In the aquatic environment, microplastic (MP; <5 mm) is a cause of concern because of its persistence and potential adverse effects on biota. Studies of microlitter impacts are mostly based on virgin and spherical polymer particles as model MP. However, in pelagic and benthic environments, surfaces are always colonized by microorganisms forming so-called biofilms. The influence of such biofilms on the fate and potential effects of MP is not understood well. Here, we review the physical interactions of early microbial colonization on plastic surfaces and their reciprocal influence on the weathering processes and vertical transport as well as sorption and release of contaminants by MP. Possible ecological consequences of biofilm formation on MP, such as trophic transfer of MP particles and potential adverse effects of MP, are virtually unknown. However, evidence is accumulating that the biofilm−plastic interactions have the capacity to influence the fate and impacts of MP by modifying the physical properties of the particles. There is an urgent research need to better understand these interactions and increase the ecological relevance of current laboratory testing by simulating field conditions in which microbial life is a key driver of biogeochemical processes.

Plastic in the global oceans fulfills two of the three conditions for pollution to pose a planetary boundary threat because it is causing planetary-scale exposure that is not readily reversible. Plastic is a planetary boundary threat if it is having a currently unrecognized disruptive effect on a vital Earth system process. Discovering possible unknown effects is likely to be aided by achieving a fuller understanding of the environmental fate of plastic. Weathering of plastic generates microplastic, releases chemical additives, and likely also produces nanoplastic and chemical fragments cleaved from the polymer backbone. However, weathering of plastic in the marine environment is not well understood in terms of time scales for fragmentation and degradation, the evolution of particle morphology and properties, and hazards of the chemical mixture liberated by weathering. Biofilms that form and grow on plastic affect weathering, vertical transport, toxicity, and uptake of plastic by marine organisms and have been underinvestigated. Laboratory studies, field monitoring, and models of the impact of weathering on plastic debris are needed to reduce uncertainty in hazard and risk assessments for known and suspected adverse effects. However, scientists and decision makers must also recognize that plastic in the oceans may have unanticipated effects about which we are currently ignorant. Possible impacts that are currently unknown can be confronted by vigilant monitoring of plastic in the oceans and discovery-oriented research related to the possible effects of weathering plastic.

Carbon nanotubes (CNT) have numerous industrial applications and may be released to the environment. In the aquatic environment, pristine or functionalized CNT have different dispersion behavior, potentially leading to different risks of exposure along the water column. Data included in this review indicate that CNT do not cross biological barriers readily. When internalized, only a minimal fraction of CNT translocate into organism body compartments. The reported CNT toxicity depends on exposure conditions, model organism, CNT-type, dispersion state and concentration. In the ecotoxicological tests, the aquatic organisms were generally found to be more sensitive than terrestrial organisms. Invertebrates were more sensitive than vertebrates. Single-walled CNT were found to be more toxic than double-/multi-walled CNT. Generally, the effect concentrations documented in literature were above current modeled average environmental concentrations. Measurement data are needed for estimation of environmental no-effect concentrations. Future studies with benchmark materials are needed to generate comparable results. Studies have to include better characterization of the starting materials, of the dispersions and of the biological fate, to obtain better knowledge of the exposure/effect relationships.

BackgroundTungsten carbide nanoparticles are being explored for their use in the manufacture of hard metals. To develop nanoparticles for broad applications, potential risks to human health and the environment should be evaluated and taken into consideration.ObjectiveWe aimed to assess the toxicity of well-characterized tungsten carbide (WC) and cobaltdoped tungsten carbide (WC-Co) nanoparticle suspensions in an array of mammalian cells.MethodsWe examined acute toxicity of WC and of WC-Co (10% weight content Co) nanoparticles in different human cell lines (lung, skin, and colon) as well as in rat neuronal and glial cells (i.e., primary neuronal and astroglial cultures and the oligodendro cyte precursor cell line OLN-93). Furthermore, using electron microscopy, we assessed whether nanoparticles can be taken up by living cells. We chose these in vitro systems in order to evaluate for potential toxicity of the nanoparticles in different mammalian organs (i.e., lung, skin, intestine, and brain).ResultsChemical–physical characterization confirmed that WC as well as WC-Co nanoparticles with a mean particle size of 145 nm form stable suspensions in serum-containing cell culture media. WC nanoparticles were not acutely toxic to the studied cell lines. However, cytotoxicity became apparent when particles were doped with Co. The most sensitive were astrocytes and colon epithelial cells. Cytotoxicity of WC-Co nanoparticles was higher than expected based on the ionic Co content of the particles. Analysis by electron microscopy demonstrated presence of WC nanoparticles within mammalian cells.ConclusionsOur findings demonstrate that doping of WC nanoparticles with Co markedly increases their cytotoxic effect and that the presence of WC-Co in particulate form is essential to elicit this combinatorial effect.

Bringing together topic-related European Union (EU)-funded projects, the so-called “NanoSafety Cluster” aims at identifying key areas for further research on risk assessment procedures for nanomaterials (NM). The outcome of NanoSafety Cluster Working Group 10, this commentary presents a vision for concern-driven integrated approaches for the (eco-)toxicological testing and assessment (IATA) of NM. Such approaches should start out by determining concerns, i.e., specific information needs for a given NM based on realistic exposure scenarios. Recognised concerns can be addressed in a set of tiers using standardised protocols for NM preparation and testing. Tier 1 includes determining physico-chemical properties, non-testing (e.g., structure–activity relationships) and evaluating existing data. In tier 2, a limited set of in vitro and in vivo tests are performed that can either indicate that the risk of the specific concern is sufficiently known or indicate the need for further testing, including details for such testing. Ecotoxicological testing begins with representative test organisms followed by complex test systems. After each tier, it is evaluated whether the information gained permits assessing the safety of the NM so that further testing can be waived. By effectively exploiting all available information, IATA allow accelerating the risk assessment process and reducing testing costs and animal use (in line with the 3Rs principle implemented in EU Directive 2010/63/EU). Combining material properties, exposure, biokinetics and hazard data, information gained with IATA can be used to recognise groups of NM based upon similar modes of action. Grouping of substances in return should form integral part of the IATA themselves.

On behalf of the OECD Working Party on Manufactured Nanomaterials (WPMN) an expert meeting on ecotoxicology and environmental fate of nanomaterials (NMs) took place in January 2013 in Berlin. At this meeting experts from science, industry and regulatory bodies discussed the applicability of OECD test guidelines (TGs) for chemicals to nanomaterials. The objective was to discuss the current state of the relevant science and provide recommendations to the OECD WPMN on (1) the need for updating current OECD TGs and the need for developing new ones specific to nanomaterials; and (2) guidance needed for the appropriate and valid testing of environmental fate and ecotoxicity endpoints for NMs. Experts at the workshop agreed that the majority of the OECD TG for chemicals were generally applicable for the testing of NM, with the exception of TG 105 (water solubility) and 106 (adsorption-desorption). Additionally, the workshop also highlighted considerations when conducting OECD chemical TG on nanomaterials (e.g., sample preparation, dispersion, analysis, dosimetry and characterisation). These considerations will lead to the future development of proposals for new TG and guidance documents (GDs) to ensure that OECD TG give meaningful, repeatable, and accurate results when used for nanomaterials. This report provides a short overview of topics discussed during the meeting and the main outcomes. A more detailed report of the workshop will become available through the OECD, however, due to the urgency of having OECD TG relevant for nanomaterials, this brief report is being shared with the scientific community through this communication.

We described in 2017 how weathering plastic litter in the marine environment fulfils two of three criteria to impose a planetary boundary threat related to "chemical pollution and the release of novel entities": (1) planetary-scale exposure, which (2) is not readily reversible. Whether marine plastics meet the third criterion, (3) eliciting a disruptive impact on vital earth system processes, was uncertain. Since then, several important discoveries have been made to motivate a re-evaluation. A key issue is if weathering macroplastics, microplastics, nanoplastics, and their leachates have an inherently higher potential to elicit adverse effects than natural particles of the same size. We summarize novel findings related to weathering plastic in the context of the planetary boundary threat criteria that demonstrate (1) increasing exposure, (2) fate processes leading to poorly reversible pollution, and (3) (eco)toxicological hazards and their thresholds. We provide evidence that the third criterion could be fulfilled for weathering plastics in sensitive environments and therefore conclude that weathering plastics pose a planetary boundary threat. We suggest future research priorities to better understand (eco)toxicological hazards modulated by increasing exposure and continuous weathering processes, to better parametrize the planetary boundary threshold for plastic pollution.

The usage of engineered nanomaterials (NM) offers many novel products and applications with advanced features, but at the same time raises concerns with regard to potential adverse biological effects. Upon release and emission, NM may interact with chemicals in the environment, potentially leading to a co-exposure of organisms and the occurrence of mixture effects. A prominent idea is that NM may act as carriers of chemicals, facilitating and enhancing the entry of substances into cells or organisms, subsequently leading to an increased toxicity. In the literature, the term 'Trojan-horse effect' describes this hypothesis. The relevance of this mechanism for organisms is, however, unclear as yet. Here, a review has been performed to provide a more systematic picture on existing evidence. It includes 151 experimental studies investigating the exposure of various NM and chemical mixtures in ecotoxicological in vitro and in vivo model systems. The papers retrieved comprised studies investigating (i) uptake, (ii) toxicity and (iii) investigations considering both, changes in substance uptake and toxicity upon joint exposure of a chemical with an NM. A closer inspection of the studies demonstrated that the existing evidence for interference of NM-chemical mixture exposure with uptake and toxicity points into different directions compared to the original Trojan-horse hypothesis. We could discriminate at least 7 different categories to capture the evidence ranging from no changes in uptake and toxicity to an increase in uptake and toxicity upon mixture exposure. Concluding recommendations for the consideration of relevant processes are given, including a proposal for a nomenclature to describe NM-chemical mixture interactions in consistent terms.