Comment on the paper "Microplastic contamination of an unconfined groundwater aquifer in Victoria, Australia".

This paper was written to comment on a few important problems of an original paper published in this journal. In the original paper, polyamide (PA) ropes, a kind of plastic, were used for groundwater sampling. Also, polycarbonate, another plastic, was also used as a filter paper although their potential contamination was later evaluated. Although the original authors reported that high levels of PA were not found in any of the 21 groundwater samples, it is still necessary to only use equipment(s) made of non-plastic at every step of the method for an accurate and reliable analysis of the presence of microplastic in groundwater. The original authors collected a total of 3 l for each borehole (1 l for each sample), but for an unbiased and reliable analysis of microplastics, bigger volumes of groundwater samples should be collected. Furthermore, the original authors computed the Pearson correlation coefficients between the analyzed plastic types, but omitted the normality test of the data distribution. If the collected data are not normally distributed, then Spearman rank correlation coefficients are a better option. In addition, we found some important misstatements regarding the results of the analysis.

MCDataset: a public reference dataset of Monte Carlo simulated quantities for multilayered and voxelated tissues computed by massively parallel PyXOpto Python package.

SIGNIFICANCE: Current open-source Monte Carlo (MC) method implementations for light propagation modeling are many times tedious to build and require third-party licensed software that can often discourage prospective researchers in the biomedical optics community from fully utilizing the light propagation tools. Furthermore, the same drawback also limits rigorous cross-validation of physical quantities estimated by various MC codes. AIM: Proposal of an open-source tool for light propagation modeling and an easily accessible dataset to encourage fruitful communications amongst researchers and pave the way to a more consistent comparison between the available implementations of the MC method. APPROACH: The PyXOpto implementation of the MC method for multilayered and voxelated tissues based on the Python programming language and PyOpenCL extension enables massively parallel computation on numerous OpenCL-enabled devices. The proposed implementation is used to compute a large dataset of reflectance, transmittance, energy deposition, and sampling volume for various source, detector, and tissue configurations. RESULTS: The proposed PyXOpto agrees well with the original MC implementation. However, further validation reveals a noticeable bias introduced by the random number generator used in the original MC implementation. CONCLUSIONS: Establishing a common dataset is highly important for the validation of existing and development of MC codes for light propagation in turbid media.

Operando Monitoring the Insulator-Metal Transition of LiCoO2.

LiCoO2 (LCO) is one of the most-widely used cathode active materials for Li-ion batteries. Even though the material undergoes an electronic two-phase transition upon Li-ion cell charging, LCO exhibits competitive performance in terms of rate capability. Herein the insulator-metal transition of LCO is investigated by operando Raman spectroscopy complemented with DFT calculations and a developed sampling volume model. We confirm the presence of a Mott insulator α-phase at dilute Li-vacancy concentrations (x > 0.87, x in LixCoO2), which gradually transitions to primarily a metallic ß-phase as x approaches 0.75. In addition, we find that the charge-discharge intensity trends of LCO Raman-active bands exhibit a characteristic hysteresis, which, unexpectedly, narrows at higher cycling rates. When comparing these trends to our numerical model of laser penetration into a spatially heterogeneous particle we provide compelling evidence that the insulator-metal transition of LCO follows a two-phase route at very low cycling rates, which is suppressed in favor of a solid-solution route at rates above 20 mA/gLCO (∼C/10). The observations explain why LCO exhibits competitive rate capabilities despite being observed to undergo an intuitively slow two-phase transition route: a kinetically faster solid-solution transition route becomes available when the active material is cycled at rates >C/10. Operando Raman spectroscopy combined with sample volume modeling and DFT calculations is shown to provide unique insights into fundamental processes governing the performance of state-of-the-art cathode materials for Li-ion batteries.

Safe Sampling Volume determinations of 12 volatile organic compounds on Carboxen 1003, Carbopack-X & Tenax-TA.

Pumped sorbent tube sampling is a well established method for the sampling of volatile organic compounds (VOCs) and semi volatile organic compounds (SVOCs) in ambient, indoor and workplace atmospheres1. Safe sampling volumes and breakthrough volumes have been published for commonly found VOCs on widely used sorbents such as Tenax, however for newer sorbents and less commonly found VOCs there is less robust data. The Safe Sampling Volumes (SSVs) were determined from 15 tests of Retention Volume on 12 VOCs across the 3 sorbents. VOCs tested were: Aldehydes (C5, C6, C8, C9), Ketones (C4, C6), Alcohols (C3, C4), Furan, Limonene, Isoprene and Ethyl Acetate. 12 VOC / sorbent combinations gave SSVs large enough for practical sampling of indoor atmospheres, while SSVs for Furan on Carbopack-X, Isovaleraldehyde on Tenax TA and Methyl Ethyl Ketone on Tenax TA gave SSVs that were too small to be of practical use. This work identifies suitable sorbents and sampling volumes for the complete range of species tested.

On the representativeness of pump water samples versus manta sampling in microplastic analysis.

To broaden the understanding of sources, pathways and sinks for microplastic pollution in the environment, the exact and representative determination of pollution levels is crucial. Still, sampling techniques differ greatly between studies and the influence of these differences is not fully understood. Thus, we evaluate the representativeness of manta trawling and pump sampling for microplastics in a freshwater lake. While large microplastics are not captured by most pump sampling approaches due to their low abundance, small and fibrous microplastics pass the relatively coarse nets of volume-reduced techniques. Testing different water volumes for pump samples, we show that sample volumes should be large enough to minimize overestimation induced by scaling up results. Moreover, we discuss the influence of sample numbers for microplastic analysis. Finally, we argue that manta trawling and pump sampling are complementary techniques, as they cover different parts of the overall microplastic pollution.

Fine-scale spatial patterns in microbial community composition in an acid mine drainage.

Microbial community composition is essential for aquatic ecosystem functions and has been explored across diverse environments and various spatial scales. However, documented patterns are often based on samples from spatially/geographically separated locations or sites. Here, we define sampling volume as spatial scale and examine (by Illumina 16S rRNA sequencing) microbial community composition over a scale of 1 mL to 10 L in an acid mine drainage. ß-Diversity analysis revealed that all samples grouped very tightly according to spatial scales and variations between every two scales were significant. Notably, mean ß-diversity within each group was negatively correlated with spatial scales, indicating patchy microbial distribution. Partition of ß-diversity further revealed that it was the relative abundances of some microbial taxa that largely changed among spatial scales. Phylogenetic analysis showed that microbial lineages were not randomly distributed, but displayed a tendency of more phylogenetically clustering at smaller spatial scales. Thus, we documented fine-scale spatial patterns in microbial community composition within a continuous aquatic environment, which may have practical implications for adequate sampling of aquatic systems in future studies.

Development of an analytical method for crystalline content determination in amorphous solid dispersions produced by hot-melt extrusion using transmission Raman spectroscopy: A feasibility study.

The development of a quantitative method determining the crystalline percentage in an amorphous solid dispersion is of great interest in the pharmaceutical field. Indeed, the crystalline Active Pharmaceutical Ingredient transformation into its amorphous state is increasingly used as it enhances the solubility and bioavailability of Biopharmaceutical Classification System class II drugs. One way to produce amorphous solid dispersions is the Hot-Melt Extrusion (HME) process. This study reported the development and the comparison of the analytical performances of two techniques, based on backscattering and transmission Raman spectroscopy, determining the crystalline remaining content in amorphous solid dispersions produced by HME. Principal Component Analysis (PCA) and Partial Least Squares (PLS) regression were performed on preprocessed data and tended towards the same conclusions: for the backscattering Raman results, the use of the DuoScan™ mode improved the PCA and PLS results, due to a larger analyzed sampling volume. For the transmission Raman results, the determination of low crystalline percentages was possible and the best regression model was obtained using this technique. Indeed, the latter acquired spectra through the whole sample volume, in contrast with the previous surface analyses performed using the backscattering mode. This study consequently highlighted the importance of the analyzed sampling volume.

Evaluation of a pointwise microcirculation assessment method using liquid and multilayered tissue simulating phantoms.

A fiber-optic probe-based instrument, designed for assessment of parameters related to microcirculation, red blood cell tissue fraction (fRBC), oxygen saturation (SO2), and speed resolved perfusion, has been evaluated using state-of-the-art tissue phantoms. The probe integrates diffuse reflectance spectroscopy (DRS) at two source-detector separations and laser Doppler flowmetry, using an inverse Monte Carlo method for identifying the parameters of a multilayered tissue model. Here, we characterize the accuracy of the DRS aspect of the instrument using (1) liquid blood phantoms containing yeast and (2) epidermis-dermis mimicking solid-layered phantoms fabricated from polydimethylsiloxane, titanium oxide, hemoglobin, and coffee. The root-mean-square (RMS) deviations for fRBC for the two liquid phantoms were 11% and 5.3%, respectively, and 11% for the solid phantoms with highest hemoglobin signatures. The RMS deviation for SO2 was 5.2% and 2.9%, respectively, for the liquid phantoms, and 2.9% for the solid phantoms. RMS deviation for the reduced scattering coefficient (µs'), for the solid phantoms was 15% (475 to 850 nm). For the liquid phantoms, the RMS deviation in average vessel diameter (D) was 1 µm. In conclusion, the skin microcirculation parameters fRBC and SO2, as well as, µs' and D are estimated with reasonable accuracy.