Bioaccessibility Of Heavy Metals In Soil-crop System Around Typical Lead-acid Power Plants In Shandong Province

With the rapid development of industrialization and urbanization in China,China is facing a huge challenge in soil prevention and control.The heavy metal emissions(especially lead)caused by the rapid development of the battery industry have brought serious pollution to the surrounding soil,crops and air environment,and have received widespread attention.Heavy metals in soil can accumulate in crops and enter the food chain,posing a potential risk to human health.In addition,soil ingestion is one of the important pathways for human exposure to heavy metals.Heavy metals have toxic effects,and over time,and they will accumulate highly in the living body,which in turn can cause serious diseases.Therefore,this experiment took the soil-crop system around a typical lead-acid power plant in Shandong Province as the research object,and investigated the distribution patterns of heavy metal contents in soil and wheat.The absorption and accumulation capacity of wheat on heavy metals and potential human health risks were analyzed.In order to better understand the harm caused by oral ingestion of heavy metals in soil,the bioaccessibility of soil heavy metals at different stages of digestion was evaluated by in vitro methods(combination of PBET model and SHIME model).Subsequently,16 S r RNA high-throughput sequencing was used to analyze the effects of soil heavy metal exposure on the structure and species richness of gut microbial community.The specific results of the study are as follows:(1)The soil samples around the lead-acid power plant had a certain degree of accumulation of heavy metals,especially Pb.The concentration of Pb in all samples exceeded the local soil background value,with a range of 23.8～303.4 mg/kg;while the concentration of Cd ranged from 0.057～6.181 mg/kg,with a large degree of variation.In addition,the result of Spearman correlation analysis showed that the concentrations of cadmium,zinc and chromium in the soil showed a significant positive correlation with the concentration of lead(P < 0.05),indicating that they may come from the same source of pollution.The results of the analysis of five metal elements(lead,cadmium,zinc,copper and manganese)in wheat showed that the lead content in some(27.78%)of the wheat in the region exceeded the national standard limit(GB2762-2022),while the cadmium levels were all within the national standard limit.(2)The capacity of wheat to uptake and accumulate heavy metals was quantified by calculating the bioconcentration factor(BCF),and the result showed that the enrichment capacity of wheat for heavy metals was Zn > Cd > Cu > Mn > Pb.Although the local soils generally exhibited some heavy metal Pb accumulation effects,wheat did not show a strong ability to uptake and accumulate elemental Pb.Subsequently,the potential human health risks from wheat ingestion were evaluated,and the results indicated that the target hazard quotients(THQ)for metals in wheat were all below the safety threshold of 1 and were unlikely to cause harmful health effects in adults;however,the hazard index(HI)was slightly above 1,indicating that a carcinogenic risk may occur from consumption of wheat in this region.(3)The bioaccessibility of heavy metals in the soil around the lead-acid power plant in the stomach,small intestinal and colon stages was evaluated by combining the PBET model and the SHIME model,and the results showed that the bioaccessibility of lead and cadmium in the stomach,small intestinal and colon stages showed a decreasing trend,and the gut microorganisms further reduced the bioaccessibility of lead and cadmium.(4)Exposure to exogenous soil heavy metals altered the structure and species richness of the gut microflora.At the phylum level,the relative abundance of Firmicutes and unidentified Bacteria was reduced,while the relative abundance of Proteobacteria,Synergistota,Bacteroides and Actinobacteria increased.Heavy metal concentrations and their bioaccessibility were correlated with microbial species,among which 4 microbial species were significantly positively correlated with cadmium bioaccessibility at the colon stage,7 microbial species were significantly negatively correlated with it,and only Bifidobacterium species was significantly positively correlated with total Cd;no microbial species was found to be significantly correlated with total Pb and its bioaccessibility.In summary,the soil and wheat samples around the lead-acid power plant showed a certain cumulative effect on heavy metals,especially the content of Pb in the soil;wheat has a relatively weak capacity to absorb and accumulate heavy metals and is less contaminated.The bioaccessibility of soil heavy metals was investigated by in vitro methods,and the results showed that soil heavy metals are not 100% absorbed and utilized in the human body,and that health risk assessment based on total concentrations would overestimate the human health risk they generate;furthermore,there is a strong link and interaction between exogenous soil heavy metal exposure and gut microorganisms.