Responses of a free-living marine nematode community to mercury contamination: results from microcosm experiments

Are anticoagulant drugs ecotoxic for meiobenthic nematodes from Saudi Arabia? First data on taxon/functional diversity and computational evidences

Community-level effects of anticoagulants have little been studied in the laboratory. In the current study, the different effects of Warfarin and Tinzaparin, individually or in combination, on meiofauna were investigated for the first time using two concentrations (5 and 25 mg·l-1) of Warfarin (W1 and W2) and Tinzaparin (T1 and T2) for 30 days. The results obtained highlighted the highest tolerance of nematodes and amphipods toward the two anticoagulants tested. Moreover, nematode abundance and taxonomic diversity decreased directly after exposure to T2 and T2W1 because of the high mortality of diatom feeders and their replacement by non-selective deposit feeders (case of Tinzaparin) or omnivores-carnivores (case of Warfarin). The relative taxon/functional similarity between controls and mixtures T1W1 and T2W2 recommends that the toxicity of Tinzaparin can be attenuated by Warfarin. Finally, the computational study of Warfarin supports its potential ecotoxicity since it satisfactorily bound and interacted with GLD-3 and SDP macromolecules.

Emergent properties of free-living nematode assemblages exposed to multiple stresses

Biological communities are currently facing multi-stressor scenarios whose ecological impacts are challenging to estimate. In that respect, considering the complex nature of ecosystems and types and interaction among stressors is mandatory. Microcosm approaches using free-living nematode assemblages can effectively be used to assess complexity since they preserve the interactions inherent to complex systems when testing for multiple stress effects. In this study, we investigated the interaction effects of three stress factors, namely i-metallic mixture of Cu, Pb, Zn, and Hg (control [L0], low, [L1] and high [L2]), ii- CO2-driven acidification (pH 7.6 and 8.0), and iii- temperature rise (26 and 28 °C), on estuarine free-living nematode assemblages. Metal contamination had the greatest influence on free-living nematode assemblages, irrespective of pH and temperature scenarios. Interestingly, whilst the most abundant free-living nematode genera showed significant decreases in their densities when exposed to contamination, other, less abundant, genera were apparently favored and showed significantly higher densities in contaminated treatments. The augmented densities of tolerant genera may be attributed to indirect effects resulting from the impacts of toxicity on other components of the system, indicating the potential for emergent effects in response to stress. Temperature and pH interacted significantly with contamination. Whilst temperature rise had potentialized contamination effects, acidification showed the opposite trend, acting as a buffer to the effects of contamination. Such results show that temperature rise and CO2-driven acidification interact with contamination on coastal waters, highlighting the importance of considering the intricate interplay of these co-occurring stressors when assessing the ecological impacts on coastal ecosystems.

The multifaceted effects of fluoranthene and polystyrene on the taxonomic composition and associated functional traits of marine meiofauna, by using single and mixture applications

The current experiment measured the multifaceted effects of polystyrene and fluoranthene, acting alone or in a mixture on marine meiofauna, but with a special focus on nematodes' morphological and functional traits. The results showed changes in the abundances for all tested concentrations of both compounds. The nematode communities exposed to the highest concentrations of fluoranthene (30 ng.g-1 Dry Weight (DW)) and polystyrene (100 mg.kg-1 DW) alone or in a mixture, were significantly less diverse compared to control and were associated with significant changes in the percentage of taxonomic composition and feeding-guilds. The most sensitive taxa to fluoranthene comprised epistratum feeders, whereas the nematodes mostly affected by polystyrene were omnivores-carnivores. A new functional tool, the Index of Sensitivity (IOS), proved to be reliable in depicting the changes that occurred in the taxonomic and functional features of the nematofauna.

Molecular interactions of polyvinyl chloride microplastics and beta-blockers (Diltiazem and Bisoprolol) and their effects on marine meiofauna: Combined in vivo and modeling study

The ecotoxicological effects of beta-blockers (i.e. Diltiazem and Bisoprolol) and their interactions with the microplastic polyvinyl chloride on marine meiofauna were tested in laboratory microcosms. An experimental factorial design was applied, using meiobenthic fauna collected from the Old Harbor of Bizerte (NE Tunisia), but with a main focus on the nematode communities. The meiobenthic invertebrates were exposed to two concentrations of Diltiazem and Bisoprolol, of 1.8 µg.L^-1 and 1.8 mg.L^-1, respectively, and one concentration of polyvinyl chloride (i.e. 20 mg.kg^-1), separately and mixed. The overall meiofauna abundance was significantly reduced in all treatments, mainly that of polychaetes and amphipods. Moreover, the juveniles-gravid female ratios of the nematode communities were the lowest in the 1.8 µg.L^-1 Bisoprolol treatment and for the 1.8 mg.L^-1 mixture of Diltiazem and microplastics, suggesting that different dosages influence the maturity status of the examined species. The demographic results were also supported by in silico approach. The simulation of molecular interactions revealed acceptable binding affinities (up to -8.1 kcal/mol) and interactions with key residues in the germ line development protein 3 and sex-determining protein from Coenorhabditis elegans. Overall, the experimental outcome strongly indicates synergistic interactions among the beta-blockers Diltiazem and Bisoprolol and the microplastic polyvinyl chloride on marine nematode communities.

How effective is wastewater treatment? A case study under the light of taxonomic and feeding features of meiobenthic nematodes

A microcosm bioassay was designed to assess the efficacy of wastewater treatment methods used in sewage plants. The taxonomic and feeding characteristics of a meiobenthic nematode assemblage from Ghar El Melh lagoon (Tunisia) were used to achieve this goal. Nematode assemblages were exposed for 30 days to untreated wastewater (UW) obtained from the sewage treatment plant of Sidi Ahmed (Tunisia) and three mixtures with treated wastewater (TW33 = 33%, TW66 = 66%, and TW100 = 100%). Concerning the nematode abundance, the exposure to either treated wastewater (TW33-100) or untreated wastewater (UW) had no significant effect. In contrast, Shannon-Wiener index and Pielou's Evenness were clearly reduced by contamination with both types of wastewater, with a more pronounced negative impact prior to treatment in the sewage plant. The multivariate analyzes revealed a change in the taxonomic composition of the nematofauna in response to the contamination by untreated or treated wastewater. The relative abundances of species in wastewater replicates compared to controls reflected this taxonomic restructuring. Finally, Ascolaimus elongatus, Terschellingia communis, and Kraspedonema octogoniata were less represented in all experimentally treated units and could be considered as 'sensitive taxa to wastewater'. While, Paracomesoma dubium, appears to be a 'tolerant and/or opportunistic' species, showing increased relative abundances under all wastewater treatments.

The individual and combined effects of cadmium, polyvinyl chloride (PVC) microplastics and their polyalkylamines modified forms on meiobenthic features in a microcosm

A microcosm experiment was carried out to study the ecotoxicity and interactions between heavy metals and polyvinyl chloride microplastics. Fifteen treatments were tested and results were examined after one month. In details, this work aims to study the ecotoxicological effects of cadmium (10 and 20 mg kg^-1 Dry Weight DW), polyvinyl chloride (PVC) and its modified forms; PVC-DETA (PD) and PVC-TETA (PT) (20 and 40 mg kg^-1 DW), separately and in mixtures, on meiofauna from Bizerte lagoon (NE Tunisia) with focus on nematode features. The results obtained showed that individual treatments were toxic for meiofauna and particularly for free-living nematodes. No clear trends characterized the numerical responses but significant reductions were observed for diversity indices. Moreover, the binary combinations of contaminants have a lesser toxic effect compared to their individual effects. This effect could be related to the high-capacity chelating ability of PVC and its polymers against cadmium.

Ecotoxic response of nematodes to ivermectin, a potential anti-COVID-19 drug treatment

At the end of March 2020, ivermectin was confirmed as a drug for COVID-19 treatment. A significant amount of ivermectin could deposit into sediments of the semi-closed Mediterranean Sea, where three European COVID-19 epicenters are located: Italy, Spain, and France. Meiobenthic nematodes were exposed to three ivermectin doses (1.8 ng.g^-1, 9 ng.g^-1, and 18 ng.g^-1) for 10 days. Ivermectin caused a great reduction in abundance. However, the diversity indices decreased only at high doses. Ivermectin disadvantaged the 1B-Cr-Id functional type (non-selective deposit feeders and nematodes with circular or indistinct amphids) and benefited the 2A-REL-Sp type (epistrate feeders and nematodes with rounded or elongated loop amphids). Thus, Trophic Diversity and Amphideal Diversity index values increased with sedimentary ivermectin enrichment. Large amphideal foveas were more efficient for 2A-REL-Sp nematodes to avoid ivermectin. The responses of the functional type 2A-REL-Sp and corresponding taxa predict post-COVID-19 environmental concerns and the bioaccumulation of ivermectin in seafoods.

Effects of Mercury (Hg) on Soil Nematodes: A Microcosm Approach

Mercury (Hg), one of the most toxic heavy metals, is commonly used in the gold extraction process in small-scale mining operations in many countries. Our previous field work on the impact of mining on soil nematode assemblages in a small-scale mining area in Sibutad, the Philippines, revealed no significant negative effects despite sometimes strongly elevated Hg concentrations. Using a microcosm approach, we now applied similar Hg concentrations as commonly found in these field sites (2.5, 5, and 10 mg/kg Hg) and determined their impact on nematode assemblages from a different soil with different physicochemical soil attributes. Our results demonstrate (a) limited "bottling" effects (incubation effects) after a 45-day incubation period: a nematode abundance decrease of up to 37%, but absence of significant differences in diversity and nematode assemblage composition; (b) that total nematode abundance already decreased at Hg concentrations (2.5 mg/kg), which did not yield significant impacts on other nematode assemblage descriptors, such as assemblage composition and different diversity indices; and (c) that the Hg concentrations found in the Sibutad field sites can be detrimental to soil nematode assemblages. The discrepancy between our microcosm and the field-based results is probably related to differences in physicochemical soil attributes (e.g., OM contents, soil pH), which suggests that nematode-based environmental assessments should be interpreted in a context-dependent manner.

The response of cultured meiofaunal and benthic foraminiferal communities to lead exposure: Results from mesocosm experiments

Lead (Pb) is regarded as a highly toxic element that poses a serious threat to biota. A mesocosm experiment was performed to assess the influence of Pb on meiofaunal (metazoans within 45-500 μm) and benthic foraminiferal (protozoan) communities. To this end, sediments bearing such communities were incubated in mesocosms, exposed to different levels of Pb in seawater, and monitored for up to 8 wk. Concentrations of Pb <1 ppm in water did not promote a significant increase of this metal in sediments. Relatively high concentrations of Pb seemed to affect meiofaunal and benthic foraminiferal communities by reducing their richness or diversity, and the abundance of the most sensitive taxa. The mesocosm approach can be considered an effective method to document the responses of meiofaunal and benthic foraminiferal communities to various kinds and concentrations of pollutants over time. This approach allows the evaluation of dose-response relationships, validates the outcomes of field studies, and possibly confirms the sediment quality guidelines and thresholds. Environ Toxicol Chem 2018;37:2439-2447. © 2018 SETAC.

Trophic restructuring (Wieser 1953) of free-living nematode in marine sediment experimentally enriched to increasing doses of pharmaceutical penicillin G

Trophic structure of free living nematode from Bizerte lagoon was tested by a microcosmic study after 30 days of exposure with 5 increasing doses of pharmaceutical penicillin G (D1: 3 mg L(-1), D2: 30 mg L(-1), D3: 300 mg L(-1), D4: 600 mg L(-1), D5: 700 mg L(-1)). Results showed significant differences between nematode assemblages from undisturbed controls and those from penicillin G treatments. Selective deposit-feeders (1A) or nonselective deposit-feeders (1B), very abundant in the control microcosm, were significantly affected and their dominance declined significantly. Epistrate feeders (2A) were significantly gradual increase for all microcosms treated with penicillin G, appeared to be more tolerant to the antibiotic and to take advantage of the growing scarcity of other trophic groups. Compared to the control microcosms, omnivorous-carnivorous (2B) was found to be higher in all treated microcosms, with the exception of those treated with D5. Trophic index (Σθ(2)) was significantly reduced in all microcosms treated whereas trophic ratio 1B/2A appears to be insignificant.

Critical review of mercury sediment quality values for the protection of benthic invertebrates

Sediment quality values (SQV) are commonly used-and misused-to characterize the need for investigation, understand causes of observed effects, and derive management strategies to protect benthic invertebrates from direct toxic effects. The authors compiled more than 40 SQVs for mercury, nearly all of which are "co-occurrence" SQVs derived from databases of paired chemistry and benthic invertebrate effects data obtained from field-collected sediment. Co-occurrence SQVs are not derived in a manner that reflects cause-effect, concentration-response relationships for individual chemicals such as mercury, because multiple potential stressors often co-occur in the data sets used to derive SQVs. The authors assembled alternative data to characterize mercury-specific effect thresholds, including results of 7 laboratory studies with mercury-spiked sediments and 23 studies at mercury-contaminated sites (e.g., chloralkali facilities, mercury mines). The median (± interquartile range) co-occurrence SQVs associated with a lack of effects (0.16 mg/kg [0.13-0.20 mg/kg]) or a potential for effects (0.88 mg/kg [0.50-1.4 mg/kg]) were orders of magnitude lower than no-observed-effect concentrations reported in mercury-spiked toxicity studies (3.3 mg/kg [1.1-9.4 mg/kg]) and mercury site investigations (22 mg/kg [3.8-66 mg/kg]). Additionally, there was a high degree of overlap between co-occurrence SQVs and background mercury levels. Although SQVs are appropriate only for initial screening, they are commonly misused for characterizing or managing risks at mercury-contaminated sites. Spiked sediment and site data provide more appropriate and useful alternative information for characterization and management purposes. Further research is recommended to refine mercury effect thresholds for sediment that address the bioavailability and causal effects of mercury exposure. Environ Toxicol Chem 2015;34:6-21. © 2014 SETAC.

Impacts of bioremediation schemes for the mitigation of a low-dose anthracene contamination on free-living marine benthic nematodes

A microcosm experiment was used to examine (1) the effects of different bioremediation schemes on degradation of anthracene and the structure of free-living marine nematodes in a lightly contaminated (4.5 μg g(-1)) sediment from Bizerte lagoon and (2) the responses of the nematode community upon an artificial spiking of a low dose anthracene (1 μg g(-1)). For that purpose sediment microcosms were incubated in laboratory for 40 days. Bioremediation techniques decreased the anthracene contamination, and interestingly, biodegradation were more efficient when anthracene was artificial supplied into the sediment suggesting that the addition of bioavailable anthracene stimulated the bacterial community to adjust towards a PAH-degrading community. Spiking with this low dose of anthracene provoked significant changes in the nematode community structure and abundance, with the elimination of specific species such as Mesacanthion diplechma, the decrease of the dominant species Oncholaimus campylocercoides and the increase in abundance of opportunistic species such as Spirinia parasitifera. This would suggest a low tolerance of the nematode community despite the presence of a weak anthracene contamination in the sediment that could have allow dominance of an anthracene tolerant nematode species. Anthracene toxicity was alleviated in biostimulation treatments, leading to a strong increase in nematode abundance, concomitantly with changes in the nematode community structure; Prochromadorella neapolitana became the most abundant species.

A molecular-based approach for examining responses of eukaryotes in microcosms to contaminant-spiked estuarine sediments

Ecotoxicological information for most contaminants is limited to a small number of taxa, and these are generally restricted to comparatively hardy organisms that are readily extractable from test media and easily identifiable. Advances in DNA sequencing can now provide a comprehensive view of benthic invertebrate diversity. The authors applied 454 pyrosequencing to examine the responses of benthic communities in microcosms exposed to sediments with elevated concentrations of triclosan, the endpoint being eukaryl communities that have successfully vertically migrated through the manipulated sediments. The biological communities associated with the 3 treatments (control triclosan, low triclosan [14 mg/kg], and high triclosan [180 mg/kg]) clustered into 3 groups: control/low (n = 6 controls and 4 low), moderate (n = 2 low), and high (n = 5 high). One sample was discarded as an outlier. The most pronounced change as a response to triclosan was the loss of number of metazoan operational taxonomic units (OTUs), indicative of the control/low and moderate groups, with this being most evident in the range of taxa associated with the classes Chromadorea and Bivalvia and the phylum Kinorhyncha. The authors also describe a range of other taxa that aided discrimination between the groups; compare findings with traditionally obtained meio- and macrofaunal communities obtained from the same experiment; and illustrate some of the advantages and limitations associated with both the molecular and traditional approaches. The described approach illustrates the capacity for amplicon sequencing to provide ecologically relevant information that can be used to strengthen an understanding of how sedimentary communities respond to a range of environmental stressors.

An assessment of the impact of chromium-amended sediment on a marine nematode assemblage using microcosm bioassays

Microcosms were used to assess the impact of chromium on free-living marine nematodes. Nematodes were exposed to three chromium concentrations (500 ppm (dm, dry mass), 800 ppm (dm) and 1,300 ppm (dm)), and effects were examined after 4 weeks. Results showed significant differences between univariate measures of control nematodes and those from medium- and high-chromium microcosms. Most, decreased significantly with increasing level of chromium contamination. The medium-chromium treatment seems to be the minimal concentration that could has a negative effect on nematodes. Results from multivariate analyses demonstrated that responses of nematode species to chromium treatments were varied: Leptonemella aphanothecae was eliminated at all doses tested and seemed to be intolerant species to chromium; Daptonema normandicum and Sabatieria longisetosa which significantly increased at 500 ppm chromium (dm) appeared to be "opportunistic" species at this dose whereas the two Bathylaimus species (Bathylaimus capacosus and Bathylaimus tenuicaudatus) which increased at all the doses tested seemed to be "chromium resistant". As we think such "opportunistic" and "resistant" species could be used as sensitive indicators of unsafe marine food. The use of microcosms has allowed the effects of the chromium on nematodes to be assessed individually, which was not possible in the field.