Characterization, Fate and Effects of Nanomaterials 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 level 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 gradients. 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 on 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 number of submissions among the six available nano sessions. Twelve platform presentations were delivered, of which eight presentations addressed toxicity of silver nanoparticles; two addressed toxicity of titanium dioxide nanoparticles; one investigated toxicity of organic pigment red, copper oxide and carbon nanotubes nanoparticles; and one presented data on immunotoxicity of plastic nanoparticles.
Five presentations deployed higher tiers in toxicity studies (focusing on the community or ecosystem level by using a microcosm, mesocosm or in situ approach) in an effort to provide testing under more relevant environmental conditions.
The session was very well attended, and for several presentations it was standing room only. The key points for the twelve presentations are as follows:
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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 that were chronically exposed to environmentally relevant concentrations of silver nanoparticles in whole lake ecosystems 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
- Biophysical Interactions at the Bio-Nano Interface: Relevance for Aquatic Nanotoxicology
Ismael Rodea-Palomares and Francisca Fernández-Piñas (Autonomous University of Madrid)
The session focused on how Engineered NanoMaterials (ENMs) interact with cells and organisms, which are the basic mechanisms of this interaction and how this interaction influences the biological activity of the ENMs. Nanomaterials are a type of material with properties implying a multi-variable complexity, which may affect their toxicological potential if released to the environmental compartments. This complexity is related to their colloidal nature, which distinguishes them radically from dissolved chemicals, especially in the aquatic environment. A clear advance in systematization of the studies was evident in the presented works. Special emphasis was posed on the development of methods for the systematic study of the effects of some intrinsic (particle-specific) and extrinsic (externally driven) physicochemical properties on the bioactivity of the ENMs, such as colloidal stability, and its relationship with homo- and hetero-agglomeration, shape, surface charge and coatings. An important issue of discussion was uptake or internalization of ENMs, and if so, the intracellular fate and relationship with cell toxicity. In this regards, steps forward in the biodynamic modeling of ENMs distribution at the organism level have been achieved in simplified food web chains. In addition, some presentations dealt with further layers of complexity, and the effect of co-exposure of ENMs with other classes of pollutants was explored to test the so-called “Trojan horse” hypothesis. Namely, ENMs may interact or complex with other co-occurring contaminants and be indirectly toxic by enhancing the absorption or bioaccumulation of other pollutants. In addition, mixture effects of binary combinations of nanoparticles were addressed.
The session concluded that methods in aquatic nano-ecotoxicology are clearly reaching a stand-alone level of development, which allows future research to start to address and solve specific features of ENM’s fate and bioactivity in aquatic systems.
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- Challenges for Environmental Risk Assessment of Nanomaterials: Addressing Knowledge Gaps, Protection Goals and Regulatory Perspectives
Birgit Sokull-Kluettgen (JRC), Anu Kapanen (ECHA) and Annemette Palmqvist (Roskilde University)
The increasing use of nanomaterials (NMs) in consumer products leads to a growing concern about their safe use and possible impact on human health and the environment. This has led to a need to address the use of NMs in a regulatory context. Nanomaterials are currently regulated within a broad range of regulatory frameworks such as REACH, the Biocidal Products Regulation, the Cosmetic Products Regulation (within the EU) and other chemical control schemes (outside the EU), including provisions for risk and safety assessment. This session discussed the recent regulatory and scientific advances in regulatory risk assessment (RA) of engineered nanomaterials. The focus of the session was on linking scientific outcomes to regulatory needs. Five platform and 27 poster presentations addressed such diverse aspects of NM environmental risk assessment (ERA) as the adequacy of standard test guidelines to cover nano-specific behavior and effects; potential for development of categorization and read-across frameworks for NMs; general challenges and limitations to take into account for ecological risk assessment of NMs; as well as specific challenges for hazard assessment of NMs under the EU chemical regulation, REACH. The session highlighted the importance of including knowledge from and supporting activities of scientific, industry and NGO communities to ensure scientifically robust decision-making.
The evolution of risk assessment of manufactured nanomaterials over the past ten years was presented from a regulatory (Canadian) perspective. While ten years ago the assessment of nanomaterials was completely novel, and the application of the traditional risk assessment paradigm was questioned, recent developments such as the OECD Council Recommendation state that nanomaterials can be safely assessed under existing regulatory assessment frameworks if nano-specific properties are taken into consideration. More specifically, it was presented that national and international regulatory initiatives are moving towards more streamlined approaches supported by activities such as the OECD Working Party on Manufactured Nanomaterials (WPMN), focusing on publication of guidance documents (e.g., OECD Test Guidelines and guidance documents). It was also pointed out that categorization frameworks are necessary and appropriate for NMs in order to address ERA issues. In addition, it was concluded that knowledge of properties, as well as physical-chemical properties, determine NM behaviour. Factors such as the aggregation and agglomeration state are necessary to predict environmental impacts.
The applicability of the standard OECD Test Guidelines (TGs) on toxicity in aquatic and sediment organisms was further discussed based on results from a 2014 OECD workshop. While these TGs are generally adequate for testing NMs, they require additional guidance to improve consistency and repeatability of the results. The identified gaps in TGs derive mainly from the particulate or fibrous nature of NMs leading to agglomeration, settling, particle dissolution and transformations during exposure. Key limitation and the knowledge gaps of the current TGs identified were (1) the state of knowledge concerning NM behaviours in test systems, the variability and heterogeneity in these behaviors, and their relevance for hazard assessment, (2) limitations of methods and approaches for measuring and monitoring NM characteristics and exposure during ecotoxicity assays and (3) controlling the instability of the test material.
A presented strategy for grouping and read-across of NMs emphasized that a first step is to collect available and relevant information on the NM and all the different forms of the NM to be considered for grouping. Relevant physical–chemical parameters listed included chemical composition, surface characteristics (coating, functionalization, capping agent), impurities, particle size, surface area, water solubility, particle size and shape, surface charge and reactivity. It was stated that grouping should be supported by a hypothesis that describes the specific elements for the group, including elements such as unique behavior under specified conditions and time scales relevant to the ecotoxicological endpoint. If there is not sufficient data to support the grouping hypothesis, a tiered testing strategy was proposed. Such a tiered testing strategy could include testing of parameters affecting behavior in the environment (Tier 1) and ecotoxicity assessment (Tier 2).
The information in REACH registration dossiers regarding industrial chemicals in Europe serves as a basis for regulatory decision-making. The main challenges in regulatory risk assessment observed, when the information in the REACH registration dossiers for aquatic toxicity data was assessed, was demonstrated to relate to the lack of information or level of reporting of the available information. The majority of the challenges may be overcome with appropriate documentation of the sample characteristics, sample preparation and detailed test protocols. With support of the foreseen adoption of new or updated test guidelines or guidance documents on protocols for dispersion and dissolution and ecotoxicity test protocols, the quality of information in the regulatory decision-making is expected to improve.
Major data gaps and future needs for ERA of NMs as perceived by participants in a recent workshop (9 November 2014, Vancouver) were presented. These needs included:
- Development of protocols for routine measurement of NM concentrations in environmental samples
- Long-term effect studies with population relevant endpoints
- Studies on bioavailability, uptake and elimination kinetics
- Studies carried out under realistic release and exposure patterns
- A continued hypothesis-driven approach to test how NM characteristics affect fate and effects.
The presentation was concluded with 5 key messages:
- Uncertainties, challenges and limitations should be acknowledged in the ERA of NMs
- Test guidelines, as well as language and terminology, need to mature to embrace particle-specific complexities
- Data generation for RA should be directed by value of information analysis
- Guidelines must be developed to rank and select nano-tailored (non-standard) tests for inclusion in ERA
- Focus should be on publishing studies with no observed effects as well as studies showing effects of NMs
Poster spotlights gave a glimpse of the extensive poster exhibition related to RA of nanomaterials. Posters under the spotlight described how NMs are regulated under REACH, the GUIDEnano strategy for NM environmental hazard assessment along the life cycle, and the development of a decision support framework for sustainable nanotechnologies.
The session was well attended, and the presentations in general prompted interesting and relevant discussions among speakers and the audience, which could have easily continued beyond the time set for questions. It was interesting to discover that some key issues were repeated in several presentations and discussions, indicating that the same consensus has been reached independently in different working-groups and meetings. Some key take-home messages on the advances within ERA of NMs were:
- The risk assessment of NMs in a regulatory setting remains a scientific challenge for all stakeholders, and collaboration between individual stakeholders is essential to ensure the safe use of nanomaterials
- There are many scientific advances to support regulatory decision-making such as the development and adjustment of OECD TGs and other guidance documents to take potential nano-specific complexities into account
- Development of grouping and read-across strategies are important in light of the many different forms NMs on the market
- There is a need for harmonization of the approaches for characterization as well as guidance on minimum characterization of NMs necessary to be cost effective, based on scientific knowledge of how NM characteristics affect fate and effect
- Better documentation of experimental design, nanoparticle type and properties (e.g., shape, coating, size, and aggregation and agglomeration state) and potential modifications to standard test guidelines, as well as a focus on publishing both no-effect studies and studies with observed effects, is necessary to reduce uncertainties in ERA of NMs
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