Frameworks commonly used in trace metal ecotoxicology (e.g., biotic ligand model (BLM) and tissue residue approach (TRA)) are based on the established link between uptake, accumulation and toxicity, but similar relationships remain unverified for metal-containing nanoparticles (NPs). The present study aimed to (i) characterize the bioaccumulation dynamics of PVP-, PEG-, and citrate-AgNPs, in comparison to dissolved Ag, in Daphnia magna and Lumbriculus variegatus; and (ii) investigate whether parameters of bioavailability and accumulation predict acute toxicity. In both species, uptake rate constants for AgNPs were ∼ 2-10 times less than for dissolved Ag and showed significant rank order concordance with acute toxicity. Ag elimination by L. variegatus fitted a 1-compartment loss model, whereas elimination in D. magna was biphasic. The latter showed consistency with studies that reported daphnids ingesting NPs, whereas L. variegatus biodynamic parameters indicated that uptake and efflux were primarily determined by the bioavailability of dissolved Ag released by the AgNPs. Thus, principles of BLM and TRA frameworks are confounded by the feeding behavior of D. magna where the ingestion of AgNPs perturbs the relationship between tissue concentrations and acute toxicity, but such approaches are applicable when accumulation and acute toxicity are linked to dissolved concentrations. The uptake rate constant, as a parameter of bioavailability inclusive of all available pathways, could be a successful predictor of acute toxicity.

The United Nations' Sustainable Development Goals have been established to end poverty, protect the planet, and ensure prosperity for all. Delivery of the Sustainable Development Goals will require a healthy and productive environment. An understanding of the impacts of chemicals which can negatively impact environmental health is therefore essential to the delivery of the Sustainable Development Goals. However, current research on and regulation of chemicals in the environment tend to take a simplistic view and do not account for the complexity of the real world, which inhibits the way we manage chemicals. There is therefore an urgent need for a step change in the way we study and communicate the impacts and control of chemicals in the natural environment. To do this requires the major research questions to be identified so that resources are focused on questions that really matter. We present the findings of a horizon-scanning exercise to identify research priorities of the European environmental science community around chemicals in the environment. Using the key questions approach, we identified 22 questions of priority. These questions covered overarching questions about which chemicals we should be most concerned about and where, impacts of global megatrends, protection goals, and sustainability of chemicals; the development and parameterization of assessment and management frameworks; and mechanisms to maximize the impact of the research. The research questions identified provide a first-step in the path forward for the research, regulatory, and business communities to better assess and manage chemicals in the natural environment.

Environmental context. Nanoparticles may be passed from primary producers to predators higher up the food chain, but little is currently known about this transfer. We studied the accumulation dynamics of silver nanoparticles by algae, and then from algae to zooplankton. Using the biodynamic approach, we reconstructed the accumulation process to show that diet is the primary route of uptake for silver nanoparticles.Abstract. This study investigated the bioaccumulation dynamics of silver nanoparticles (Ag NPs) with different coatings (polyvinyl pyrrolidone, polyethylene glycol and citrate), in comparison with aqueous Ag (added as AgNO 3 ), in a simplified freshwater food chain comprising the green alga Chlorella vulgaris and the crustacean Daphnia magna. Algal uptake rate constants (k u ) and membrane transport characteristics (binding site density, transporter affinity and strength of binding) were determined after exposing algae to a range of either aqueous Ag or Ag NP concentrations. In general, higher k u values were related to higher toxicity in the algae. Transmission electron microscopy images were used to investigate the internalisation of Ag NPs in algal cells following exposure to low concentrations for 72 h (mimicking inhibition tests) or high concentrations for 4 h (mimicking preparation for daphnia dietary exposure). Ag NPs were only visualised in algal cells exposed to high Ag NP concentrations. To establish D. magna biodynamic model constants, organisms were fed Ag-contaminated algae and depurated for 96 h. Assimilation efficiencies ranged from 10 to 25 % and the elimination of accumulated Ag followed a two-compartmental model, indicating lower loss rate constants for polyvinyl pyrrolidone-, and polyethylene glycol-coated Ag NPs. Biodynamic model results revealed that in most cases, food is the dominant pathway of Ag uptake in D. magna. Despite the predicted low steady-state body burdens in D. magna, dietary uptake of Ag was possible from aqueous and particulate forms of Ag.

Despite the rapid ongoing expansion in the use of nanomaterials, we still know little about their biological interaction and biodistribution within the human body. If medically relevant nanoparticles can cross specific cell barriers they may disseminate through the body beyond the original target and may reach particularly sensitive areas such as the foetus. This study utilised an in vitro barrier model of the placenta to explore toxicity, uptake and transport of iron oxide and silica nanoparticles. The findings indicate that these nanoparticles can transfer extensively across the placental barrier model but physico-chemical characteristics such as surface chemistry impact upon both uptake and transport. Iron oxide cytotoxicity was evident at lower doses and shorter exposure compared with silica and may be of clinical relevance. In vivo correlation of in vitro findings is essential but in vitro models may provide worst case-exposure estimates to help reduce the amount of testing required.

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