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Accurate quantification of nanoparticles (NPs) in complex media remains a considerable challenge when assessing the risk that manufactured nanoparticles pose for humans and environment. The radiolabeling of nanoparticles is a valuable tool for conducting lab-studies with realistic systems and realistically low NP concentrations. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, SiO2, CeO2 and TiO2 nanoparticles. The labeling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labeling utilizing the recoil of a nuclear reaction to implant a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag, [124/125/131I]CNTs, [48V]TiO2, [13/1419Ce]CeO2, [7Be]MWCNT, [64Cu]SiO2, [44/45Ti]TiO2, etc. for accurate quantification in complex media at environmentally relevant low concentrations. The nanoparticles labeled by our methods can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. The methods are adaptable for a wide range of other nanoparticles. The labeled particles have been successfully used in release studies, environmental mobility studies, fate studies in waste water treatment and plant uptake studies.

Background There is a steadily increasing quantity of silver nanoparticles (AgNP) produced for numerous industrial, medicinal and private purposes, leading to an increased risk of inhalation exposure for both professionals and consumers. Particle inhalation can result in inflammatory and allergic responses, and there are concerns about other negative health effects from either acute or chronic low-dose exposure. Results To study the fate of inhaled AgNP, healthy adult rats were exposed to 11/2-hour intra-tracheal inhalations of pristine Ag-105-radiolabeled, 20 nm AgNP aerosols (with mean doses across all rats of each exposure group of deposited NP-mass and NP-number being 13.5 +/- 3.6 mu g, 7.9 +/- 3.2 center dot 10(11), respectively). At five time-points (0.75 h, 4 h, 24 h, 7d, 28d) post-exposure (p.e.), a complete balance of the [Ag-105]AgNP fate and its degradation products were quantified in organs, tissues, carcass, lavage and body fluids, including excretions. Rapid dissolution of [Ag-105]Ag-ions from the [Ag-105]AgNP surface was apparent together with both fast particulate airway clearance and long-term particulate clearance from the alveolar region to the larynx. The results are compatible with evidence from the literature that the released [Ag-105]Ag-ions precipitate rapidly to low-solubility [Ag-105]Ag-salts in the ion-rich epithelial lining lung fluid (ELF) and blood. Based on the existing literature, the degradation products rapidly translocate across the air-blood-barrier (ABB) into the blood and are eliminated via the liver and gall-bladder into the small intestine for fecal excretion. The pathway of [Ag-105]Ag-salt precipitates was compatible with auxiliary biokinetics studies at 24 h and 7 days after either intravenous injection or intratracheal or oral instillation of [Ag-110m]AgNO3 solutions in sentinel groups of rats. However, dissolution of [Ag-105]Ag-ions appeared not to be complete after a few hours or days but continued over two weeks p.e. This was due to the additional formation of salt layers on the [Ag-105]AgNP surface that mediate and prolonge the dissolution process. The concurrent clearance of persistent cores of [Ag-105]AgNP and [Ag-105]Ag-salt precipitates results in the elimination of a fraction > 0.8 (per ILD) after one week, each particulate Ag-species accounting for about half of this. After 28 days p.e. the cleared fraction rises marginally to 0.94 while 2/3 of the remaining [Ag-105]AgNP are retained in the lungs and 1/3 in secondary organs and tissues with an unknown partition of the Ag species involved. However, making use of our previous biokinetics studies of poorly soluble [Au-195]AuNP of the same size and under identical experimental and exposure conditions (Kreyling et al., ACS Nano 2018), the kinetics of the ABB-translocation of [Ag-105]Ag-salt precipitates was estimated to reach a fractional maximum of 0.12 at day 3 p.e. and became undetectable 16 days p.e. Hence, persistent cores of [Ag-105]AgNP were cleared throughout the study period. Urinary [Ag-105]Ag excretion is minimal, finally accumulating to 0.016.Conclusion The biokinetics of inhaled [Ag-105]AgNP is relatively complex since the dissolving [Ag-105]Ag-ions (a) form salt layers on the [Ag-105]AgNP surface which retard dissolution and (b) the [Ag-105]Ag-ions released from the [Ag-105]AgNP surface form poorly-soluble precipitates of [Ag-105]Ag-salts in ELF. Therefore, hardly any [Ag-105]Ag-ion clearance occurs from the lungs but instead [Ag-105]AgNP and nano-sized precipitated [Ag-105]Ag-salt are cleared via the larynx into GIT and, in addition, via blood, liver, gall bladder into GIT with one common excretional pathway via feces out of the body.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as soil, natural waters, plants, sewage sludge, etc. is very challenging using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabeling, which may be of crucial value in enabling such research. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, SiO2, CeO2 and TiO2 nanoparticles. The labeling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labeling utilizing the recoil of a nuclear reaction to implant a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag, [124/125/131I]CNTs, [48V]TiO2, [139Ce]CeO2, [7Be]MWCNT, [64Cu]SiO2, [44/45Ti]TiO2, etc.. The methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations. The labeled particles have been successfully used in release studies, environmental mobility studies, fate studies in waste water treatment and plant uptake studies.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories, a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as soil, natural waters, plants, sewage sludge, etc. is nearly impossible using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabeling, which may be of crucial value in enabling such research. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, SiO2, CeO2 and TiO2 nanoparticles. The labeling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labeling utilizing the recoil of a nuclear reaction to implant a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag, [124/125/131I]CNTs, [48V]TiO2, [139Ce]CeO2, [7Be]MWCNT, [7Be]SiO2, [44/45Ti]TiO2, etc.. The methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations. The labeled particles have been successfully used in release studies, environmental mobility studies, fate studies in waste water treatment and plant uptake studies.

A major challenge in nanosafety research is the sensitve detection of nanoparticles at environmentally relevant concentration in the complex systems involved. It is said that many studies in the field of nanosafety research „do not offer any kind of clear statement on the safety of nanomaterials“, in part because of the unrealistically high concentrations used. The radiolabelling of nanoparticles can help overcoming this obstacle as it provides an easy way of reliably detecting nanoparticles in minute concentrations despite the complexity of the matrix. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, CeO2, Silica and TiO2 nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticles, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag0, [124/125/131I]CNTs, [139Ce]CeO2, [48V]TiO2, [7Be]MWCNT, [7Be]SiO2, [44/45Ti]TiO2, etc.. All the particles were evaluated for radiolabel stability and alteration of the particle properties. Using the so-labelled nanoparticles we achieved to measure the release of nanoparticles from surface coatings, the transport of nanoparticles in porous media, the interaction of nanoparticles with complex media such as sewage sludge and the uptake of nanoparticles in plants. The easy quantification of nanoparticle fractions inside the various systems allows the extraction of crucial information in order to understand and evaluate the different processes involved.

Colloids and nanoparticulate matter play an important role in the environment since they can act as carriers for (toxic) compounds and thereby enhance migration of substances that might normally be immobile under the given environmental conditions. The carrier properties of colloidal clay particles, humic substances and silica actinide colloids may play an important role in nuclear waste repositories. However, monitoring of these colloids in complex systems such as geological formations or groundwater is nearly impossible using conventional methods, especially at environmentally relevant concentrations and the high background load of other colloids or dissolved species of the same element. This obstacle can be overcome by the use of radiolabelling, which may be of crucial value in enabling such research. We have developed various methods of introducing radiotracers into natural organic colloids such as humic or fulvic acids [1] and some of the most common technical nanoparticles, such as Ag0 [2], carbon and TiO2 nanoparticles [3]. Current studies are dealing with radiolabelling of CeO2 and quantum dots. Five different approaches can be pursued in the radiolabelling of colloids or nanoparticles: (1) Radiosynthesis – the synthesis of a compound using radioactive material (2) Radiochemistry – the binding of a radioactive tracer to an existing compound (3) In-diffusion – the in-diffusion of radioisotopes into existing particles (4) Direct Activation – the activation of existing particles by proton irradiation (5) Recoil labelling – the implantation of radionuclides into an existing particles using the recoil of a nuclear reaction Radiosynthesis can be used to produce custom-made radiolabelled nanoparticles provided a suitable radiotracer is available. If the labelling is isotopic no difference in properties compared to non-radioactive particles are expected. We used this method to produce radiolabelled [105/110mAg]Ag nanoparticles. Binding a radiotracer to a compound is a way of radiolabelling existing commercial or natural materials by a suitable radiochemical protocol. Carbon nanotubes and humic acids were successfully labelled with radioactive Iodine following the one-pot Iodogen method to yield [124/125/131I]CNTs and [125I]humic acid. No significant change in properties was detected compared to the original compounds. Commercial TiO2 and Ag0 nanoparticles were labelled by the in-diffusion of isotopic radionuclides into surface defects and lattice structure at elevated temperatures. The resulting [110mAg]Ag0 and [44/45Ti]TiO2 nanoparticles showed no change in properties and the radiolabel proved to be stable under various conditions. If a cyclotron is available, nanoparticles can be radiolabelled by activation via proton irradiation. The proton irradiation causes a nuclear reaction in the nanopowder producing the radiolabel inside the particles. Commercial TiO2 particles were labelled with 48V via a 48Ti(p,n)48V reaction. If no suitable radiotracers/nuclear reactions are available for the above described methods, nanoparticles can be labelled utilising the recoil of a nuclear reaction to implant a radiotracer. Typically a mixture of a lithium compound and the to-be-labelled particles is irradiated with protons. The nuclear reaction 7Li(p,n)7Be produces 7Be which is implanted in the nanoparticles due to the recoil of the nuclear reaction. [7Be]MWCNT were produced successfully. Table 1 shows the results for radiolabelling of particles. The described methods are adaptable for a wide range of other nanoparticles or colloids. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. In the research area of radioactive waste repositories the radiolabelling of humic substances, clay colloids and actinide silica colloids may be of particular interest. Table 1: Comparison of the radiolabelling procedures and the resulting radiolabelled NP analysis. Radiolabeling procedure Resulting NP Half-life of the radionuclide Activity concentration [MBq/mg] Detection limit [ng/L] Radiosynthesis [110mAg]Ag0 250 d 1.5 33 [105Ag]Ag0 41.3 d 0.65 77 Radiochemistry [124I]CNT 4.2 d 8.0 6 [125I]CNT 59.4 d 19.9 2 [131I]CNT 8.0 d 3.7 14 In-Diffusion [110mAg]Ag 250 d 1 50 [44Ti]TiO2 60.4 a 0.01 5000 [45Ti]TiO2 3.08 h 135 0.5 Direct Activation [48V]TiO2 15.97 d 3.7 14 [7Be]MWCNT 53.29 d 0.041 1000 Recoil Labelling [7Be]TiO2 0.3 170 [7Be]SiO2 [4] 53.29 d 1.4 36 [7Be]MWCNT 0.055 1000 References: [1] Franke, K., Patt, J.T., Kupsch, H., Warwick, P.: Radioiodination of Humic Substances via Azocoupling with 3-[125I]Iodoaniline. Environ Sci Technol 42(11) (2008) 4083 - 4087. [2] Hildebrand, H., Franke, K.: A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media. J Nanopart Res 14 (2012) 1142. [3] Hildebrand, H., Schymura, S., Holzwarth, U., Gibson, N., Dalmiglio, M., Franke, K.: Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection. J Nanopart Res, submitted. [4] Holzwarth, U., Bellido, E., Dalmiglio, M., Kozempel, J., Cotogno, G., Gibson, N.: 7Be-recoil radiolabelling of industrially manufactured silica nanoparticles. J Nanopart Res 16 (2014) 2574.

Detection and quantification of engineered nanoparticles (NPs) in complex environmental or biological media is a major challenge since NP concentrations are generally expected to be low compared to elemental background levels. This study presents three different options for radiolabeling of commercial titania NP (TiO2-NP, AEROXIDE® P25, Evonik Industries, mean diameter 21 nm) for particle detection, localization and tracing under various experimental conditions. The radiolabeling procedures ensure stability and consistency of important particle properties such as size and morphology. For the first time, detection (and quantification) limits for TiO2-NPs in concentrations as low as 0.5 ng/L can be realized.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories, a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as geological formations, ground water or organisms is nearly impossible or at least extremely laborious in terms of sample preparation using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research under laboratory conditions. Radiolabelling allows to localize, to trace and to detect nanoparticles in complex media without intensive sample pre-treatment for the measurements. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, CeO2, Silica and TiO2 nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag0 [1], [124/125/131I]CNTs, [139Ce]CeO2, [48V]TiO2 [2], [7Be]MWCNT, [7Be]SiO2 [3], [44/45Ti]TiO2 [4], etc.. The radiolabelled nanoparticles were intensively tested concerning radiolabel stability and nanoparticle properties (size, zeta potential) were compared with the original (non-labelled) material. It could be shown, that radiolabels are suitable for application in scientific studies under the individual experimental conditions and nanoparticle properties remained largely unalterd by the radiolabelling procedure. The developed radiolabelling methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. This means that nanoparticles can be localized also in e.g. intact geological samples or during transport studies using appropriate detector arrangement. Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations. [1] H. Hildebrand and K. Franke: A new radiolabeling method for commercial Ag0 nanopowder with 110mAg for sensitive nanoparticle detection in complex media, J Nanopart Res (2012) 14:1142. [2] K. Abbas, I. Cydzik, R. Del Torchio, M. Farina, E. Forti, N. Gibson, U. Holzwarth, F. Simonelli, W. Kreyling: Radiolabelling of TiO2 nanoparticles for radiotracer studies, J Nanopart Res (2010) 12:2435–2443. [3] U. Holzwarth, E. Bellido, M. Dalmiglio, J. Kozempel, G. Cotogno, N. Gibson: 7Be-recoil radiolabelling of industrially manufactured silica nanoparticles, J Nanopart Res (2014) 16:2574. [4] H. Hildebrand, S. Schymura, U. Holzwarth, N. Gibson, M. Dalmiglio, K. Franke: Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection in complex matrices, J Nanopart Res (2015) 17:278.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles in applications outside of research laboratories, a careful risk assessment of their release into the environment becomes mandatory. However, the monitoring of nanoparticles in such complex natural systems as geological formations or ground water is nearly impossible using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research. We have developed various methods of introducing radiotracers into some of the most common nanoparticles, such as Ag, carbon, Silica and TiO2 nanoparticles. The labelling techniques are the synthesis of the nanoparticles using radioactive starting materials, the binding of the radiotracer to the nanoparticles, the activation of the nanoparticles using proton irradiation, the recoil labelling utilizing the recoil of a nuclear reaction to introduce a radiotracer into the nanoparticle, and the in-diffusion of radiotracers into the nanoparticles at elevated temperatures. Using these methods we have produced [105/110mAg]Ag, [124/125/131I]CNTs, [48V]TiO2, [7Be]MWCNT, [7Be]SiO2, [44/45Ti]TiO2, etc.. The methods are adaptable for a wide range of other nanoparticles. The so-labelled nanoparticles can be detected at minimal concentrations well in the ng/L range even with a background of the same element and without complicated sample preparations necessary. Using our methods one can radiolabel commercial nanoparticle samples for sensitive detection in environmentally relevant trace concentrations.

Dinoflagellate cysts are useful for reconstructing upper water conditions. For adequate reconstructions detailed information is required about the relationship between modern day environmental conditions and the geographic distribution of cysts in sediments. This Atlas summarises the modern global distribution of 71 organic-walled dinoflagellate cyst species. The synthesis is based on the integration of literature sources together with data of 2405 globally distributed surface sediment samples that have been prepared with a comparable methodology and taxonomy. The distribution patterns of individual cyst species are being compared with environmental factors that are known to influence dinoflagellate growth, gamete production, encystment, excystment and preservation of their organic-walled cysts: surface water temperature, salinity, nitrate, phosphate, chlorophyll-a concentrations and bottom water oxygen concentrations. Graphs are provided for every species depicting the relationship between seasonal and annual variations of these parameters and the relative abundance of the species. Results have been compared with previously published records; an overview of the ecological significance as well as information about the seasonal production of each individual species is presented.The relationship between the cyst distribution and variation in the aforementioned environmental parameters was analysed by performing a canonical correspondence analysis. All tested variables showed a positive relationship on the 99% confidence level. Sea-surface temperature represents the parameter corresponding to the largest amount of variance within the dataset (40%) followed by nitrate, salinity, phosphate and bottom-water oxygen concentration, which correspond to 34%, 33%, 25% and 24% of the variance, respectively. Characterisations of selected environments as well as a discussion about how these factors could have influenced the final cyst yield in sediments are included.

The employment of radiotracers is a versatile tool for the detection of nano-particulate materials in complex systems such as environmental samples or organisms. With the increasing usage of nanoparticles (NPs) in applications outside of research laboratories a careful risk assessment of their release into the environment becomes mandatory. However the monitoring of nanoparticles in such complex natural systems as geological formations or ground water is nearly impossible using conventional methods, especially at environmentally relevant concentrations. This obstacle can be overcome by radiolabelling, which may be of crucial value in enabling such research. We present here two different radiolabelling strategies for Ag0-NP, TiO2-NP and MWCNTs. Both strategies involve proton bombardment using a cyclotron and cause the incorporation of radioactive isotopes inside the NPs. The first option is to directly activate the NPs by proton irradiation, which proved useful for MWCNTs and TiO2-NP. 12C gets activated using a (p,3d) nuclear reaction to 7Be while 48Ti gets activated to 48V by a (p,n) reaction. The second option, which is generally adoptable for NPs that do not show useful nuclear reactions, is to mix the NP powder with a lithium containing compound like LiH and irradiate it to create 7Be out of 7Li via a (p,n) reaction. The recoil of the 7Be from the nuclear reaction causes the incorporation of the radiotracer into the structure of the NP. The methods were tested for labelling yield, achievable activity concentration, pH-dependent stability of the labeling and the influence on NP-properties. Data thus obtained enables the selection of a radiolabelling method appropriate for different experimental conditions. 48V labeled TiO2-NPs were successfully employed to study the NP release out of surface coatings not measurable using conventional methods.

Engineered nanoparticles (NPs) such as silver and titania are widely used in consumer products e.g. as functional additives in surface coatings. Due to aging or abrasion of these nanocomposites, particle release becomes likely and further transport e.g. in environmental systems could be assumed. For conventional nanocomposites, accurate and sensitive detection and quantification of NP release is still a challenge due to the fact that released fractions might be small but nevertheless significant. The application of radiotracers provides the excellent option of “visibility”, traceability and quantification of NPs in complex media. Therefore, different radiolabelling strategies for engineered nanopowders (TiO2 P 25, Evonic Industries, dp = 21 nm; Ag0, Sigma Aldrich, dp < 100 nm) were established using a diffusive introduction of 110mAg radionuclides (t1/2 = 250 d) into Ag0-NPs (Hildebrand & Franke, 2012) and 44Ti radionuclides (t1/2 = 63 a) into TiO2-NPs through a low-temperature annealing procedure. Another radiolabelling strategy is the direct activation of Ag0 and TiO2 nanopowders that was done via proton irradiation using a Scanditronix MC40 cyclotron (Abbas et al. 2010, Holzwarth et al. 2012). Both methods were tested with respect to radiolabelling yield, achievable activity concentration, pH-dependent stability of the radiolabelling and the influence on NP properties. Results obtained show an appropriate selection of radiolabelling methods suitable for different experimental conditions for NP release studies. Abbas K, Cydzik I, Del Torchio R, Farina M, Forti E, Gibson N, Holzwarth U, Simonelli F, Kreyling W (2010) J Nanopart Res 12:2435–2443. Holzwarth U, Bulgheroni A, Gibson N, Kozempel J, Cotogno G, Abbas K, Simonelli F, Cydzik I (2012) J Nanopart Res 14:880. Hildebrand H and Franke K (2012) J Nanopart Res 14:1142.

Engineered nanoparticles (NPs) such as silver and titania are widely used in consumer products e.g. as functional additives in surface coatings. Due to aging or abrasion of these nanocomposites, particle release becomes likely and further transport e.g. in environmental systems could be assumed. Figure 1 shows results from a worst-case scenario study where NP release was enforced due to the use of a quite labile surface coating and photooxidative degradation of the nanocomposite catalysed by TiO2 anatase NPs. For conventional, more stable nanocomposites, accurate and sensitive detection and quantification of NP release is still a challenge due to the fact that released fractions might be small but nevertheless significant. The application of radiotracers provides the excellent option of “visibility”, traceability and quantification of NPs in complex media. Therefore, different radiolabelling strategies for engineered nanopowders (TiO2 P 25, Evonic Industries, dp = 21 nm; Ag0, Sigma Aldrich, dp < 100 nm) were established using a diffusive introduction of 110mAg radionuclides (t1/2 = 250 d) into Ag0-NPs (Hildebrand & Franke, 2012) and 44Ti radionuclides (t1/2 = 63 a) into TiO2-NPs through a low-temperature annealing procedure. Another radiolabelling strategy is the direct activation of Ag0 and TiO2 nanopowders that was done via proton irradiation using a Scanditronix MC40 cyclotron (Abbas et al. 2010, Holzwarth et al. 2012). Both methods were tested with respect to labelling yield, achievable activity concentration, pH-dependent stability of the labelling and the influence on NP properties. Results obtained show an appropriate selection of radiolabeling methods suitable for different experimental conditions for NP release studies. Figure 1: Time-dependent degradation of a polyacrylate TiO2 nanocomposite by UV-A-irradiation (intensity ~ 15 mW/cm2) ;A) original, B) after 2 days (50.000x); C) 4 days, D) 8 days, E) 16 days (75.000x); SEM micrographs: Leibniz Institute for Surface Modification. Abbas K, Cydzik I, Del Torchio R, Farina M, Forti E, Gibson N, Holzwarth U, Simonelli F, Kreyling W (2010) J Nanopart Res 12:2435–2443. Holzwarth U, Bulgheroni A, Gibson N, Kozempel J, Cotogno G, Abbas K, Simonelli F, Cydzik I (2012) J Nanopart Res 14:880 Hildebrand H and Franke K (2012) J Nanopart Res 14:1142.