| A large number of industrial "three wastes" which contains toxic and harmful pollutants are generated through the production process of Coke and its by-products,and the polycyclic aromatic hydrocarbons(PAHs)are the characteristic pollutants in the coking production process.China has the largest coke production capacity in the world.The rapid development of coking industry in recent years has created even more severe PAHs pollution in China than any other countries of the world.Along with the attention of the importance of food security and health,it is particularly important to study the influence of characteristic pollutants systematically in coking industry on the surrounding farmland ecological environment and the risk to people’s health.In this study,16 kinds of PAHs with great harm and representative optimal control were selected as observation markers.Based on the long-term investigation and monitoring around typical coking enterprises in Shanxi Province,the impacts of PAHs emissions from coking enterprises on farmland soil-wheat was systematically examined.This study has also provided the scientific evidence for soil environmental protection and food safety production in the surrounding farmland of coking enterprises.The main conclusions are as follows:1.PAHs are mainly discharged into the atmospheric environment through coking industrial waste gas,then entering the surrounding farmland soil environment through atmospheric dry and wet deposition.From the model simulation results,the closer to the coking plant the greater the deposition of PAHs,therefore,the stronger the cumulative effect on the soil environment.In terms of the composition,2~3 rings were the main contribution ofΣ16PAHs in the waste gas of coking enterprises,then followed by 4 rings.5~6 rings were considered to be the lowest.2.The concentration range of Σ16PAHs on the surface farmland soil in the study area was from 2072.0 to 8034.5 ng/g,and the average value was 4209.7 ng/g,which is at a high level compared with other relevant research areas in China.In terms of composition,3~4rings were the main contribution of 16 PAHs,followed by 5~6 rings,and the lowest was 2-ring.This was mainly due to the 2-ring PAHs are low molecular weight,which is easy to volatilize and degrade,as well as difficult to accumulate.The concentration of PAHs in farmland surface soil in the study area has certain peculiarity,in which it tends to be decreased by the increasing distance from the coking enterprises and accumulates with time.It was obviously affected by the emission of PAHs in the waste gas of coking enterprises.The results of the soil environmental risk assessment have shown that the pollution risk has already existed in the farmland surface soil in the study area,especially the distance was less than 1000 m away from the coking plant,in which the average concentration of TEQBa P has exceeded 1000 ng/g,and considered as a serious pollution.With the increasing operation time of the coking enterprises among the study area,the toxicity of PAHs in surrounding farmland soil will be accumulated gradually,and the pollution risk cannot be ignored.3.There were significant differences in the biochemical properties of the farmland surface soil between the downwind three groups and the upwind control group.The soil p H of the downwind three groups was significantly lower than that of the upwind control group at the level of 0.05.Soil alkali hydrolyzable nitrogen,organic matter,sucrase and phosphatase were significantly higher than the upwind control group at the level of 0.05.In comparison to the upwind control group,total amounts of bacterial OTUs and the number of unique OTUs in the downwind three groups of soil samples are less its richness of bacterial species is lower,moreover,the flora structure has a great difference.Among the three downwind groups,the soil p H of 1500 m group was more neutral,and the contents of soil alkali hydrolyzable nitrogen,available phosphorus,organic matter and phosphatase of 1500 m group were significantly higher than those of 1000 m group and 2000 m group.The total amount of OTUs,unique OTUs and sobs index of 1500 m group were also significantly higher than those in the other two groups,and the richness of bacterial species was higher.In conclusion,the impact of PAHs emission from coking enterprises on the biochemical properties of farmland surface soil in the study area was complex,it did not necessarily change regularly with the increasing distance of the coking plant.Furthermore,it may have both promoted and inhibited effects of the soil bacterial diversity at the same time.4.The content of PAHs in surface soil of farmland in the study area was significantly positively correlated with soil organic matter at the level of 0.05,and negatively correlated with available potassium at the level of 0.05,but not with other soil chemical properties and enzyme activities.It is indicated that the organic matter and available potassium in farmland surface soil in the study area may be affected by the emission of PAHs from the coking enterprises.Soil bacterial community had significant positive correlation with the concentration of soil 4-ring and 5-ring PAHs and Σ16PAHs,which indicates that the PAHs of the farmland soil in the study area has certain impacts on the bacteria community,in which 4-ring and 5-ring PAHs are still considered as the main components.Regarding to other the soil chemical properties and Enzyme activity index,the content of soil PAHs in soil had less impact on soil bacterial community;whereas the impact of soil PAHs pollution on soil bacteria had certain variability.The content of the study area’s PAHs in soil had significant positive correlation with the relative abundance of dominant phylum Proteobacteria,the dominant genus Rb41 and Sphingomonas.Rb41 and Sphingomonas were enriched in the downwind 1000 m group,and their abundance tended to decrease from the increasing distance of the coking plant.5.The content of Σ16PAHs in 2020 wheat seed samples in the study area ranged from55.6 to 117.8ng/g,with an average of 83.2 ng/g.From the composition of PAHs,2~4 rings were the main contribution of 16 PAHs,in which Nap,Phe,Fla,Pyr and Bb F were mainly in wheat seeds.From the perspective of spatial distribution,the closer to the coking plant,the higher the PAHs pollution level of crop seeds.Pearson correlation analysis showed that there was a significant positive correlation between the content of PAHs in farmland surface soil and those in wheat seeds.This indicates that the wheat in the study area has been affected by the emission of PAHs from the coking enterprises.6.The results of the Health Risk Assessment have shown that certain health risk has indeed existed among both adults and children through their ingestion of wheat seeds in the study area,though it was within the acceptable range.From the perspective of spatial trend,the carcinogenic risk and non-carcinogenic risk of ingestion of wheat seeds has shown that the closer to the coking plant,the higher the risk.The non-carcinogenic risk of 1000 m group and1500 m group was significantly higher than that of 2000 m group and control group at the level of 0.05.It explains that more attention should be paid on the study of the environmental safety of wheat seeds,which within 1500 m away from the downwind of the coking enterprises in the study area. |
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