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

Impact of global change on environmental hazards of different clays: A case study on Aliivibrio fischeri

The effects of global change in marine ecosystems are expected to lower pH from the current 8.1-7.5-7.0, which will have significant impacts on marine species. The purpose of this study is to investigate whether the ecotoxicity of ten different natural clays change significantly in response to the acidification process and what factors are associated with the observed changes. In this study, the ecotoxicological response of a bacterium (Aliivibrio fischeri) was tested under current (pH= 8.1) and acidified (pH 7.5 and 7.0) conditions. The ecotoxicity detected in the solid phase test (SPT protocol) and in the contact water was affected by the pH, which increased the ecotoxicity from 2/10 clays (pH 8.10) to 7/10 clays (pH 7.00), also shifting the detected effects from low to high toxicity values. The analyses performed on the natural clays studied show that pH can affect the release of metals, metalloids and rare earths from the clays into the contact water phase, affecting the toxicity observed. This phenomenon depends on the type of clay and is closely related to its mineralogical composition. As consequence, in a globally changing scenario, ecotoxicity, even of natural materials such as clay, cannot be considered stable, but must be accurately revaluated depending on the mineralogical and chemical composition of the clay. Moreover, the mineralogical composition of clays showed different efficiency in absorbing bacteria on the surface of clay particles. It was found that live bacterial cells were absorbed on the clay surface in numbers that were dependent on both clay types and pH levels.

Toxic response of the bacterium Vibrio fischeri to sodium lauryl ether sulphate residues in excavated soils

Sodium lauryl ether sulphate (SLES) is the main chemical component in several lubricant products used for soil conditioning in the mechanized excavation industry using Earth Pressure Balance-Tunnel Boring Machines. During the tunnelling process, huge amounts of excavated soil are produced and the SLES presence can affect the subsequent re-use of this material as a by-product. Currently, there is still no regulatory indication of reliable and sensitive bioassays for monitoring soil quality during the excavation process. The main objective of this work was to verify if the Vibrio fischeri screening test was suitable as a consistent and precautionary tool for this specific purpose. Firstly, the ecotoxicity (EC₂₀ and EC₅₀) of the SLES standard solution and three commercial products (SLES content from 10 to 50%) were evaluated to select the most environmental friendly product. Subsequently, soil samples from about 2 years of tunnelling in a real construction site, conditioned with the selected product, were evaluated for their environmental compatibility with the prescriptions of an Italian site-specific protocol. The latter established 2 mg/L as a threshold value for SLES concentration in soil water extracts and a no toxic response (≤20%) for the Vibrio fischeri test. The comparison of the bacterium bioluminescence inhibition values (%) with analytical determinations showed an ecotoxicity when SLES was >2 mg/L. The toxicity was directly related to SLES concentration, indicating that the V. fischeri test and the SLES analyses are suitable tools for assessing excavated soil as a by-product, ensuring its safe reuse in accordance with a green production process (circular economy).

Bioremediation of Olive Mill Wastewater sediments in evaporation ponds through in situ composting assisted by bioaugmentation

The common method for the disposal of olive oil mill wastewater (OMW) has been its accumulation in evaporation ponds where OMW sediments concentrate. Due to the phytotoxic and antimicrobial effect of OMW, leaks from ponds can pollute soils and water bodies. This work focuses on the search for microorganisms that can be used as inocula for bioremediation of polluted matrices in OMW ponds by means of in situ composting. Two fungi isolated from OMW sediments, Aspergillus ochraceus H2 and Scedosporium apiospermum H16, presented suitable capabilities for this use as a consortium. Composting eliminated the phyto- and ecotoxicity of OMW sediments by depleting their main toxic components. Inoculation with the fungal consortium improved the bioremediation efficacy of the technique by hastening the decrease of phytotoxicity and ecotoxicity and enhancing phytostimulant property of compost produced. This procedure constitutes a promising strategy for bioremediation of OMW polluted sites.

Iron and Iron Oxide Nanoparticles Synthesized Using Green Tea Extract: Improved Ecotoxicological Profile and Ability to Degrade Malachite Green

In recent years, iron-based nanoparticles (FeNPs) have been successfully used in environmental remediation and water treatment. This study examined ecotoxicity of two FeNPs produced by green tea extract (smGT, GTFe) and their ability to degrade malachite green (MG). Their physicochemical properties were assessed using transmission electron microscopy, X-ray powder diffraction, dynamic light scattering, and transmission Mössbauer spectroscopy. Using a battery of ecotoxicological bioassays, we determined toxicity for nine different organisms, including bacteria, cyanobacterium, algae, plants, and crustaceans. GTFe, amorphous complex of Fe(II, III) ions and polyphenols from green tea extract, proved low capacity to degrade MG and was toxic to all tested organisms. Superparamagnetic iron oxide NPs (smGT) derived from GTFe, showed no toxic effect on most of the tested organisms up to a concentration of 1g/L, except for algae and cyanobacterium and removed 93 % MG at concentration 125 mg Fe/L after 60 minutes. The procedure described in this paper generates new superparamagnetic iron oxide NPs from existing and toxic GTFe, which are nontoxic and has degradative potential for organic compounds. These findings suggest low ecotoxicological risks and suitability of this green-synthesized FeNPs for environmental remediation purposes.

Rapid in situ toxicity testing with luminescent bacteria Photorhabdus luminescens and Vibrio fischeri adapted to a small portable luminometer

The present study demonstrates development of a rapid testing protocol based on a small portable luminometer using flash kinetic assessment of bacterial bioluminescence. The laboratory comparisons based on six model organic toxicants and two metals showed significant correlations between responses of freshwater bacteria Photorhabdus luminescens and standard marine bacterial species Vibrio fisheri. While P. luminescens was less sensitive in standard arrangements, the responses of both organisms were comparable in the newly introduced portable luminometer setup. The applicability and reproducibility of the portable luminometer protocol was further demonstrated in the assessment of 43 European wastewater effluents that were simultaneously tested for toxicity and analysed for 150 organic and 20 inorganic contaminants grouped into 13 major chemical classes. Clear association between the toxic responses in both compared bacterial species and the elevated levels of inorganic compounds (toxic metals), chlorophenols and benzotriazole anticorrosives was observed. The new protocol with a portable luminometer provides a fast (30 s) response and may be used as a tool for rapid in situ toxicity evaluation of freshwater environmental samples such as effluents.

Bioluminescent Vibrio fischeri Assays in the Assessment of Seasonal and Spatial Patterns in Toxicity of Contaminated River Sediments

Several bacteria-based assays, notably Vibrio fischeri luminescence assays, are often used as environmental monitoring tool for toxicity in sediments that may serve as both sinks and secondary source of contamination in aquatic ecosystems. In this study, we used 30-s kinetic bioassays based on V. fischeri to evaluate the toxicity associated to sediments from five localities with different contamination inputs (Morava River and its tributary Drevnice River in the south-eastern part of the Czech Republic). Toxicity assessed as half maximal inhibitory concentration (IC₅₀) over the course of a year-long sampling was compared in bottom sediments and freshly trapped particulate material. Standard approach based on testing of aqueous elutriates was compared with toxicity of whole sediments (contact suspension toxicity). Bottom sediments showed lower toxicity compared to freshly trapped suspended materials in all cases. On the other hand, standardized elutriates induced generally weaker effects than suspended sediments likely due to losses during the extraction process. Toxicity generally increased during winter reaching maximum peaks in early spring months in all five sites. Total organic carbon (TOC) was found to be highly correlated with toxic effects. Toxicity from sites with direct industrial and agricultural water inputs also correlated with concentrations of metals, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). Single time point sampling followed by the extraction and testing of elutriates, do not truly reflect the spatial and temporal variability in natural sediments and may lead to underestimation of ecotoxic risks.

Bioaccumulation and molecular effects of sediment-bound metals in zebrafish embryos

Predicting the bioavailability and effects of metals in sediments is of major concern in context with sediment risk assessment. This study aimed to investigate the bioavailability and molecular effects of metals spiked into riverine sediments to zebrafish (Danio rerio) embryos. Embryos were exposed to a natural and an artificial sediment spiked with cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) individually or as a mixture at concentrations ranging from 150 to 3000 mg/kg dry weight (dw) over 48 h, and uptake of metals was determined. Furthermore, transcript abundances of the metallothioneins MT1 and MT2, the metal-responsive element-binding transcription factor (MTF) and the genes sod1, hsp70 and hsp90α1 were measured as indicators of metal-induced or general cellular stress. D. rerio embryos accumulated metals from sediments at concentrations up to 100 times greater than those spiked to the sediment with the greatest bioaccumulation factor (BAF) for Cu from artificial sediment (275.4 ± 41.9 (SD)). Embryos accumulated greater concentrations of all metals from artificial than from natural sediment, and accumulation was greater when embryos were exposed to individual metals than when they were exposed to the mixture. Exposure of embryos to Zn or the mixture exhibited up to 30-fold greater transcript abundances of MT1, MT2 and hsp70 compared to controls which is related to significant uptake of Zn from the sediment. Further changes in transcript abundances could not be related to a significant uptake of metals from sediments. These studies reveal that metals from spiked sediments are bioavailable to D. rerio embryos directly exposed to sediments and that the induction of specific genes can be used as biomarkers for the exposure of early life stages of zebrafish to metal-contaminated sediments.

Adaptation of the Daphnia sp. acute toxicity test: miniaturization and prolongation for the testing of nanomaterials

Manufacturing of nanomaterials (NMs) is often complex and expensive, and their environmental risks are poorly understood or even unknown. An economization of testing NMs is therefore desirable, which can be achieved by miniaturizing test systems. However, the downsizing of test vessels and volumes can enlarge the surface/volume ratio (SVR) which in turn can affect the bioavailable concentration of adsorbing substances like NMs. The present study focused on the miniaturization of the acute toxicity test with Daphnia magna. The adaptations were verified with three reference substances, the non-adsorbing potassium dichromate (K2Cr2O7) and as potentially highly-adsorbing substances silver nanoparticles (AgNPs) and silver nitrate (AgNO3). The miniaturized test was conducted in 24-well microtiter plates (MT) and simultaneously compared to the OECD standard test (ST). Furthermore, the test duration was prolonged from 48 to 96 h since NMs tend to show effects only after extended exposure. The toxicity of K2Cr2O7 and AgNPs continued to increase within the prolonged test span. The test comparisons with K2Cr2O7 did not reveal any significant differences between ST and MT. AgNO3 toxicity was significantly decreased in MT compared to ST due to the enlarged SVR. The toxicity of AgNPs in MT after 24 h was equal to ST. Contrary to our expectations an exposure longer than 24 h resulted in an increase of AgNP toxicity in MT, possibly due to enhanced dissolution of silver. Microtiter plates are appropriate alternative test vessels for the Daphnia sp. acute toxicity test; thus, its miniaturization is feasible. The enlarged SVR has to be taken into account since it can affect the toxicity of potentially adsorbing substances. Furthermore, the standard test duration of 48 h might underestimate the toxicity of many substances, especially of NMs.

Effects of Americium-241 and humic substances on Photobacterium phosphoreum: bioluminescence and diffuse reflectance FTIR spectroscopic studies

The integral bioluminescence (BL) intensity of live Photobacterium phosphoreum cells (strain 1883 IBSO), sampled at the stationary growth stage (20 h), was monitored for further 300 h in the absence (control) and presence of (241)Am (an α-emitting radionuclide of a high specific activity) in the growth medium. The activity concentration of (241)Am was 2 kBq l(-1); [(241)Am]=6.5×10(-11) M. Parallel experiments were also performed with water-soluble humic substances (HS, 2.5 mg l(-1); containing over 70% potassium humate) added to the culture medium as a possible detoxifying agent. The BL spectra of all the bacterial samples were very similar (λ(max)=481±3 nm; FWHM=83±3 nm) showing that (241)Am (also with HS) influenced the bacterial BL system at stages prior to the formation of electronically excited states. The HS added per se virtually did not influence the integral BL intensity. In the presence of (241)Am, BL was initially activated but inhibited after 180 h, while the system (241)Am+HS showed an effective activation of BL up to 300 h which slowly decreased with time. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, applied to dry cell biomass sampled at the stationary growth phase, was used to control possible metabolic responses of the bacteria to the α-radioactivity stress (observed earlier for other bacteria under other stresses). The DRIFT spectra were all very similar showing a low content of intracellular poly-3-hydroxybutyrate (at the level of a few percent of dry biomass) and no or negligible spectroscopic changes in the presence of (241)Am and/or HS. This assumes the α-radioactivity effect to be transmitted by live cells mainly to the bacterial BL enzyme system, with negligible structural or compositional changes in cellular macrocomponents at the stationary growth phase.

Quantitative PCR enumeration of total/toxic Planktothrix rubescens and total cyanobacteria in preserved DNA isolated from lake sediments

The variability of spatial distribution and the determinism of cyanobacterial blooms, as well as their impact at the lake scale, are still not understood, partly due to the lack of long-term climatic and environmental monitoring data. The paucity of these data can be alleviated by the use of proxy data from high-resolution sampling of sediments. Coupling paleolimnological and molecular tools and using biomarkers such as preserved DNA are promising approaches, although they have not been performed often enough so far. In our study, a quantitative PCR (qPCR) technique was applied to enumerate total cyanobacterial and total and toxic Planktothrix communities in preserved DNA derived from sediments of three lakes located in the French Alps (Lake Geneva, Lake Bourget, and Lake Annecy), containing a wide range of cyanobacterial species. Preserved DNA from lake sediments was analyzed to assess its quality, quantity, and integrity, with further application for qPCR. We applied the qPCR assay to enumerate the total cyanobacterial community, and multiplex qPCR assays were applied to quantify total and microcystin-producing Planktothrix populations in a single reaction tube. These methods were optimized, calibrated, and applied to sediment samples, and the specificity and reproducibility of qPCR enumeration were tested. Accurate estimation of potential inhibition within sediment samples was performed to assess the sensitivity of such enumeration by qPCR. Some precautions needed for interpreting qPCR results in the context of paleolimnological approaches are discussed. We concluded that the qPCR assay can be used successfully for the analysis of lake sediments when DNA is well preserved in order to assess the presence and dominance of cyanobacterial and Planktothrix communities.