Exploring the fate of heavy metals from mining and smelting activities in soil-crop system in Baiyin, NW China.

The activity and fate of heavy metals (HMs) from mining and smelting activities in farmland soil is of great significance to effectively prevent the excessive enrichment of HMs in crops. This study focuses on Baiyin area, a typical mining city in northwest China. In this example, the sources, speciation, and fate of HMs in the farmland soil, and the migration and enrichment characteristics of HMs in the different parts of crops planted in different areas were studied in detail combining the chemical sequential extraction and Pb isotope approaches. Results showed that the mean anthropogenic contributions of HMs in farmland soils were approximately 85%, 88%, 76%, and 41% for the ore district (OD), Xidagou sewage irrigation area (XSIA), Dongdagou sewage irrigation area, and the Yellow River irrigation area, respectively, and the risk that HMs were excessively accumulated in crops in OD and XSIA was high. Compared with soil residual fractions, the isotope ratios 206Pb/207Pb in non-residual fractions (1.1304-1.1669) were closer to the values of local ores, suggesting that anthropogenic HMs from mining and smelting activities were mainly enriched in the non-residual fractions. The isotope ratios 206Pb/207Pb in crops (1.1398-1.1686) further confirmed that those anthropogenic HMs were more easily absorbed and concentrated by crops. HMs contents in leaves from OD and XSIA were generally higher than that in roots, suggesting that atmospheric deposition in OD and XSIA had a greater impact on the HMs concentration of crop leaves，while the excess rate of HMs in grain/fruit was the lowest in all parts of crops. The division and classification of crop planting in mining area can effectively help minimize the risk that HMs from anthropogenic source enter the human body through the food chain.

Lead isotopic fingerprinting as a tracer to identify the pollution sources of heavy metals in the southeastern zone of Baiyin, China.

Baiyin (Gansu Province, China) is a heavily industrialized city with non-ferrous metal mining, ore dressing, and chemical production. The surrounding district has suffered from serious heavy metals (HMs) contamination over half a century. In this study, a Pb isotopic approach was adopted to trace the sources of HMs and explore the environmental behaviors of HMs in the area surrounding Baiyin. HMs concentrations in topsoil showed a clear decrease as the distance from the ore district increased, which suggested that atmospheric transportation is one of the main pathways of HMs dispersal. The Dongdagou irrigation area was an exception where contaminated water from Dongdagou had been used for a long time. The plots of 206Pb/207Pb vs. 208Pb/206Pb and 1/Pb vs. 206Pb/207Pb from the topsoil samples could be described in terms of a binary mixing model with the two average 206Pb/207Pb end-members being (1) the mining and smelting activities (1.1494) and (2) the soil background (1.1992). The relative anthropogenic contribution quickly decreased from 88.3% in the ore district to 30.6% in the Yellow River irrigation area. These results suggested that HMs in the Baiyin District were mainly contributed by anthropogenic mining and smelting activities. The isotope ratios of 206Pb/207Pb in the sediments maintained a consistent low level from the ore district to the Yellow River irrigation area, thereby suggesting that HMs from anthropogenic sources could also be transported over a long distance in the river systems. Moreover, the positive correlation between S content and HMs concentrations in topsoil and sediment confirmed that the HMs mainly originated from the sulfide deposits and smelters.

Experimental Study on Residual Bending Strength of Corroded Reinforced Concrete Beam Based on Micromagnetic Sensor.

This paper presents a nondestructive test method to evaluate the residual bending strength of corroded reinforced concrete beam by analyzing the self-magnetic flux leakage (SMFL) signals. The automatic scanning device was equipped with a micromagnetic sensor and sensor-based experimental details were introduced. Next, the theoretical formula of the normal component HS(z) of the SMFL signal that originated from the corroded region was derived based on the magnetic dipole model and the experimental results were discussed. The results indicate that the experimental data of HS(z) are consistent with the theoretical calculations, both location and extent of the steel bars corrosion can be qualitatively determined by using HS(z). The gradient K of HS(z) is approximately linearly related to the loss rate, S, of the bending strength, which can be used to evaluate the residual bending strength of the corroded reinforced concrete beam. This work lays the foundation for evaluating the residual bending strength of corroded reinforced concrete beams using the SMFL signal; the micromagnetic sensor is further applied to the civil engineering.