Occurrence, distribution, and partitioning of antibiotics in surface water and sediment in a typical tributary of Yellow River, China.

The antibiotic distributions, partitioning, and migration pathways in river basins have withdrawn great attention in the past decades. This study investigates 26 antibiotics of five classifications in surface water and sediment samples at 23 sites in Fenhe River, a typical tributary of Yellow River. There are 21 antibiotics found in the water samples at the concentration from 113.8 to 1106.0 ng/L, in the decreasing order of SAs > QNs > MLs > TCs > CAs. Fifteen antibiotics were detected in the sediment at the concentrations from 25.11 to 73.22 µg/kg following the decreasing order of SAs > MLs > TCs > QNs > CAs. The antibiotic concentrations vary greatly in surface water, generally lower in upstream and in reservoirs, and reaching highest in the midstream of the Fenhe River after passing Taiyuan and Jinzhong, and then lower again in the downstream. The antibiotic concentrations in sediment have a less variation in the entire river basin, but become high in the downstream. The results show the water-sediment partitioning coefficients of antibiotics generally were lower than those in other areas, having a migration path from the water to suspended solids, and then accumulated in sediment. The water-sediment partitioning coefficients also vary across the basin. The water-sediment partitioning coefficients of sulfacetamide and tetracycline are higher than the water-sediment partitioning coefficients of other antibiotics, with less variation across the basin, the water-sediment partitioning coefficients of azithromycin, enrofloxacin, and roxithromycin are low in the midstream of the river, and high at the river source and downstream. The water-sediment partitioning coefficients are significantly affected by the pH of sediment and the particle size of sediment. The prediction models of water-sediment partitioning coefficients for antibiotics are constructed with the selected effecting factors. The simulation values of antibiotics except chlortetracycline and erythromycin are highly consistent with the observed values, indicating that the prediction model is reliable.

[Distribution and Sources of Microplastics in Farmland Soil Along the Fenhe River].

This study investigated the distribution and sources of microplastics smaller than 1 mm in farmland soil along the Fenhe River. Microplastics in soil samples were separated and extracted using the traditional density centrifugation method. The quantity and type of microplastics were examined with a stereomicroscope. The micro-morphology of plastic particles were observed with a scanning electron microscope-energy dispersive spectrometer. The chemical composition was determined using Fourier transform infrared spectroscopy. The results indicate that the average abundance of microplastics in farmland soil along the Fenhe River is 290.5 n ·kg-1. These microplastics occur as fibers, films, fragments, and foams. Fiber microplastics are the most abundant, accounting for 52.67% of the total, and are mostly composed of polyethylene. Films and fragments mainly consist of polypropylene whereas the foams consist of polystyrene. Soil samples from different parts of the Fenhe River can be ranked according to the microplastics content in the following order:downstream>midstream>upstream. The abundance of microplastics in soil from the downstream region of the Fenhe River was 500.0 n ·kg-1, twice that of from the upstream and midstream regions. The results of the random forest model indicate that the sources of microplastics in farmland soil along the Fenhe River are closely related to the amount of agricultural films, population, gross domestic product, and industrial production. Among these factors, the amount of agricultural films is a key factor that influences the occurrence of microplastics in farmland soil along the Fenhe River.

Retrospection of recent 30-year changes in the process of soil wind erosion in the Luanhe River Source Area of North China using Cesium-137.

The Luanhe River Source Area belongs to typical semi-arid, agro-pastoral ecotone of North China. It is very important for the prevention and treatment of soil erosion in North China to analyze and evaluate quantitatively the recent 30-year changes in the process of soil wind erosion in this area. Based on long field observations, soil samples from different depths in a representative wind-deposited soil profile in the Luanhe River Source Area were collected. Then the (137)Cs activity of soil samples from different depths in the soil profile was determined using a GEM series HPGe (high-purity germanium) coaxial detector system (ADCAM-100), and their soil properties, such as the soil particle fraction and so on, were analyzed. According to the detected (137)Cs activity of different depths, a continuous time sequence of the wind-deposited soil profile in the study area was established. Furthermore, through assumption on a soil relative wind erosion intensity index (SWEI), recent 30-year changes in the process of soil wind erosion in the Luanhe River Source Area were retrospected . The analysis results revealed that weaker soil wind erosion occurred in the study area from the 1970s to the early 1980s and from the late 1980s to the mid to late 1990s. Conversely, intense periods of soil wind erosion occurred in the mid-1980s and from the late 1990s to 2002.