Rapid detection and risk assessment of soil contamination at lead smelting site based on machine learning

A general prediction model for seven heavy metals was established using the heavy metal contents of 207soil samples measured by a portable X-ray fluorescence spectrometer(XRF)and six environmental factors as model correction coefficients.The eXtreme Gradient Boosting(XGBoost)model was used to fit the relationship between the content of heavy metals and environment characteristics to evaluate the soil ecological risk of the smelting site.The results demonstrated that the generalized prediction model developed for Pb,Cd,and As was highly accurate with fitted coefficients(R~2)values of 0.911,0.950,and 0.835,respectively.Topsoil presented the highest ecological risk,and there existed high potential ecological risk at some positions with different depths due to high mobility of Cd.Generally,the application of machine learning significantly increased the accuracy of pXRF measurements,and identified key environmental factors.The adapted potential ecological risk assessment emphasized the need to focus on Pb,Cd,and As in future site remediation efforts.

Migration and distribution characteristics of soil heavy metal(loid)s at a lead smelting site

Heavy metal(loid)s contamination is a constant issue at smelting sites.It is essential to investigate the spatial distribution and migration characteristics of heavy metal(loid)s in the soil for environmental management and remediation strategies of non-ferrous smelting sites.In this study,203 soil samples from 57 sites were collected in a typical lead smelting site.The findings demonstrated that there were significant Pb,Zn,Cd,and As contamination in soil samples.The spatial distribution of heavy metal(loid)s showed strong spatial heterogeneity,the contaminated soil areas of Pb,As,Cd,and Zn were 99.5%,98.9%,85.3%,and 72.4%,respectively.Pb,Cd,and As contamination of the soil reached a depth of 5 m,which migrated from the surface to deep soil layers.The leaching contents of Zn,Pb,and As decreased obviously in 3-4 m soil layer,but the leaching content of Cd was still high,which indicated the high migration of Cd.With the increase of depth,the proportion of acid soluble fraction of heavy metal(loid)s decreased,and the residual fraction increased.The acid soluble fraction of Cd accounted for a higher proportion,and As mainly existed in reducible and residual fractions in soil.According to the calculation of the migration factor,the migration of heavy metal(loid)s in soils were ordered as Cd>Zn>Pb>As.The outcomes are advantageous for risk reduction and site remediation for non-ferrous metal smelting sites.

Effects of soil metal(loid)s pollution on microbial activities and environmental risks in an abandoned chemical smelting site

Abandoned chemical smelting sites containing toxic substances can seriously threaten and pose a risk to the surrounding ecological environment.Soil samples were collected from different depths(0 to 13 m)and analyzed for metal(loid)s content and fractionation,as well as microbial activities.The potential ecological risk indices for the different soil depths(ordered from high to low)were:1 m(D-1)>surface(S-0)>5 m(D-5)>13 m(D-13)>9 m(D-9),ranging between 1840.65-13,089.62,and representing extremely high environmental risks,of which Cd(and probably not arsenic)contributed to the highest environmental risk.A modified combined pollution risk index(MCR)combining total content and mobile proportion of metal(loid)s,and relative toxicities,was used to evaluate the degree of contamination and potential environmental risks.For the near-surface samples(S-0 and D-1 layers),the MCR considered that As,Cd,Pb,Sb,and Zn achieved high and alarming degrees of contamination,whereas Fe,Mn,and Ti were negligible or low to moderate pollution degrees.Combined microcalorimetry and enzymatic activity measurements of contaminated soil samples were used to assess the microbial metabolic activity characteristics.Correlation analysis elucidated the relationship between metal(loid)s exchangeable fraction or content and microbial activity characteristics(p<0.05).The microbial metabolic activity in the D-1 layer was low presumably due to heavy metal stress.Enzyme activity indicators and microcalorimetric growth rate(k)measurements were considered sensitive indicators to reflect the soil microbial activities in abandoned chemical smelting sites.

A practical method for identifying key factors in the distribution and formation of heavy metal pollution at a smelting site

Smelting activities are the main pathway for the anthropogenic release of heavy metals(HMs)into the soil-groundwater environment.It is vital to identify the factors affecting HMs pollution to better prevent and manage soil pollution.The present study conducted a comprehensive investigation of HMs in soil from a large abandoned Zn smelting site.An integrated approach was proposed to classify and quantify the factors affecting HMs pollution in the site.Besides,the quantitative relationship between hydrogeological characteristics,pollution transmission pathways,smelting activities and HMs pollutionwas established.Results showed that the soils were highly contaminated by HMs with a pollution index trend of As>Zn>Cd>Pb>Hg.In identifying the pollution hotspots,we conclude that the pollution hotspots of Pb,As,Cd,and Hg present a concentrated distribution pattern.Geo-detector method results showed that the dominant driving factors for HMs distribution and accumulation were the potential pollution source and soil permeability.Additionally,the main drivers are variable for different HMs,and the interaction among factors also enhanced soil HMs contamination.Our analysis illustrates how the confounding influences from complex environmental factors can be distilled to identify key factors in pollution formation to guide future remediation strategies.

Spatial distribution, environmental risks, and sources of potentially toxic elements in soils from a typical abandoned antimony smelting site

The rapid development of the smelting industry increases the release of antimony(Sb)into the soil environment,which threatens human health and ecosystems.A total of 87 samples were collected from an abandoned Sb smelting site to evaluate pollution characteristics and environmental risks of the potentially toxic elements(PTEs).The contents of As,Cu,Ni,Pb,Sb,and Zn in the fresh soils determined by P-XRF were 131,120,60,145,240,and 154 mg/kg,respectively,whilst following drying,grinding,and sieving pretreatments,the corresponding contents increased to 367,179,145,295,479,and 276 mg/kg,respectively.There was a significant correlation between the data obtained by P-XRF and ICP-OES in the treated samples,which showed the application feasibility of P-XRF.The average contents of Sb and As were 440.6 and 411.6 mg/kg,respectively,which exceeded the control values of the development land in GB 36600-2018.The ecological risk levels of the six PTEs decreased in the following order:As>Sb>Pb>Zn>Ni>Cu.Non-carcinogenic risk revealed that As,Pb,and Sb posed health risks for children,whilst for carcinogenic risk,the risk values for As and Ni were higher than the limit values for both children and adults.Anthropogenic sources accounted for more than 70.0%of As,Pb,and Sb concentrations in soils,indicating a significant influence on PTEs accumulation.The findings provide a basis for quick determination of the contamination characteristics and risk control of PTEs at Sb smelting sites.

Washing out heavy metals from contaminated soils from an iron and steel smelting site

Washing is a promising method for separating contaminants bound to the particles of soil ex-situ by chemical mobilization. Laboratory batch washing experi- ments were conducted using deionized water and varying concentrations of oxalic acid, citric acid, tartaric acid, acetic acid, hydrochloric acid and ethylenediaminetetra acetic acid （EDTA） to assess the efficiency of using these chemicals as washing agents and to clean up heavy metals from two heavily polluted soils from an iron and streel smelting site. The toxicity reduction index and remediation costs were analyzed, and the results showed that the soils were polluted with Cd, Pb and Zn. Hydrochloric acid and EDTA were more efficient than the other washing agents in the remediation of the test soils. The maximum total toxicity reduction index showed that 0.5 mol·L^-1 hydro- chloric acid could achieve the remediation with the lowest costs.

Evolution of the“ancient Kedah”:A study on urban forms at Sungai Batu Archaeological Complex(SBAC),Bujang Valley,Kedah,Malaysia

Archaeological research at the Sungai Batu Archaeological Complex(SBAC),which has been carried out until 2023,aims to complete the chronological data and urbanization process of the ancient Kedah.This study will especially prove that the ongoing urbanization process is aimed at developing the iron smelting industry and trade in ancient Kedah,especially in SBAC.This is because archaeological research at SBAC has proven that with the existence of the ancient Kedah iron smelting workshop at SBAC,river jetties,port management,rituals,and Buddhist monuments began to be erected,all of which can be determined by chronometric dating.The results of the chronometric dating have proven that the ancient Kedah Kingdom existed since the 6th century BC and was oriented towards the trade of iron resources,which allowed the use of the area to grow rapidly.The process of urbanization and land use clearly conforms to Lynch’s principle,which emphasizes the principles of 1)paths,2)edges,3)districts,4)nodes,and 5)landmarks in the development process of land use and urbanization in the complex.