RESUMEN
Organophosphate esters (OPEs), extensively used as flame retardants, are widely detected in various regions and environments. The potential toxicity of OPEs has caused great concern in recent years. Based on the global distillation model, the Tien Shan glaciers, such as Urumqi Glacier No. 1, could be as a potential "sink" for OPEs. However, little is known about the concentration, distribution, potential sources, and ecological risks of OPEs in Tien Shan glaciers. In this study, fresh snow samples were collected at various altitudes on the Urumqi Glacier No. 1, eastern Tien Shan, China. The total concentrations of ten OPEs (Σ10OPEs) ranged from 116 to 152 ng/L. The most abundant OPE was tris-(2-chloroisopropyl) phosphate (TCIPP), contributing to 74 % of the total OPEs. Σ10OPEs, tri-n-butyl phosphate (TnBP), and TCIPP concentrations showed positive correlations with altitude, indicating the effect of cold condensation on OPEs deposition. Based on air mass back-trajectory analysis and principal component analysis, we found that emissions from both traffic and household products in indoor environment were the important sources, and OPEs on the Urumqi Glacier No. 1 might mainly originate from Europe. Our assessment also showed triphenyl phosphate (TPhP) posed a low ecological risk in snow. This is the first systematic study of OPEs on the Tien Shan glaciers.
RESUMEN
Objective: To study the long-term morphological stability of three-dimensional (3D) printed photosensitive resin dental models under natural light and dark conditions. Methods: Eighty sets of resin dental models were made by the desktop 3D printer from one digital standard model set, and randomly divided into two groups, namely natural light group (40 sets) and dark group (40 sets). All resin models were stored in sealed bags, with 4 model sets from each group randomly collected after 1, 3, 5, 7, 14, 21, 28, 40, 60, or 90 days of storage and 3D scanned using an optical model scanner. The root-mean-square error (RMSE) was calculated to represent the mean deviation of the difference between the digital standard model and the scanned resin model. Meanwhile, three linear indexes (the width between the canines, the width between the first molars, and the arch length) of the resin dental model were measured and compared with the corresponding values of the standard model. RMSE and the linear measurements between the digital standard model and the scanned resin models were compared between the natural light group and the dark group and among models from different time points. Results: Compared with the digital standard model, the RMSE values of 96.9% (155/160) resin dental models were less than 0.1 mm within 90-day storage. Also, at the same time point, there was no significant difference in the RMSE between the natural light group and the dark group (P>0.05). 75.0% (360/480) of the absolute values of the linear differences (differences in inter-canine width, intra-molar width, and arch length between the digital standard model and the scanned resin model) were within 0.2 mm, and about 0.1% (3/480) of the linear differences were greater than 0.5 mm, and all of the linear differences were within 0.6 mm. Conclusions: 3D-printed resin dental models can be stored stably under natural light and dark conditions for a long time.
RESUMEN
Stable isotopes of oxygen (δ18O) and hydrogen (δD) in precipitation can be used as dual conservative tracers in the hydrologic cycle and help to understand hydrological and atmospheric processes. Although long-term monthly precipitation global isotope datasets are available in some locations, currently there are limited daily precipitation isotope data, particularly in the Midwest region of the USA. In this study we report a daily precipitation δ18O and δD dataset from March 2014-December 2017 in Dayton, Ohio, the USA. The daily δ18O and δD vary from -28.0 to 0.4, and -214.0 to 9.0 respectively. The data exhibit strong seasonality with lower δ18O and δD values in the winter and higher values in the summer. The precipitation isotopic values are mainly controlled by temperature, and show no correlation with precipitation amount and relative humidity. However, δ18O-temperature relationship varies among different seasons. The correlation is the strongest in winter (R2 = 0.56), weaker in spring (R2 = 0.28) and fall (R2 = 0.24), and almost non-existent in summer (R2 = 0.1). The slope values also vary with highest value in winter (0.68/OC) and much smaller in other seasons. The HYSPLIT back trajectory analyses show that Pacific, Gulf of Mexico, Arctic and Continental moistures are the main sources for southwestern Ohio with different seasonal contributions. The isotopic compositions of precipitation from different sources show small intra-season variations but large seasonal variability. Our daily-resolved dataset provides new insights into the main controls on the isotopic composition of precipitation and its seasonal variations, which could help to understand atmospheric processes and enable their proper use in interpretation of paleoclimate proxies, particularly those with seasonal bias.
