The field of IC 2602: Strömgren‐Hβ photometry approach

A homogeneous data‐base collating all uvbyβ photometry available at present for O‐B9 stars in the field of IC 2602 is presented. The characteristics of the field are studied. Four spatially coherent groups can be distinguished. A low reddened compact group located at 156 ± 6 pc is identi.ed with IC 2602, followed by background layers at 546 ± 33 pc, 1117 ± 61 pc, and possibly at 2626 ± 163 pc. The apparent depth of the first three layers is about 1 kpc, which is consistent with the thickness of a spiral arm. There is an indication for the existence of a region free of massive luminous stars between 1.2 and 2.6 kpc, which could be associated with interarm space between the Local Association and the distant spiral structures toward Carina. A comparison between the photometric and Hipparcos parallaxes is presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Distribution of fluoride in surface water and a health risk assessment in the upper reaches of the Yongding River

The excessive exposure to high concentrations of fluoride in drinking water can lead to a serious disease called fluorosis. The upstream region of the Yongding River is an ecological protection area for Beijing. Some studies have reported that there is a high concentration of fluoride in the groundwater in this area. However, there are few data on the distribution of fluoride in surface water and health risk assessments in this area. In this study, the fluoride concentrations were determined by using the spectrophotometric method using data from 2013 to 2017 from 9 surface water quality monitoring stations in the upper reaches of the Yongding River. The health risks of fluoride were assessed using the approach developed by the United States Environmental Protection Agency(US EPA). The results indicated that the fluoride content in the drinking water ranged from 0.30 to 1.50 mg L~(-1), with an average of 0.86 mg L~(-1). In total, 22.7% of the analyzed samples exceeded the Chinese limit of 1.0 mg L~(-1) for fluoride, and 5.5% of samples had less than the permissible limit of 0.5 mg L~(-1). Higher fluoride concentrations and fluorosis hotspots were found to be predominately located downstream of the Yanghe River close to the Guanting Reservoir, where 71.4% of samples exceeded the limit of 1.0 mg/L~(-1). The spatial distribution of high fluoride concentrations was found to be primarily determined by industry. The hazard quotient(HQ) index for children, teenagers and adults indicated that 19.6%, 15.6%, and 5.1% of the samples in the upper reaches of the Yongding River, respectively, posed health hazards to the associated groups. Furthermore, the HQ index more than 1 for children, teenagers and adults had values of 64.3%, 56.1%, and 19.4%, respectively, in samples from the downstream region of the Yanghe River. Therefore, there are potential risks of dental and skeletal fluorosis in the upper river reaches of the Yongding River. It is imperative to take measures to reduce the fluoride pollution in surface water and control fluorosis. Action should be taken to improve the disposal of industrial waste.     

Evidence for glaciation in the Northern Hemisphere back to 44 Ma from ice-rafted debris in the Greenland Sea

The widely accepted age estimate for the onset of glaciation in the Northern Hemisphere ranges between 2 and 15 million years ago (Ma). However, recent studies indicate the date for glacial onset may be significantly older. We report the presence of ice-rafted debris (IRD) in ～ 44 to 30 Ma sediments from the Greenland Sea, evidence for glaciation in the North Atlantic during the Middle Eocene to Early Oligocene. Detailed sedimentological evidence indicates that glaciers extended to sea level in the region, allowing icebergs to be produced. IRD may have been sourced from tidewater glaciers, small ice caps, and/or a continental ice sheet.