Session Summaries from SETAC Barcelona
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- Aquatic Nanotoxicology: From Freshwater to Seawater—Overcoming the Difficulties of Standard Toxicity Tests and the Implications for Higher Tier Toxicity Testing
Boris Jovanovic, Ludwig Maximilian University and Julian Blasco, Spanish National Research Council
The purpose of this session was to present the latest advancement in the field of aquatic nanotoxicology. Many physicochemical parameters have different profiles from freshwater toward estuarine environment and seawater, effecting structure, reactivity and toxicity of nanoparticles. Thus, it is important to understand the evel of variability between observed toxic effects of nanomaterials toward aquatic organisms of both similar or different trophic levels and of similar or different habitats. One of the specific objectives of this session was to bring together the available information regarding nanoparticles effects on aquatic organisms across different salinity gradient. The additional focus of this session was on higher tier toxicity studies aiming at the population, community, or ecosystem level by employing microcosms, mesocosms, or in situ testing, and whether toxic effects are occurring at environmental relevant concentrations or not.
This session received a total of 43 platform and poster abstract submissions which was the highest rate of submissions among the six available nano-sessions. Twelve presentations were accepted as platforms and were delivered in the session with: eight presentations addressing toxicity of silver nanoparticles, two addressing toxicity of titanium dioxide nanoparticles, one investigating toxicity of organic pigment red, copper oxide, and carbon nanotubes nanoparticles, and finally one presenting data on immunotoxicity of plastic nanoparticles.
Five presentations deployed higher tiers in toxicity studies (focusing on the community or ecosystem level by using microcosm/mesocosm/in situ approach) in an effort to provide testing under more relevant environmental conditions.
The session was very well attended and in the case of several presentations there were no empty seats in the room while additional public was standing in the back of the room. The key points for the twelve presentations are included bellow:
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- Aggregation of silver and titanium dioxide nanoparticles is much greater in the environment with a higher salinity than in the environment of lower salinity.
- Overall results showed a successful transfer of silver nanoparticles through the food web.
- In general ionic form of silver was more toxic than silver nanoparticles.
- Fish chronically exposed to environmentally relevant concentrations of silver nanoparticles added to a whole lake ecosystem accumulated silver in liver and muscle tissues.
- Environmentally relevant concentrations of TiO2 nanoparticles in a chronic outdoor mesocosm study did not effect the overall function and productivity of the freshwater ecosystem although TiO2 displayed an effect on certain species and physicochemical parameters of water.
- Fish Model Species in Environmental Toxicology
Jessica Legradi, Institute of Environmental Studies, VU University; Juliette Legler, Institute of Environmental Studies VU University and Eduarda Santos, Biosciences, University of Exeter
Fish models are used commonly in ecotoxicity testing to investigate the impact of chemicals on the aquatic environment. A range of OECD guidelines are available, which use different fish species and target different toxicological endpoints. These studies, however, are limited to relatively few species, but fish offer far greater utility for research, spanning basic developmental biology, neurobiology, endocrinology and immunology. The small size of some available fish species including the zebrafish (Danio rerio) or medaka (Oryzias latipes) and their robust nature makes them ideally suited for application in automated high throughput screens. Furthermore, early life stages of these species offer all the key attributes of a complex in vivo system (e.g. including metabolism), as well as attributes of in vitro assays, as tests can be carried out in multiwell plates formats with small sample volumes and run in comparatively short periods of time. These attributes make them well suited for ecotox testing of environmental extracts and in effect directed analysis (EDA) to detect unknown contaminants in environmental samples. Research on fish over the last decade has been greatly facilitated by the availability of sequenced genomes, which are available for over 12 species with more pending. This facility, together with advances in genetic and epigenetic studies, including gene knockout and transgenesis technologies, is greatly facilitating understanding of the molecular mechanisms of toxicology, and thereby helping to study and define adverse outcome pathways (AOPs).
The fish models session attracted 53 platform and poster presentations discussing the use of a wide range of fish models to address environmental toxicology questions. Currently, the zebrafish is the most widely used fish model species in laboratory studies because of its practical advantages to conduct toxicological experiments. These include its well characterized development and reproduction, its rapid life cycle, and availability of genomics and genetic resources. This was reflected in the large proportion of presentations where zebrafish was used as a model organism, both during this session and across the meeting. However, zebrafish may not be the most representative model for fish species commonly found in the aquatic environments of Europe and across the globe. Therefore, there is a need to expand environmental toxicology studies to other, more representative fish model systems. Presentations on the utility of the three-spined stickleback, and other environmentally relevant species, provided ways forward to bridge the gap between laboratory models and environmental reality. Data utilizing state-of-the-art technologies on genomics, proteomics, metabolomics and epigenetics were presented, advancing our understanding of mechanistic pathways of chemical toxicity.
The challenges of analyzing and interpreting these datasets within the context of realistic environmental conditions is considerable but, in the long term, it will facilitate a better understanding of the mechanistic pathways resulting in adverse impacts at the individual and population levels. It was interesting to see that fish toxicology studies are moving forward from testing individual compounds within simple dose-response exposure scenarios, to more complex experiments that better represent the reality of environmental exposures. Influences of environmental factors, including changes in oxygen concentrations, were shown to alter the toxicological responses to a metal. The complexity of environmental mixtures and their effects are well known but generally poorly considered in laboratory studies. Examples of the complexity of the responses to environmental mixtures included datasets demonstrating that two major components of the contraceptive pill acted antagonistically and suppressed the endocrine disrupting potential of the individual compounds in three-spined sticklebacks. In-depth analysis using temporal and tissue-specific high resolution approaches provided new insights on thyroid disruption, reactive oxygen species formation, and the Ah-receptor cascade. Passive dosing, mimicking more realistic environmental exposures to individual compounds and their mixtures was discussed, and its applicability to determine the toxicity of environmental samples (including soils) were shown. In addition, fish embryos were shown to successfully guide chemical detection and identification in an effect-directed analysis.
The outcomes of the session provide evidence for the wide use of the zebrafish as a model species, and their suitability to conduct high throughput toxicity screening, and mechanistic analysis of chemical effects, particularly during embryo development. There is a clear need to continue to develop other environmentally relevant fish models in order to better protect the fish populations in the natural environment.
Author information: Jessica Legradi, Jessica.Legradi@vu.nl
- Monitoring and Modeling-Based Approaches for Identification and Prioritization of Hazardous Emerging Pollutants in European Freshwater Resources
Werner Brack, UFZ Leipzig; Jos van Gils, DELTARES and Jaroslav Slobodnik, Environmental Institute
The variety of chemicals emitted to and found in the environment is continuously growing, with today about 90 million known chemicals registered in the CAS, and thousands of compounds that may be detected in environmental samples, many of them unknown. One of the major challenges in pollution research and the regulation of environmental quality is identifying and to prioritizing chemicals of concern that might require management and regulation. One major starting point for chemical prioritization is bringing together the chemicals that are produced, used and registered (e.g. under REACH) together with criteria on persistence, mobility, toxicity and modeling of fate, transport and risk. Complementary prioritization can be based on compounds detected in the environment, including transformation products and by-products of technical processes. The latter can be detected by chemical-analytical and effect-based screening tools and identified on a local scale with effect-directed analysis. This will help to answer the key question: Are we monitoring and assessing the right chemicals?
Eleven platform presentations and four poster spotlights were delivered in the session. The first talk given by Carvalho from JRC presented the current prioritization approach under the Water Framework Directive (WFD) as a starting point for discussions on new approaches. Complementary to WFD, REACH, the other major piece of regulation supporting the protection of water resources, was used by Neumann from German UBA to propose an assessment concept of persistent, mobile and toxic chemicals. This approach was complemented by Scheringer with a model to identify those organic chemicals with a potential for long-term environmental contamination. Toxic pressure assessment often relies on data-rich chemicals while Posthuma proposed a novel approach for a solutions-focused approach designed to address the spatio-temporal variability of contaminant mixture risks including data-poor compounds inspired by the Threshold of Toxicological Concern concept. Prioritization on a European scale is supported by an integrated model system delivered in EU FP7 project SOLUTIONS from emissions via fate and transport up to human and ecological risk assessment presented by van Gils. This approach has been tested and validated for PFOS and PFOA in the Danube River catchment, where Lindim identified major sources of these compounds. Registered chemicals under REACH and other regulations were analytically screened for in various water types by Sjerps from KWR, while Tollefsen promoted a bioassay-assisted identification and prioritization of toxicity drivers. These tools help include the whole mixture of knowns and unknowns into environmental assessment and understand which fraction of observed effects can be actually explained by known chemicals. Escher demonstrated that this fraction can be rather small for more integrative endpoints such as oxidative stress. On a more local scale, toxicant identification can be supported by EDA based on in vitro assays. A new, miniaturized version of AMES test on 384 well plates for EDA was presented by Zwart. Majewski showed that transformation products, for example from pharmaceuticals, may retain toxic properties of the parent solution and contribute to overall effects.
The session was very well attended in a room that hardly was able to host the huge audience during many presentations. We saw that big challenges such as the ever growing number of anthropogenic chemicals in the environment potentially impacting on ecosystems and human health also promotes fireworks of innovative ideas to prioritize chemicals and to reduce complexity without a priori excluding data poor and unknown chemicals. This session was a big step towards a consistent set of monitoring and modeling-based prioritization concepts and addressing major knowledge gaps and uncertainty. Since the subject is a key issue, and currently significant progress is being made in projects like SOLUTIONS and beyond, this dialogue will be continued in upcoming SETAC meetings.
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- Periphyton Ecology and Ecotoxicology—How Much Complexity and Reproducibility are Required to Connect Both Perspectives?
Alexandra Kroll, Eawag, Dübendorf, CH; Marianne Matzke, CEH, Wallingford; Helena Guasch, University of Girona, Girona and Mechthild Schmitt-Jansen, UFZ, Leipzig, D
The aim of this session was to bring together periphyton ecology and ecotoxicology to see what both disciplines can learn from each other and what is necessary to combine in order to better understand community processes and toxicity mechanisms associated with ecosystem impairment.
Periphyton is an essential component of stream ecosystems, shows dynamic responses to stressors, and is commonly used as a community model to analyze and indicate effects of water quality and pollutants. Periphyton ecology is based on the community structure, uses species identification, fingerprinting and sequencing to describe its statues, and recent developments focus on ecosystem functions and functional traits. Periphyton ecology is mostly studied in field approaches leading to a lower reproducibility. On the other hand, periphyton ecotoxicology uses model ecosystems to reduce complexity enabling a higher reproducibility. Typically, periphyton ecotoxicology employs classical descriptors of functions such as biomass, effects on photosynthesis, or the metabolic profile. Recent developments include extracellular chemistry or the 3D structure of the community.
From all the presentations it became obvious that molecular techniques (e.g. sequencing, fingerprinting) are now well established but always used alongside of classical endpoints such as biomass, photosynthesis (e.g. determination of lead pigments) or species composition (by microscopy). Also the concept of pollution-induced community tolerance (PICT) is applied more widely. It is accepted that we need to introduce more ecological realism into risk assessment strategies for chemical stressors and that this can only be done by applying community models and acknowledging the fact that chemicals rarely act alone but mostly in combination with other stressors. On the other hand, reproducibility and controlled studies are needed to infer mechanisms of action.
We asked the presenters to answer the question from their point of view how much complexity and reproducibility is needed to connect both perspectives – periphyton ecology and ecotoxicology and the main messages can be summarized as follows:
- Toxicological observations should be put into a multi-stressor context (chemical, temperature, pH) and various temporal/spatial scales should be used.
- Chemical and physical parameters have to be measured and documented to make complex settings comparable.
- A high complexity is needed to understand effects of chemicals on ecosystems but that this complexity is difficult to reproduce. The general danger is that too much complexity limits the understanding of effects. However periphyton might be the perfect tool to elucidate the underlying processes as it is a ‘relatively simple’ model responding in short times and is linked to basic and important ecosystem functions and processes.
- These processes are the intersection linking periphyton composition, communities and ambient environments when being under pollutant stress.
- It is important to determine global patterns of response and to cover a wider range of case studies to account for spatio-temporal variability in biofilms.
Asking the audience (by distributing blank cards to be filled) and the presenters for their opinions on the posed questions was a great success in the chairs’ eyes as it stimulated an overall discussion. We intend to keep this scheme for the next session to be submitted and will include the topic in the upcoming open periphyton workshop in spring 2016.
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