FORURENS Nanoparticle Characterisation in Environmental Media: Linking exposure to effects

The main research focus of NanoCharm is characterisation of the physico-chemical form of nanoparticles in environmental media, with emphasis on the exposure part of dose-effect tests. Our central hypothesis was that the lack of data on chemical characterization of NP in environmental and exposure media is undermining the robustness of ecotoxicological studies. Without this knowledge, the effects of NP can be either under or overestimated, resulting in a lack of confidence in the scientific results. Work has included developing and testing characterisation protocols for environmental test media for c elegans (nematodes), algae and fish, including studies of changes in the toxicity of nanoparticles over time. By linking toxicity to media characterization, we were able to identify a nano-specific component to the toxicity for both c. elegans and algae. In addition, tests of changes in the response of c elegans following multigenerational exposure to both Ag nanoparticles and Ag ions, showed adaptation to Ag nanoparticles. Uptake and bioavailability studies using radiolabeled Ag, Ce and Sn have been carried out with fish and earthworms, and results indicated that diet can be a significant source of NP to fish. A variety of methods were used to characterise exposure, including electron microscopy, filtration and dynamic light scattering (DLS). The results demonstrated that the stability of NPs and ions in test media varied with concentration, but in a non-linear manner. Interestingly, the lower concentrations showed a higher stability, whilst aggregation and precipitation was enhanced at higher concentrations. These were linked for the first time with non-linear responses in ecotoxicity for different types of NPs (Zn, Ce, Ag, Ti). The results should improve the robustness and interpretation of NP toxicity studies.

The overall objective of NanoCharm was to improve the robustness of nanoparticle ecotoxicology by developing methods for the characterization of nanoparticles in environmental and test media. The key achivements of the project have been development and modification of methods for radioisotope labeling of Ag, Fe, Ce and Sn nanoparticles, as well as methods for particle characterization to study the behavior of nanoparticles in environmental toxicity test media. These methods have been used in a series of uptake and toxicological studies in c elegans, algae and fish, leading to new information on the impact of particle stability and transformation on bioavailability and toxicity of nanomaterials. Recognition of the importance of these methods led to participation of the research team in two EU projects (NanoRem and NanoReg), as well as contributed to two PhD thesis.

Despite the research initiatives taken during the past decade, there remains a considerable amount of uncertainty about the toxicity of nanoparticles (NPs) released into the environment. One of the major sources of uncertainty in ecotoxicological tests is the shortage of data on chemical characterization of NP in environmental and exposure media. Our central hypothesis is that this lack of knowledge is undermining the robustness of ecotoxicological studies. Without this information, the effects of NP can be either under or overestimated, resulting in a lack of confidence in the scientific results. The project proposes to address this issue through the development and application of methods and experimental protocols focused specifically on the detection and characterization of NP in test media. We will use three contrasting types of NPs - Ag, Fe and U and four recognised ecotox test systems - C elegans, earthworm (E fetida), daphnia and fish (salmonids). The selected NPs reflect a broad spectrum of chem ical properties, and will enable us to test a range of specific hypothesis. The first part of the work is concerned with modification and optimization of state of the art techniques to characterize the physico-chemical forms of NP in test media. These inc lude radiotracer techniques, field flow fractionation, TEM/SEM and synchrotron-based methods. The second part will investigate NP and conjugate ion stability and transformation kinetics in environmental media, with the aim of optimizing test media conditi ons for ecotoxicology effect tests. Finally, the applicability of the techniques will be demonstrated in focused, hypothesis based-studies to compare the bioavailability and effects of nanoparticles and ionic species in test organisms. The outputs of the project will be documentation of method applicability for different NPs, optimized test protocols and information on mobility and uptake. Such data are urgently required within ecological risk assessment.