@misc{hildebrandt_microplastics_as_2021, author={Hildebrandt, L., Nack, F., Zimmermann, T., Pröfrock, D.}, title={Microplastics as a Trojan horse for trace metals}, year={2021}, howpublished = {journal article}, doi = {https://doi.org/10.1016/j.hazl.2021.100035}, abstract = {Due to an assumed lack of anionic binding sites (most plastics are non-polar), scientists long considered virgin particulate plastics inert towards metal ions. However, we proved significant metal sorption to microplastics at neutral pH and release in a solution mimicking gastrointestinal chemistry serving as a proof-of-principle for environmental and human bioavailability. Competitive ion-exchange incubation experiments comprised 55 metals and metalloids. Fast kinetics were observed with 45 %–75 % of As, Be, Bi, Cr, Fe, In, Pb, Th, Sn and the rare-earth element ions being sorbed after 1 h. The investigated metal and metalloid cations showed significant differences in the extent of sorption, based upon which a distinct categorization was possible. Microplastics are not only a potential danger for aquatic and human life, but - as demonstrated in this paper - also serve as a Trojan Horse for dissolved metal cations. The corresponding effects on aquatic and human health will gain higher importance in the near future due to the predicted increases of marine plastic litter and microplastic sorbents.}, note = {Online available at: \url{https://doi.org/10.1016/j.hazl.2021.100035} (DOI). Hildebrandt, L.; Nack, F.; Zimmermann, T.; Pröfrock, D.: Microplastics as a Trojan horse for trace metals. Journal of Hazardous Materials Letters. 2021. vol. 2, 100035. DOI: 10.1016/j.hazl.2021.100035}} @misc{hildebrandt_comparison_and_2021, author={Hildebrandt, L., Zimmermann, T., Primpke, S., Fischer, D., Gerdts, G., Pröfrock, D.}, title={Comparison and uncertainty evaluation of two centrifugal separators for microplastic sampling}, year={2021}, howpublished = {journal article}, doi = {https://doi.org/10.1016/j.jhazmat.2021.125482}, abstract = {For the first time in microplastic research, an expanded uncertainty was calculated according to the “Guide to the expression of Uncertainty in Measurement” (JCGM 100:2008). Bottom-up uncertainty evaluation revealed the different sampling methods (~ 44%), sample replicates (~ 26%) and the different detection techniques (~ 16%) as the major sources of uncertainty. Depending on the number of particles detected in the samples, the relative expanded uncertainty (Urel (k =2)) ranged from 24% up to > 200% underpinning tremendous importance of sound uncertainty evaluation. Our results indicate that scientist should rethink many “observed patterns” in the literature due to being insignificant and herewith not real.}, note = {Online available at: \url{https://doi.org/10.1016/j.jhazmat.2021.125482} (DOI). Hildebrandt, L.; Zimmermann, T.; Primpke, S.; Fischer, D.; Gerdts, G.; Pröfrock, D.: Comparison and uncertainty evaluation of two centrifugal separators for microplastic sampling. Journal of Hazardous Materials. 2021. vol. 414, 125482. DOI: 10.1016/j.jhazmat.2021.125482}} @misc{lechthaler_canola_oil_2020, author={Lechthaler, S., Hildebrandt, L., Stauch, G., Schüttrumpf, H.}, title={Canola Oil Extraction in Conjunction with a Plastic Free Separation Unit Optimises Microplastics Monitoring in Water and Sediment}, year={2020}, howpublished = {journal article}, doi = {https://doi.org/10.1039/D0AY01574A}, abstract = {Microplastics are widely distributed in the environment and to define contamination hot spots, environmental samples have to be analysed by means of cost- as well as time-efficient and reliable standardised protocols. Due to the lipophilic characteristics of plastic, oil extraction as a fast and density-independent separation is beneficial for the crucial extraction step. It was extensively validated (480 experiments) in two test setups by using canola oil and a cost-effective, plastic-free separation unit with spiked microplastic (19 different polymer types) in the density range from ρ = 11 - 1,760 kg/m³ and in the size range from 0.02 mm - 4.4 mm. Thus, an innovative, new method combination was developed and profoundly validated for water and sediment samples using only a short settling time of 15 minutes. Some experiments were also carried out with zinc chloride to obtain additional reference data (particles ≤ 359 µm). The total mean recovery rate was 89.3%, 91.7% within the larger microplastic fraction and 85.7% for the small fraction. Compared to zinc chloride (87.6%), recovery rates differed not significantly with oil (87.1%). Furthermore, size limits were set, since the method works best with particles 0.02 mm ≥ d ≤ 3 mm. The proposed method exhibits higher efficiency (84.8% for 20 - 63 µm) for the potentially most harmful microplastic size fraction than the classic setup using brine solution. As a result, oil is a comparably effective separation medium and offers further advantages for separating water and sediment samples due to its density independence, simple and fast application and environmental friendliness. Based on this, a new extraction protocol is presented here that confirms oil separation as a sound and effective separation in microplastic analysis and identifies previously missing information.}, note = {Online available at: \url{https://doi.org/10.1039/D0AY01574A} (DOI). Lechthaler, S.; Hildebrandt, L.; Stauch, G.; Schüttrumpf, H.: Canola Oil Extraction in Conjunction with a Plastic Free Separation Unit Optimises Microplastics Monitoring in Water and Sediment. Analytical Methods. 2020. vol. 12, no. 42, 5128-5139. DOI: 10.1039/D0AY01574A}} @misc{hildebrandt_a_metrologically_2020, author={Hildebrandt, L., von der Au, M., Zimmermann, T., Reese, A., Ludwig, J., Pröfrock, D.}, title={A metrologically traceable protocol for the quantification of trace metals in different types of microplastic}, year={2020}, howpublished = {journal article}, doi = {https://doi.org/10.1371/journal.pone.0236120}, abstract = {The presence of microplastic (MP) particles in aquatic environments raised concern about possible enrichment of organic and inorganic pollutants due to their specific surface and chemical properties. In particular the role of metals within this context is still poorly understood. Therefore, the aim of this work was to develop a fully validated acid digestion protocol for metal analysis in different polymers, which is a prerequisite to study such interactions. The proposed digestion protocol was validated using six different certified reference materials in the microplastic size range consisting of polyethylene, polypropylene, acrylonitrile butadiene styrene and polyvinyl chloride. As ICP-MS/MS enabled time-efficient, sensitive and robust analysis of 56 metals in one measurement, the method was suitable to provide mass fractions for a multitude of other elements beside the certified ones (As, Cd, Cr, Hg, Pb, Sb, Sn and Zn). Three different microwaves, different acid mixtures as well as different temperatures in combination with different hold times were tested for optimization purposes. With the exception of Cr in acrylonitrile butadiene styrene, recovery rates obtained using the optimized protocol for all six certified reference materials fell within a range from 95.9% ± 2.7% to 112% ± 7%. Subsequent optimization further enhanced both precision and recoveries ranging from 103% ± 5% to 107 ± 4% (U; k = 2 (n = 3)) for all certified metals (incl. Cr) in acrylonitrile butadiene styrene. The results clearly show the analytical challenges that come along with metal analysis in chemically resistant plastics. Addressing specific analysis tools for different sorption scenarios and processes as well as the underlying kinetics was beyond this study’s scope. However, the future application of the two recommended thoroughly validated total acid digestion protocols as a first step in the direction of harmonization of metal analysis in/on MP will enhance the significance and comparability of the generated data. It will contribute to a better understanding of the role of MP as vector for trace metals in the environment.}, note = {Online available at: \url{https://doi.org/10.1371/journal.pone.0236120} (DOI). Hildebrandt, L.; von der Au, M.; Zimmermann, T.; Reese, A.; Ludwig, J.; Pröfrock, D.: A metrologically traceable protocol for the quantification of trace metals in different types of microplastic. PLoS One. 2020. vol. 15, no. 7, e0236120. DOI: 10.1371/journal.pone.0236120}} @misc{zimmermann_substituting_hf_2020, author={Zimmermann, T., von der Au, M., Reese, A., Klein, O., Hildebrandt, L., Pröfrock, D.}, title={Substituting HF by HBF4 – an optimized digestion method for multi-elemental sediment analysis via ICP-MS/MS}, year={2020}, howpublished = {journal article}, doi = {https://doi.org/10.1039/D0AY01049A}, abstract = {Determination of elemental mass fractions in sediments plays a major role in evaluating the environmental status of aquatic ecosystems. Herewith, the optimization of a new total digestion protocol and the subsequent analysis of 48 elements in different sediment reference materials (NIST SRM 2702, GBW 07313, GBW 07311 and JMC-2) based on ICP-MS/MS detection is presented. The developed method applies microwave acid digestion and utilizes HBF4 as fluoride source for silicate decomposition. Similar to established protocols based on HF, HBF4 ensures the dissolution of the silicate matrix, as well as other refractory oxides. As HBF4 is not acutely toxic; no special precautions have to be made and digests can be directly measured via ICP-MS without specific sample inlet systems, evaporation steps or the addition of e.g. H3BO3, in order to mask excess HF. Different acid mixtures with and without HBF4 were evaluated in terms of digestion efficiency based on the trace metal recovery. The optimized protocol (5 mL HNO3, 2 mL HCL, 1 mL HBF4) allows a complete dissolution of the analyzed reference materials, as well as quantitative recoveries for a wide variety of certified analytes. Low recoveries for e.g. Sr, Ba and rare earth elements due to fluoride precipitation of HF-based digestions protocols, can be avoided by the usage of HBF4 instead. Based on the usage of high purity HBF4 all relevant trace, as well as matrix elements can be analyzed with sufficiently low LOQs (0.002 μg L−1 for U up to 6.7 μg L−1 for Al). In total, 34 elements were within a recovery range of 80%–120% for all three analyzed reference materials GBW 07313, GBW 07311 and JMC-2. 14 elements were outside a recovery range of 80%–120% for at least one of the analyzed reference materials.}, note = {Online available at: \url{https://doi.org/10.1039/D0AY01049A} (DOI). Zimmermann, T.; von der Au, M.; Reese, A.; Klein, O.; Hildebrandt, L.; Pröfrock, D.: Substituting HF by HBF4 – an optimized digestion method for multi-elemental sediment analysis via ICP-MS/MS. Analytical Methods. 2020. vol. 12, no. 30, 3778-3787. DOI: 10.1039/D0AY01049A}} @misc{hildebrandt_a_nanoplastic_2020, author={Hildebrandt, L., Mitrano, D., Zimmermann, T., Pröfrock, D.}, title={A Nanoplastic Sampling and Enrichment Approach by Continuous Flow Centrifugation}, year={2020}, howpublished = {journal article}, doi = {https://doi.org/10.3389/fenvs.2020.00089}, abstract = {Substantial efforts have been undertaken to isolate and characterize plastic contaminants in different sample matrices in the last years as the ubiquitous presence of particulate plastic in the environment has become evident. In comparison, plastic particles <1 µm (nanoplastic) in the environment remain mostly unexplored. Adequate techniques for the enrichment, as well as the detection of nanoplastic, are lacking but are urgently needed to assess the full scope of (potential) nanoplastic pollution. Use of Pd-doped nanoplastic particles constitutes a powerful tool to develop new analytical approaches, as they can be traced accurately and with ease in a variety of complex matrices by highly sensitive, time-efficient and robust ICP-MS(/MS) techniques. In this lab-scale study, for the first time, the capability of continuous flow centrifugation to retain nanoplastic particles (∼160 nm) from ultrapure water, as well as from filtered and unfiltered water from the German Elbe River was evaluated. Depending on the pump rate, the retention efficiency for the nanoplastic particles in ultrapure water ranged from 92% ± 8% (1 L h−1) to 53% ± 5% (5 L h−1) [uc (n = 3)] and from 75% ± 5% to 65% ± 6% (uc) (2.5 L h−1) in river water. Recirculating the water through the system two and three times at the highest tested flow rate led to retention efficiencies >90%. In a proof-of-principle setup, it was demonstrated that operating two continuous flow centrifuges sequentially at different rotational speeds bears the potential to enable size- and density-selective sampling of the colloidal fraction. A significant fraction of the spiked nanoplastic particles [76% ± 5% (uc)] could be separated from a model mixture of natural particles with a well-defined mean size of approximately 3 µm. While the certified reference plankton material used here was quantitatively retained in the first centrifuge rotor together with 23.0% ± 2.2% of the effective dose of the spiked nanoplastic, the remaining fraction of the nanoplastic could be recovered in the second rotor (53% ± 5%) and the effluent [24.4% ± 2.4% (uc)]. Based on the good retention efficiencies and the demonstrated separation potential, continuous flow centrifugation has proven to be a very promising technique for nanoplastic sampling and enrichment from natural water samples.}, note = {Online available at: \url{https://doi.org/10.3389/fenvs.2020.00089} (DOI). Hildebrandt, L.; Mitrano, D.; Zimmermann, T.; Pröfrock, D.: A Nanoplastic Sampling and Enrichment Approach by Continuous Flow Centrifugation. Frontiers in Environmental Science. 2020. vol. 8, 89. DOI: 10.3389/fenvs.2020.00089}} @misc{hildebrandt_evaluation_of_2019, author={Hildebrandt, L., Voigt, N., Zimmermann, T., Reese, A., Proefrock, D.}, title={Evaluation of continuous flow centrifugation as an alternative technique to sample microplastic from water bodies}, year={2019}, howpublished = {journal article}, doi = {https://doi.org/10.1016/j.marenvres.2019.104768}, abstract = {The scientific and public interest regarding environmental pollution with microplastic has considerably increased within the last 15 years. Nevertheless, up to now there is no widely applied standard operation procedure for microplastic sampling, resulting in a lack of inter-study comparability. In addition, many studies on microplastic occurrences do not indicate a sound methodological validation of the applied methods and procedures. This study presents an alternative volume-reduced sampling technique to sample the entire load of suspended particulate matter including microplastic particles in natural waters, based on continuous flow centrifugation. For the lab-scale validation of the proposed instrumental setup, six different microplastic types (PE, PET, PS, PVDC, EPS and PP) were used. The particles covered a size range from 1 μm to 1 mm and a density range from 0.94 g mL−1 to 1.63 g mL−1. Recoveries ranged from 95.0% ± 2.3%–99.1% ± 0.3% for virgin powders and from 96.1% ± 0.6%–99.4% ± 0.2% (1 SD, n = 2–3) for microplastic suspended in river water for 40 days. Gravimetric and microscopic analysis of the effluent indicates efficient removal of microplastic from the suspensions. Static light scattering analysis of the microplastic suspensions prior to and after centrifugation confirmed that no change of the particle size distribution has occurred – neither through aggregation nor through size-discrimination during centrifugation. Moreover, the system was tested in the field and used twice to sample suspended particulate matter from the Elbe estuary directly on site. Based on these first lab-scale experiments, continuous flow centrifugation proves a promising technique bearing potential to alleviate drawbacks such as contamination, filter clogging and particle size-discrimination of commonly used volume-reduced microplastic sampling approaches.}, note = {Online available at: \url{https://doi.org/10.1016/j.marenvres.2019.104768} (DOI). Hildebrandt, L.; Voigt, N.; Zimmermann, T.; Reese, A.; Proefrock, D.: Evaluation of continuous flow centrifugation as an alternative technique to sample microplastic from water bodies. Marine Environmental Research. 2019. vol. 151, 104768. DOI: 10.1016/j.marenvres.2019.104768}} @misc{lorenz_spatial_distribution_2019, author={Lorenz, C., Roscher, L., Meyer, M.S., Hildebrandt, L., Prume, J., Loeder, M.G.J., Primpke, S., Gerdts, G.}, title={Spatial distribution of microplastics in sediments and surface waters of the southern North Sea}, year={2019}, howpublished = {journal article}, doi = {https://doi.org/10.1016/j.envpol.2019.06.093}, abstract = {Microplastic pollution within the marine environment is of pressing concern globally. Accordingly, spatial monitoring of microplastic concentrations, composition and size distribution may help to identify sources and entry pathways, and hence allow initiating focused mitigation. Spatial distribution patterns of microplastics were investigated in two compartments of the southern North Sea by collecting sublittoral sediment and surface water samples from 24 stations. Large microplastics (500−5000 μm) were detected visually and identified using attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. The remaining sample was digested enzymatically, concentrated onto filters and analyzed for small microplastics (11−500 μm) using Focal Plane Array (FPA) FTIR imaging. Microplastics were detected in all samples with concentrations ranging between 2.8 and 1188.8 particles kg−1 for sediments and 0.1–245.4 particles m−3 for surface waters. On average 98% of microplastics were <100 μm in sediments and 86% in surface waters. The most prevalent polymer types in both compartments were polypropylene, acrylates/polyurethane/varnish, and polyamide. However, polymer composition differed significantly between sediment and surface water samples as well as between the Frisian Islands and the English Channel sites. These results show that microplastics are not evenly distributed, in neither location nor size, which is illuminating regarding the development of monitoring protocols.}, note = {Online available at: \url{https://doi.org/10.1016/j.envpol.2019.06.093} (DOI). Lorenz, C.; Roscher, L.; Meyer, M.; Hildebrandt, L.; Prume, J.; Loeder, M.; Primpke, S.; Gerdts, G.: Spatial distribution of microplastics in sediments and surface waters of the southern North Sea. Environmental Pollution. 2019. vol. 252 B, 1719-1729. DOI: 10.1016/j.envpol.2019.06.0