediment samples from XR were analyzed, and the biological risks of the PAHs on the benthic organisms were assessed using sediment quality guidelines. The results showed that the occurrence level of the 16 USEPA priority PAHs in the surface sediments ranged from 190 to 983 ng/g (dry weight) with a mean concentration of 452 ± 215 ng/g. The concentration of phenanthrene was the highest with a mean concentration of 104 ± 44 ng/g. The compositions and principal components analysis indicated that the PAHs in the sediments in XR were mainly from pyrogenic sources which could be attributed to the open burning of rice straws and coal combustion of the local industries in the XR basin. The PAH contamination in the sediments was considered to be moderate, and has posed a small adverse biological effect on the benthic organisms.     

Composition and source identification of polycyclic aromatic hydrocarbons in mangrove sediments of Peninsular Malaysia: indication of anthropogenic input

This is a comprehensive study of the composition, origin and sources of specific polycyclic aromatic hydrocarbons (PAHs) in sediments of mangrove estuary in the western part of Peninsular Malaysia. Mangrove sediments were analyzed for 17 PAHs by gas chromatography–mass spectrometry. Total PAH concentrations in the sediments ranged from 20 to 112 ng/g on a dry-weight basis. High molecular weight PAHs were abundant in the sediments. Parent PAH ratios revealed that pyrogenic input has important contribution to the sedimentary PAHs. Ratios of alkylated PAHs indicate that the sedimentary PAHs were influenced by petrogenic PAHs, which implies that petrogenic input has contribution to the sedimentary PAHs but that it is not a major factor in distribution of PAHs within the estuary. Combustion-derived PAHs show a positive and very strong correlation with total PAHs (R ² = 0.926, p < 0.05). Total methylphenanthrenes show very weak correlation with total PAHs (R ² = 0.0928, p < 0.05). The PAH concentrations were found to increase with distance from the upstream of the estuary to the coastal area of the Straits of Malacca. For the assessment of sediment contamination using biological thresholds, none of the individual studied PAH compounds exceeded the values of the effect range low–effect range median guideline and the threshold effects level–probable effects level guideline. This study demonstrates that the sediments of the mangrove ecosystem facing the Straits of Malacca and Sumatra are influenced by anthropogenic PAH inputs as a result of human activities such as biomass burning, vehicle emissions and boating activities.     

Polycyclic aromatic hydrocarbons (PAHs) in Xuzhou urban street dust: concentration and sources

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments and are considered as the priority pollutants. The main objectives of this study were (1) to assess the contamination extent of 16 PAHs compounds in urban street dust and (2) to identify the anthropogenic sources of contamination. Forty-nine samples were analysed for 16 PAHs by gas chromatography/mass spectrometry. Results showed that total PAHs concentrations varied from 2174 to 24,499 ng/g with an average value of 6616 ng/g. Total PAHs concentrations showed a significant correlation with the total organic carbon (TOC) content (r = 0.599, p < 0.0001), suggesting likely that TOC can influence the distribution of PAHs in Xuzhou street dust. Source identification indices suggested that the primary source of PAHs was automobile exhausts. A factor analysis was performed, and three factors were extracted from the available dataset, explaining a total variance of approximately 84.7%. Results from the factor analysis could be indicative of PAHs with different origins.     

Survey of polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons in Jiaxing city, China

Polycyclic aromatic hydrocarbon (PAH) and nitrated PAH (NPAH) products are toxic. Thus, determination of their concentrations is of great interest to researchers of soil and water pollution control. In this work, soil samples, surface water samples, and groundwater samples were collected, and the concentrations of 16 priority PAHs and 15 NPAHs were determined using an HPLC-ultraviolet detector. Results showed that the total PAH concentrations ranged within 489.69–1,670.11 ng/g (average = 905.89 ng/g) in soil samples, 4.00–23.4 μg/l (average = 9.84 μg/l) in surface water samples, and 2.14–22.3 μg/l (average = 8.37 μg/l) in groundwater samples. The NPAH concentrations were one to two orders of magnitude lower than the PAH concentrations and ranged within 22.72–128.70 ng/g (average = 63.88 ng/g) in soil samples. 2-Nitropyrene and 6-nitrochrysene were the most abundant compounds, accounting for about 14.3 and 26.5 %, respectively. Source analysis revealed that most PAHs originated from coal combustion around the study area, whereas NPAH studies suggested that the primary emission of gasoline engines and daytime OH reactions were the dominant sources of these compounds.     

Polycyclic aromatic hydrocarbons (PAHs) in particle-size fractions of urban topsoils

Polycyclic aromatic hydrocarbons’ (PAHs) concentrations in bulk samples are commonly used to assess contamination but PAHs are unevenly distributed among particle-size fractions. Seventeen urban surface soil samples from the city of Xuzhou, China, were collected and then fractionated into five size fractions (2,000–300, 300–150, 150–75, 75–28, and <28 μm). The concentrations of 12 US EPA PAHs were measured using gas chromatograph/mass spectrometry in various fractions, and the bulk soil samples and distribution patterns of PAHs in different particle-size fractions were investigated. The mean concentration of total PAHs in bulk soil samples was 1,879 ng/g. The median concentrations for all individual PAH were higher for the 75–2,000 μm fraction than for the <75 μm fraction. The distribution factors for various PAHs in <28 μm soil fraction were closely correlated (r = ?0.661, p < 0.019) to bulk soil fugacity capacity. The values of PAH isomer indicated that traffic emissions might be the major origin of PAHs in Xuzhou surface soils. Spearman correlation analysis was performed and the result suggested that soil organic carbon might be a factor controlling the concentrations of PAHs in soils.     

Assessment of organic pollutants (PAH and PCB) in surface water: sediments and shallow groundwater of Grombalia watershed in northeast of Tunisia

Toxic organic compounds in wastewater are serious threats for both human and environment healthy states. This study investigates the potential sources of surface water, sediment and groundwater pollution by polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyl (PCBs) as discharged by wastewater into the River of Oued El bey in northeastern Tunisia. Analysis indicates that the concentration of PAHs and PCBs are high in wastewater and vary from 0.37 to 0.83 mg/L and from 0.28 and 1.18 mg/L, respectively. The spatial distribution of PAHs and PCB in surface water showed a variation between 0.37 to 9.91 mg/L and between 0.1 to 0.47 mg/L, respectively. However, the quality of surface water is changed after wastewater evacuation at Oued Tahouna. The determination of PAH and PCB pollutants in groundwater shows a great interest in the development of water resources. The Concentration of these pollutants varying from 0.0204 to 1.93 mg/L and from 0.0052 to 0.196 mg/L, respectively. For PAH, analysis reveals also that naphtelene, fluorene, anthracene and chrysene are the most detected PAHs compounds in water and sediment samples while benzo[b]fluoranthene and benzo[a]pyrene are less present and in trace level. Higher concentrations of PAHs and PCBs are found in samples taken close to industrial areas of Bouargoub and Soliman, and wastewater discharge locations in Soliman. Analysis of the spatial distribution of PAHs and PCBs clearly link their higher concentration in water and sediments to wastewater and manufacturing discharges in the study area. In surface sediment, the organic pollutants are present. The cluster analysis for organic pollutants in different state and different matrix highlight a relationship between the wastewater evacuation and the water qualities which confirmed the direct response of the pollution sources on the surface water and groundwater organic pollution quality.     

Temporal trends of aliphatic and polyaromatic hydrocarbons in the Bohai Sea, China: Evidence from the sedimentary record

This work reports the historical trends and sources of aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) in two ²¹⁰Pb dated sediment cores extracted from the central mud areas of Bohai Sea (Bohai). The TOC/TN ratio of the bulk organic matter (OM) and the composition of the n-alkanes suggest that the sedimentary organic matter was of mixed marine and terrigenous sources. The coarser sediment grain size and decreasing C/N ratios since ∼1976 could be attributed to the relocation of the Yellow River mouth causing a decreased influence of Yellow River derived sediments and associated OM into the central Bohai. The concentration of total 16 PAHs in the two cores ranged from 34.2-202 ng/g (mean, 91.5) for BC1, and from 53.3-186 ng/g (mean, 103) for BC2, with a high abundance of 2-3 ring PAHs. Perylene in the two cores mainly originated from terrigenous sources via riverine discharge and thus could be potentially related to changes in the sediment load from the Yellow River into the Bohai over time. Petroleum inputs could be revealed by ratios of methylphenanthrenes to phenanthrene (MP/P) and the patterns of more stable geochemical biomarkers (hopanes and steranes) along the two cores, in addition to the presence of unresolved complex mixtures (UCM) in the surface layers. Source diagnostic ratios of PAHs indicated a pyrogenic origin from biomass and coal combustion with a minor petroleum contribution. Downcore trends of compositional PAHs profiles were in agreement with the socio-economic development in China in the past decades. This temporal variation of sedimentary PAHs can also reflect a different evolution stage of energy structure in China as compared with those of the western developed countries.     

Levels and sources of polycyclic aromatic hydrocarbons (PAHs) in selected irrigated urban agricultural soils in Accra, Ghana

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments including urban soils. Elevated concentrations of PAHs in urban soils are caused by incomplete combustion of petroleum and coal. This study assesses 16 individual PAH compounds in a total of 112 surficial soil samples. The objective was to assess and compare the levels of contamination as well as examine the main sources of PAHs in four urban agricultural soils using molecular ratios of some specific hydrocarbons. The study showed that PAH levels in soil ranged from 1.23 ng/kg in soil collected from Dzorwulu to 2.95 ng/kg in soil collected from Ghana Broadcasting Cooperation (GBC) vegetable irrigation site. Of the total PAHs, the more water soluble PAHs (2–4 rings), which tend to be concentrated in the vapour phase were found to dominate the soils. The percentage dominance were Dzorwulu (52.8 %), Marine Drive (62.5 %), CSIR (53.2 %) and GBC (49.2 %). However, there were significant levels of the more carcinogenic PAHs (5–6 rings) present with percentages as 47.1, 37.5 46.8 and 50.8 % for Dzorwulu, Marine Drive, CSIR and GBC vegetable irrigation sites, respectively, and therefore, may impact negatively on public health. Based on the classification by the Institute of Soil Science and Plant Cultivation in Pulawy, Poland, urban soils in Accra could be classified as contaminated to different levels. Molecular ratios of Flu/pyr and PA/Ant were calculated to determine the main sources of PAHs. Results showed that PAHs could originate mainly from incomplete combustion of petroleum products, especially from atmospheric fallout from automobile exhausts. The study further showed that B(a)P concentration of 0.05 ng/kg in soil from GBC urban vegetable irrigation site requires immediate clean-up exercise and monitoring to mitigate human health impact.     

Polycyclic aromatic hydrocarbons in surface sediments of Laizhou Bay,Bohai Sea,China

Concentration, distribution, and sources of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated in surface sediments of Laizhou Bay, China. Total PAH concentrations ranged from 97.2 to 204.8 ng/g, with a mean of 148.4 ng/g. High concentrations of PAHs were found in the fine-grained sediments on both sides of the Yellow River estuary (YRE). In contrast, low levels of PAHs were observed in relatively coarse grain sediments, suggesting hydrodynamics influence the accumulation of sedimentary PAHs. The YRE and its adjacent area is the main sink for Yellow River-derived PAHs. Both PAH isomer ratios and principal component analysis (PCA) with multivariate linear regression (MLR) were applied to apportion sources of PAHs. Results indicated that both pyrogenic and petrogenic PAH sources were important. Further PCA/MLR analysis showed that the contributions of coal combustion, petroleum combustion and a combined source of spilled oil and biomass burning were 41, 15 and 44%, respectively. From an ecotoxicological viewpoint, the studied area appears to have low levels of PAH pollution.     

Concentrations and possible sources of PAHs in sediments from Bohai Bay and adjacent shelf

Concentrations, spatial distribution and sources of 16 polycyclic aromatic hydrocarbons (PAHs) listed by the United States Environmental Protection Agency as priority pollutants were investigated in surface sediments of Bohai Bay, North China. Total concentrations of PAHs were in the range of 140.6–300.7 ng/g (dry wt), with an average of 188.0 ng/g. The three predominant PAHs were phenanthrene, acenaphthene and naphthalene. Sedimentary PAH concentrations of the north and central Bohai Bay were higher than those of the southern side of this bay. PAHs source analysis suggested that PAHs in most of the sediments were mainly from grass, wood and coal incomplete combustion. At other stations near the estuaries (Luanhe River Estuary and Chaohe River Estuary) or the oil drilling platform, both petrogenic and pyrogenic inputs were significant. The pyrogenic PAHs close to the oil drilling platform were mainly from petroleum combustion.     

Uptake, accumulation and translocation of polycyclic aromatic hydrocarbons by winter wheat cultured on oily sludge-amended soil

The purpose of this study is to comparatively investigate the plant uptake, accumulation and translocation behaviors of polycyclic aromatic hydrocarbons (PAHs) as priority pollutants in soil contaminated with oily sludge. The influence of different oily sludge application doses on the uptake of contaminants was studied together with the profile of individual PAH in roots, straws and leaves of winter wheat. Pot experiments were conducted using oily sludge application doses of 0, 5, 10, 15 and 20 percent, respectively. The total PAHs contents of control soil and oily sludge were 16.96 and 3504.66 μg/g, respectively. Analysis for the contents of the 16 PAHs was carried out with a HPLC-UV using plant tissue samples obtained at the 265th day of growth. The total PAHs contents in treated winter wheat were 9.02-334.81 ng/g for roots, 8.45-336.52 ng/g for straws and 10.70-406.32 ng/g for leaves. In addition to 5% of oily sludge dose, the total PAHs content in leaves was always highest under other doses of oily sludge application. With respect to individual PAH, the content did not show a significant plant tissue related trend. However, both the total content and individual content of PAHs in treated winter wheat tissues did increase with increasing oily sludge application dose. Another analysis for the control soil indicates that the degradation rate of PAHs was significantly enhanced by winter wheat after 265 days of growth based on the residual concentrations of PAHs in planted and unplanted soils.     

Effects of estuarine organic matter biogeochemistry on the bioaccumulation of PAHs by two epibenthic species

Polycyclic aromatic hydrocarbon (PAH) biota-sediment accumulation factors (BSAF) were quantified in sediments from two sites in southeastern Louisiana in a 14 d microcosm study usingPalaemonetes pugio, andRangia cuneata and two radiolabeled PAHs, phenanthrene and benzo[a]pyrene (b[a]p). For both PAHs studied, mean BSAFs were significantly higher (p<0.0001) in both organisms in sediments from Bayou Trepagnier, (BSAF=0.628 g OC g TLE⁻¹), a brackish swamp, compared to Pass Fourchon (0.065 g OC g TLE⁻¹), a coastal salt marsh. In order to explain observed patterns in BSAFs, organic carbon-normalized PAH distribution coefficients between the sediment and freely dissolved phases (K_OC)_OBS were determined as well as the various geochemical variables of particulate and dissolved organic matter (POM and DOM, respectively). These included analyses of particle surface area, total organic carbon (TOC), carbon to nitrogen ratios (C∶N), and dissolved organic carbon (DOC). Bayou Trepagnier was higher in surface area, TOC, C∶N, as well as DOC suggesting that the difference in BSAFs may be attributed to compositional differences in POM and DOM between sites. We can not exclude the possibility that other factors (such as differences in organism behavior resulting from contrasting sediment characteristics) were responsible for BSAFs varying between the two sites. Phenanthrene BSAFs were typically higher than b[a]p BSAFs, suggesting contaminants were limited in their desorption from sediment particles as a function of PAH molecular weight. Mean BSAFs for both PAHs were higher on Day 7 than on Day 14. The reason for this decrease is unclear, but did not appear to be due to organisms becoming increasingly stressed in the microcosms. Visual observations indicated that animals remained feeding while no decreases in organism total lipid levels were detected. The trends in BSAFs between sites and over the time course of this experiment suggest that contaminant bioaccumulation in estuarine systems should not be considered to be an equilibrium process.     

Biogeochemistry of Ethanol and Acetaldehyde in Freshwater Sediments

This study reports the first ethanol and acetaldehyde measurements in sediment porewaters collected at multiple freshwater locations. Ethanol concentrations ranged from 11 to 2535 nM and acetaldehyde concentrations ranged from 6 to 320 nM. A significant positive correlation (p < 0.001) was observed between ethanol concentrations and the percent organic carbon content of sediments (TOC). Porewater depth profiles at two sites within the same lake indicated potential diffusion of ethanol into sediments from the overlying water at a lower TOC site and upwards diffusion from sediment into the water column at a higher TOC site. Diffusion of water column ethanol into sediments was observed at individual sites from October to January, whereas the opposite was true from June to August indicating the seasonal variability of ethanol flux from sediments. Changes in ethanol concentrations during a long-term sediment incubation experiment showed an inverse relation with acetaldehyde concentrations. The lack of a quantitative conversion was likely due to other sources and sinks that control their abundance. Our study provided new information on the biogeochemistry of ethanol in freshwater sediments and shed light on the potential role of ethanol in the global carbon cycle.     

Sources and bioavailability of polynuclear aromatic hydrocarbons in Galveston Bay, Texas

Oyster and sediment samples collected from six sites in Galveston Bay from 1986 to 1998 were analyzed for polynuclear aromatic hydrocarbons (PAHs). Total concentrations of parent PAHs in oysters ranged from 20 ng g⁻¹ at one site to 9,242 ng g⁻¹ at another and varied randomly with no clear trend over the 13 year period at any site. Concentrations of alkylated PAHs, which are indications of petroleum contamination, varied from 20 to 80,000 ng g⁻¹ in oysters and were in higher abundance than the parent PAHs, indicating that one source of the PAH contaminants in Galveston Bay was petroleum and petroleum products. Four to six ring parent PAHs, which are indicative of combustion source , were higher than those of 2–3 ring parent PAHs, suggesting incomplete combustion generated PAHs was another source of PAHs into Galveston Bay. Concentrations of parent PAHs in sediments ranged from 57 to 670 ng g⁻¹ and were much lower than those in oysters. Sediments from one site had a high PAH concentration of 5,800 ng g⁻¹. Comparison of the compositions and concentrations of PAHs between sediment and oysters suggests that oysters preferentially bioaccumulate four to six ring PAHs. PAH composition in sediments suggests that the sources of PAH pollution in Galveston Bay were predominantly pyrogenic, while petroleum related PAHs were secondary contributions into the Bay.     

Chemical characteristics and pollution sources of petroleum hydrocarbons and PAHs in sediments from the Beiluohe River,Northern China

To determine the degree of hydrocarbon contamination and the contribution of local petroleum industries to contaminant loadings in sediments from the Beiluohe River, China, 12 surface sediment samples were collected for geochemical analysis in 2005. Sediment samples were extracted by organic solvents, separated by silica gel column chromatography and the profiles of n-alkanes, biomarkers and polycyclic aromatic hydrocarbons (PAHs) in sediments were analyzed by gas chromatography with flame ionization detector and gas chromatography/mass spectroscopy. Concentrations of total hydrocarbons in the sediments varied from 12.1 to 3,761.5 μg g⁻¹ dry wt, indicating that most sediments in Beiluohe River was only slightly to moderately contaminated by hydrocarbons. Concentrations of PAHs for six samples (sum of 16 isomers) varied from 17.7 to 407.7 ng g⁻¹ dry wt and at present low levels of PAHs did not cause adverse biological effects in Beiluohe River sedimentary environment. PAH compositions, n-alkanes and biomarker profiles all suggested that there were different sources of contaminations in studied areas. n-Alkanes reflect two distinct sources: a fossil n-alkane series from crude oil at sites S40, S43, S87 and plantwax n-alkanes at sites S39 and S45. Judged by their PAH ratios, the sediments at site S15 were pyrolytic, sediments at S17 and S43 were petrogenic, and sediments at S39, S40 and S64 had a mixture source of pyrolytic and petrogenic.     

Characterization and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in sediments in the Yellow River Estuary, China

Concentrations and sources of polycyclic aromatic hydrocarbons (PAHs) were investigated in surface sediments of the Yellow River Estuary (YRE). The isobath-parallel tidal and residual currents play important roles in the variation of PAH distribution, such that the contamination level of PAHs in fine-grained sediments is significantly higher than in the relatively coarse grain size sediments. Both diagnostic ratios and principal component analysis (PCA) with multivariate linear regression (MLR) were used to apportion sources of PAHs. The results revealed that pyrogenic sources are important sources of PAHs. Further analysis indicated that the contributions of coal combustion, traffic-related pollution and mixed sources (spills of oil products and vegetation combustion) were 35, 29 and 36 %, respectively, using PCA/MLR. Pyrogenic sources (coal combustion and traffic-related pollution) contribute 64 % of anthropogenic PAHs in sediments, which indicates that energy consumption could be a predominant factor in PAH pollution of YRE. Acenaphthylene and acenaphthene are the two main species of PAHs with more ecotoxicological concern in YRE.     

Risk assessment of polycyclic aromatic hydrocarbons in the West Port semi-enclosed basin (Malaysia)

Sediment samples collected from the West Port, the west coastal waters of Malaysia, were analyzed by standard methods to determine the degree of hydrocarbon contamination and identify the sources of polyaromatic hydrocarbons (PAHs). Concentrations of PAHs in the port sediments ranged from 100.3 to 3,446.9 μg/kg dw. The highest concentrations were observed in stations close to the coastline, locations affected by intensive shipping activities and industrial input. These were dominated by high-molecular-weight PAHs (4–6 rings). Source identification showed that PAHs originated mostly pyrogenically, from the combustion of fossil fuels, grass, wood, and coal or from petroleum combustion. Regarding ecological risk estimation, only station 7 was moderately polluted, the rest of the stations suffered rare or slight adverse biological effects with PAH exposure in surface sediment, suggesting that PAHs are not considered as contaminants of concern in the West Port.     

Levels and distributions of polycyclic aromatic hydrocarbons (PAHs) in middle reach of Huaihe River,China: anthropogenic influences and ecological risks

Polycyclic aromatic hydrocarbons (PAHs) are a group of aromatic hydrocarbons with high toxicity to human health. PAH emissions from industrial activities have become the primary sources of PAH contamination in Chinese watersheds. Here, we analyzed 10 individual priority PAHs in 120 water samples taken from middle reach of Huaihe River, China. The results show that the PAH levels in studied watershed are significantly lower as compared to other Chinese watersheds, approaching or slightly exceeding the PAH levels in watersheds from selected European and North American countries. We observe rather large variation in spatial and vertical PAH distributions, pointing to PAH inputs from local industrial emissions, and PAH cycle among atmosphere, water and sediment. Individual PAH ratios (i.e., phenanthrene/anthracene and fluorene/pyrene) and principal components analysis suggest a primarily pyrolytic PAH sources (combustion of coal and coke) in water column. Other accompanying PAH sources include emissions from steel industry and gasoline. Total toxic benzo[a]pyrene equivalent of PAHs in studied water column indicates that PAHs in watershed of middle reach of Huaihe River pose limited toxicity to the environment.     

Sediment Accretion in Tidal Freshwater Forests and Oligohaline Marshes of the Waccamaw and Savannah Rivers,USA

Sediment accretion was measured at four sites in varying stages of forest-to-marsh succession along a fresh-to-oligohaline gradient on the Waccamaw River and its tributary Turkey Creek (Coastal Plain watersheds, South Carolina) and the Savannah River (Piedmont watershed, South Carolina and Georgia). Sites included tidal freshwater forests, moderately salt-impacted forests at the freshwater–oligohaline transition, highly salt-impacted forests, and oligohaline marshes. Sediment accretion was measured by use of feldspar marker pads for 2.5 year; accessory information on wetland inundation, canopy litterfall, herbaceous production, and soil characteristics were also collected. Sediment accretion ranged from 4.5 mm year^?1 at moderately salt-impacted forest on the Savannah River to 19.1 mm year^?1 at its relict, highly salt-impacted forest downstream. Oligohaline marsh sediment accretion was 1.5–2.5 times greater than in tidal freshwater forests. Overall, there was no significant difference in accretion rate between rivers with contrasting sediment loads. Accretion was significantly higher in hollows than on hummocks in tidal freshwater forests. Organic sediment accretion was similar to autochthonous litter production at all sites, but inorganic sediment constituted the majority of accretion at both marshes and the Savannah River highly salt-impacted forest. A strong correlation between inorganic sediment accumulation and autochthonous litter production indicated a positive feedback between herbaceous plant production and allochthonous sediment deposition. The similarity in rates of sediment accretion and sea level rise in tidal freshwater forests indicates that these habitats may become permanently inundated if the rate of sea level rise increases.     

Polybrominated diphenyl ethers and its methoxylated analogues in biota and sediment samples from two freshwater lakes in Yangtze River delta

In the present study, sediments and biotas from two freshwater lakes in Yangze delta area were collected and analyzed for polybrominated diphenyl ethers (PBDEs) and methoxylated PBDEs (MeO–PBDEs). The concentrations of PBDEs in sediments and biotas ranged from 0.41 to 5.8 ng/g dry weight and from 4.6 to 100 ng/g lipid weight, respectively, while those of MeO–PBDEs were much lower (sediment: <LOQ-0.014 ng/g dry weight, biota: <LOQ-2.1 ng/g lipid weight). The levels of both brominated substances in sediments and biotas were in the moderate to low range compared with other studies. Different BDE congeners were found between two lakes probably due to the different exogenous sources and metabolic stages. Similar occurrence of higher brominated congeners (e.g., BDE-209) in sediments and biotas indicated sediments as a possible source of PBDEs for biotas. The different contribution of lower and higher brominated congeners between sediments and biotas may be due to the combined effect of biotransformation and bioavailability.