scholarly journals A search for heavy-metal stars: abundance analyses of hot subdwarfs with Subaru★

2019 ◽  
Author(s):  
Naslim N ◽  
C S Jeffery ◽  
V M Woolf
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
High Surface ◽  
Surface Enrichment ◽  
Metal Enrichment ◽  
Small Subgroup ◽  
Show Evidence ◽  
Hot Subdwarfs ◽  
Chemical Peculiarity ◽  
Heavy Metal Enrichment

Abstract The discovery of extremely zirconium- and lead-rich surfaces amongst a small subgroup of hot subdwarfs has provoked questions pertaining to chemical peculiarity in hot star atmospheres and about their evolutionary origin. With only three known in 2014, a limited search for additional ‘heavy-metal’ subdwarfs was initiated with the Subaru telescope. Five hot subdwarfs having intermediate to high surface enrichment of helium were observed at high-resolution and analyzed for surface properties and abundances. This paper reports the analyses of four of these stars. PG 1559+048 and FBS 1749+373, having only intermediate helium enrichment, show strong lines of triply ionized lead. PG 1559+048 also shows a strong overabundance of germanium and yttrium. With more helium-rich surfaces, Ton 414 and J17554+5012, do not show evidence of heavy-metal enrichment. This limited survey suggests that extreme enrichment of ‘heavy metals’ by selective radiative levitation in hot subdwarf atmospheres is suppressed if the star is too helium-rich.

scholarly journals Soil Heavy Metal Distribution with Depth around a Closed Landfill and Their Uptake by Datura stramonium

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Peace Makuleke ◽  
Veronica M. Ngole-Jeme
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Transfer Coefficient ◽  
Datura Stramonium ◽  
Metal Transfer ◽  
Control Site ◽  
Soil Samples ◽  
Metal Enrichment ◽  
Soil Heavy Metal ◽  
Heavy Metal Enrichment

Landfills are major sources of environmental pollution. This study evaluated heavy metal concentrations in soils and plants around the closed Lumberstewart landfill in Bulawayo, Zimbabwe, to determine the pollution potential of a closed landfill and the risks they present to plants growing in this environment and surrounding communities. Soil samples were collected at depths of 0–30 cm, 30–60 cm, and 60–90 cm around the landfill and at a control site and characterized for various properties and concentrations of Cd, Cu, Cr, Fe, Ni, and Zn. Samples of Datura stramonium, collected from the same sites where soil samples were collected, were also analyzed for the same heavy metals. The soils were sandy, mostly acidic (5.01 < pH < 7.65) with low organic matter content (<2%) and cation exchange capacity (<15 meq/100 g). These properties varied with depth around the landfill. Heavy metals concentrations in the soils and Datura stramonium followed the order Fe > Zn > Cu > Cr > Ni > Cd with samples from around the landfill having higher concentrations than samples from the control site. Soil heavy metal enrichment was highest at a depth of 30–60 cm. Pollution load index (PLI) values indicated that all sites around the landfill were polluted (PLI > 1). Heavy metal transfer coefficient in Datura stramonium ranged between 0.0 and 209 with <60% of the variation observed in heavy metal transfer coefficient in Datura stramonium explained by the extent of heavy metal enrichment in the soils. More than 20 years after closure of the landfill, there are indications that leachate migration may still be going on around the landfill. Monitoring of environments around closed landfills needs to be ongoing to mitigate negative impacts on humans and the environment.

scholarly journals Environmental Background Values and Ecological Risk Assessment of Heavy Metals in Watershed Sediments: A Comparison of Assessment Methods

Water ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 51
Author(s):  
Jianbo Liao ◽  
Xinyue Cui ◽  
Hai Feng ◽  
Shangkun Yan
Keyword(s):  
Heavy Metals ◽  
Risk Assessment ◽  
Heavy Metal ◽  
Risk Index ◽  
Aquatic Organisms ◽  
Total Content ◽  
Metal Enrichment ◽  
Background Values ◽  
Positive Linear Correlation ◽  
Heavy Metal Enrichment

The distribution and assessment of heavy metal pollution in sediments have been extensively studied worldwide. Risk assessment methods based on total content, background values, and sediment quality guidelines are widely applied but have never been compared. We systematically sorted out these evaluation methods, obtained evaluation results using actual monitoring data, and compared their applicability. The results showed that the background values of different metals are significantly different, which may depend on their mobility. Geoaccumulation index (Igeo) and enrichment factor (EF) values invariably decreased with the increase of background values for individual heavy metal enrichment risk assessment. Compared with EF, Igeo also showed a significant positive linear correlation with heavy metal content. Pollution load index (PLI), modified contamination degree (mCd), and potential ecological risk index (RI) showed significant differences in response to background values and evaluation levels for the comprehensive risk of heavy metal enrichment, but their distribution trends along with the sampling points were basically identical. Toxic risk index (TRI), mean ERM quotient (mERMQ), and contamination severity index (CSI) were used to evaluate the damage degree of complex heavy metals to aquatic organisms and shared a similar whole-process distribution trend. The modified hazard quotient (mHQ), which is used to evaluate the toxicity of a single heavy metal to aquatic organisms, showed a significant positive linear correlation with the total content of each heavy metal, indicating that the toxic effect on organisms can be predicted through the direct monitoring. The results of this study have important guiding significance for the selection of evaluation methods for heavy metal pollution in sediments.

scholarly journals Heavy metal enrichment in the riparian sediments and soils of the Three Gorges Reservoir, China

2015 ◽  
Vol 367 ◽  
pp. 244-250 ◽  
Author(s):  
Q. Tang ◽  
Y. Bao ◽  
X. He ◽  
A. Wen
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Three Gorges Reservoir ◽  
Riparian Zone ◽  
Three Gorges ◽  
Metal Enrichment ◽  
Vertical Transfer ◽  
The Three Gorges ◽  
Riparian Soils ◽  
Heavy Metal Enrichment

Abstract. The Three Gorges Reservoir encompasses a riparian zone with a vertical height of 30 m and a total area of 349 km2 that has been subjected to alternate inundation and exposure due to regular impoundment. Sedimentation on the riparian landforms constitutes an important pathway for riverine contaminant redistribution. In an attempt to understand heavy metal enrichment since water inundation, riparian sediments and soils were sampled along five transects in a typical riparian zone composed of cultivated bench terraces in the middle reaches. Heavy metals (Cr, Ni, Cu, Zn, As, Cd and Pb) were determined to characterize the lateral distribution and vertical transfer ratio. The results indicated that all heavy metals were enriched to varying extents both in the riparian sediments and soils, compared with regional background contents in soils and the reference levels in sediments. However, heavy metal levels in the riparian sediments were generally higher than those in the riparian soils, while those in the upper riparian soils (0–5 cm) were overall slightly higher than those in the lower riparian soils (5–10 cm). There was a decreasing trend of heavy metal contents with increasing elevation. The elevated levels of heavy metals in the riparian sediments may be attributed to sediment yields from upstream anthropogenic sources, especially during major rainstorms in the wet season when large loads of contaminated sediment may be produced from diffuse source areas. Heavy metals can also be adsorbed to pure sediment in the course of mobilization or after deposition. Considering that the riparian soils are local weathering products without mobilization, the enrichment of heavy metals may principally be ascribed to chemical adsorption from dissolved fractions or vertical transfer from overlaid sediments. Heavy metal enrichment may further be affected by the specific type of hydrologic regime such that relatively long flooding duration caused by water impoundment and natural floods was responsible for the relatively higher levels of heavy metals in the lower portions of the riparian zone.

Earthworm Processing of Livestock Manure and Accumulation of Heavy Metals

2012 ◽  
Vol 573-574 ◽  
pp. 1129-1133 ◽  
Author(s):  
Ji Cai Qiu
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Organic Waste ◽  
Cow Dung ◽  
Optimum Conditions ◽  
Metal Enrichment ◽  
Heavy Metal Elements ◽  
Enrichment Techniques ◽  
Animal Feces ◽  
Strong Ability

The earthworm is an omnivorous animal low saprophytic, has a strong ability to decompose organic waste. The earthworm can directly grows on dung, consume a large amount of organic waste, numerous research reports, earthworm on heavy metal elements have very strong enrichment. Therefore, the use of earthworms as a bioreactor for animal feces, excessive heavy metals to biological concentration, reduce the content of heavy metals in animal feces, is a task that is worth to discuss. Taking the rural animal feces in the largest number, the most widely distributed of cow dung as study objects, to carry out the earthworm absorption in cow dung, Zn Pb Cu, the study of the optimum conditions for the further study of Earthworm on cattle manure, heavy metal enrichment techniques provide a basis.

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