Development of a reference artificial sediment for chemical testing adapted to the MELA sediment contact assay

Towards bioprocess engineering of cable bacteria: Establishment of a synthetic sediment

Cable bacteria, characterized by their multicellular filamentous growth, are prevalent in both freshwater and marine sediments. They possess the unique ability to transport electrons over distances of centimeters. Coupled with their capacity to fix CO2 and their record-breaking conductivity for biological materials, these bacteria present promising prospects for bioprocess engineering, including potential electrochemical applications. However, the cultivation of cable bacteria has been limited to their natural sediment, constraining their utility in production processes. To address this, our study designs synthetic sediment, drawing on ion exchange chromatography data from natural sediments and existing literature on the requirements of cable bacteria. We examined the effects of varying bentonite concentrations on water retention and the impacts of different sands. For the first time, we cultivated cable bacteria on synthetic sediment, specifically the freshwater strain Electronema aureum GS. This cultivation was conducted over 10 weeks in a specially developed sediment bioreactor, resulting in an increased density of cable bacteria in the sediment and growth up to a depth of 5 cm. The creation of this synthetic sediment paves the way for the reproducible cultivation of cable bacteria. It also opens up possibilities for future process scale-up using readily available components. This advancement holds significant implications for the broader field of bioprocess engineering.

Spiking organic chemicals onto sediments for ecotoxicological analyses: an overview of methods and procedures

Laboratory testing with spiked sediments with organic contaminants is a valuable tool for ecotoxicologists to study specific processes such as effects of known concentrations of toxicants, interactions of the toxicants with sediment and biota, and uptake kinetics. Since spiking of the sediment may be performed by using different strategies, a plethora of procedures was proposed in the literature for spiking organic chemicals onto sediments to perform ecotoxicological analyses. In this paper, we reviewed the scientific literature intending to characterise the kind of substrates that were used for spiking (i.e. artificial or field-collected sediment), how the substrates were handled before spiking and amended with the organic chemical, how the spiked sediment was mixed to allow the homogenisation of the chemical on the substrate and finally how long the spiked sediment was allowed to equilibrate before testing. What emerged from this review is that the choice of the test species, the testing procedures and the physicochemical properties of the organic contaminant are the primary driving factors affecting the selection of substrate type, sediment handling procedures, solvent carrier and mixing method. Finally, we provide recommendations concerning storage and characterization of the substrate, equilibrium times and verification of both equilibration and homogeneity.

Exposure to four chemical UV filters through contaminated sediment: impact on survival, hatching success, cardiac frequency, and aerobic metabolic scope in embryo-larval stage of zebrafish

UV filters are widely used in many pharmaceutical and personal care products such as sunscreen and cosmetics to protect from UV irradiation. Due to their hydrophobic properties and relative stability, they have a high capacity to accumulate in sediment. Little information is available on their ecotoxicity on fish. In aquatic ecosystems, fish eggs could be directly affected by UV filters through contact with contaminated sediment. The aim of this study was to investigate the individual toxicity of four UV filters: benzophenone-3 (BP3), butyl methoxydibenzoylmethane (BM), bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT), and methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), in embryo-larval stages of zebrafish Danio rerio. Fish eggs were exposed to single UV filters by contact with spiked sediment during 96 h at a concentration of 10 μg g^-1. Among the four UV filters tested, BP3 was the more toxic, reducing cardiac frequency and increasing standard metabolic rate of larvae.

The effects of exposure to crude oil or PAHs on fish swim bladder development and function

The failure of the swim bladder to inflate during fish development is a common and sensitive response to exposure to petrochemicals. Here, we review potential mechanisms by which petrochemicals or their toxic components (polycyclic aromatic hydrocarbons; PAHs) may affect swim bladder inflation, particularly during early life stages. Surface films formed by oil can cause a physical barrier to primary inflation by air gulping, and are likely important during oil spills. The act of swimming to the surface for primary inflation can be arduous for some species, and may prevent inflation if this behavior is limited by toxic effects on vision or musculature. Some studies have noted altered gene expression in the swim bladder in response to PAHs, and Cytochrome P450 1A (CYP1A) can be induced in swim bladder or rete mirabile tissue, suggesting that PAHs can have direct effects on swim bladder development. Swim bladder inflation failure can also occur secondarily to the failure of other systems; cardiovascular impairment is the best elucidated of these mechanisms, but other mechanisms might include non-inflation as a sequela of disruption to thyroid signaling or cholesterol metabolism. Failed swim bladder inflation has the potential to lead to chronic sublethal effects that are as yet unstudied.

In vitro and in vivo screening for environmentally friendly benzophenone-type UV filters with beneficial tyrosinase inhibition activity

Benzophenones (BPs) are a group of chemically similar organic compounds commonly used in formulations of sunscreen and other personal care products as UV filters to protect our skin against sunlight overexposure. Studies have shown that the occurrence of certain BPs (e.g., BP-3 and its metabolite BP-1) in multiple environmental matrices may increase the incidence of coral planulae bleaching and estrogenic effects on aquatic life. Currently, most BPs are not yet comprehensively screened in vitro and in vivo for their ecotoxicity under environmentally relevant concentrations. This study systematically assessed the in vitro and in vivo toxicity and activity of the 7 most commonly used BPs (BP-1, BP-2, BP-3, BP-4, BP-6, BP-7 and BP-8) to select BP alternatives with lower ecotoxicity and extra beneficial functions. BP-2 (LC₅₀ = 18.43 µM) was least toxic and BP-3 (LC₅₀ = 4.10 µM) and BP-8 (LC₅₀ =1.62 µM) were less and most toxic, respectively, in terms of 96-hr acute mortality of medaka larvae. BP-2 at environmentally relevant concentrations (5-50 nM) did not significantly alter locomotion and oxidative stress responses of medaka larvae from 24-hr to 7-day exposure, whereas BP-3 and BP-8 at 5 nM induced hypoactivity or changed fish swimming angles. Only BP-2 was able to inhibit in vitro mushroom tyrosinase activity, with EC₅₀ value 19.7 µM. Also, BP-2 could effectively suppress melanin formation and tyrosinase activity in zebrafish embryos. Among the 7 tested BPs, BP-2 was the least toxic and the most environmentally friendly UV filter with extra benefit for tyrosinase inhibition and could be a promising alternative to the use of toxic BPs.

Toxicity assessment of pollutants sorbed on environmental microplastics collected on beaches: Part II-adverse effects on Japanese medaka early life stages

While microplastics are present in great abundance across all seas and oceans, little is known about their effects on marine life. In the aquatic environment, they can accumulate a variety of chemicals and can be ingested by many marine organisms including fish, with chronic physical and chemical effects. The purpose of this paper is to evaluate the toxic effects of pollutants sorbed at the surface of environmental microplastics (MPs), collected on various beaches from three islands of the Pacific Ocean. Developmental toxicity of virgin MPs or artificially coated with B[a]P and environmental MPs from Easter Island, Guam and Hawaii was evaluated on embryos and prolarvae of Japanese medaka. Mortality, hatching success, biometry, malformations, EROD activity and DNA damage were analyzed after exposure to DMSO extracts. No toxicity was observed for extracts of virgin MPs whatever the endpoint considered. Extracts of virgin MPs coated with 250 µg.g^-1 of B(a)P induced lethal effects with high embryo mortality (+81%) and low hatching rate (-28%) and sublethal effects including biometry and swimming behavior changes, increase of EROD activity (+94%) and DNA damage (+60%). Environmental MPs collected on the three selected islands exhibited different polymer, pollutant and toxicity patterns. The highest toxicity was detected for MPs extract from Hawaï with head/body length and swimming speed decreases and induction of EROD activity and DNA stand breaks. This study reports the possible sublethal toxicity of organic pollutants sorbed on MPs to fish early life stages.

Release of anthracene from estuarine sediments by crab bioturbation effects

To investigate bioturbation effects on anthracene (Ant) release from sediments to the overlying water, indoor microcosms were developed. Naturally contaminated estuarine sediments were exposed to the crab Helice tiensinensis over 70 days and compared with sediments with no crab. Bioturbation by crab could significantly increase the release of both particulate and dissolved Ant. The releases of particulate Ant with bioturbation treatments were 2.3-11.7 times higher than in the control treatments. However, the releases of dissolved Ant with bioturbation treatments were 1.7-3.7 times higher than in the control treatments. The ratio of particulate Ant/total Ant varied from 89 % to 98 % in the bioturbation treatments, which was significantly higher than in the control treatments. These results indicate that crab bioturbation significantly enhanced both particulate and dissolved Ant release from sediment, but the particulate Ant is the predominant process.

Assessing the toxicity of sediments using the medaka embryo-larval assay and 2 other bioassays

Sediments are sinks for aquatic pollutants, and analyzing toxicity in such complex matrices is still challenging. To evaluate the toxicity of bioavailable pollutants accumulated in sediments from the Bizerte lagoon (Tunisia), a novel assay, the medaka embryo-larval assay by sediment contact, was applied. Japanese medaka (Oryzias latipes) embryos were incubated in direct contact with sediment samples up to hatching. Lethal and sublethal adverse effects were recorded in embryos and larvae up to 20 d postfertilization. Results from medaka embryo-larval assay were compared with cytotoxicity (Microtox®), genotoxicity (SOS chromotest), and pollutant content of sediments. The results highlight differences in the contamination profile and toxicity pattern between the different studied sediments. A significant correlation was shown between medaka embryo-larval assay by sediment contact and SOS chromotest responses and concentrations of most organic pollutants studied. No correlation was shown between pollutant levels and Microtox. According to the number of sediment samples detected as toxic, medaka embryo-larval assay by sediment contact was more sensitive than Microtox, which in turn was more sensitive than the SOS chromotest; and medaka embryo-larval assay by sediment contact allowed sediment toxicity assessment of moderately polluted sediments without pollutant extraction and using an ecologically realistic exposure scenario. Although medaka embryo-larval assay by sediment contact should be tested on a larger sample set, the results show that it is sensitive and convenient enough to monitor the toxicity of natural sediments. Environ Toxicol Chem 2016;35:2270-2280. © 2016 SETAC.

Environmental concentrations of benz[a]anthracene induce developmental defects and DNA damage and impair photomotor response in Japanese medaka larvae

Benz[a]anthracene (BaA) is a ubiquitous polycyclic aromatic hydrocarbon found in numerous aquatic ecosystems. However, ecotoxicological data in aquatic organisms are scarce. To remedy this lack of data, Japanese medaka (Oryzias latipes) embryos were exposed to BaA and toxic effects were investigated at multiple toxicological endpoints. Japanese medaka embryos were incubated onto BaA-spiked artificial sediment for 9 days at low or moderate environmental concentrations ranging from 0.9 to 12 µgg(-1) dw. BaA-exposed embryos exhibited significant tachycardia. BaA exposure was also shown to increase CYP1A activity in the hepato-biliary tissue as well as craniofacial deformities and DNA damage in pro-larvae. The photomotor response of BaA-exposed larvae was reduced in comparison to the control group. According to this set of tests, the lowest tested and observed effect concentration (LOEC) for Japanese medaka early life stages was equivalent to 0.92 µgg(-1) dw of BaA. This concentration fall into the range of concentrations frequently encountered in sediments of polluted aquatic ecosystems. Taking into consideration these results, BaA represents a threat for fish early life stages in particular those developing onto or into contaminated sediments.

Long-term disruption of growth, reproduction, and behavior after embryonic exposure of zebrafish to PAH-spiked sediment

A natural sediment spiked with three individual polycyclic aromatic hydrocarbons (PAHs; pyrene, phenanthrene and benzo[a]pyrene) was used to expose zebrafish embryos and larvae during 4 days. The total PAH concentration was 4.4 μg g(-1) which is in the range found in sediment from contaminated areas. Quantification of metabolites in the larvae after exposure confirmed the actual contamination of the larvae and indicated an active metabolism especially for pyrene and benzo[a]pyrene. After a transfer in a clean medium, the larvae were reared to adulthood and evaluated for survival, growth, reproduction, and behavior. Measured endpoints revealed a late disruption of growth (appearing at 5 months) and a trend toward a lower reproductive ability. Adults of embryos exposed to sediment spiked with PAHs displayed lethargic and/or anxiety-like behaviors. This latter behavior was also identified in offspring at larval stage. All together, these effects could have detrimental consequences on fish performances and contribution to recruitment.

Developmental toxicity of PAH mixtures in fish early life stages. Part II: adverse effects in Japanese medaka

In aquatic environments, polycyclic aromatic hydrocarbons (PAHs) mostly occur as complex mixtures, for which risk assessment remains problematic. To better understand the effects of PAH mixture toxicity on fish early life stages, this study compared the developmental toxicity of three PAH complex mixtures. These mixtures were extracted from a PAH-contaminated sediment (Seine estuary, France) and two oils (Arabian Light and Erika). For each fraction, artificial sediment was spiked at three different environmental concentrations roughly equivalent to 0.5, 4, and 10 μg total PAH g(-1) dw. Japanese medaka embryos were incubated on these PAH-spiked sediments throughout their development, right up until hatching. Several endpoints were recorded at different developmental stages, including acute endpoints, morphological abnormalities, larvae locomotion, and genotoxicity (comet and micronucleus assays). The three PAH fractions delayed hatching, induced developmental abnormalities, disrupted larvae swimming activity, and damaged DNA at environmental concentrations. Differences in toxicity levels, likely related to differences in PAH proportions, were highlighted between fractions. The Arabian Light and Erika petrogenic fractions, containing a high proportion of alkylated PAHs and low molecular weight PAHs, were more toxic to Japanese medaka early life stages than the pyrolytic fraction. This was not supported by the toxic equivalency approach, which appeared unsuitable for assessing the toxicity of the three PAH fractions to fish early life stages. This study highlights the potential risks posed by environmental mixtures of alkylated and low molecular weight PAHs to early stages of fish development.