Partitioning characteristics of PAHs between sediment and water in a shallow lake

Goal, Scope and Background

Distribution of hydrophobic organic contaminants in abiotic compartments is essential for describing their transfer and fate in aquatic ecosystems. Taihu Lake is the third largest freshwater lake in China. Water quality of Taihu Lake has deteriorated greatly during the last decades and has threatened the water supply. The aim of the present study was to investigate the partitioning of polycyclic aromatic hydrocarbons (PAHs) among overlying water, suspended particulate matter (SPM), sediments, and pore water in Meiliang Bay, Taihu Lake and to provide useful information for the ecological engineering in this area.

Materials and Methods

Overlying water and surface sediment were sampled from six sites in Meiliang Bay, Taihu Lake, China. Within 72 h of sampling, sediments were centrifuged to obtain the pore water. Overlying water samples were filtered to separate dissolved and SPM samples. After extraction, samples were purified following a clean-up procedure. PAH fraction was obtained by elution with a mixture of hexane: DCM (7:3, V/V) and analyzed by GC/MS.

Results

PAHs concentrations in overlying water varied from 37.5 ng/L to 183.5 ng/L. Concentrations of PAHs in pore water were higher than those in overlying water. The total concentrations of 16 priority PAHs in sediments ranged from 2091.8 ng/g-dw to 4094.4 ng/g-dw. PAHs concentrations on SPM were decreased with suspended solid concentrations (SSC). Total PAHs concentrations on SPM varied in the range of 3369.6 ng/g-dw to 7531.1 ng/g-dw. The partition coefficients between sediment and overlying water (log K _oc) for PAHs with log K _ow<5 were positively correlated with their octanol-water partition coefficients (log K _ow) (n=39, r=0.79, p<0.0001). Partition coefficients between sediment and pore water (log K _oc′) for all PAHs were also significantly correlated with their log K _ow values (n=48, r=0.82, p<0.0001).

Discussion

In general, PAHs derived from combustion sources tend to bind strongly to soot particles in natural sediment. Consequentially, K _oc values observed in the natural environment could be orders of magnitude higher than those predicted by linear correlation relationships under laboratory conditions. In the present study, the ratio of log K _oc values to log K _ow values falls consistently above 1, indicating that the sediment soot carbon in the bay was more attractive for PAHs than n-octanol. The log K _oc′ was also higher than that predicted under laboratory conditions, suggesting that the measured pore water PAH concentrations were lower than those predicted. That is to say, not all the sediment PAHs can be available to partition rapidly into sediment pore waters. A variation in soot content is a possible reason. Furthermore, concentrations of PAHs on SPM were higher than those in sediments. The compositions of PAHs on SPM and in sediments were similar, indicating the importance of re-suspension process of sediments in the partitioning process of the shallow lake.

Conclusions

The results indicated the equilibrium partitioning model could be used to predict PAHs distribution in various phases of a shallow lake in the stagnation period, but re-suspension processes should be considered to modify the relationship between log K _ocs and log K _ows.

Recommendations and Perspectives

Concentration, particle size and composition of resuspended particles could affect the relationship between log K _ocs and log K _ows. Further work should be done under field conditions, especially where a steady thermodynamic equilibrium state could be assumed.

     

Harmonisation, standardisation for soil and sediment fractionation studies, and usefulness in assessment and risk management

Single and sequential extraction procedures are often used to study the environmental fate of trace elements from soils and sediments. Although these schemes are quite popular, they are prone to various sources of errors, which require them to be thoroughly controlled. Owing to their operationally-defined character, the only way to compare analytical data is to stick closely to procedures that have been collaboratively studied and written in the form of an operating protocol. Groups of scientists have hence developed ‘harmonised’ procedures that are used as a reference for fractionation studies. A higher level is the formal standardisation of the procedures by official standardisation bodies, which also fulfils the need for achieving the comparability of data obtained by different laboratories from different countries. This paper discusses aspects of harmonisation (consensus obtained by groups of scientists) and standardisation (adoption of standards as mandated by an international organisation) as applied to single and extraction schemes for trace element fractionation studies, including quality control aspects.     

不同规格鱼鳞坑坡面侵蚀过程及特征研究

探究不同雨强下鱼鳞坑措施的坡面侵蚀规律及特征,对进一步明晰该措施的径流泥沙调控机制具有重要意义。该研究采用小区模拟降雨试验,研究3种雨强(40,70和100 mm/h)条件下2种规格鱼鳞坑坡面的蓄水保土效益及侵蚀过程,并探讨鱼鳞坑坡面水沙特征及其与细沟形态之间的关系。结果表明,鱼鳞坑的径流泥沙调控作用明显但也存在阈值,在措施被冲垮前,各处理减流效益和减沙效益分别为66.02%~82.20%和85.77%~91.91%;平均径流强度和输沙速率分别为平整坡面的18.87%~33.21%和10.04%~15.38%;当鱼鳞坑被冲垮后,坡面产流量和产沙量分别为平整坡面的1.00~1.22倍和1.39~3.53倍,其平均径流强度和输沙速率分别为鱼鳞坑冲垮前的4.60~7.46倍和13.70~16.75倍。鱼鳞坑坡面径流含沙率在措施冲垮前后的差异较大,水沙关系线性拟合的斜率在措施被冲垮前为0.020和0.035,而冲垮后斜率为0.205和0.231,同时坡面总产沙量和峰值产流产沙量与细沟形态显著相关。因此,鱼鳞坑措施对坡面产流产沙特征及形态的影响在其调控阈值前后有较大差异。研究可为鱼鳞坑坡面水土流失的研究可为区域水土保持措施配置及管理提供相应的依据。     

末次间冰期-冰期旋回黄土环境敏感粒度组分的提取及意义

采用粒级-标准偏差方法对黄土高原西部、河西走廊及河南西部等6个剖面末次间冰期-冰期旋回的黄土-古土壤粒度进行了系统分析，提取了对环境变化敏感的粒度组分。各剖面的环境敏感粒度组分主要分为粗细两个组分，并显示出一定的区域性差异和不同的沉积学意义。敏感组分主要受物源和沉积后成壤作用的影响：冰沟和罗家湾剖面可能受源区的影响更大而使敏感组分偏粗，暖和湾和扣马剖面可能由于后期风化的影响较大而使敏感组分偏细。对扣马剖面末次冰期旋回堆积的L1和S1的粒级一标准偏差分析表明，L1的敏感组分与全剖面相似；而S1的敏感组分与全剖面存在较大差异，可能与成壤作用有关。     

Bioassay-directed Fractionation of Organic Extracts of Marine Surface Sediments from the North and Baltic Sea - Part II: Results of the biotest battery and development of a biotest index (8 pp)

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Part I: Determination and identification of organic pollutants Part II: Results of the biotest battery and development of a biotest index

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Preamble. This series of two papers presents the results of an interdisciplinary research project (ISIS) dealing with bioassay-directed fractionation of marine sediment extracts. Part I presents the extraction and fractionation procedure as well as the results of chemical analysis, including non-target analysis of sediments. Part II describes the results of the biotest battery in relation to chemicals possibly causing parts of the observed effects. A biotest index is used to compare the toxicities of the samples.

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AUTHORS / AFFILIATIONS Ninja Reineke (3), Werner Wosniok (4), Dirk Danischewski (1), Heinrich Hühnerfuss (3), Angelika Kinder (5), Arne Sierts-Herrmann (5), Norbert Theobald (2), Hans-Heinrich Vahl (6), Michael Vobach (1), Johannes Westendorf (6) and Hans Steinhart (5).

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(1) Federal Research Centre for Fisheries, Institute for Fishery Ecology, Palmaille 9, 22767 Hamburg, Germany (2) Federal Maritime and Hydrographic Agency, Bernhard-Nochtstr. 78, 20359 Hamburg, Germany (3) University of Hamburg, Institute for Organic Chemistry, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany (4) University of Bremen, Institute of Statistics, Bibliothekstr. 1, 28334 Bremen, Germany (5) University of Hamburg, Institute for Food Chemistry, Grindelallee 117, 20146 Hamburg, Germany (6) University of Hamburg, University Hospital Hamburg-Eppendorf, Department for Toxicology, Vogt-Kölln-Str. 30, 22527 Hamburg, Germany (7) Eurofins Wiertz-Eggert-Jörissen, Stenzelring 14b, 21107 Hamburg, Germany

Goal, Scope and Background

The ecological relevance of contaminants in mixtures is difficult to assess, because of possible interactions and due to lacking toxicity data for many substances present in environmental samples. Marine sediment extracts, which contain a mixture of environmental contaminants in low concentrations, were the object of this study. The extracts were investigated with a set of different biotests in order to identify the compound or the substance class responsible for the toxicity. For this goal, a combination of biotests, biotest-directed fractionation and chemical analysis has been applied. Further on, a strategy for the development of a biotest index to describe the toxicity of the fractions without a prior ranking of the test results is proposed. This article (Part II) focuses on the biological results of the approach.

Methods

The toxicological potential of organic extracts of sediments from the North Sea and the Baltic Sea was analyzed in a bioassay-directed fractionation procedure with a set of biotests: luciferase reporter gene assays on hormone receptor and Ah receptor, arabinose resistance test, fish embryo test (Danio rerio), comet assay, acetylcholinesterase inhibition test, heat-shock protein 70 induction, oxidative stress and luminescence inhibition test (Vibrio fischeri). The test results provided the basis for the calculation of a biotest index by factor analysis to compare the toxicity of the samples and fractions.

Results and Discussion

Results of 11 biotests on different fractionation levels of the samples were described and discussed with regard to the occurrence of contaminants and their toxic potentials. Polychlorinated biphenyls, polycyclic aromatic hydrocarbons, quinones, brominated indoles and brominated phenols were in the focus of interest. A biotest index was constructed to compare the toxic responses in the samples and to group the biotest results.

Conclusion

The procedure presented in this study is well suited for bioassay-directed fractionation of marine sediment extracts. However, in relatively low contaminated samples, high enrichment factors and sufficient fractionation is necessary to allow identification of low concentrations of contaminants which is required to link effects and possible causes. In the present case, the relation between substances and effects was difficult to uncover due to relatively low concentrations of pollutants compared to the biogenic matrix and to the remaining complexity of the fractions. The results, with respect to the brominated phenols and indoles in the samples, highlight the successful use of bioassay directed fractionation in the case of high concentrations and high toxicity.

Recommendation and Outlook

In general, it has been shown that a marine risk assessment requires focusing on the input of diffuse sources and taking into account the fact of mixture toxicity. Effects resulting from biogenic substances will make the assessment of the influence of anthropogenic substances even more difficult.     

Combined effects of best management practices on water quality in oxbow lakes from agricultural watersheds

Water quality conditions in three oxbow lakes were examined before and after best management practices (BMPs) implementation within the Mississippi Delta. Experimental design called for the development of structural and cultural treatments to reduce sediment and associated pollutants entering watershed oxbow lakes. Three watersheds were selected and developed with different levels of BMPs. Changes in lake water quality were used as measures of management success. Analyses of water quality data prior to the implementation of BMPs suggested the lakes were stressed and ecologically damaged due to excessive sediment inflow. Significant improvements in water quality were observed with the use of cultural and structural BMPs. Sediments decreased 34–59%, while Secchi visibility and chlorophyll generally increased. The most dramatic improvements in water quality occurred in the two watersheds that featured cultural practices and combinations of cultural and structural practices. Reducing suspended sediment concentrations in these oxbow lakes favored phytoplankton production resulting in increased chlorophyll concentrations and higher concentrations of dissolved oxygen. Cultural BMPs, more so than structural BMPs, play a vital role in improving lake water quality, and are needed in addition to structural measures to ensure improved water quality in oxbow lakes receiving agricultural runoff.     

On-site remediation of chromium-contaminated sediments by combination of sediment washing and stabilization with magnesium oxide/limestone mixtures

Goal, Scope and Background  The remediation of heavy-metalcontaminated soils and sediments is of significant value to industrial areas around the world. The spread of such pollutants can result in a potential risk of entering the groundwater system and being transported to potential receptors. Leaching techniques can be an effective treatment option for the metal removal from soils and sediments. This approach consists of washing or leaching the contaminated soil with an appropriate reagent and the subsequent treatment of the leaching in an above-ground installation (on-site treatment) where metals can be removed and concentrated into a smaller volume. Among the heavy metals, chromium is a commonly identified soil contaminant, particularly in sites with intensive economic activities including agriculture, industrial, mining and mineral,processing. Objective  The objective of this work was the evaluation and development of a leaching process for the remediation of soils and sediments polluted with chromium at laboratory scale. Chromium soil pollution was generated after the breakdown of a channel containing chromium wastes from a tannery plant. The pollution extension has been estimated to be on the order of thousands of tonnes of soil to be treated, with chromium contents ranging from 500 to 17,000 mg kg^-1 soil. Methods  The whole process investigated in this study integrates three stages; a) chromium leaching from a sediment using a diluted sulphuric acid solution, b) treatment of the leaching effluents with a magnesium oxide/limestone mixture for the precipitation of chromium hydroxide after acidity neutralisation, and c) polishing step to remove the eventual remaining chromium by adsorption onto natural zeolite. The amount of contaminated sediment treated ranged from 0.5 to 2 kg with chromium contents of between 2000 and 17,000 mg kg^-1. Results and Discussion  The paper describes results on the performance of the process and the optimisation of steps including influence of acid sulphuric concentration, chromium removal efficiency as well as alkaline reactive mixture proportions. Effluents from the leaching cells showed a significant decay on the chromium concentration with the increase of leaching runs and a high content of acidity (pH values close to 0.5). The treatment of these effluents in a second cell containing magnesium oxide/ limestone mixtures resulted in a high efficiency in neutralisation of acidity (pH values around 7) and chromium removal (concentrations below 5 mg 1^-1). The passage through a third compartment containing zeolite as an adsorbent decreased the chromium concentration below 0.5 mg 1^-1, Conclusions  From the results obtained on the chromium leaching and immobilisation with magnesium oxide/limestone mixture at a laboratory scale, it could be pointed out that: (a) diluted sulphuric acid solutions (3%) demonstrated a high efficiency on chromium removal from sandy polluted soils on the kilogram scale, (b) mixtures of magnesium oxide/limestone demonstrated a high capacity to neutralise the residual high acidity present on the effluents and to remove chromium by precipitation and (c) between the limestone and caustic magnesia mixtures, those containing more than 60% of caustic magnesia provide the higher efficiency. Recommendation and Outlook  Future work would be directed to the evaluation of the integrated process of leaching and chromium precipitation on column at a scale of 100 to 1000 kg.     

A new plant-based bioassay for aquatic sediments

Background, Goal and Scope  To date, standardised bioassays for the assessment of the ecotoxicological potential in sediments and dredged material use test organisms like bacteria, algae and crustaceae. This paper presents the development and application of a novel sediment contact test (whole sediment) withMyriophyllum aquaticum, a representative of rooted aquatic macrophytes. The aim of the present study is to demonstrate the value of a sediment contact test with rooted macrophytes as a supplement to existing test batteries in order to improve the assessment of sediment toxicity. Methods  The newly developed sediment contact test withMyriophylhim aquaticum was applied to natural whole sediments. For performing the test, whorls ofMyriophyllum aquaticum were directly planted in the native sediment and incubated in the light at 24°C (cf. section results and discussion). The end points of the test were the number of the shoots and the fresh weight of the whole plants. The duckweed growth inhibition test withLemna minor according to ISO/DIS 20079 was performed in pore waters from sediment samples. The results of the sediment contact test withMyriophyllum aquaticum were compared with each other and with those of the aquatic duckweed test. Results and Discussion  A test protocol for the new plant-based sediment contact test using the aquatic plantMyriophyllum aquaticum as an indicator was developed. The best control sediment proved to be the OECD sediment (OECD 207). A test period of 10 days appeared to be sufficient for the test. The increase of biomass and the derived growth rate were found to be the most suitable evaluation parameters. The growth behaviour ofMyriophyllum aquaticum differed depending on the origin of sediments. Therefore, plant-affecting contamination, that is bound in sediments, was indicated. Conclusions  The novel sediment contact test withMyriophyllum aquaticum can indicate phytotoxic effects in sediments. Therefore, it allows a better assessment of the overall-toxicity in whole sediments. Recommendations and Outlook  The sediment contact test withMyriophyllum aquaticum is a valuable tool for the evaluation of the ecotoxicological risk potential of waters and sediments. It should become a complement to a standardised test battery generally used for the assessment of sediment toxicity.     

上海郊区河流沉积物N、P释放的初步研究

A laboratory study was conducted to observe the release of nitrogen and phosphorus from the sedimentsunder both anaerobic and aerobic conditions. The samples used were five creek sediments and a fish-pondsediment (as a comparison) obtained from suburban Shanghai. High loads of nitrogen and phosphoruswere found in the creek sediments. Total nitrogen of the sediments ranged from 1.17 to 5.95 g kg^-1; totalphosphorus from 608.63 to 2 033.95 mg kg^-1. Making up more than 90% of the total nitrogen, organicnitrogen was the dominant nitrogen fraction in the sediments; where as inorganic phosphorus was the dominant phosphorus fraction, which made up more than 85 percent of the total phosphorus. Cabound phosphorus fraction dominated inorganic phosphorus, which occupied more than 50% of the total. A large amount of ammonium was released from the sediments under both aerobic and anaerobic conditions, and the anaerobic releases were slightly greater than the aerobic. In addition, ammonium contents in the aerobic waters decreased sharply after reaching the peaks because of strong nitrification, compared with the relatively maintained ammonium peaks in the anaerobic waters. Anaerobic phosphate releases were much greater than the aerobic and the released ortho-phosphate was mainly from Fe-bound phosphorus. Ammonium and ortho-phosphate releases from the sample of the dredged creek were the lowest, showing that creek dredging could effectively remove contaminants from the surface of sediments and weaken the release potentials of nitrogen and phosphorus. Ammonium and ortho-phosphate releases from the fish-pond sediment were greater than those from the creek sediments though its total nitrogen and phosphorus were not the highest, which was probably due to the larger amount of biologically degraded organic matter in the fish-pond sediment.     

The use of dialysis cells for investigating pore water composition in wetland substrata,with particular reference to dissolved iron and sulphide

Abstract

Details and some evaluation are given of the use of a dialysis method for sampling pore water from depth in wetland substrata (peats), with particular reference to measurement of concentrations of ion species with stabilities dependent on redox potential. The method is based upon the burial and subsequent retrieval (after equilibration) of cells made from dialysis membrane filled with deionized water. Preliminary results of field investigations of concentrations of dissolved iron and sulphide in the pore water of base‐rich mires, as sampled by this method, are given. Results suggest that the method could have very considerable application and that its potential, and possible problems, deserve further examination.