Application of a new sediment contact test with <Emphasis Type="Italic">Myriophyllum aquaticum</Emphasis> and of the aquatic <Emphasis Type="Italic">Lemna</Emphasis> test to assess the sediment quality of Lake Skadar

Goal, Scope and Background  Situated in the transboundary belt between Montenegro and Albania, Lake Skadar is the largest freshwater reservoir in Southeastern Europe. Because of the wide range of endemic, rare or endangered plant and animal species it supports, Lake Skadar and its extensive adjacent wetlands are internationally recognised as a site of significance and importance (Ramsar site). Within the last 10 to 20 years, Lake Skadar was exposed to intensive pollution. For the assessment of the ecotoxic load of the sediments sampled in Lake Skadar, a triad approach was recently applied. Overall, a complex spectrum of ecotoxic loads was elucidated. The aim of the present study was to use plant-based bioassays for assessing the sediment quality of Lake Skadar in order to facilitate and complement the triad test battery. The newly developed sediment contact test with Myriophyllum aquaticum and the aquatic growth inhibition test with Lemna minor were applied to native sediments and pore water, respectively, allowing the investigation of different toxicity-effects caused by particle-bound pollutants as well as pollutants in the interstitial water. This investigation is the first application of the novel sediment contact test with Myriophyllum aquaticum to lake sediments. Methods  Sediment samples were taken from nine selected sites at Lake Skadar and investigated by the sediment contact assay with Myriophyllum aquaticum. The pore water was extracted from these sediment samples to be analysed in the aquatic growth inhibition test with Lemna minor. The results of the sediment contact tests were compared with each other and with those of the aquatic growth inhibition test. Results and Discussion  Both applied macrophyte biotests revealed distinct changes in the growth behaviour of the two macrophytes subsequent to the exposure to the investigated natural sediments of Lake Skadar. The Myriophyllum sediment contact test revealed significant toxicity in the sediment samples from Radus and Kamenik, whereas the aquatic Lemna test showed inhibition effects for the samples from Sterbeq, Plavnica and Kamice. Data obtained with the newly developed Danio rerio contact test and the Arthrobacter globiformis contact test confirmed the Myriophyllum results. Analyses of the heavy metal content in the sediments revealed low or moderate contamination levels. Correlation analyses between the content of heavy metals in the sediments and growth inhibition of Myriophyllum aquaticum showed a significant correlation between Cr concentrations and growth inhibition. Comparable findings are available for a German river system. In contrast, no significant correlation between inhibition rates and concentration of metals could be observed with Lemna minor. Conclusions  It was shown that the newly developed sediment contact test with Myriophyllum aquaticum is applicable to lake sediments. In both the sediment contact test with Myriophyllum aquaticum on whole sediments and the aquatic growth inhibition test with Lemna minor on pore water, plant growth was influenced by the natural sediments and its components. Therefore, both test systems were found to be suitable for the detection of phytotoxic effects upon exposure to sediments. Myriophyllum aquaticum as test organism of the contact test grows directly in the sediment without an additional water-layer. Thus, it is able to detect toxicity caused by particle-bound phytotoxic substances as well as pore water-related contamination, while the floating Lemna minor can only detect effects emanating from pore water. Significant differences of the results were observed between these two test systems and, accordingly, the two different exposure scenarios. Hence, none of the tests can replace the other one and, as a consequence, both should be included into a test battery for the assessment of sediment toxicity. Recommendations and Perspectives  Both plant assays were shown to be reliable tools for the evaluation of the eco-toxicological risk potentials of pore water and solid-phase sediment. They should become a complement to the standardised test battery generally used for comprehensive hazard assessment. ESS-Submission Editor: Dr. Ulrike Kammann (ulrike.kammann@ifo.bfa-fisch.de)     

A new sediment contact assay to assess particle-bound pollutants using zebrafish (<Emphasis Type="Italic">danio rerio</Emphasis>) embryos

Goal, Scope and Background. Based on a bioassay battery covering only primary producers and consumers as well as degraders, the potential ecological hazard of sediments to vertebrates cannot be estimated comprehensively. Therefore, there is an urgent need to develop and standardize integrated vertebrate-based test systems for sediment investigation strategies. Whereas vertebratebased in vitro systems have frequently been used for the investigation of aqueous samples, there is a significant lack of whole sediment assays. Thus, the purpose of the present study was: (1) to develop a rapid and reliable, but comprehensive method to investigate native sediments and particulate matters without preceding extraction procedures; (2) to compare the hazard potential of solid phase sediments to the effects of corresponding pore waters and organic extracts in order to characterize the bioavailability of the particle-bound pollutants; and (3) to relatively evaluate the embryotoxic effects of sediments from the catchment areas of the rivers Rhine, Neckar and Danube. Methods (or Main Features).  To investigate the toxicity of sediment samples on vertebrates, the standard embryo toxicity test with the zebrafish (Danio rerio; Hamilton-Buchanan 1922) according to DIN 38415-6 was modified with respect to exposure scheme and toxicological endpoints. Sediments from the catchment area of the Neckar River were assessed using pore waters, acetonic extracts and native sediments in order to get inside into the potential bioavailability of particle-bound pollutants. A comprehensive test protocol for the investigation of native sediments in the embryo toxicity test with the zebrafish is presented. Results and Discussion.  The fish embryo assay with Danio rerio can be carried out with both aqueous and organic sediment extracts as well as native (whole, solid phase) sediment samples. Elongation of exposure time from 48 to up to 196 h significantly increased the mortality. Using the fish egg assay with native sediments, a broad range of embryotoxic effects could be elucidated, including clear-cut dose-response curves for the embryotoxic effects of contaminated sediments; in contrast, absence of embryotoxic effects could be demonstrated even for the highest test concentrations of unpolluted sediments. With native sediments, embryotoxicity was clearly higher than with corresponding pore waters, thus corroborating the view that — at least for fish eggs — the bioavailability of particle-bound lipophilic substances in native sediments is higher than generally assumed. The relative ranking of sediment toxicity was identical using both native sediments and sediment extracts, EC₂₀ values of the latter, however, being eight time lower higher than with the native sediments. A comparison of the embryo toxic effects of samples from the Neckar area with locations along the Rhine and Danube rivers elucidated a broad range of results, thus indicating different levels of contamination. Conclusions.  A modified protocol of the zebrafish embryo test allows the assessment of sediment toxicity in both aqueous extracts and native sediments. The isolated investigation of pore waters may result in a clear-cut underestimation of the bioavailability of lipophilic particle-bound substances (as determined by native sediments). Recommendations and Perspectives.  The zebrafish embryo test with native (whole, solid phase) sediments appears very promising for the evaluation of the bioavailable fraction of lipophilic particle-bound substances and can therefore be recommended for the evaluation of vertebrate toxicity in tiered sediment test strategies and dredging directives such as the HABAB-WSV. Whereas acetone extracts may be tested as a rough estimation of embryotoxicity, native sediment samples will provide a more comprehensive and realistic insight into the bioavailable hazard potential     

The multispecies freshwater biomonitor a potential new tool for sediment biotests and biomonitoring

Behavioural changes are used as early warning systems for water quality monitoring or as rapid and sensitive endpoints in toxicity bioassays. In this study, the automated measurement of behavioural patterns of the thrichopteranHydropsyche angustipennis (Curtis 1834) has been recorded for the first time in sediment with the Multispecies Freshwater Biomonitor, MFB. The MFB recorded different types of behaviour in sediment with the same accuracy as in water. Behavioural differences of the larvae exposed to ‘water only’ and ‘sediment only’ have been described. In ‘choice’ experiments, the larvae preferred the ‘water only’ compartment.     

The need for new concepts in risk management of sediments historical developments, future perspectives and new approaches

Being part of a highly dynamic system, contaminated sediments are especially in need of an integrated management approach. Due to change in importance from source to diffuse pollution and the variety of chemical substances in the environ-ment, different scientific fields need to cooperate and incorpo-rate their data in a common risk assessment scheme. Public perception of risk that is associated with sediments and with chemical data is low while the acceptance of ecotoxico-logical data with decision makers is often missing. A growing demand of the public to be involved in decision processes and informed about environmental problems demands a change of methods and concepts in the future. Necessity of an integration of risk assessment and management procedures has been suggested in order to increase the efficiency of the process and the early involvement of public concern. As the confidence in experts’ opinions decreases, a strong need for communication with and transparency for all involved parties arises.     

Soil ciliate bioassay for the pore water habitat a missing link between microflora and earthworm testing in soil toxicity assessment

Background, Scope and Goal. The chemical, pesticide and biocide legislation of the European Union assembles a variety of bioassays. Among the ecotoxicological tests involved, the testing strategy for the aquatic compartment builds up on three tests reflecting the main trophic levels (algae,Daphnia, fish). For the soil compartment at least one trophic level for a basic food chain is missing, namely between microflora and earthworms. Protozoa are an ideal missing link as they were shown to be the most prominent faunal contributors to nutrient cycling in soil ecosystems and as they represent the lacking first level consumers as well as the highly diverse microfauna. As protozoa inhabit the soil pore water, they can serve as direct indicators for the solved and thus bioavailable portion of xenobiotics. In order to widen the spectrum of available toxicity tests for a meaningful effect assessment for the soil compartment, a test with the soil ciliateColpoda inflata (Ciliophora, Protozoa), introduced by Pratt et al. (1997), was improved.     

A new growth medium for the study of siderophore-mediated interactions

Summary A microbial growth medium, RSM, was developed to study the role of siderophores (microbial Fe-transport compounds) in the inhibition of the take-all pathogen, Gaeumannomyces graminis var. tritici, by Pseudomonas putida strain B10. The inorganic constituents of the medium were designed to mimic the rhizosphere while the organic composition was designed to promote rapid growth and siderophore production. The antibiosis experiments were highly reproducible and the antagonism appeared to be due to production of pseudobactin, the siderophore of B10. On plates amended with chrome azurol S, G. graminis did not produce siderophores while other fungi did. The growth of G. graminis on plates prepared with Fe chelate buffers was inhibited at a free ferric ion concentration of 10^–24.6 M, although three other fungi were not inhibited, even at 10^–25.5 M, presumably due to their greater production of siderophores. In liquid medium amended with Fe chelate buffers, both the doubling time and the lag phase of P. putida increased as the free ferric ion concentration was reduced. A wide variety of fungi and bacteria were found to grow on this medium. Because the inorganic composition of RSM is based on that of the rhizosphere, the development of this medium may be a first step towards the study of the chemistry and biology of the rhizosphere under well defined conditions.     

Chronic toxicity of unresolved complex mixtures (UCM) of hydrocarbons in marine sediments

Background, Aim and Scope  Unresolved complex mixtures (UCM) of hydrocarbons, containing many thousands of compounds which cannot be resolved by conventional gas chromatography (GC), are common contaminants of sediments but little is known of their potential to affect sediment-dwelling organisms. Evidence exists for reduced health status in mussels, arising from aqueous exposure to aromatic UCM components acting through a narcotic mode of action. However, UCM contaminants in sediments may not be sufficiently bioavailable to elicit toxic effects. The aim of our study was therefore to measure the sublethal effects of chronic exposure to model UCM-dominated oils at environmentally realistic concentrations and compare this to effects produced by a UCM containing weathered crude oil. A further aim was to determine which, if any, fractions of the oils were responsible for any observed toxicity. Materials and Methods  Whole oils were spiked into estuarine sediment to give nominal concentrations of 500 μg g⁻¹ dry weight. Juveniles of the estuarine amphipod Corophium volutator were exposed to the contaminated sediment for 35 days and their survival, growth rate and reproductive success quantified. Using an effect-directed fractionation approach, the oils were fractionated into aliphatic and two aromatic fractions by open column chromatography and their toxicity assessed by further chronic exposures using juvenile C. volutator. Results  The growth rates of amphipods were reduced following exposure to the oils although this was only statistically significant for the weathered oil; reproductive success was reduced by all oil exposures. Sediment spiked with UCM fractions also caused reduced growth and reproduction but no particular fraction was found to be responsible for the observed toxicity. Survivorship was not affected by any oil or fraction. Discussion  The study showed that chronic exposure to sediments contaminated by UCM-dominated oils could have population level effects on amphipods. The observed effects could not be explained by hydrocarbons resolved by conventional GC and effects were similar for both UCM-dominated and weathered oils. All of the fractions appeared to contribute to the observed effects; this is in contrast to previous research which had shown that an aliphatic UCM did not cause adverse effects in mussels. Conclusions  To our knowledge, this is the first study to demonstrate population-level effects arising from exposure to sediments contaminated by realistic environmental concentrations of UCM hydrocarbons. The results are consistent with many compounds, at very low individual concentrations, contributing towards the overall observed toxicity. Recommendations  Risk assessments of contaminated sediments should take into account the contribution towards the potential for toxic effects from UCM hydrocarbons. Studies into sediment contamination should report both aliphatic and aromatic UCM concentrations to aid risk assessments. ESS-Submission Editor: Henner Hollert (hollert@uni-heidelberg.de) This paper has been developed from a presentation at SETAC Europe 16^th Annual Meeting 2006 held at the The Hague, The Netherlands.     

Importance of dose metrics for lethal and sublethal sediment metal toxicity in the oligochaete worm Lumbriculus variegatus

Background, Aims, and Scope  There is an increasing demand for controlled toxicity tests to predict biological effects related to sediment metal contamination. In this context, questions of metal-specific factors, sensitivity of toxicity endpoints, and variability in exposure duration arise. In addition, the choice of the dose metrics for responses is equally important and is related to the applicability of the concept of critical body residue (CBR) in exposure assessments, as well as being the main focus of this study. Methods  Experiments were conducted to assess toxicity of Cd, Cr, Cu and Pb to the oligochaete worm Lumbriculus variegatus with the aim of determining CBRs for two response metrics. Mortality and feeding activity of worms exposed to sediment-spiked metals were used as end-points in connection with residue analyses from both the organisms and the surrounding media. Results  LC50 values were 0.3, 1.4, 5.2, and 6.7 mg/L (from 4.7 μmol/L to 128.0 μmol/L), and the order of toxicity, from most toxic to least toxic, was Cu > Cd > Pb>Cr. By relating toxicity to body residue, variability in toxicity among the metals decreased and the order of toxicity was altered. The highest lethal residue value was obtained for Cu (10.8 mmol/kg) and the lowest was obtained for Cd (2.3 mmol/kg). In the 10-d sublethal test, both time and metal exposure were an important source of variation in the feeding activity of worms. The significant treatment effects were observed from worms exposed to Cd or Pb, with the controls yielding the highest feeding rate. However, quantitative changes in the measured endpoint did not correlate with the exposure concentrations or body residues, which remained an order of magnitude lower than in the acute exposures. Discussion  Both response metrics were able to detect a toxic effect of the metals. However, the ranking of metal toxicity was dependant on the choice of the dose metric used. An attempt to form a causal mortality-mediated link between tissue residues and metal toxicity was successful in water-only exposures. The results also indicated that egestion rate was a sensitive toxicity end point for predicting the effects of sediment contamination. Conclusions  By relating the biological response with the tissue metal residues, toxicity data was comparable to both environmental media as well as different response metrics and time scales. The results also revealed the importance of metal toxicity ranking on a molar basis and, furthermore, a direct link to the CBR concept was established. Recommendations and Perspectives  There is a growing demand for methods to assess the effects of contaminated sediments to benthic fauna and whole aquatic ecosystems. Such information is needed for sediment quality guidelines that are currently being developed in many countries and remediation processes. The use of body residues as a dose metric in metal toxicity studies may help to overcome difficulties related to bioavailability issues commonly faced in sediment toxicity studies. ESS-Submission Editor: Prof. Dr. Henner Hollert (henner.hollert@bio5.rwth-aachen.de)     

Earthworm avoidance test for soil assessments

For ecotoxicological assessments of contaminated or remediated soils pointing to the habitat function of soils for biocenoses, standardized tests with earthworms (acute test, reproduction test) are available among others. Tests used for routine applications should be sensitive and indicate impacts on test organisms after short test periods. The usually applied earthworm tests do not satisfactorily fulfil these criteria. Therefore, in the present work, a behavioural test with earthworms (test criterion: avoidance) was investigated in detail using uncontaminated, artificially contaminated and originally contaminated soils. It was demonstrated that the avoidance behaviour is primarily determined by pollutants, and not by chemical-physical soil properties. The sensitivity of the presented test reaches the sensitivity of established tests. For waste sites, a considerably higher sensitivity was determined. An avoidance behaviour of at least 80% of the worms leaving the soil to be assessed is proposed as a criterion for toxicity.     

黄土高原半干旱区水土保持植被恢复限度——以人工柠条林为例

为了确定水资源不足地区植被恢复潜力和水土保持林建设目标,在黄土丘陵半干旱区宁夏固原上黄试区,对相同立地条件的16年生人工柠条林进行疏伐,建立不同密度林地,进行林分密度、森林植被水土保持效益和土壤水分关系的定位实验。结果表明：平均基径随密度的增加而减少,二者为线性关系;盖度随密度的增加而增大,盖度与密度为对数关系;林冠截留随密度的增加而增大,二者为指数关系;地表径流随密度的增加而减少,二者为对数关系;泥沙含量随密度的减少而增加,二者关系可用倒S形曲线描述。虽然密度增加,盖度增加,森林植被水土保持效益增强,但是受土壤水资源的限制,柠条林有一个最大恢复限度。当超过限度时,势必会引发或加剧土壤旱化。     

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.

     

A new approach to trenching experiments for measuring root-rhizosphere respiration in a lowland tropical forest

Soil respiration in tropical forests is a major source of atmospheric CO₂. The ability to partition soil respiration into its individual components is becoming increasingly important to predict the effects of disturbance on CO₂ efflux from the soil as the responses of heterotrophic and autotrophic respiration to change are likely to differ. However, current field methods to partition respiration suffer from various methodological artefacts; root-rhizosphere respiration is particularly difficult to estimate. We used trenched subplots to estimate root-rhizosphere respiration in large-scale litter addition (L+), litter removal (L−) and control (CT) plots in a lowland tropical semi-evergreen forest in Panama. We took a new approach to trenching by making measurements immediately before-and-after trenching and comparing them to biweekly measurements made over one year. Root-rhizosphere respiration was estimated to be 38%, 17% and 27% in the CT, L+, and L− plots, respectively, from the measurements taken immediately before and one day after trenching in May-June 2007. Biweekly measurements over the following year provided no estimates of root-rhizosphere respiration for the first seven months due to decomposition of decaying roots. We were also unable to estimate root-rhizosphere respiration during the dry season due to differences in soil water content between trenched and untrenched soil. However, biweekly measurements taken during the early rainy season one year after trenching (May-June 2008) provided estimates of root-rhizosphere respiration of 39%, 24% and 36% in the CT, L+, and L− plots, respectively, which are very similar to those obtained during the first day after trenching. We suggest that measurements taken immediately before and one day after root excision are a viable method for a rapid estimation of root-rhizosphere respiration without the methodological artefacts usually associated with trenching experiments.