Distinct embryotoxic effects of lithium appeared in a new assessment model of the sea urchin: the whole embryo assay and the blastomere culture assay

Lithium: A review on concentrations and impacts in marine and coastal systems

The Lithium (Li) industry has been expanding worldwide, over the last decades, and projections expect an increasing demand for its production in the coming years. It has been identified as an emerging pollutant and it occurs widely in aquatic environments, raising concern about its effects on ecosystems. Besides the increasing research on this topic, there is still limited understanding and discussion on the marine and coastal implications of Li occurrence. The present review aims to fill these knowledge gaps by analysing the literature concerning Li occurrence and its effects on marine and coastal ecosystems, including transition areas. Since 1960, the number of publications has increased, especially over the last decade, and available information has reported Li in water and sediments of these areas, while few studies investigated Li in tissues of biota. Among all the studied ecosystems, Chile reported one of the highest Li concentrations. Regarding the adverse effects of Li in aquatic organisms, Bacillariophyceae, Scyphozoa, Bivalvia, Gastropoda, Cephalopoda, Polychaeta, Malacostraca, Echinoidea and Actinopteri were the studied taxonomic classes, and development inhibition, malformations, cellular and metabolic alterations, and behaviour changes were some of the observed impacts. This review might be particularly important in the mitigation of Li pollution as well as in the implementation of new directives and thresholds, as it highlights the impacts of Li and the urgent need to address new solutions and alternatives, meeting the Agenda 2030 for sustainable development.

How will different scenarios of rising seawater temperature alter the response of marine species to lithium?

Marine ecosystems are suffering from the gradual rise in temperature due to climate change. Warming scenarios and the intensification of extreme climate events, such as marine heatwaves (MHWs), have been negatively affecting marine organisms. In addition, they are also threatened by anthropogenic pollution. Lithium (Li) is an emerging pollutant that has become a major concern due to its increasing use in a variety of applications. Understanding its influence on marine environments in combination with warming scenarios is crucial, as very little is known about its impact on marine organisms, especially when also considering the increasingly concerning impacts of climate change. With this in mind, this research aimed to assess how different scenarios of increasing temperature may affect the response of Mytilus galloprovincialis to Li. Mussels bioaccumulation levels, as well as physiological and biochemical biomarkers were analyzed after 28 days of exposure to Li under different temperature scenarios (control - 17 °C; warming - 21 °C and marine heatwave - MHW). The results indicate that mussels accumulated Li, independently of the temperature scenario. The respiration rate was higher in contaminated mussels than in the non-contaminated ones, with no differences among temperature scenarios. Furthermore, the metabolic rate decreased in non-contaminated mussels exposed to 21 °C and MHW, while mussels exposed to the combination of Li and MHW presented the highest metabolic rate. The mussels exposed to MHW and Li evidenced the highest cellular damage but Li was not neurotoxic in M. galloprovincialis. This study highlighted that MHW + Li was the most stressful condition, inducing clear negative effects in this species that can impair the growth and reproduction of an entire population. In general, the presented results highlight the importance of future studies in which it is necessary to combine the effects of pollutants and climate change scenarios, namely extreme weather events such as MHWs.

The impact of temperature on lithium toxicity in the gastropod Tritia neritea

The most important use of lithium (Li) is in rechargeable batteries. The growing use of Li, incorrect disposal of Li-based applications, and inefficient recycling strategies for their elimination will result in the release of this metal into the aquatic systems. Alongside with the impacts caused by pollutants, organisms in coastal ecosystems are also facing environmental changes as those related with climate change scenarios, namely, seawater temperature rise. In this context, the present study aimed to evaluate the influence of temperature on Li toxicity, using the Nassariid gastropod Tritia neritea as model species. Metabolism and oxidative stress related biomarkers were evaluated after a 28-day exposure period. The results demonstrated that temperature enhanced the toxic impacts of Li, most probably due to snail increased sensitivity when under warming conditions. As a consequence of inefficient antioxidant and biotransformation capacity, lipid peroxidation was observed in Li-contaminated snails at 21 ºC, demonstrating a significant interaction between both factors. Regarding snails' metabolic capacity, Li did not affect snails, but a clear decrease on their metabolism was observed at increased temperature (with or without Li) which may limit snail defense capacity. Overall, the present findings demonstrated the impacts derived from Li towards marine intertidal gastropods, evidencing enhanced threats under predicted warming conditions. Considering the role of T. neritea in the ecosystem functioning, impacts on this species may greatly affect other populations and eventually the entire community.

Large-scale survey of lithium concentrations in marine organisms

Trace metals such as Cu, Hg, and Zn have been widely investigated in marine ecotoxicological studies considering their bioaccumulation, transfer along trophic webs, and the risks they pose to ecosystems and human health. Comparatively, Li has received little attention, although this element is increasingly used in the high-tech, ceramics/glass, and medication industries. Here, we report Li concentrations in more than 400 samples, including whole organisms and different organs of bivalves, cephalopods, crustaceans, and fish. We investigated species from three contrasting biogeographic areas, i.e. temperate (Bay of Biscay, northeast Atlantic Ocean), tropical (New Caledonia, Pacific Ocean), and subpolar climates (Kerguelen Islands, southern Indian Ocean), among diverse trophic groups (filter-feeders to meso-predators) and habitats (benthic, demersal, and pelagic). Although Li is homogeneously distributed in the ocean (at 0.18 μg/mL), Li concentrations in soft tissues vary greatly, from 0.01 to 1.20 μg/g dry weight. Multiple correspondence analyses reveal two clusters of high and low Li concentrations. Li distributions in marine organisms appear to be mostly geographically independent, though our results highlight a temperature dependency in fish muscles. Li is consistently bio-reduced through the trophic webs, with filter-feeders showing the highest concentrations and predatory fish the lowest. Strong variations are observed among organs, consistent with the biochemical similarity between Na and Li during transport in the brain and in osmoregulatory organs. Fish gills and kidneys show relatively high Li concentrations (0.26 and 0.15 μg/g, respectively) and fish brains show a large range of Li contents (up to 0.34 μg/g), whereas fish liver and muscles are Li depleted (0.07 ± 0.03 and 0.06 ± 0.08 μg/g, respectively). Altogether, these results provide the first exhaustive baseline for future Li ecotoxicology studies in marine coastal environments.

Long-term preservation of echinoderm sperm under non-cryo condition for ecotoxicological bioassay

The preservation of sea urchin gametes was examined to make them more convenient material for research and education, especially on the embryology and ecotoxicology field. The possibility of egg preservation for enough period, two weeks to one month, were reported (Epel et al., 2004; Kiyomoto et al., 2014). The sperm storage is usually done without seawater (dry sperm) for several days. This storage period is lengthened by the addition of antibiotics up to 10 days (Hata, 1998). To maximize the preserved period, we examined the dilution or replacement of seminal plasma with seawater containing antibiotics. Because the activation of sperm is induced by dilution, the condition to inhibit flagella motility was also investigated. Neither high potassium nor low pH improved the period of sperm preservation. The dilution of dry sperm around 100 times with normal seawater containing antibiotics was enough to keep the motility and fertilization ability for longer period, where sperm motility was prevented possibly by the effect of carbon dioxide.

Diatom-derived oxylipins induce cell death in sea urchin embryos activating caspase-8 and caspase 3/7

Diatoms are an important class of unicellular algae that produce bioactive secondary metabolites with cytotoxic activity collectively termed oxylipins, including polyunsaturated aldehydes (PUAs), hydroxyacids (HEPEs), oxo-acids and epoxyalcohols. Previous results showed that at higher concentrations, the PUA decadienal induced apoptosis on copepods and sea urchin embryos via caspase-3 activation; at lower concentrations decadienal affected the expression levels of the caspase-8 gene in embryos of the sea urchin Paracentrotus lividus. In the present work, we studied the effects of other common oxylipins produced by diatoms: two PUAs (heptadienal and octadienal) and four hydroxyacids (5-, 9- 11- and 15-HEPE) on P. lividus cell death and caspase activities. Our results showed that (i) at higher concentrations PUAs and HEPEs induced apoptosis in sea urchin embryos, detected by microscopic observation and through the activation of caspase-3/7 and caspase-8 measured by luminescent assays; (ii) at low concentrations, PUAs and HEPEs affected the expression levels of caspase-8 and caspase-3/7 (isolated for the first time here in P. lividus) genes, detected by Real Time qPCR. These findings have interesting implications from the ecological point of view, given the importance of diatom blooms in nutrient-rich aquatic environments.

Development of a new integrative toxicity index based on an improvement of the sea urchin embryo toxicity test

The sea urchin embryo toxicity test is classically used to assess the noxious effects of contaminated marine waters and sediments. In Italian guidelines on quality of dredged sediments, the standard toxicity criteria used for this assay are based on a single endpoint at 48 hours of development, corresponding to the pluteus stage. Different typologies of abnormalities, including those which occur at earlier stages, are not categorized, thus preventing the evaluation of the actual teratogenic hazards. A new integrative toxicity index has been developed in this study based on the analysis of two developmental stages, at 24 and 48h post-fertilization, and the differentiation between development delays and germ layers impairments: the new toxicity index is calculated by integrating the frequency of abnormal embryos with the severity of such abnormalities. When tested on dredged sediments, the evaluation of increasing levels of toxicity affecting embryonic outcomes enhanced the capability to discriminate different samples, appearing particularly relevant to validate the sea urchin embryo toxicity assay, and supporting its utility in practical applications such as the sediments classification in harbor areas.

Preserved echinoderm gametes as a useful and ready-to-use bioassay material

Marine animals, and sea urchin species in particular, have several advantages for use in environmental research. However, the spawned eggs of the sea urchin quickly lose fertility, although the fertile period can be lengthened by the addition of antibiotics to the sea water (Epel et al., 2004). We evaluated five species of Japanese sea urchin and the gametes of Hemicentrotus pulcherrimus could be maintained for 2 weeks or more at low temperature with the addition of antibiotics to sea water. We also demonstrated the practicality of shipping these preserved gametes as experimental material for universities and schools to use immediately for bioassays of physical and chemical impacts on the marine environment.

Defensome against toxic diatom aldehydes in the sea urchin Paracentrotus lividus

Many diatom species produce polyunsaturated aldehydes, such as decadienal, which compromise embryonic and larval development in benthic organisms. Here newly fertilized Paracentrotus lividus sea urchins were exposed to low concentration of decadienal and the expression levels of sixteen genes, implicated in a broad range of functional responses, were followed by Real Time qPCR in order to identify potential decadienal targets. We show that at low decadienal concentrations the sea urchin Paracentrotus lividus places in motion different classes of genes to defend itself against this toxic aldehyde, activating hsp60 and two proteases, hat and BP10, at the blastula stage and hsp56 and several other genes (14-3-3ε, p38 MAPK, MTase, and GS) at the prism stage. At this latter stage all genes involved in skeletogenesis (Nec, uni, SM50 and SM30) were also down-expressed, following developmental abnormalities that mainly affected skeleton morphogenesis. Moreover, sea urchin embryos treated with increasing concentrations of decadienal revealed a dose-dependent response of activated target genes. Finally, we suggest that this orchestrated defense system against decadienal represents part of the chemical defensome of P. lividus affording protection from environmental toxicants.

Stress response gene activation protects sea urchin embryos exposed to X-rays

We used Paracentrotus lividus sea urchin embryos, a well-established model in developmental biology and ecotoxicology, for investigation on stress/anti-apoptotic protein expression elicited in response to harmful ionizing radiation, such as X-rays. We evaluated the acute effects of a high-dose exposure (5 Gy) on P. lividus analyzing by Western blotting the accumulation levels of HSP60, HSP70, BAG3 and a putative p63 at 24 and 48 h after irradiation. We found an increase in the HSP70, BAG3, and p63 protein levels only 48 h after irradiation, whereas no HSP60 increase was detected either at 24 or 48 h. Levels of the mRNA coding for HSP70 and p63 were also investigated by relative RT-PCR and were found to increase 24 h after irradiation, returning to their initial levels at 48 h. Results demonstrate the presence of an adaptive regulatory mechanism operating at the transcriptional level at 24 h, followed by a translational activation at 48 h post-irradiation. In conclusion, our findings confirm the sea urchin embryo as a sensible bioindicator of cell damage and we propose this model for studies on the protective pathways activated in response to X-rays. The novel result of the involvement of BAG3 and p63 in the response to X-rays, never tested so far in any other embryonic system, opens the way for their use as biomarkers of X-ray hazards.