Variation In Pb Content Research Articles

Threshold and interaction effects of environmental variables affecting the spatial distribution of Pb

Understanding the spatial distribution of soil Pb and its potential influence mechanism is significant for controlling Pb pollution in tea plantations and guaranteeing food safety. The linear and nonlinear relationships between Pb and environmental variables have been widely studied, but the threshold and interaction effects of its environmental variables are often neglected. In this study, 81 tea plantation soils were collected and determined the thresholds and interaction effects of environmental variables on Pb through the GBDT model. The results revealed that the 10 selected environmental variables together explained 71.01 % of the variation in Pb content, with the top three factors being pH, total phosphorus (TP), and distance from roads (dis_road). Most environmental variable had threshold effects on Pb. By visualizing the interaction of pH, TP, and dis_road on Pb concentration, we show that both two-way and three-way interactions are able to further explain its variation. The interaction between TP and dis_road alone accounts for 5.70 %, between pH and dis_road alone accounts for 7.92 %, and between pH and TP alone accounts for 5.83 % of the variation in Pb concentration. However, the three-way interaction between pH, TP, and dis_road alone explains 11.85 % of the variation in Pb concentration. Understanding these interactions is important for gaining insight into the underlying processes leading to Pb pollution and promoting the tea industry’s sustainable development in China and abroad.

Spatial distribution of lead concentration in peri-urban soil: Threshold and interaction effects of environmental variables

Understanding the spatial distribution of soil lead concentration in peri-urban soil and its underlying mechanism is critical to controlling lead contamination, ensuring food safety, and maintaining sustainable urban development. Although the linear and nonlinear relationships between Pb and environmental variables have been extensively studied, the threshold and interaction effects of environmental factors on Pb content are often ignored. This study aims to investigate the threshold and interaction effects and obtain the spatial distribution of Pb content via gradient boosting decision tree. The peri-urban area of Wuhan City, China, was selected as the study area, where soil health was threatened by agricultural production and urbanization and industrialization process. Results showed that the 14 covariates can explain 61.9 % variation of Pb content, in which anthropogenic factors played a major role. Specifically, the Pb content was mainly affected by distance from the industrial enterprises and gasoline stations, population density, elevation, and total nitrogen, which denoted that Pb contamination was mainly originated from industrial production, gasoline stations, urbanized population, and fertilization. All environmental variables had threshold effects on Pb, and the relationship between Pb and these variables mutated when the threshold was exceeded. The results of threshold effects exhibited that Pb was elevated in locations near industrial enterprises (<4 km) or gasoline stations (<1.5 km), with a dense population (>5 person/hectare), and with low elevation (<25 and 45–65 m). The two-way and three-way interaction effects of covariates on Pb content was determined, indicating that the influence of environmental variables on Pb concentration is a complex interaction rather than a simple superposition. These findings highlight the consideration of threshold and interaction effects to understand the underlying processes that lead to Pb contamination, and have important implications for sustainable urban development.

Changing Degree Model of Pb Content Transported by Ocean Currents

Based on the survey data of the waters of Jiaozhou Bay in May, August and October 1992, the change of Pb content and its deposition process in the surface and bottom waters of Jiaozhou Bay were studied. According to the definition and model of Dongfang Yang’s content changing degree, the variation of Pb content at surface and bottom and of Pb content transported by main sea current formed a peak line in the southeast waters of Jiaozhou Bay. The Pb content on the surface reached its peak in August. From May to August, Dongfang Yang’s content changing degree was 79.84°. However, from August to October, it was -85.29°. Specifically, in surface water, Dongfang Yang’s content changing degree from May to August was 62.48°. From August to October, Dongfang Yang’s content changing degree was -39.00°. In the bottom water, Dongfang Yang’s content changing degree from May to August was 70.41°. From August to October, Dongfang Yang’s content changing degree was -80.03°. It indicates that the change of Pb content in surface nearshore waters passed through by the main sea current was determined by the change of Pb content transported by the current. The change of Pb content in surface seawater through the change of ocean currents increases or decreases the increase or decrease of Pb content in surface water —The Pb content of surface water increased or decreased with the increase or decrease of Pb content transported by main sea currents. The Pb content temporal variation in the surface and bottom of the southeastern waters of Jiaozhou Bay from May to October reveals the Pb content settling law: With the increase of Pb content in surface water, the Pb content in bottom water rose faster than that in surface water. When the Pb content in surface water decreased, the Pb content in bottom water decreased much faster than that in surface water. Therefore, the change mechanism of surface and bottom water caused by source transport is proposed with the corresponding model block diagram and changing degree model of Pb content transported by ocean currents.

Variations of Pb Content in the Bottom Waters of the Jiaozhou Bay from the South of the Bay Mouth to the Central Bay Area

According to research data of the Jiaozhou Bay waters in 1992, current variation and horizontal distribution of Pb content in the bottom waters of the Jiaozhou Bay from the south of the bay mouth to the center of the bay were studied. The results show that in May, August, and October, Pb content in the Jiaozhou Bay water ranges from 4.20 to 24.39μg/L, which is in line with the national Class II, Class III, and Class IV seawater quality standards. This result indicates that in May, August and October, in the studied waters, the water quality was slightly, moderately and heavily polluted by Pb content, further revealing that under the effect of vertical water bodies, the bottom waters from the south of the bay mouth to the southeast of the bay, to the center and the southwest of the bay have been severely polluted by human discharge of Pb content. In addition, in the bottom waters of the Jiaozhou Bay from the south of the bay mouth to the center of the bay, Pb content showed high settlement: in May, the southeastern waters; in August, in the central waters; in October, in the southern waters. Therefore, the lead content of Jiaozhou Bay in different months and different places showed high deposition.

The influence of the Pb Content of Source Transport on its Distribution in the Bottom Layer

Based on the survey data of Jiaozhou Bay in 1992, the vertical distribution and seasonal variation of Pb in the surface and bottom waters from the bay center to the south of the bay mouth were studied, and the seasonal distribution, range and horizontal distribution trend of Pb content in the surface and bottom waters were determined. The results show that in May, August and October, Pb content in the waters from the south of the bay mouth to the center of the bay, and in the whole water body from the surface to the bottom, ranged from 4.20 to 24.39 μg/L, which met the national sea water quality standard of class II, class III and class IV. In other words, water quality was mildly, moderately and severely polluted by Pb. In the surface and bottom water, the Pb content was from low to high in May, October and August; In addition, the seasonal change of Pb content in the water body from low to high was as follows: spring, autumn and summer. In May, August and October, when the content of Pb in the surface layer was high, the corresponding bottom layer was high. And when the content of Pb in the surface layer was relatively high, and the corresponding bottom layer was relatively high. It shows that in May, August and October, the loss of Pb content from the surface layer to the bottom layer was relatively large. Further, in the waters from the southeast to the center, in May and August, the horizontal distribution trend of Pb in the surface layer was opposite to that in the bottom layer. But in October, the horizontal distribution trend of Pb in the surface layer was consistent with that in the bottom layer. What’s more, from May to October, the seasonal variation of Pb content in the bottom layer of the water body in the southeastern Jiaozhou Bay was mainly decided by that of Pb content transported by the open ocean current. In the water body in the center of Jiaozhou Bay, the seasonal change of Pb content in the bottom layer was different from that in the surface layer and from that in the ocean current. In terms of time scale, in the waters from the southern bay mouth to the center of the bay, in May, August and October, the Pb content in the surface and the bottom layer changed in the same range, maintaining the consistency. Furthermore, in terms of spatial scale, in May and August, according to the high content and increasing trend of Pb transported by the open sea current, the horizontal distribution trend of Pb in the surface layer was opposite to that in the bottom layer. Nonetheless, in October, the Pb content transported by the open sea current was relatively low and showed a trend of decrease. And the horizontal distribution of Pb in the surface layer was consistent with that in the bottom layer.

Compositional dependence of thermal transport and optical properties of Se85 Ge15-x Pbx (0≤ x ≤10) chalcogenide glassy alloys

In the present work, the ratio of germanium (Ge) to lead (Pb) is varied keeping the concentration of selenium(Se) fixed in the glassy system, Se85 Ge15-x Pbx (0 ≤ x ≤ 10) to optimize the thermal transport and optical properties. The differential scanning calorimetry (DSC) measurements were carried out in the non-isothermal mode to know glass transition temperature (Tg), crystallization temperature (Tc) and melting temperature (Tm). DSC scans of some samples(4 ≤ x ≤ 10) exhibit two glass transition temperatures (Tg), which indicates the presence of co-existing phases in glassy samples. The values of effective thermal conductivity (λe),effective thermal diffusivity(χe) and volumetric heat capacity(QCp) have been determined using transient plane source (TPS) measurements. These parameters show a non-monotonous behavior with the variation of Pb content in the prepared series. These results are explained in terms of chemical bond approach, changes in thermal transfer processes and mechanism of phonon scattering under transitions from dilute to concentrated solid solution. Band gap and Urbach energy have been estimated using Uv–Vis spectroscopy. Optical band gap (~0.65 eV) is minimum for the sample having 4 at.% of Pb. A signature of exciton formation is obtained for this critical composition. Results are explained using structural defect model and by degree of disorder induced, as indicated by a change in intensity and position of the Raman peak corresponding to Se–Se bonds.

Influences of Pb content on the critical current of Bi-2223 multi-filamentary tapes

Multifilament Bi-2223/Ag tapes with different Pb contents in precursor powders were fabricated by powder in tube (PIT) method. The influence of Pb contents on the phase formation, microstructure and critical current density of Bi-2223/Ag tapes were systematically investigated. X-ray photoelectron spectroscopy (XPS) demonstrated that the content and oxidation states change of Pb ions can influence the carrier concentration of superconducting phase. Scanning electron microscopy (SEM) revealed that the variation of Pb content can lead to the difference in microstructure due to the change of thermodynamic properties. The results showed that with the Pb content of x=0.35 in the nominal composition of Bi2−xPbxSr2Ca2Cu3Oy, proper content of liquid phase can be formed during the sintering process, thus maximum critical current (Ic) was obtained. The correlation between the transport property, carrier concentration and Pb content was discussed.

High precision in-situ Pb isotopic analysis of sulfide minerals by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry

An in-situ microanalysis of Pb isotopic compositions in sulfide minerals is carried out by using femtosecond laser-ablation multi-collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS). High-temperature-activated carbon was used to filter Hg contained in the carrier gas, which reduced the Hg background signal by 48% and also lowered the detection limit of the analysis. Fractionation and mass discrimination effects existing in the ICP-MS analytical processes were corrected using an internal reference Tl in conjunction with an external reference NIST SRM 610. The proposed method was used to analyze the Pb isotopic compositions of chalcopyrite, pyrite, and sphalerite from the Dulong Sn-Zn-In polymetallic ore district. The results showed that in this ore district, the sulfide minerals and different grains of the same sulfide mineral show a large variation in Pb content up to 1000-fold. The studied pyrites show relatively higher Pb contents and homogeneous Pb isotopic compositions, whereas the sphalerites have low Pb contents but most variable Pb isotopic compositions. It is suggested that the large variation of Pb isotopic composition may reflect a late hydrothermal superimposition on the primary sulfide formation. In addition, radiogenic Pb accumulated by radioactive decay of trace amounts of U over time in the host minerals may also be one of the causes for the large variation range of Pb content and Pb isotopic composition of those low-Pb sphalerites. Chalcopyrite and sphalerite grains with Pb content greater than 10 ppm presented a consistent Pb isotopic distribution, whereas all the sulfide grains with Pb content greater than 100 ppm had consistent Pb isotopic composition within 2s measurement uncertainties. The in-situ analysis of Pb isotopic composition agreed well with the results obtained by conventional chemical methods within 2s measurement uncertainties, indicating that the data obtained by fsLA-MC-ICP-MS are reliable. Additionally, this study indicates that the Pb isotopic composition could truthfully record the source of ore-forming minerals only for sulfide minerals with high Pb content. On the contrary, the Pb isotopic composition of low-Pb sulfide minerals may be affected by trace amounts of U in the host minerals that may lead to a highly radiogenic Pb isotope ratio. Alternatively, it is also possible that late fluid metasomatic overprinting may alter the Pb isotopic compositions.

Study on the Transport Processes of Pb in Jiaozhou Bay

Based on investigation dada on Pb in April, June, July and October 1982, this paper analyzed the transportation of Pb in Jiaozhou Bay. Results showed that atmosphere deposition, ocean current from the offshore, and the transportation of the head of the islands were the major sources of Pb. These different sources determined different transportation processes of Pb, displayed seasonal variations of Pb content and distribution.

Phase transitional studies of polycrystalline Pb0.4Sr0.6TiO3 films using Raman scattering

Pb 0.4 Sr 0.6 TiO 3 films with submicron size grains have been prepared on Pt substrates by the metalorganic decomposition method. X-ray diffraction analysis reveals that the films are polycrystalline with a perovskite crystal structure and negligible tetragonal splitting at room temperature. The room temperature Raman spectrum, however, shows all the characteristic phonon modes of a tetragonal ferroelectric phase. These modes lose their intensity with an increase in temperature but persist even up to 150 °C. This is in agreement with the dielectric permittivity versus temperature data which show a broad peak–room temperature, and ferroelectric hysteresis persisting up to ∼140 °C. Both Raman and dielectric data are interpreted as due to the presence of a distribution of phases in the film perhaps caused by a variation in Pb content along the film thickness and/or near grain boundary regions.

Model of lead loss in Pb(MgxNb1−x)Oz ion beam sputtered thin films

Thin films of Pb(MgxNb1−x)Oz (hereafter called PMN) have been deposited on carbon substrate by reactive ion beam sputtering, from a mixed oxide–metal multicomponent target composed of magnesium oxide, and metallic niobium and lead. The substrate temperature and sputtering gas composition (oxygen pressure during deposition) were varied and their effects on the film composition and compositional uniformity were investigated. The major effect seen was the systematic variation in Pb content with changes in temperature and gas composition. We also observed a spatial variation in Pb composition across the substrate and believe this to be caused by film bombardment by argon ions specularly reflected by the target surface. This was supported by results showing a systematic reduction in Pb content in films subjected to secondary ion bombardment during film growth. The selective Pb depletion in PMN films is discussed in terms of various mechanisms found in reactive sputtering environments.

Differential accumulation of lead in living and decaying grass on roadside verges

Dead and decaying grass from roadside verges is shown to accumulate more Pb from automotive exhaust fumes than living material. This is thought to be due to the breakdown of the cuticle and the resultant increase in the plants' permeability to water. Results from experiments with different extractants suggest that Pb may be bound in three different ways by both live and dead grass. The variation in Pb content of roadside grass from place to place and from time to time is explained in terms of varying proportions of live and dead leaves and other factors. The capacity of dead grass to bind Pb is compared with that of mosses.