A Study On Heavy Metals Pollution And Their Effects On Bacterial Community In Farmland Soil Nearby A Smelting Plant

ObjectiveTo evaluate the condition of heavy metal pollution and explore the influence of heavy metal contamination on the bacteria community in the farmland soil near a lead and zinc smelting factory.MethodsSeven agricultural observation areas(G1~G7)were selected with different distances(from 741 m to 2556m)to the main chimney of the smelting plant,from the west side of the factory(the leeward side of the dominant wind direction).Twenty-eight mixed soil samples were collected totally in four seasons.The concentrations of heavy metals(Hg,As,Pb,Cd,Cu,Zn,Ni,and Cr)in agricultural soils were detected by solid mercury meter method,atomic fluorescence spectrometry,inductively coupled plasma emission spectrometry and inductively coupled plasma mass spectrometry determination,respectively.Single cumulative index method,Nemerow index method and Hakanson potential ecological risk index method were used to assess the accumulation of heavy metals and potential ecological risk of the farmland.Health risk assessment model recommended by USEPA was used to evaluate the non-carcinogenic risk and carcinogenic risk of 8 kinds of heavy metals to adults and children.Polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE)technique and Illumina MiSeq sequencing based on16 S rRNA gene were applied for investigating the diversity and structure of bacterial community.Results1.The condition of heavy metals pollution: the contents of Cd,Pb,As,Hg,Cu,and Zn were found excess the standard.Cd and Pb pollution were serious in 28 samples with the highest exceed standard multiples up to 42.33 and 6.43,respectively.Six heavy metals' contents in G1 and G2 were higher than that in G4-G7,and the differences were statistically significant(P<0.05).Six kinds of heavy metals contents were negatively related to the distance of the factory(P<0.05).Positive relationshipof six kinds of heavy metals contents was found significantly(P<0.05).And contents of As,Ni,Cr in different seasons were different with statistical significance(P<0.05).2.Potential ecological risk assessment: Single cumulative indexes of Cd,Pb and Hg ranged from 9.25 to 342.69 and reached up to most severe level.Nemerow indexes of seven observation areas were also most severe between 731.13 and30588.88,the range of Hakanson potential ecological risk indexes of Cd and Pb was370.00~10280.70 and the total potential ecological risk(1620.29~14059.37)of seven observation areas was extremely severe.3.Health risk assessment: The non carcinogenic health risk index of lead by hand exposure way on children was 2.44,and the maximum total no carcinogenic risk value of children's health from eight kinds of heavy metals in agricultural soils was3.42,which exceeded the no-carcinogenic risk limit value.the carcinogenic health risks of As for adults and children(1.36×10-5~4.28×10-5and 9.56×10-5~3.00×10-4)compared with Hazard Index were 13.6~42.8 times and 95.6~300 times respectively.4.The DGGE profile indicated that 23 bands were found in the first season,which was the most abundant.While only 10 bands were found in the third season,which was the least.There were five kinds of bacteriophytas found that were proteobacteria,actinobacteria,acidobacteria,chloroflexi,and pseudomonas respectively.Proteobacteria was the dominant bacterial in all soils samples.Principal component analysis and cluster analysis showed that the difference of bacteria community structure was slight in G1 and G2,both with severe contamination of heavy metals.However,when compared to the other areas their differences were significant.What's more,redundancy analysis showed that the distribution of bacteria community was affected by heavy metals and the physiochemical factors in seven areas,especially in G1,G2,G6 and G7.5.34 phylums,99 classes,138 orders,152 familys and 166 genuses and 50 species were detected by Illumina MeSeq sequencing method.Proteobacteria,actinobacteria,and acidobacteria were the dominant bacterials in all soils samples which were about more than 95% of the relative abundance of all microbes.The Chao index,ACE index,Simpson index and Shannon index of the G1 observation areawere the lowest,that were 4009.14,4180.53,9.40 and 0.994 respectively,and far lower than those in the G7 observation area which had the highest bacterial diversity.The distribution of the abundance of bacteroidetes,armatimonadetes,elusimicrobia and chlorobi were significantly different among seven observation areas(P < 0.05).The relative abundance of chlorobi in G1 observation area was highest,and the difference was statistically significant compared to that in G2~G7(P values were less than 0.05).Cpmpared with G7,the relative abundance of armatimonadetes in G1 observation area was significant decreased(P < 0.05).Compared with G3-G7 observation areas,relative abundances of arthrobacter,blastococcus and cupriavidus in G1 observation area were increasing significantly and relative abundances of thermomonas and candidatus solibacter were reducing significantly(P values were less than 0.05).Redundancy analysis showed that the content of heavy metals had geart influence on the bacterial community than the moisture content factor.Conclusion1.Cd,Pb and Hg are the major pollutants in observed farmland.Concentrations of Cd,Pb and Hg there reach up to severe accumulation and have an extremely severe ecological risk.The concentration of lead has non-carcinogenic to the health of children,and arsenic level has carcinogenic risk to the health both of children and adult.2.Heavy metals pollution reduces the bacteria microbial diversity and is the main factor influencing the distribution of microbial communities.The abundance of armatimonadetes,thermomonas,and candidatus solibacter are mainly reduced.