A review on the application of microbial toxicity tests for deriving sediment quality guidelines

Where the rubber meets the road: Emerging environmental impacts of tire wear particles and their chemical cocktails

About 3 billion new tires are produced each year and about 800 million tires become waste annually. Global dependence upon tires produced from natural rubber and petroleum-based compounds represents a persistent and complex environmental problem with only partial and often-times, ineffective solutions. Tire emissions may be in the form of whole tires, tire particles, and chemical compounds, each of which is transported through various atmospheric, terrestrial, and aquatic routes in the natural and built environments. Production and use of tires generates multiple heavy metals, plastics, PAH's, and other compounds that can be toxic alone or as chemical cocktails. Used tires require storage space, are energy intensive to recycle, and generally have few post-wear uses that are not also potential sources of pollutants (e.g., crumb rubber, pavements, burning). Tire particles emitted during use are a major component of microplastics in urban runoff and a source of unique and highly potent toxic substances. Thus, tires represent a ubiquitous and complex pollutant that requires a comprehensive examination to develop effective management and remediation. We approach the issue of tire pollution holistically by examining the life cycle of tires across production, emissions, recycling, and disposal. In this paper, we synthesize recent research and data about the environmental and human health risks associated with the production, use, and disposal of tires and discuss gaps in our knowledge about fate and transport, as well as the toxicology of tire particles and chemical leachates. We examine potential management and remediation approaches for addressing exposure risks across the life cycle of tires. We consider tires as pollutants across three levels: tires in their whole state, as particulates, and as a mixture of chemical cocktails. Finally, we discuss information gaps in our understanding of tires as a pollutant and outline key questions to improve our knowledge and ability to manage and remediate tire pollution.

Large-scale sediment toxicity assessment over the 15,000 km of coastline in the Yellow and Bohai seas, East Asia

The Yellow and Bohai seas have long been contaminated by persistent toxic substances (PTSs) from numerous (un)known anthropogenic sources. In this study, we used Vibrio fischeri bioassay to evaluate ecotoxicological profiles associated with sedimentary PTSs contamination at a large marine ecosystem (LME) scale. A total of 125 surface sediments collected from the coastal areas of the Yellow and Bohai seas were analyzed both for aqueous and organic extracts. Not surprisingly, the results indicated site-dependent toxicities, but most sites were identified as non-toxic to V. fischeri. For aqueous extracts and organic extracts, 13% and 8% of samples, respectively exhibited marginal toxicity, while 0% and 2% of samples exhibited moderate toxicity. However, it should be noted that organic extracts (mean TU = 56) induced stronger toxicities than aqueous samples (mean TU = 0.4). This result generally back-supported the high toxicity potentials associated with sedimentary sink of organic pollutants. Several PTSs measured in the samples indicated a significant contribution to the observed V. fischeri toxicities. Of note, polycyclic aromatic hydrocarbons (PAHs; r = 0.28, p < 0.05), styrene oligomers (r = 0.41, p < 0.01), and alkylphenols (r = 0.38, p < 0.05) showed significant associations to the observed bacterial inhibition. Among PAHs, benzo[a]anthracene and phenanthrene exhibited a significant contribution to the observed V. fischeri toxicities. Meantime, salinity which reflects the distance from the point sources of land-driven pollutants along the rivers and estuaries in the Yellow and Bohai seas was a key environmental variable representing the sample toxicities. Overall, the present study provides baseline information for evaluating the potential sediment toxicity to implement responsible coastal management at an LME scale, and elsewhere.

Analysis of biofilm bacterial communities under different shear stresses using size-fractionated sediment

Microorganisms are ubiquitous in aqueous environments and are crucial for biogeochemical processes, but their community structures and functions remain poorly understood. In this paper, a rotating reactor was designed to study the effects of substrata and flow conditions on sediment bacterial communities using 16S rRNA gene sequencing, assaying three groups of size-fractionated sediments and three different levels of applied shear stress. Proteobacteria, Firmicutes, and Bacteroidetes were the dominant phyla of the microbial communities, with more anaerobic bacteria and opportunistic pathogens being detected under static water conditions, while more aerobic bacteria were detected under dynamic water flow conditions. Most of the top 10 genera were present in all the samples; however, there were significant differences in the species abundance. Paludibacter and Comamonadaceae_unclassified were the most abundant genera under static and dynamic conditions, respectively. Under static water conditions, the medium-grained sediment had the highest microbial diversity, followed by the fine and coarse sediments. Under dynamic water flow conditions, a higher flow velocity corresponded to a greater microbial diversity. Overall, there was no significant difference in the community richness or diversity between the static and dynamic water flow conditions. This study is beneficial for further understanding the heterogeneities of microbial communities in natural aquatic ecosystems.

The Daphnia magna role to predict the cadmium toxicity of sediment: Bioaccumlation and biomarker response

To evaluate Daphnia magna role to predict the Cd toxicity in contaminated sediment, the Cd accumulation, metallothionein (MT), and mortality of D. magna exposed to overlying water system or water-sediment coexistence system were measured. The mortality, Cd accumulation, and MT in D. magna increased with the increasing Cd content in sediment. The Cd accumulation and MT in D. magna exposed to the coexistence system were significantly higher than those exposed to the overlying water system because of the ingestion of Cd-containing sediments by D. magna. However, the mortality did not significantly differ in the two systems, suggesting that mortality was less sensitive than accumulation and MT. The Cd accumulation/MT index can explain why the two systems had the similar mortality but different Cd accumulation and MT. Not all the percentage composition of nonresidual fractions (e.g., exchangeable, carbonate bound, and organic bound phases) significantly correlated with the difference values of Cd accumulation and MT, as well as Cd accumulation/MT. However, these indexes increased with the percentage composition of the nonresidual fractions, indicating that the distribution of Cd chemical fractions is crucial for its bioavailability and biotoxicity.

Impact of bio-palladium nanoparticles (bio-Pd NPs) on the activity and structure of a marine microbial community

Biogenic palladium nanoparticles (bio-Pd NPs) represent a promising catalyst for organohalide remediation in water and sediments. However, the available information regarding their possible impact in case of release into the environment, particularly on the environmental microbiota, is limited. In this study the toxicity of bio-Pd NPs on the model marine bacterium V. fischeri was assessed. The impacts of different concentrations of bio-Pd NPs on the respiratory metabolisms (i.e. organohalide respiration, sulfate reduction and methanogenesis) and the structure of a PCB-dechlorinating microbial community enriched form a marine sediment were also investigated in microcosms mimicking the actual sampling site conditions. Bio-Pd NPs had no toxic effect on V. fischeri. In addition, they had no significant effects on PCB-dehalogenating activity, while showing a partial, dose-dependent inhibitory effect on sulfate reduction as well as on methanogenesis. No toxic effects by bio-Pd NPs could be also observed on the total bacterial community structure, as its biodiversity was increased compared to the not exposed community. In addition, resilience of the microbial community to bio-Pd NPs exposure was observed, being the final community organization (Gini coefficient) of samples exposed to bio-Pd NPs similar to that of the not exposed one. Considering all the factors evaluated, bio-Pd NPs could be deemed as non-toxic to the marine microbiota in the conditions tested. This is the first study in which the impact of bio-Pd NPs is extensively evaluated over a microbial community in relevant environmental conditions, providing important information for the assessment of their environmental safety.

Applicability of drinking water treatment residue for lake restoration in relation to metal/metalloid risk assessment

Drinking water treatment residue (DWTR), a byproduct generated during potable water production, exhibits a high potential for recycling to control eutrophication. However, this beneficial recycling is hampered by unclear metal/metalloid pollution risks related to DWTR. In this study, the pollution risks of Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn due to DWTR application were first evaluated for lake water based on human health risk assessment models and comparison of regulatory standards. The risks of DWTR were also evaluated for sediments on the basis of toxicity characteristics leaching procedure and fractionation in relation to risk assessment code. Variations in the biological behaviors of metal/metalloid in sediments caused by DWTR were assessed using Chironomus plumosus larvae and Hydrilla verticillata. Kinetic luminescent bacteria test (using Aliivibrio fischeri) was conducted to analyze the possibility of acute and chronic detrimental effects of sediment with DWTR application. According to the obtained results, we identify a potential undesirable effect of DWTR related to Fe and Mn (typically under anaerobic conditions); roughly present a dosage threshold calculation model; and recommend a procedure for DWTR prescreening to ensure safe application. Overall, managed DWTR application is necessary for successful eutrophication control.

Bacterial toxicity assessment of drinking water treatment residue (DWTR) and lake sediment amended with DWTR

Drinking water treatment residue (DWTR) seems to be very promising for controlling lake sediment pollution. Logically, acquisition of the potential toxicity of DWTR will be beneficial for its applications. In this study, the toxicity of DWTR and sediments amended with DWTR to Aliivibrio fischeri was evaluated based on the Microtox(®) solid and leachate phase assays, in combination with flow cytometry analyses and the kinetic luminescent bacteria test. The results showed that both solid particles and aqueous/organic extracts of DWTR exhibited no toxicity to the bacterial luminescence and growth. The solid particles of DWTR even promoted bacterial luminescence, possibly because DWTR particles could act as a microbial carrier and provide nutrients for bacteria growth. Bacterial toxicity (either luminescence or growth) was observed from the solid phase and aqueous/organic extracts of sediments with or without DWTR addition. Further analysis showed that the solid phase toxicity was determined to be related mainly to the fixation of bacteria to fine particles and/or organic matter, and all of the observed inhibition resulting from aqueous/organic extracts was identified as non-significant. Moreover, DWTR addition not only had no adverse effect on the aqueous/organic extract toxicity of the sediment but also reduced the solid phase toxicity of the sediment. Overall, in practical application, the solid particles, the water-soluble substances transferred to surface water or the organic substances in DWTR had no toxicity or any delayed effect on bacteria in lakes, and DWTR can therefore be considered as a non-hazardous material.

Assessment of heavy metals bioavailability and toxicity toward Vibrio fischeri in sediment of the Huelva estuary

Relationship between toxicity and bioavailable metals in sediments from the Huelva estuary and its littoral of influence was analyzed. Toxicity was assessed with Microtox® bioassay using a marine luminescent bacterium: Vibrio fischeri. Bioavailable metals were considered as both, acid extractable fraction of BCR procedure and the sum of exchangeable and bound to carbonates fractions of Tessier sequential extraction. A bioavailable metals index was calculated to integrate results in a single figure. Toxicity and bioavailable metals showed a similar pattern. Higher levels were found in the estuary than in the littoral (140 TU/g). In Huelva estuary, highest levels were found in the Tinto estuary (5725 TU/g), followed by the Odiel estuary (5100 TU/g) and the Padre Santo Canal (2500 TU/g). Results in this area were well over than those in nearby estuaries. Furthermore, they are similar to or even higher than those in other polluted sediments around the world. Bioavailable metal index showed a stronger correlation with acid extractable fraction of BCR (R(2) = 0.704) than that for the sum of exchangeable and bound to carbonates fractions of Tessier (R(2) = 0.661). These results suggest that bioavailable metals are an important source of sediment toxicity in the Huelva estuary and its littoral of influence, an area with one of the highest mortality risks of Spain.

Potential of the microbial assay for risk assessment (MARA) for assessing ecotoxicological effects of herbicides to non-target organisms

Many microbiotests that have been proposed for use in the risk assessment of environmental pollutants have the drawback of lacking relevant published data on various aspects of their test application possibilities and therefore do not receive the regulatory recognition which they may deserve. The MARA bioassay lacks published data for many relevant environmental pollutants, particularly pesticides and this may limit its use in regulatory framework. The present study has assessed the sensitivity of the MARA bioassay relative to other established bioassays (Daphnia magna and Oreochromis niloticus) to two widely used herbicide formulations: Roundup (having glyphosate as active ingredient) and Herbextra (with the active ingredient being 2,4-dichlorophenoxyacetic acid-2,4-D). Roundup was found to be more toxic than Herbextra in all three bioassays. The D. magna EC50 s obtained for Roundup and Herbextra were respectively 5.55 and 356.61 mg/l while the LC50 s for O. niloticus were 11.30 and 222,28 mg/l respectively. In the case of the MARA bioassay microbial toxic concentrations (MTCs) for individual species ranged from 6.85 to 468 mg/l with an overall mean MTC of 101.82 mg/l for glyphosate and from 74.67 to 13,333 mg/l for 2,4-D giving an overall mean MTC of 2855.88 mg/l. Although the overall MTCs from the MARA bioassay were much higher than the LC50 s and EC50 s from the fish and daphnia bioassays respectively, the most sensitive MARA organism for each of the herbicides had MTCs that were comparable to or lower than the corresponding endpoints from the other bioassays implying that the MARA assay is a potentially useful bioassay for risk assessment of pesticides.

New methodological improvements in the Microtox® solid phase assay

The classic Microtox® solid phase assay (MSPA) based on the inhibition of light production of the marine bacteria recently renamed Aliivibrio fischeri suffers from various bias and interferences, mainly due to physico-chemical characteristics of the tested solid phase. To precisely assess ecotoxicity of sediments, we have developed an alternative method, named Microtox® leachate phase assay (MLPA), in order to measure the action of dissolved pollutants in the aqueous phase. Two hypotheses were formulated to explain the observed difference between MSPA and MLPA results: a real ecotoxicity of the solid phase or the fixation of bacteria to fine particles and/or organic matter. To estimate the latter, flow cytometry analyses were performed with two fluorochromes (known for their ability to stain bacterial DNA), allowing correction of MSPA measurements and generation of new (corrected) IC50. Comparison of results of MLPA with the new IC50 MSPA allows differentiating real ecotoxic and fixation effect in classic MSPA especially for samples with high amount of fines and/or organic matter.

Toxicity and potential risk assessment of a river polluted by acid mine drainage in the Iberian Pyrite Belt (SW Spain)

Metal contamination from acid mine drainage (AMD) is a serious problem in the southwest of the Iberian Peninsula, where the Iberian Pyrite Belt is located. This zone contains original sulfide reserves of about 1700Mt distributed among more than 50 massive sulfide deposits. Weathering of these minerals releases to the waters significant quantities of toxic elements, which severely affect the sediments and surface waters of the region. The main goal of this paper is to evaluate the toxicity and the potential risk associated with the mining areas using Microtox test and different factors which assess the degree of contamination of the sediments and waters. For this, a natural stream polluted by AMD-discharge from an abandoned mine has been studied. The results show that elevated concentrations of Cu, As and Zn involve an important potential risk on the aquatic environment, associated both with sediments and waters. Microtox test informs that the sediments are extremely or very toxic, mainly related to concentrations of Fe, As, Cr, Al, Cd, Cu and Zn. Pollution is mainly transferred to the sediments increasing their potential toxicity. A natural creek affected by AMD can store a huge amount of pollution in its sediments while exhibiting a not very low water pH and low water metal concentration.

Spatio-temporal distribution of organic and inorganic pollutants from Lake Geneva (Switzerland) reveals strong interacting effects of sewage treatment plant and eutrophication on microbial abundance

Variation with depth and time of organic matter (carbon, nitrogen, phosphorus), inorganic pollutant (mercury), as well as bacterial abundance and activity, were investigated for the first time in sediment profiles of different parts of Lake Geneva (Switzerland) over the last decades. The highest organic contents (about 32%), mercury concentration (27 mg kg(-1)), bacterial abundance (in order of 9×10(9) cell g(-1) dry sediment), and bacterial activity (1299 Relative Light Units (RLU)) were found in the highly polluted sediments contaminated by the waste water treatment plant (WWTP) discharge, which deposited during the period of cultural eutrophication. Such data, which contrast with the other sampled sites from deeper and more remote parts of the lake, prove that the organic matter and nutrients released from the municipal WWTP have considerable effects on bacterial abundance and activities in freshwater sediments. In fact, the relatively unpolluted deepwater sites and the coastal polluted site show large synchronous increases in bacterial densities linked to the anoxic conditions in the 1970s (lake eutrophication caused by external nutrient input) that subsequently increased the nutrient loading fluxes. These results show that the microbial activities response to natural or human-induced changing limnological conditions (e.g., nutrient supply, oxygen availability, redox conditions) constitutes a threat to the security of water resources, which in turn poses concerns for the world's freshwater resources in the context of global warming and the degradation of water quality (oxygen depletion in the bottom water due to reduced deep waters mixing). Moreover, the accumulation of inorganic pollutants such as high mercury (methyl-mercury) concentration may represent a significant source of toxicity for sediment dwelling organisms.

Novel approach for assessing heavy metal pollution and ecotoxicological status of rivers by means of passive sampling methods

In order to study the pollution of fluvial ecosystems, it is necessary to analyze not only the levels of chemical contaminants in water, but also those accumulated in the sediment matrix, as well as to assess its ecotoxicological status. Eleven Catalan (Spain) river sections (one sampling point per river) located near urban and industrial areas were sampled during winter of 2009. Water pollutants were collected by using passive samplers as Diffusive Gradient in Thin-Films (DGTs) and Semi-Permeable Membrane Devices (SPMDs). Point water samples were also collected. The concentrations of potentially toxic elements (PTE) in water, filtered water, DGTs and sediment samples were analyzed. Aqueous and organic solvent extracts of sediments samples and organic extracts of SPMDs were performed to assess acute toxicity to Vibrio fischeri by Microtox(®), and chronic toxicity to the green alga Pseudokirschneriella subcapitata. Microtox(®) test was also performed with DGT extracts. The results show that metals content of Catalan river waters are below the freshwater screening US EPA benchmarks, excepting some industrial areas (for Hg, Pb, and Zn). In contrast, sediments levels of some rivers were far above freshwater sediment screening US EPA benchmarks (for Zn, As, Cr, Pb, Ni, Hg, and Mn), particularly in the most industrialized areas. A good correlation was found between toxicity values of extracts (from sediments and DGTs) and PTE levels in sediments. The current results support the suitability of using combined point and passive sampling methods for assessing the chemical and ecotoxicological status of aqueous environments.

Comparison of aerobic and anaerobic [3H]leucine incorporation assays for determining pollution-induced bacterial community tolerance in copper-polluted, irrigated soils

Pollution-induced community tolerance (PICT) constitutes a sensitive and ecologically relevant impact parameter in ecotoxicology. We report the development and application of a novel anaerobic [(3) H]leucine incorporation assay and its comparison with the conventional aerobic [(3) H]leucine incorporation assay for PICT detection in soil bacterial communities. Selection of bacterial communities was performed over 42 d in bulk soil microcosms (no plants) and in rice (Oryza sativa) rhizosphere soil mesocosms. The following experimental treatments were imposed using a full factorial design: two soil types, two soil water regimes, and four Cu application rates (0, 30, 120, or 280 µg g(-1)). Bacterial communities in bulk soil microcosms exhibited similar Cu tolerance patterns when assessed by aerobic and anaerobic PICT assays, whereas aerobic microorganisms tended to be more strongly selected for Cu tolerance than anaerobic microorganisms in rhizosphere soil. Despite similar levels of water-extractable Cu, bacterial Cu tolerance was significantly higher in acid sulfate soil than in alluvial soil. Copper amendment selected for significant PICT development in soils subjected to alternate wetting and drying, but not in continuously flooded soils. Our results demonstrate that soil bacterial communities subjected to alternate wetting and drying may be more affected by Cu than bacterial communities subjected to continuous flooding. We conclude that the parallel use of anaerobic and aerobic [(3) H]leucine PICT assays constitutes a valuable improvement over existing procedures for PICT detection in irrigated soils and other redox gradient environments such as sediments and wetlands.

Kinetic bacterial bioluminescence assay for contact sediment toxicity testing: relationships with the matrix composition and contamination

The present study represents the first broader evaluation of the rapid 30-s kinetic bioluminescence assay with Vibrio fisheri (microplate format modification) for contact toxicity testing of whole sediments. The present study focused on river sediments from the Morava River basin, Czech Republic, repeatedly sampled during 2005 to 2006 and analyzed for geological and geochemical parameters, content of toxic metals, major organic pollutants, and toxicity. High natural variation in toxicity (50% inhibitory concentration [IC50] values ranging from 0.8 to >80 mg sediment dry wt/ml) was found (among different sampling periods and years, among sites), and this could be related to the sediment dynamics affected by spring high flows and summer droughts. From the 46 sediment descriptors, exchangeable protons (H(+)) was the only parameter that consistently correlated with toxicity. Three other descriptors (i.e., content of organic carbon plus two parameters from the detailed silicate analysis of sediments: percentage of SO(3) representing total sulfur content, structural water H(2)O+) also significantly correlated with toxicity. There were only minor and variable correlations with contamination. We propose sediment safety guideline categories for the V. fisheri kinetic test with severe toxicity threshold of IC50 < 1 mg dry wt/ml. Although sediments are considered a rather stable matrix in comparison with river water, we confirmed high variability and dynamics that should be reflected in monitoring plans and field studies.

Applications of microbial cell sensors

Since the first microbial cell sensor was studied by Karube et al. in 1977, many types of microbial cell sensors have been developed as analytical tools. The microbial cell sensor utilizes microbes as a sensing element and a transducer. The characteristics of microbial cell sensors as sensing devices are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial cell sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial cell sensors have the advantages of tolerance to measuring conditions, a long lifetime, and good cost performance, and have the disadvantage of a long response time. In this review, applications of microbial cell sensors are summarized.

Adaptation of anaerobically grown Thauera aromatica, Geobacter sulfurreducens and Desulfococcus multivorans to organic solvents on the level of membrane fatty acid composition

The effect of different solvents and pollutants on the cellular fatty acid composition of three bacterial strains: Thauera aromatica, Geobacter sulfurreducens and Desulfococcus multivorans, representatives of diverse predominant anaerobic metabolisms was investigated. As the prevailing adaptive mechanism in cells of T. aromatica and G. sulfurreducens whose cellular fatty acids patterns were dominated by palmitic acid (C16:0) and palmitoleic acid (C16:1cis), the cells reacted by an increase in the degree of saturation of their membrane fatty acids when grown in the presence of sublethal concentrations of the chemicals. Next to palmitic acid C16:0, the fatty acid pattern of D. multivorans was dominated by anteiso‐branched fatty acids which are characteristic for several sulfate‐reducing bacteria. The cells responded to the solvents with an increase in the ratio of straight‐chain saturated (C14:0, C16:0, C18:0) to anteiso‐branched fatty acids (C15:0anteiso, C17:0anteiso, C17:1anteisoΔ9cis). The results show that anaerobic bacteria react with similar mechanisms like aerobic bacteria in order to adapt their membrane to toxic organic solvents. The observed adaptive modifications on the level of membrane fatty acid composition can only be carried out with de novo synthesis of the fatty acids which is strictly related to cell growth. As the growth rates of anaerobic bacteria are generally much lower than in the so far investigated aerobic bacteria, this adaptive response needs more time in anaerobic bacteria. This might be one explanation for the previously observed higher sensitivity of anaerobic bacteria when compared with aerobic ones.

Comparison of sediment quality guidelines (SQGs) for the assessment of metal contamination in marine and estuarine environments

Sediment quality guidelines (SQGs) are an important tool for the assessment of contamination in marine and estuarine sediments. Although such guidelines are not definitive indicators of toxicity, they can have a high predictive ability and are a vital tool for identifying areas with potentially adverse biological effects. In the present study, 15 sets of common SQGs have been compared, including values for Australia/New Zealand, Canada, Hong Kong, Norway, the Netherlands, the USA and regions within the USA (Puget Sound/Washington, New York and Florida). The majority of these SQGs are based on the weight-of-evidence approach. In particular, the sub-group of TEL/PEL-based values have a very high degree of comparability; values not belonging to this uniform group show substantial variations.

Influence of contact duration on sediment-associated copper fractionation and bioavailability

Frequent utilization of copper formulations as aquatic herbicides and algaecides can lead to potentially elevated sediment-copper concentrations. This research investigated relationships between copper fractionation (through sequential extractions) and bioavailability in three reservoir sediments over a 60d contact duration. Copper was initially associated with exchangeable, carbonate, and oxidizable fractions for copper-amended sediments; and redistributed to the reducible and oxidizable fractions after 60d. Hyalella azteca mortality declined over time for organisms exposed to copper-amended reservoir sediments, indicating concomitant declines in sediment copper bioavailability. Comparisons between sequential extractions and organism responses indicated that bioavailability was primarily associated with the exchangeable fraction. Results of this research indicated fractionation and bioavailability of amended copper in sediments were influenced by contact duration along with sediment and overlying water characteristics. The influence of contact duration on copper bioavailability in sediments is important for assessing potential risks incurred by repeated applications of copper-containing algaecides in reservoirs.

Estimating the environmental impact of micro-pollutants in the low Ebro River (Spain): an approach based on screening toxicity with Vibrio fischeri

The aim of this study was to assess the likely impacts on the ecosystems due to agricultural, human, and industrial activities carried out in an ecologically important area of the Ebro River (Spain). For it, a screening site specific ecological risk assessment was conducted. Considering the presence of high levels of potentially toxic substances, such as metals and chlorinated organic compounds, aqueous and organic extracts were used to assess toxicity in sediments by using the photo-luminescent bacteria Vibrio fischeri (Microtox) as screening response variable. Sediment samples collected during 2005-2006 in the last course of the Ebro River and its Delta have been analyzed. Toxic responses have shown strong relationships to the levels of pollutants in the area. Moreover, various sites presented some toxicity level, probably because of other factors associated with reducing environments into the sediments. Results indicate that Microtox bioassay is an appropriate tool to perform risk assessment studies at screening level.

Sediment contamination, bioavailability and toxicity of sediments affected by an acute oil spill: Four years after the sinking of the tanker Prestige (2002)

Sediment contamination and three bioassays were used to determine the sediment quality four years after an oil spill (Prestige, 2002): the Microtox test, a 10-day bioassay using the amphipod Ampelisca brevicornis, and a polychaete 10-day toxicity test with the lugworm Arenicola marina. In addition, bioaccumulation of PAHs was examined in the polychaete after 10 days of exposure. The results obtained from the toxicity tests and bioaccumulation analyses were statistically compared to the sediment chemical data, in order to assess the bioavailability of the contaminants, their effects, and their relationship with the oil spill. The sediments studied were from two areas of the Galician Coast (NW Spain): the Bay of Corme-Laxe and the Cíes Island, located in the Atlantic Island National Park. The results point to a decrease in contamination with respect to previous studies and to the disappearance of the acute toxicity four years after the oil spill. However an important bioaccumulation of PAHs was detected in the organisms exposed to sediments from Corme-Laxe, suggesting that despite the recovery of the environmental quality of the area, effects in the biota might be occurring.

Linking pollution induced community tolerance (PICT) and microbial community structure in chronically metal polluted estuarine sediments

We tested the ability of pollution induced community tolerance (PICT) to detect the effects of chronic metal pollution on estuarine sediment microbial communities, along a gradient spanning two orders of magnitude in metal concentrations. In tandem, we investigated the associated microbial community structure using terminal restriction fragment length polymorphism (T-RFLP). Tolerance of microbes to Cu, measured as IC50 (inhibitory concentration 50%), was strongly correlated with pore water Cu concentration (r(2)=0.842). No strong correlation existed for other metals tested, highlighting the ability of PICT to identify the pollutant causing a toxic effect. There was no correlation between microbial community structure and community tolerance to metals tested, but analysis of community structure did provide some information on reasons for observed PICT response. PICT methodology used here provided a greater strength and consistency of association with pollutant concentration compared to microbial community structure and can be recommended as a sensitive indicator of metal pollution on estuarine sediment microbial communities.

Toxicity bioassays in core sediments from the Bay of Santander, northern Spain

The use of Vibrio fischeri as luminescence bacteria is particularly effective in evaluating contaminated sediment. In this study, the ecotoxicity of five core sediments from the Bay of Santander, northern Spain, utilising V. fischeri as marine bacterium, was carried out. Different toxicity assay procedures were applied in order to study the influence of the mobility and bioavailability of the pollutants. Basic Solid Phase Test (BSPT) in whole sediment and acute toxicity test, using pore water and three leaching test procedures as liquid extracts, were applied. In addition, the study of the influence of the pH value on the toxicity results of the leaching tests was conducted. The obtained results show toxicity units (TU50) values in BSPT test ranging from 0.42 to 39.06 with a decrease with depth as general trend and TU50 values from 0.010 to 0.389 in the liquid extracts, where TU50 is calculated as the inverse of EC50 (%). The obtained data show the historical toxicity trends of the Bay of Santander and provides a technical database for the management of contaminated sediments. Moreover, these results showed evidence that each sediment test procedure provided independent and complementary ecotoxicological responses useful for a sediment classification. In order to analyse the correlations between chemical parameters (both organic and inorganic) and the toxicity results, the self-organising map (SOM) neural network and regression equations were applied. Satisfactory correlations (R=0.93) between chemical concentrations of sum of five heavy metals and 16 PAHs and BSPT toxicity were obtained.

Risk of gastrointestinal disease associated with exposure to pathogens in the sediments of the Lower Passaic River

High levels of pathogenic microorganisms have been documented previously in waters of the Lower Passaic River in northern New Jersey. The purpose of this study was to characterize the microbial contamination of river sediments near combined sewer overflows (CSOs), a known source of pathogens. Concentrations of fecal coliform, total coliform, fecal Streptococcus, fecal Enterococcus, Pseudomonas aeruginosa, Staphylococcus aureus, Giardia lamblia, and Cryptosporidium parvum organisms were measured in 16 samples from three mudflat locations along the Lower Passaic River, as well as from an upstream location. Selected samples were also analyzed for antibiotic resistance. All of the samples contained high concentrations of total coliform, fecal coliform, fecal Streptococcus, and fecal Enterococcus organisms. Analysis of isolates of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli from several samples indicated that each strain was resistant to at least one antibiotic typically used in clinical settings. Eight of 16 samples contained Giardia, and one sample contained Cryptosporidium. With these sampling data, a quantitative microbial risk assessment was conducted to evaluate the probability of infection or illness resulting from incidental ingestion of contaminated sediments over a 1-year period. Three potential exposure scenarios were considered: visitor, recreator, and homeless person. Single-event risk was first evaluated for the three individual exposure scenarios; overall risk was then determined over a 1-year period using Monte Carlo techniques to characterize uncertainty. For fecal Streptococcus and Enterococcus, annualized risk estimates for gastrointestinal illness ranged from approximately 0.42 to 0.53 for recreators, 0.07 to 0.10 for visitors, and 0.62 to 0.72 for homeless individuals across the three sampling locations. Annualized risk of Giardia infection ranged from 0.14 to 0.64 for recreators, 0.01 to 0.1 for visitors, and 0.30 to 0.87 for homeless individuals, across all locations where detected. Cryptosporidium was detected at one location, and the corresponding annualized risk of infection was 0.32, 0.05, and 0.51 for recreators, visitors, and homeless individuals, respectively. This risk assessment suggests that pathogen-contaminated sediments near areas of CSO discharge in the Lower Passaic River could pose a health risk to individuals coming into contact with sediments in the mudflat areas.

Development of microbial sensors and their application

Many types of microbial sensors have been developed as analytical tools since the first microbial sensor was studied by Karube et al. in 1977. The microbial sensor consists of a transducer and microbe as a sensing element. The characteristics of the microbial sensors are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial sensors have the advantages of tolerance to measuring conditions, a long lifetime, and cost performance, and also have the disadvantage of a long response time. In this review, the long history of microbial sensor development is summarized.

Anaerobically grown Thauera aromatica, Desulfococcus multivorans, Geobacter sulfurreducens are more sensitive towards organic solvents than aerobic bacteria

The effect of seven important pollutants and three representative organic solvents on growth of Thauera aromatica K172, as reference strain for nitrate-reducing anaerobic bacteria, was investigated. Toxicity in form of the effective concentrations (EC50) that led to 50% growth inhibition of potential organic pollutants such as BTEX (benzene, toluene, ethylbenzene, and xylene), chlorinated phenols and aliphatic alcohols on cells was tested under various anaerobic conditions. Similar results were obtained for Geobacter sulfurreducens and Desulfococcus multivorans as representative for Fe(3+)-reducing and sulphate-reducing bacteria, respectively, leading to a conclusion that anaerobic bacteria are far more sensitive to organic pollutants than aerobic ones. Like for previous studies for aerobic bacteria, yeast and animal cell cultures, a correlation between toxicity and hydrophobicity (log P values) of organic compounds for different anaerobic bacteria was ascertained. However, compared to aerobic bacteria, all three tested anaerobic bacteria were shown to be about three times more sensitive to the tested substances.

Physico-chemical and toxicological characterization of the historic estuarine sediments: a multidisciplinary approach

The accumulation rates, the geochronology of metals and PAH contamination, and the Microtox toxicity are studied in five sediment cores (50 cm length) covering different areas of the Santander Bay, Northern Spain. Chronology given by (210)Pb and (137)Cs reveals significant differences in accumulation rates between sites (0.2-1.1 cm/year), as well as a variable degree of anthropogenic enrichment factors for Fe, Mn, Cu, Pb, Zn, Ni (from 1 to 15) and concentrations of summation Sigma 16PAHs (from 0.01 to 23.84 mg/kg dw) in sediments over the last 90 years. The results indicate the increasing contamination pressure from industrial and urban activities along the Bay. No toxic results from the Microtox test are obtained either with pore water or with normalised sediment aqueous extracts (European Norm EN 12457), suggesting low water solubility and low availability of contaminants in the studied sediments. However, the EC50 values from the Microtox Basic Solid Phase Test (BSPT) ranged from 0.03% to 2.35%, showing vertical toxicity profiles in accordance with metal and PAHs behaviour. The correlation degrees of Microtox BSPT toxicity to chemical concentration in sediment profiles are widely variable showing a high site-dependent toxicity. The oligochaete Limnodrilus hoffmeisteri has been used as a chronic bioassay over surface sediments of two of the studied sites, showing results coherent with the Microtox BSPT acute test results. Global results of the present work provide regional geochemical baselines for metals and PAHs and toxicological data now make it possible to obtain a preliminary quality assessment of the Santander Bay sediment profiles.

Use of a general toxicity test to predict heavy metal concentrations in residential soils

Significant clusters of developmental delay and mental retardation (DD/MR) were identified in children born in South Carolina. Although it is difficult to identify one factor that causes DD/MR, environmental insult including exposure of pregnant women to heavy metals can induce DD/MR in their children. Because it is expensive to measure the concentrations of individual metals in large numbers of environmental samples, the general Microtox toxicity test was used to identify highly toxic soil samples. Approximately 100 soil samples were collected from residential areas and analyzed to determine an effective concentration (EC(50)) of soil required to inhibit 50% light emission of the luminescent bacterial test organism (Vibrio fischeri). The EC(50) values were then transformed to relative toxicity units (RTU). A subset of 56 high and low toxicity soil samples was then analyzed by inductively coupled plasma-atomic emission spectrometry (EPA method 6010) for arsenic, lead, and chromium, which are known neurotoxins. The highest measured arsenic concentration was 30 times higher than the South Carolina residential soil limit. Significant correlations were found between the RTU and soil arsenic and chromium concentrations. Microtox also identified some low arsenic and chromium samples as toxic, presumably because additional unidentified toxicants were present in the soil. In general, however, the Microtox test was effective in identifying soils with elevated concentrations of arsenic and chromium, even in residential neighborhoods where limited soil toxicity was expected.

Comparing sediment quality in Spanish littoral areas affected by acute (Prestige, 2002) and chronic (Bay of Algeciras) oil spills

The quality of sediments collected from two areas of the Spanish coast affected by different sources of contaminants has been compared in this study. The areas studied are the coast of Galicia affected by the oil spill from the tanker Prestige (November 2002) and the Gulf of Cádiz which suffers continuous inputs of contaminants from industries located in the area and from oil spills. Contamination by several chemicals (metals, PCBs and PAHs) that bind to sediments was analyzed, and two toxicity tests (Microtox) and amphipod 10-day bioassay) were conducted. PAHs were identified as the compounds responsible for the toxic effects. Results show differences between an acute impact related to the sinking of the tanker Prestige and the chronic impact associated with continuous oil spills associated with the maritime and industrial activities in the Bay of Algeciras, this being the most polluted part of the two coastal areas studied in this work.

Prokaryotic gene profiling assays to detect sediment toxicity: evaluating the ecotoxicological relevance of a cell-based assay

Despite their complexity, ecotoxicological measurements using higher level responses remain a major tool in the assessment of ecosystem integrity. Nevertheless, the past decade saw an increasing number of cell based testing systems have found widespread application in ecotoxicology. One such test is bacterial bioreporters carrying a stress sensitive promoter fused to an easily detectable reporter gene. In the presence of a specific toxic stress,the expression cassette is switched on and the reporter gene is produced. This study evaluated the use of 14 different Escherichia coli bioreporter strains sensitive to different types of toxicity in the assessment of the ecological status of a small river basin in Flanders, Belgium. The river is fed at two geographically separate locations by two distinct and well-described effluents, one from a household sewage treatment facility and one from the discharge of the wastewater treatment facility of a large chemical plant. The results of the bacterial gene profiling assay were related to active biomonitoring results obtained through higher-level responses of caged Dreissena polymorpha, Chironomus riparius, and Cyprinus carpio deployed at the locations sampled for the bacterial assay. The results of the gene induction assay and the active biomonitoring data correlated well and corresponded to the flow dilution data, which is used here as a surrogate forthe chemical pollution gradient present in the river basin.

Effect of sediment turbidity and color on light output measurement for Microtox Basic Solid-Phase Test

In this work, sediment samples collected from several Spanish harbours were tested with two toxicity procedures, designed for solid samples: the Microtox Basic Solid-Phase Test (BSPT) and a modified procedure of the previous test protocol (mBSPT). According to the BSPT procedure, after initial light readings, pure bacteria were exposed to sediment suspension dilutions and light production was directly measured on suspended sediments without any further manipulation. As measurements are likely to be affected by sediment turbidity and color, a variation in initial light measurement has been here suggested, in order to consider the sample effect at all time readings during the test. Firstly, when sediment suspensions at different concentrations were added to bacteria suspension, immediately the initial light output drastically decayed by more than 50% in signal difference, resulting in a false inhibition, as effect of sample turbidity/color. This effect was more evident at high EC50 values, when slightly or not toxic samples were assessed. Secondly, the comparison of the EC50 obtained with both procedures, demonstrated that the mBSPT produced higher EC50 values (less toxic) than those obtained with the standard procedure. The mBSPT procedure resulted rapid and effective and it could be applied simultaneously with BSPT, in order to better evaluate the toxicity.

Biodiversity of vibrios

Vibrios are ubiquitous and abundant in the aquatic environment. A high abundance of vibrios is also detected in tissues and/or organs of various marine algae and animals, e.g., abalones, bivalves, corals, fish, shrimp, sponges, squid, and zooplankton. Vibrios harbour a wealth of diverse genomes as revealed by different genomic techniques including amplified fragment length polymorphism, multilocus sequence typing, repetetive extragenic palindrome PCR, ribotyping, and whole-genome sequencing. The 74 species of this group are distributed among four different families, i.e., Enterovibrionaceae, Photobacteriaceae, Salinivibrionaceae, and Vibrionaceae. Two new genera, i.e., Enterovibrio norvegicus and Grimontia hollisae, and 20 novel species, i.e., Enterovibrio coralii, Photobacterium eurosenbergii, V. brasiliensis, V. chagasii, V. coralliillyticus, V. crassostreae, V. fortis, V. gallicus, V. hepatarius, V. hispanicus, V. kanaloaei, V. neonatus, V. neptunius, V. pomeroyi, V. pacinii, V. rotiferianus, V. superstes, V. tasmaniensis, V. ezurae, and V. xuii, have been described in the last few years. Comparative genome analyses have already revealed a variety of genomic events, including mutations, chromosomal rearrangements, loss of genes by decay or deletion, and gene acquisitions through duplication or horizontal transfer (e.g., in the acquisition of bacteriophages, pathogenicity islands, and super-integrons), that are probably important driving forces in the evolution and speciation of vibrios. Whole-genome sequencing and comparative genomics through the application of, e.g., microarrays will facilitate the investigation of the gene repertoire at the species level. Based on such new genomic information, the taxonomy and the species concept for vibrios will be reviewed in the next years.