Pollution sources and occurrences of selected persistent organic pollutants (POPs) in sediments of the Mekong River delta, South Vietnam

The Mekong River delta is one of the largest agricultural land in the Southeast Asia. It plays a very important role for agriculture and fisheries in South Vietnam. However, comprehensive studies on the environmental pollution of persistent organic pollutants (POPs) in Mekong River delta have not been carried out in recent years. In this study, we collected sediment samples from the Mekong River to evaluate the contamination and ecological risks caused by several POPs. The contamination pattern of POPs was DDT>PCBs>CHLs>HCHs>HCB. DDTs are the most abundant pollutants, their concentration ranging from 0.01 to 110 ng/g dry wt, followed by PCBs (0.039-9.2 ng/g dry wt). DDTs and PCBs concentrations were higher in sediment from adjacent to urban areas than those from rural and agricultural sites, suggesting urban areas as important point sources of DDTs and PCBs to the river. Ratio of p,p'-DDT/p,p'-DDE was lower compared to those previously reported. However, some samples still had the ratio higher than 0.5, indicating recent input of DDT into the aquatic environments. This result shows that although the magnitude of contamination decreased over time, recent inputs of DDTs to the river still occur. Some sediment samples had concentrations of DDT compounds higher than the standards from the Canadian Environmental Quality Guideline, suggesting continuous monitoring for POPs contamination in the Mekong River is necessary.     

Prediction of the bioaccumulation of persistent organic pollutants in aquatic food webs

Predictive correlations of the bioaccumulation factor of persistent organic pollutants in aquatic biota are presented as functions of their octanol/water partition coefficient. The correlations demonstrate the importance of differentiating among the different levels in the food web and of accounting for the pollutant's bioavailability by considering the amount freely dissolved in water instead of the total concentration. They also reveal the significance of the pollutant's octanol/water partition coefficient value on its biomagnification along the levels of the trophic chain. Prediction results, finally, demonstrate that the correlations provide reasonably accurate estimates of bioaccumulation, typically within an order-of-magnitude.     

An integrated approach to model the biomagnification of organic pollutants in aquatic food webs of the Yangtze Three Gorges Reservoir ecosystem using adapted pollution scenarios

The impounding of the Three Gorges Reservoir (TGR) at the Yangtze River caused large flooding of urban, industrial, and agricultural areas, and profound land use changes took place. Consequently, substantial amounts of organic and inorganic pollutants were released into the reservoir. Additionally, contaminants and nutrients are entering the reservoir by drift, drainage, and runoff from adjacent agricultural areas as well as from sewage of industry, aquacultures, and households. The main aim of the presented research project is a deeper understanding of the processes that determines the bioaccumulation and biomagnification of organic pollutants, i.e., mainly pesticides, in aquatic food webs under the newly developing conditions of the TGR. The project is part of the Yangtze-Hydro environmental program, financed by the German Ministry of Education and Science. In order to test combinations of environmental factors like nutrients and pollution, we use an integrated modeling approach to study the potential accumulation and biomagnification. We describe the integrative modeling approach and the consecutive adaption of the AQUATOX model, used as modeling framework for ecological risk assessment. As a starting point, pre-calibrated simulations were adapted to Yangtze-specific conditions (regionalization). Two exemplary food webs were developed by a thorough review of the pertinent literature. The first typical for the flowing conditions of the original Yangtze River and the Daning River near the city of Wushan, and the second for the stagnant reservoir characteristics of the aforementioned region that is marked by an intermediate between lake and large river communities of aquatic organisms. In close cooperation with German and Chinese partners of the Yangtze-Hydro Research Association, other site-specific parameters were estimated. The MINIBAT project contributed to the calibration of physicochemical and bathymetric parameters, and the TRANSMIC project delivered hydrodynamic models for water volume and flow velocity conditions. The research questions were firstly focused on the definition of scenarios that could depict representative situations regarding food webs, pollution, and flow conditions in the TGR. The food webs and the abiotic site conditions in the main study area near the city of Wushan that determine the environmental preconditions for the organisms were defined. In our conceptual approach, we used the pesticide propanil as a model substance.     

Assessment of persistent organic pollutants in sediments from Lower Mekong River Basin

Organochlorine compounds (OCs) in sediments collected from various locations in Lower Mekong River Basin (MRB) in Laos and Thailand were examined to elucidate their occurrence, distribution and potential ecological risk. Concentration of PCBs and DDTs were higher than other OCs, ranging from 0.18 to 310 μg kg⁻¹ dry wt. and from 0.027 to 52 μg kg⁻¹ dry wt., respectively, whereas CHLs, HCHs and HCB were 1-3 orders of magnitude lower. Geographical distribution indicates that levels of PCBs, DDTs and CHLs in the Vientiane canal were significantly higher than those in mainstream of Mekong River, Phong River and its surrounding areas, indicating significant sources of these compounds in urbanized areas. Comparison with other parts of MRB indicates that PCBs were higher in Laos, whereas DDTs were more prevalent in Mekong Delta, indicating location specific contaminations of these compounds in MRB. The ratios of DDTs composition indicate possible difference in the historical input of DDT among locations in and around Mekong River. Hazard assessment of PCBs and DDTs indicate possible toxic potential particularly in areas close to point sources such as intensive human activities and agricultural areas which highlight the need for further study.     

Contamination of an arctic terrestrial food web with marine-derived persistent organic pollutants transported by breeding seabirds

At Cape Vera, Devon Island (Nunavut, Canada), a colony of northern fulmars (Fulmarus glacialis) concentrates and releases contaminants through their guano to the environment. We determined whether persistent organic pollutants (POPs) from seabirds were transferred to coastal food webs. Snow buntings (Plectrophenax nivalis) were the most contaminated species, with ∑PCB and ∑DDT (mean: 168, 106 ng/g ww) concentrations surpassing environmental guidelines for protecting wildlife. When examined collectively, PCB congeners and DDT in jewel lichen (Xanthoria elegans) were lower in samples taken farther from the seabird colony, and increased with increasing δ¹⁵N values. However, only concentrations of p’p-DDE:∑DDT and PCB-95 were significantly correlated inversely with distance from the seabird cliffs. Linkages between marine-derived POPs and their concentrations in terrestrial mammals were less clear. Our study provides novel contaminant data for these species and supports biovector transport as a source of organic contaminants to certain components of the terrestrial food web.     

Source and release mechanism of arsenic in aquifers of the Mekong Delta, Vietnam

In order to elucidate the arsenic source and its release mechanism into groundwater in the Mekong Delta, Vietnam, groundwater samples were collected from wells at different depths (20 to 440 m) and core samples (from 20 to 265 m depth) were analyzed. Based on the analytical results for groundwater and core samples, the As source in groundwater is considered to be pyrite (FeS(2)) in acid sulfate soil (ASS) under oxidizing conditions and hydrous ferric oxide (Fe(OH)(3)) under reducing conditions. Geochemical modeling demonstrated that As(III) is the dominant species and the presence of As-bearing sulfides, Fe-bearing sulfides and oxides phases may locally act as potential sinks for As. From variation between Fe and As concentrations in groundwater samples, the release mechanism of As is: dissolution of Fe(OH)(3) containing As under reducing conditions and oxidative decomposition of FeS(2) containing As under oxidizing conditions.     

Occurrence and biomagnification of organohalogen pollutants in two terrestrial predatory food chains

Organohalogen pollutants (OHPs), including dichlorodiphenyl trichloroethane and its metabolites (DDTs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDs), and dechlorane plus (DP), were determined in three raptor species, namely, the common kestrel (Falco tinnunculus), eagle owl (Bubo bubo), and little owl (Athene noctua), as well as in their primary prey items: Eurasian tree sparrow (Passer montanus) and brown rat (Rattus norvegicus). DDTs were the predominant pollutants in avian species followed by PBDEs and PCBs, then minimally contribution of HBCDs and DP. Inter-species differences in the PBDE congener profiles were observed between the owls and the common kestrels, with relatively high contributions of lower brominated congeners in the owls but highly brominated congeners in the kestrels. This result may partly be attributed to a possible greater in vivo biotransformation of highly brominated BDE congeners in owls than in kestrels. α-HBCD was the predominant diastereoisomer with a preferential enrichment of (−)-enantiomer in all the samples. No stereoselective bioaccumulation was found for DP isomers in the investigated species. Biomagnification factor (BMF) values were generally higher in the rat−owl food chain than in the sparrow−kestrel food chain. Despite this food chain-specific biomagnification, the relationships between the log BMF and log K_OW of PCBs and PBDEs followed a similar function in the two food chains, except for BDE-47, -99, and -100 in the sparrow−kestrel feeding relationship.     

Determination of primary and secondary sources of organic acids and carbonaceous aerosols using stable carbon isotopes

Stable carbon isotope ratio (δ¹³C) data can provide important information regarding the sources and the processing of atmospheric organic carbon species. Formic, acetic and oxalic acid were collected from Zurich city in August–September 2002 and March 2003 in the gas and aerosol phase, and the corresponding δ¹³C analysis was performed using a wet oxidation method followed by isotope ratio mass spectrometry. In August, the δ¹³C values of gas phase formic acid showed a significant correlation with ozone (coefficient of determination (r²) = 0.63) due to the kinetic isotope effect (KIE). This indicates the presence of secondary sources (i.e. production of organic acids in the atmosphere) in addition to direct emission. In March, both gaseous formic and acetic acid exhibited similar δ¹³C values and did not show any correlation with ozone, indicating a predominantly primary origin. Even though oxalic acid is mainly produced by secondary processes, the δ¹³C value of particulate oxalic acid was not depleted and did not show any correlation with ozone, which may be due to the enrichment of ¹³C during the gas - aerosol partitioning.The concentrations and δ¹³C values of the different aerosol fractions (water soluble organic carbon, water insoluble organic carbon, carbonate and black carbon) collected during the same period were also determined. Water soluble organic carbon (WSOC) contributed about 60% to the total carbon and was enriched in ¹³C compared to other fractions indicating a possible effect of gas - aerosol partitioning on δ¹³C of carbonaceous aerosols. The carbonate fraction in general was very low (3% of the total carbon).     

Use of carbon and nitrogen stable isotope ratios to assess the effects of environmental contaminants on aquatic food webs

In this study, the value of carbon (delta13C) and nitrogen (delta15N) stable isotope ratios were determined in nymphs of a top-predator, the common backswimmer (Notonecta glauca L.), collected in 18 m3 outdoor freshwater mesocosms used to assess the fate and ecotoxicological effects of a diphenyl ether herbicide, fomesafen, applied alone or in combination with Agral 90 (mixture of polyethoxylated derivatives of nonylphenol). Both treatments had a negative effect on delta13C values which may reflect changes in carbon fluxes across food webs in the treated ponds associated with a shift in phytoplankton structure. A decrease in delta15N values was observed in the nymphs collected in mixture-treated ponds, which was presumably due to an increase in the abundance of rotifers and Chironominae larvae in these ponds. These preliminary results indicate that stable isotope ratios may be used as shortcuts to detect qualitative or quantitative shifts in the structure of aquatic food webs caused by pollutants.     

Tracing the influence of sewage nitrogen in a coastal ecosystem using stable nitrogen isotopes

This paper reviews the use of stable nitrogen isotopes (delta15N) to delineate the influence of sewage nitrogen (N) in coastal ecosystems, drawing extensively on the case of Himmerfj?rden, a Baltic Sea bay that receives 15N-enriched tertiary treated sewage that is discharged mainly as dissolved inorganic N (DIN). Gradients of delta15N in macroalgae (Fucus vesiculosus) and surface sediments traced sewage-derived N to 24 km from the outfall but elevated delta15N values (> 7 per thousand) indicated that the sewage influence was most pronounced within 10 km. Comparison of macroalgal delta15N values before and after enhanced tertiary treatment showed a decrease in the spatial impact of sewage N from about 24 km to 12 km from the outfall and a decrease to more marine delta15N values in more recent growth tissues. Sedimentary delta15N records showed that sewage has had a dominant influence on organic matter production in the bay with dramatic increases in sedimentary delta15N during the years of maximum sewage N loads. In cases where sewage N introduces a distinct isotopic signature into a system and where it has had a dominant influence on organic matter production, delta15N values in biota and sediments can be used to trace the spatial and temporal influence of sewage N in aquatic ecosystems.     

Bioconcentration and half-life of quinalphos pesticide in rice-fish integration system in the Mekong Delta,Vietnam

In order to determine the distribution and enable the elimination of quinalphos, a popular active pesticide compound used in the Mekong Delta, an experiment was set up in a rice-fish integration system in Can Tho City, Vietnam. Fish was stocked into the field when the rice was two-months old. Quinalphos was applied twice in doses of 42.5 g per 1000 m². Water, fish and sediment samples were collected at time intervals and analyzed by a Gas Chromatography Electron Capture Detector system. The results show that quinalphos residues in fish muscles were much higher than those of the water and the bioconcentration factor (logBCF) was above 2 for the fish. The half-life of first and second quinalphos applications were 12.2 and 11.1 days for sediment, 2.5 and 1.1 days for silver barb, 1.9 and 1.3 days for common carp, and 1.1 and 1.0 days for water, respectively.     

Regional dynamics of persistent organic pollutants (POPs) in the Pearl River Delta, China: implications and perspectives

The mass transport budgets of 1,1,1-trichloro-2,2-bis(chlorophenyl)ethane (p,p′-DDT) and decabromodiphenyl ether (BDE-209) in the Pearl River Delta, South China were calculated based on previously collected data. Residual p,p′-DDT, mostly related to historical use, has largely settled into soil (780,000 kg), while the soil BDE-209 inventory (44,000 kg) is considerably smaller. Conversely, large amounts of BDE-209 currently used in numerous commercial products have resulted in a much higher atmospheric depositional flux of BDE-209 (28,100 kg/yr) relative to p,p′-DDT (310 kg/yr). The soil inventory of p,p′-DDT is predicted to decrease to half of its current value after 22 years, and the percent area containing soil p,p′-DDT at levels exceeding the effects range-medium (27 ng/g) will decrease from 40% to 20%. Finally, soil BDE-209 inventory will reach an equilibrium value of 940 tons in ∼60 years, when BDE-209 levels in 50% of soil will be above an equivalent risk guideline value (125 ng/g).     

Examination of the bioaccumulation of halogenated dimethyl bipyrroles in an Arctic marine food web using stable nitrogen isotope analysis.

Concentrations of four possibly naturally produced organohalogens--1,1'-dimethyl-3,3',4-tribromo-4,5,5'-trichloro-2,2'-bipyrrole (DBP-Br3Cl3), 1,1'-dimethyl-3,3',4,4'-tetrabromo-5,5'-dichloro-2,2'-bipyrrole (DBP-Br4Cl2), 1,1'-dimethyl-3,3',4,4',5-pentabromo-5'-chloro-2,2'-bipyrrole (DBP-Br5Cl) and 1,1'-dimethyl-3,3',4,4',5,5'-hexabromo-2,2'-bipyrrole (DBP-Br6)--were quantitated and the extent of their magnification through an entire Arctic marine food web [measured as integrated trophic magnification factors (TMFs)] were calculated. The food web consisted of three zooplankton species (Calanus hyperboreus, Mysis oculata, and Sagitta sp.), one fish species [Arctic cod (Boreogadus saida)], four seabird species [dovekie (Alle alle), black guillemot (Cepphus grylle), black-legged kittiwake (Rissa tridactyla), and glaucous gull (Larus hyperboreus)], and one marine mammal species [ringed seal (Phoca hispida)]. Trophic levels in the food web were calculated from ratios of stable isotopes of nitrogen (15N/14N). All halogenated dimethyl bipyrrole (HDBP) congeners were found to significantly (P<0.02) biomagnify, or increase in concentration with trophic level in the invertebrate--fish--seabird food web. DBP-Br4Cl2 (TMF= 14.6) was found to biomagnify to a greater extent than DBP-Br3Cl3 (TMF = 5.2), DBP-Br5Cl (TMF = 6.9), or DBP-Br6 (TMF = 7.0), even though the Kow of DBP-Br4CI2 was predicted to be lower than those of DBP-Br5Cl and DBP-Br6. None of the four HDBP congeners in ringed seals followed the general trend of increasing concentration with trophic level, which was possibly due to an ability of the seals to metabolize HDBPs.     

Food web of a confined and anthropogenically affected coastal basin (the Mar Piccolo of Taranto) revealed by carbon and nitrogen stable isotopes analyses

Carbon and nitrogen stable isotope analysis was used to examine the food web of the Mar Piccolo of Taranto, a coastal basin experiencing several anthropogenic impacts. Main food sources (algal detritus, seaweeds, particulate organic matter (POM) and sediment organic matter (SOM)) and benthic and pelagic consumers were collected during two contrasting seasons (June and April), at four sites distributed over two inlets, and characterized by different level of confinements, anthropogenic inputs and the presence of mussels farming. δ¹³C values of organic sources revealed an important contribution of POM to both planktonic and benthic pathways, as well as the influence of terrigenous inputs within both inlets, probably due to high seasonal land runoff. Although δ¹³C of both sources and consumers varied little between sampling sites and dates, δ¹⁵N spatial variability was higher and clearly reflected the organic enrichment in the second inlet as well as the uptake of anthropogenically derived material by benthic consumers. On the other hand, within the first inlet, the isotopic composition of consumers did not change in response to chemical contamination. However, the impact of polluted sediments near the Navy Arsenal in the first inlet was detectable at the level of the macrobenthic trophic structure, showing high dominance of motile, upper level consumers capable to face transient conditions and the reduction of the more resident deposit feeders. We therefore underline the great potential of matching stable isotope analysis with quantitative studies of community structure to assess the effects of multiple anthropogenic stressors.     

Estimation of Nitrogen and Phosphorus in Effluent from the Striped Catfish Farming Sector in the Mekong Delta,Vietnam

In this study an attempt is made to estimate nitrogen and phosphorus discharged to the environment from the striped catfish (Pangasianodon hypophthalmus) farming sector in the Mekong Delta (8°33′–10°55′N, 104°30′–106°50′E), South Vietnam. The sector accounted for 687,000 t production in 2007 and 1,094,879 t in 2008, with over 95% of the produce destined for export to over 100 countries. Commercial and farm-made feeds are used in catfish farming, currently the former being more predominant. Nitrogen discharge levels were similar for commercial feeds (median 46.0 kg/t fish) and farm-made feeds (median 46.8 kg/t fish); whilst, phosphorus discharge levels for commercial feeds (median 14.4 kg/t fish) were considerably lower than for farm-made feeds (median 18.4 kg/t fish). Based on the median nutrient discharge levels for commercial feeds, striped catfish production in the Mekong Delta discharged 31,602 t N and 9,893 t P, and 50,364 t N and 15,766 t P in 2007 and 2008, respectively. However, the amount of nutrients returned directly to the Mekong River may be substantially less than this as a significant proportion of the water used for catfish farming as well as the sludge is diverted to other agricultural farming systems. Striped catfish farming in the Mekong Delta compared favourably with other cultured species, irrespective of the type of feed used, when the total amounts of N and P discharged in the production of a tonne of production was estimated.     

Relationships between organic matter, black carbon and persistent organic pollutants in European background soils: Implications for sources and environmental fate

Black carbon (BC) and total organic carbon (TOC) contents of UK and Norwegian background soils were determined and their relationships with persistent organic pollutants (HCB, PAHs, PCBs, co-planar PCBs, PBDEs and PCDD/Fs) investigated by correlation and regression analyses, to assess their roles in influencing compound partitioning/retention in soils. The 52 soils used were high in TOC (range 54-460 mg/g (mean 256)), while BC only constituted 0.24-1.8% (0.88%) of the TOC. TOC was strongly correlated (p < 0.001) with HCB, PCBs, co-PCBs and PBDEs, but less so with PCDD/Fs (p < 0.05) and PAHs. TOC explained variability in soil content, as follows: HCB, 80%; PCBs, 44%; co-PCBs, 40%; PBDEs, 27%. BC also gave statistically significant correlations with PBDEs (p < 0.001), co-PCBs (p < 0.01) and PCBs, HCB, PCDD/F (p < 0.05); TOC and BC were correlated with each other (p < 0.01). Inferences are made about possible combustion-derived sources, atmospheric transport and air-surface exchange processes for these compounds.     

EROD activity and stable isotopes in seabirds to disentangle marine food web contamination after the Prestige oil spill

In this study, we measured via surgical sampling hepatic EROD activity in yellow-legged gulls from oiled and unoiled colonies, 17 months after the Prestige oil spill. We also analyzed stable isotope composition in feathers of the biopsied gulls, in an attempt to monitor oil incorporation into marine food web. We found that yellow-legged gulls in oiled colonies were being exposed to remnant oil as shown by hepatic EROD activity levels. EROD activity was related to feeding habits of individual gulls with apparent consequences on delayed lethality. Capture-recapture analysis of biopsied gulls suggests that the surgery technique did not affect gull survival, giving support to this technique as a monitoring tool for oil exposure assessment. Our study highlights the combination of different veterinary, toxicological and ecological methodologies as a useful approach for the monitoring of exposure to remnant oil after a large oil spill.     

A model for estimating the potential biomagnification of chemicals in a generic food web: Preliminary development

GOAL, SCOPE AND BACKGROUND: Bioaccumulation and biomagnification of organic pollutants have been increasingly assessed and modeled during the last years. Due to the complexity of these processes and the large variability of food webs, setting generic assessments for these parameters is really difficult. Equilibrium models, based on a compound's lipophylicity, are the main tool in regulatory proposals, such as for identifying Persistent, Bioaccumulative and Toxic Substances (PBTs), although a refinement has been claimed by the scientific community. Toxicokinetic studies offer an alternative for these estimations, where biomagnification is modeled as a succession of bioaccumulation processes, each one regulated by toxicokinetic parameters. METHODS: A review of kinetic models covering species belonging to different trophic levels and with different ecological behavior has been conducted. The results were employed for setting a conceptual model for estimating the biomagnification potential in a generic food web, which was mathematically implemented through system dynamic models developed under data sheet software. Crystal Ball was then employed for allowing Monte Carlo based probabilistic calculations. Bioaccumulation laboratory assays have been performed to estimate toxicokinetic parameters in mussels (Mytilus edulis) with two PAHs (chrysene and benzo[a]pyrene). The contamination was delivered via food. The exposure period lasted more than one month followed then by a depuration phase. The contaminant content was determined on an individual basis on five replicates. RESULTS AND DISCUSSION:. The reviewed information suggested the development of a tiered conceptual biomagnification model, starting with a simplified food chain which can be refined to more realistic and complex models in successive levels. CONCLUSIONS: The mathematical implementation of the conceptual model offers tools for estimating the potential for bioaccumulation and biomagnification of chemicals under very different conditions. The versatility of the model can be used for both comparative estimations and for validating the model. RECOMMENDATIONS AND PERSPECTIVES: Since bioaccumulation and biomagnification processes are crucial elements for a proper risk assessment of chemicals, their estimation by mathematical models has been widely tested. However, inregulatory assessments, too simplistic models are still being used quite often. The biomagnification model presented in this study should be amore accurate alternative to these models. In comparison to other previously published biomagnification models, the present one covers the time variation of bioaccumulation using just a few toxicokinetic parameters.     

Arsenic in groundwater and sediment in the Mekong River delta, Vietnam

A study of groundwater and sediment during 2007-2008 in the Mekong River delta in Vietnam (MDVN) revealed that 26%, 74%, and 50% of groundwater samples were above the US EPA drinking water guidelines for As (10 μg/L), Mn (0.05 mg/L), and Fe (0.3 mg/L). The range of As, Fe, and Mn concentrations in the MDVN were <0.1-1351 μg/L, <0.01-38 mg/L, and <0.01−14 mg/L, respectively. Elevated levels of As were found in groundwater at sampling sites close to the Mekong River and in wells less than 60−70 m deep. An inverse relationship was found between As and Mn concentrations in groundwater. Sediment samples from An Giang and Dong Thap had the highest As concentrations (18 mg/kg and 38 mg/kg, respectively). Arsenic sediment occurred mainly in the poorly crystalline Fe oxide phases. Reductive dissolution of the Fe oxide phase is not necessarily the dominant mechanism of As release to groundwater.