New methodological improvements in the Microtox® solid phase assay

Ecotoxicity testing of airborne particulate matter-comparison of sample preparation techniques for the Vibrio fischeri assay

The bioassay based on the bioluminescence inhibition of the marine bacterium Vibrio fischeri has been the most widely used test for the assessment of airborne particulate matter ecotoxicity. Most studies available use an extract of the solid sample, either made with water or organic solvents. As an alternative, a whole-aerosol test is also available where test bacteria are in actual contact with contaminated particles. In our study, different extraction procedures were compared to this direct contact test based on the V. fischeri assay and analytical measurements. The lowest PAH content and the highest EC₅₀ were determined in water extract, while the highest PAH amount and lowest EC₅₀ were measured in dichloromethane, hexane, and dimethyl-sulphoxide extracts. EC₅₀ of the direct contact test was comparable to that of the methanol extract. Our results suggest that the sensitivity of the direct contact test equals to that of extraction procedures using organic solvents, moreover, it is mimicking an environmentally realistic exposure route.

Assessment of the toxicity toward Vibrio fischeri in sediments of a mining impacted estuary in the north of Spain

This study has been carried out on the Nalón estuary, a mining impacted estuarine contaminated by metals(oid), to evaluate how the metals(oids) concentrations in the sediments contributes to the toxicity and, therefore, supposes a potential risk for the biota. For this purpose, a total of 14 surface sediment samples were collected and analysed by different techniques. Estuary sediments showed a maximum high concentration of As (68.10 μg g^-1), Hg (1.33 μg g^-1) and Pb (189.60 μg g^-1), exceeding the NOAA Effects Range Low. Likewise, these three elements were one of the most bioavailable in the sediments according to the toxicity characteristic leaching procedure performed, reaching average values of 14.28% for As, 12.81% for Hg and 9.23% for Pb. The bioavailable concentrations of As and Hg significantly correlated with toxicity (R > 0.92), suggesting that both were the main contributors to the toxicity of the sediments. Toxicity values detected (avg. 499 TU g^-1) were similar to those showed by other sites considered contaminated in the Cantabrian coastline, confirming its status as a contaminated area. The location of the highest toxicity values in the estuary was restricted to the port areas where the fine sediments that act of sink of metals(oids) are mainly deposited. This result is very important if re-mobilization of sediments take place in these areas related to dredging or other human activities.

Environmental Concentrations of Copper, Alone or in Mixture With Arsenic, Can Impact River Sediment Microbial Community Structure and Functions

In many aquatic ecosystems, sediments are an essential compartment, which supports high levels of specific and functional biodiversity thus contributing to ecological functioning. Sediments are exposed to inputs from ground or surface waters and from surrounding watershed that can lead to the accumulation of toxic and persistent contaminants potentially harmful for benthic sediment-living communities, including microbial assemblages. As benthic microbial communities play crucial roles in ecological processes such as organic matter recycling and biomass production, we performed a 21-day laboratory channel experiment to assess the structural and functional impact of metals on natural microbial communities chronically exposed to sediments spiked with copper (Cu) and/or arsenic (As) alone or mixed at environmentally relevant concentrations (40 mg kg-1 for each metal). Heterotrophic microbial community responses to metals were evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exoenzymatic, metabolic and functional genes analyses). Exposure to Cu had rapid marked effects on the structure and most of the functions of the exposed communities. Exposure to As had almost undetectable effects, possibly due to both lack of As bioavailability or toxicity toward the exposed communities. However, when the two metals were combined, certain functional responses suggested a possible interaction between Cu and As toxicity on heterotrophic communities. We also observed temporal dynamics in the functional response of sediment communities to chronic Cu exposure, alone or in mixture, with some functions being resilient and others being impacted throughout the experiment or only after several weeks of exposure. Taken together, these findings reveal that metal contamination of sediment could impact both the genetic structure and the functional potential of chronically exposed microbial communities. Given their functional role in aquatic ecosystems, it poses an ecological risk as it may impact ecosystem functioning.

Vibrio fischeri bioluminescence inhibition assay for ecotoxicity assessment: A review

Vibrio fischeri bioluminescence inhibition bioassay (VFBIA) has been widely applied for the monitoring of toxicity on account of multiple advantages encompassing shorter test duration, sensitive, cost-effective and ease of operation. Moreover, this bioassay found to be equally applicable to all types of matrices (organic & inorganic compounds, metals, wastewater, river water, sewage sludge, landfill leachate, herbicides, treated wastewater etc.) for toxicity monitoring. This review highlights the apparent significance of Vibrio fischeri bioluminescence inhibition assay for ecotoxicological screening and evaluation of diverse chemical substances toxicity profile. The biochemical and genetic basis of the bioluminescence assay and its regulatory mechanism have been concisely discussed. The basic test protocol with ongoing improvements, widespread applications, typical advantages and probable limitations of the assay have been overviewed. The sensitivity of VFBIA and toxicity bioassays has also been compared.

Assessment of baseline ecotoxicity of sediments from a prospective mining area enriched in light rare earth elements

Rare earth elements (REEs) disperse from indigenous rocks to the environment, thus making sediments one of the major sinks and sources of metal pollution. The emerging use of REEs and the subsequent opening of new mining areas may contribute to their release into surrounding ecosystems. For this reason, this study was performed in a natural area with geological material abundant in ferrocarbonatites and light REE. The aim of this work was to assess the natural REE availability and (eco)toxicity in freshwater sediments. Sediments showed high REE concentrations in samples with fine grain size fractions, and low in organic-rich sediments. The enrichment in LREE was mostly from rocks and the obtained enrichment factors (EF) confirmed that the sediments are not anthropogenically polluted. To assess REE availability and ecotoxicity, four toxicity tests were performed. REEs measured as the dissolved concentration in the test media were very low compared to the potentially available total REE in sediments and showed positive or negative correlations with fine or coarse grain sizes, respectively, and positive correlations with the content in Mg, Fe and Al. In tests performed in media supplemented with salts, the availability of REEs decreased considerably. Only some toxic effects could be linked to the REE contents in the ostracodtox and luminotox tests. However, measurement of toxicity could be influenced by the sediment properties and lead to a potential overestimation of ecotoxicity if only REE are regarded. Our study reveals that the physicochemical properties of sediments are a key factor controlling both REE availability and toxicity, whereas the determination of REE effects from toxicity tests using liquid media with salt addition will decrease REE availability and could mask toxic effects. Our findings provide new knowledge about REE behaviour in sediments and are a starting point for understanding potential REE pollution around prospective mining areas.

Novel N-Arylaminophosphonates Bearing a Pyrrole Moiety and Their Ecotoxicological Properties

A wide range of biological activities of aminophosphonates predisposes them to find applications as anticancer, antiviral, antimicrobial, antifungal, or herbicidal agents. Despite a number of positive aspects of the use of aminophosphonates, their applications may cause a risk to the environment, which is well exemplified by the case of glyphosate. Therefore, scientists see a pressing need to rate ecotoxicity of aminophosphonates. Nowadays, it is recommended to use comprehensive tools to carry out appropriate and effective risk assessments of toxic substances. For these purposes, tests based on the acute toxicity of the luminescent bacteria Aliivibrio fischeri, as well as the measurement of sub-chronic toxicity of the crustacean Heterocypris incongruens seem to be the most convenient. A series of five diphenyl N-arylamino(pyrrole-2-yl)methylphosphonates was synthesized and preliminary evaluation of their ecotoxicological properties was performed. In order to carry out such investigations, we applied the two biotests mentioned above. Results showed that the N-(4-nitrophenyl) derivative was the most toxic for bacteria in comparison to other tested compounds. As for crustaceans, N-phenyl and N-naphthyl derivatives were found to be the most harmful, simultaneously being relatively harmless for bacteria. Such a phenomenon are discussed in correlation with the literature, while its reason is discussed with respect to the aspect of structure of the tested compounds.

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.

Synthesis, Spectral Characterization of Several Novel Pyrene-Derived Aminophosphonates and Their Ecotoxicological Evaluation Using Heterocypris incongruens and Vibrio fisheri Tests

Four diphenyl pyrene-derived aminophosphonates were synthesized. Attempts were made to synthesize diphenyl N-(R)-α-methylbenzylamino(pyren-1-yl)methylphosphonate (3e) in order to obtain the chiral aminophosphonate bearing a pyrene moiety. Because these attempts failed, dimethyl and dibenzyl N-(R)-α-methylbenzyl substituted aminophosphonates 4 and 5 were synthesized and the predominant diastereoisomer of dimethyl aminophosphonate 4 was isolated. The resolution of the diastereomeric mixture of 5 failed. Aminophosphonates 3a–d and the predominant diastereoisomer of 4 were investigated in terms of their ecotoxicity using tests performed on the ostracode Heterocypris incongruens and the fluorescent bacterium Vibrio fisheri. The tests confirmed the moderate-to-high ecotoxicity of aminophosphonates 3a–d and 4, but no evident correlation between the structure and toxicity has been found.

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.

Proposed method for controlling turbid particles in solid-phase bioluminescent toxicity measurement

In the recent half century, numerous methods have been developed to assess ecological toxicity. However, the presence of solid-particle turbidity sometimes causes such tests to end with questionable results. Many researchers focused on controlling this arbitrary turbidity effect when using the Microtox® solid-phase toxicity system, but there is not yet a standard method. In this study, we examined four solid-phase sample test methods recommended in the Microtox® manual, or proposed from the literature, and compared the existing methods with our proposed method (centrifuged basic solid-phase test, c-BSPT). Four existing methods use the following strategies to control turbid particles: complete separation of liquid and solid using 0.45-μm filtration before contacting solid samples and bacteria, natural settlement, moderate separation of large particles using coarser pore size filtration, and exclusion of light loss in the toxicity calculation caused by turbidity after full disturbance of samples. Our proposed method uses moderate centrifugation to separate out the heavier soil particles from the lighter bacteria after direct contact between them. Among the solid-phase methods tested, in which the bacteria and solid particles were in direct contact (i.e., the three existing methods and the newly proposed one, c-BSPT), no single method could be recommended as optimal for samples over a range of turbidity. Instead, a simple screening strategy for selecting a sample-dependent solid-phase test method was suggested, depending on the turbidity of the solid suspension. The results of this study highlight the importance of considering solid particles, and the necessity for optimal selection of test method to reduce errors in the measurement of solid-phase toxicity.

Bioassay based luminescent bacteria: interferences, improvements, and applications

Due to the merits of being time-saving, cost effective and simple operation, the luminescent bacteria toxicity assay (LBTA) has been widely used for environmental pollution monitoring. Based on numerous studies since 2007, this critical review aims to give an overview on the mechanisms, developments and applications of LBTA. Firstly, based on the introduction of the mechanisms of LBTA, this review shows the interferences from the characteristics of testing samples (such as inorganic nutrients, color, turbidity) and summarizes the improvements on pretreatment method, test methods and test systems in recent years. Regarding the factors that affect the toxicity prediction of single chemicals, the correlation between the toxicity index expressed as median effective concentration (EC50) and characters (such as Kow, the alkyl chain length, the anion and the cation) of known chemicals, especially the emerging ionic liquids (ILs), were given an in-depth discussion. The models for predicting the joint effect of mixtures to luminescent bacteria were also presented. For the factors that affect the toxicity of actual waters, the correlation of toxicity of actual samples to luminescent bacteria and their conventional indexes were discussed. Comparing the sensitivity of the LBTA with other bioassays could indicate the feasibility of the LBTA applied on specific samples. The summary on the application of LBTA to environmental samples has been made to find the future research direction.

Assessment of the LuminoTox leachate phase assay as a complement to the LuminoTox solid phase assay: effect of fine particles in natural sediments

The LuminoTox solid phase assay (Lum-SPA), developed to assess the potential ecotoxicity of natural polluted sediments, employs stabilized thylakoids isolated from spinach plant extracts. When thylakoids are exposed to polluted samples, the action of pollutants can interfere with transmission of chlorophyll fluorescence linked to Photosystems I and II, causing a decrease in fluorescence emission. To differentiate between bulk and leachate effects, we developed a complementary assay of the Lum-SPA named the LuminoTox leachate phase assay (Lum-LPA). Twelve natural sediments were selected on the basis of their potential ecotoxicity and different quantities of fines. Results showed that in the Lum-LPA, the IC50s were always lower than those observed in the Lum-SPA. Significant inverse correlations were found between the IC50s obtained with the Lum-SPA and the percentage of fines (silt+clay fraction). In order to identify the cause of the higher ecotoxicity found in the Lum-LPA, we tested the supernatant of the liquid phase recovered after centrifugation (3000 g), and it appeared far less toxic than the Lum-LPA filtrates. To confirm the hypothesis that sensitivity in the Lum-LPA could be due to the presence of very fine particles, Photosynthetic Enzyme Complexes (PECs) were exposed to two kinds of clay materials with and without copper (0.6 mg L(-1)). Similar results were obtained in the Lum-LPA for both cases, revealing the sensitivity of this test to very fine particles.