Centennial Records of Microplastics in Lake Cores in Huguangyan Maar Lake, China.

Microplastic records from lake cores can reconstruct the plastic pollution history. However, the associations between anthropogenic activities and microplastic accumulation are not well understood. Huguangyan Maar Lake (HML) is a deep-enclosed lake without inlets and outlets, where the sedimentary environment is ideal for preserving a stable and historical microplastic record. Microplastic (size: 10-500 µm) characteristics in the HML core were identified using the Laser Direct Infrared Imaging system. The earliest detectable microplastics appeared unit in 1955 (1.1 items g-1). The microplastic abundance ranged from n.d. to 615.2 items g-1 in 1955-2019 with an average of 134.9 items g-1. The abundance declined slightly during the 1970s and then increased rapidly after China's Reform and Opening Up in 1978. Sixteen polymer types were detectable, with polyethylene and polypropylene dominating, accounting for 23.5 and 23.3% of the total abundance, and the size at 10-100 µm accounted for 80%. Socioeconomic factors dominated the microplastic accumulation based on the random forest modeling, and the contributions of GDP per capita, plastic-related industry yield, and total crop yield were, respectively, 13.9, 35.1, and 9.3% between 1955-2019. The total crop yield contribution further increased by 1.7% after 1978. Coarse sediment particles increased with soil erosion exacerbated microplastics discharging into the sediment.

Groundwater hydrochemistry, source identification and pollution assessment in intensive industrial areas, eastern Chinese loess plateau.

Groundwater is essential for regional ecological-economic system and is an important resource of drinking water, especially in the Chinese Loess Plateau (CLP), where is a typical water-limited ecosystem. Groundwater quality deterioration will affect water security and exacerbate the water shortages. Groundwater hydrochemistry, pollution source apportionment, quality and health risks were evaluated based on analysis of major ions and selected trace elements in seasonal samples of the Fen River Basin (FRB) in the eastern CLP. Groundwaters in the FRB were mainly HCO3--Ca2+-Na+ water type with low dissolved solutes in upstream samples, high values in midstream samples and medium values in downstream samples. Solutes in upstream samples were mainly derived from carbonate weathering, while those in midstream and downstream samples came from silicate weathering, evaporites dissolution and anthropogenic sources. Self-organizing map (SOM) showed the hydrochemistry remained unchanged from dry to wet season for most sampling points. The seasonal variations of Ag, Cd, Ni, Pb, and Tl were significant due to anthropogenic input. High NO3- in upstream and downstream samples resulted primarily from sewage discharge, and high SO42- in midstream and downstream samples was from gypsum- and coal-related industries. In addition, anthropogenic input related to coal industries significantly aggravates pollution of As, Ni, Ag, Fe, and Mn. Influenced by evaporites and anthropogenic input, midstream samples had high salinity, total hardness and water quality indices (WQIs) and were unsuitable for irrigation or drinking purposes. Seasonal variation of WQI in the FRB was unsignificant except Jiaokou River sub-basin, where groundwater quality was worse in the wet season than the dry season due to coal mining. Great attention should be paid to the high non-carcinogenic risks of exposure to F, V, Mn, and Cr via dermal absorption, particularly for children. Overall, groundwater quality in the FRB was best in upstream, medium in midstream and worst in midstream based on different index. Groundwater quality is deteriorated by anthropogenic input and the sewage discharge in the FRB should be strictly controlled. Our report provides a reference for groundwater pollution evaluation and source identification in similar areas.

Evaluation of the thermal/optical reflectance method for discrimination between char- and soot-EC.

Many optical, thermal and chemical methods exist for the measurement of elemental carbon (EC) but are unable or neglect to differentiate between the different forms of EC such as char- or soot-EC. The thermal/optical reflectance (TOR) method applies different temperatures for measuring EC and organic carbon (OC) contents through programmed, progressive heating in a controlled atmosphere, making available eight separate carbon fractions - four OC, one pyrolyzed organic carbon, and three EC. These fractions were defined by temperature protocol, oxidation atmosphere, and laser-light reflectance/transmittance. Stepwise thermal evolutional oxidation of the TOR method makes it possible to distinguish char- from soot-EC. In this study, different EC reference materials, including char and soot, were used for testing it. The thermograms of EC reference materials showed that activation energy is lower for char- than soot-EC. Low-temperature EC1 (550 degrees C in a 98% He/2% O2 atmosphere) is more abundant for char samples. Diesel and n-hexane soot samples exhibit similar EC2 (700 degrees C in a 98% He/2% O2 atmosphere) peaks, while carbon black samples peaks at both EC2 and EC3 (800 degrees C in a 98% He/2% O2 atmosphere). These results supported the use of the TOR method to discriminate between char- and soot-EC.