Research On The Ecological Health Risk And Toxicity Effects Of Soil From Coal Gangue Stacking Area

In recent years,due to rapid economic developments and soaring demands for coal,China has become the largest coal producing and consuming country in the world.In 2019,raw coal production in China reached 3.85 billion tons,accounting for about 50% of the total global production.Although Chinese Government has vigorously promoted the use of clean energy sources,such as nuclear powers,wind powers,solar energies and natural gases,but so far,coal still accounts for 69.3% of China's total energy production and has always maintained its first place.Solid wastes produced and discharged in processes of coal mining and dressing constitute 10%-30% of raw coal productions,which is called coal gangue.Total accumulative stockpile of gangues in China has reached 7.0 billion tons,by 2017,more than 1,600 large-scale coal gangue hills had occupied 15,000 hectares,and approximately 150-300 million tons of additional gangues were generated per year.Shanxi Province,a major energy province with abundant coal resources in China,where accumulated coal gangues generated through coal mining exceed 1 billion tons and still increase at a rate of 50 million tons per year.Coal gangue hills are prone to spontaneous combustions and release a large amount of toxic and harmful substances(mainly heavy metals and polycyclic aromatic hydrocarbons(PAHs))into surrounding environment through weathering and rainwater leaching,causing ecological fragilities for surrounding environment and potential health risks for local residents.Due to complex soil pollutions caused by coal gangue accumulations,researches on soil pollutions,ecological health risk assessments and toxicological effects of coal gangue stacking areas are still limited,especially systematic studies on exposure-effect-mechanisms.In this study,we analyzed pollution characteristics and ecological health risks of soil samples around three typical coal gangue stacking areas in Shanxi Province,and further explored their toxicity effects and mechanisms.This work is aimed to provide technical supports and scientific bases for managements and controls of soil ecological health risks in coal gangue stacking areas.1.Mining activities will cause serious pollutions to surrounding soil environment.Although existing studies have shown that soil in coal gangue stacking areas is contaminated by heavy metals and PAHs,researches on contributions of these components to ecological health effects are still very limited.Considering that compositions and structures of soil pollutants caused by gangues in different areas with different accumulation characteristics are quite different,therefore,in this study,gangue samples from three typical coal gangue stacking areas of Qinyuan,Gujiao and Yangquan,Shanxi Province as well as soil samples with different distances from gangue hills to downstream villages were collected.Contents of 8 heavy metals(Cd,Cr,Cu,Ni,Pb,V,As and Zn)in coal gangues and soil samples were determined through inductively coupled plasma-mass spectrometry detector(ICP-MS),and contents of 16 priority control PAHs(Na,Ac L,Ac,Fl,Bg Hi P,Ip,Db Ah A,Bb Fa,p HE,An,Fa,Ba A,Ch R,Py,Ba P and Bk Fa)in coal gangues and soil samples were determined by a gas chromatography-mass spectrometry detector(GC-MS).Through analyses of physical and chemical components,we found that contents of heavy metals and PAHs in soil samples from coal gangue stacking areas to downstream villages showed a trend that is changing with distances and time accumulations.Furthermore,single factor pollution,Nemero comprehensive pollution and potential ecological hazard indexes were used to evaluate ecological risks of heavy metals on soils around the three coal gangue stacking areas.Results showed that soil samples from the three coal gangue stacking areas were heavily polluted by Cd.Risk quotient and RQ-TEQ composite model were used to evaluate ecological risks of PAHs in soils.Results showed that Na,Ac L,Ac,Fl,Bb Fa,p HE,An,Fa,Ba A and Py in soil samples from Qinyuan,Gujiao and Yangquan were in the middle risk level.In addition,PAHs in Qinyuan gangue and 1000 m soil samples,Gujiao and Yangquan gangues constituted lower ecological risks.Results of health risk assessment showed that non-carcinogenic risk values of heavy metals in village soils contributed more,and the risk of children were significantly higher than that of adults.2.Environmental pollution caused by coal gangue accumulation is becoming an increasing serious problem,crops are the first trophic level in the human food chain,the security and production of crops are closely related to human well-being.In this chapter,we used maize(Zea mays L.)as the model organism.Seven cultivars of maize seeds were treated with agricultural soil leachate around coal gangue stacking area at various concentrations of 0,1:27,1:9,1:3 and 1:1,and investigated the germination rates and seedling growth index of seven maize cultivars.The objective of this study was to estimate the phytotoxicities of agricultural soil samples contaminated by coal gangue accumulation.Through the tolerance indices(TI)of each morphological traits in seedlings of seven maize cultivars,maize cultivars tolerant and sensitive to coal gangue accumulation were screened,and the tolerance mechanism were investigated.The results revealed that the agricultural soil leachate treatment could inhibit seed germination and the growth of roots and shoots and that the soil leachate-induced phytotoxicities were cultivar-dependent.At the same exposure concentration,the tolerant maize cultivars(Dafeng 30)displayed lower toxicity symptoms than the sensitive maize cultivars(Xianyu 335)in terms of growth inhibition,ROS generation,lipid peroxidation(MDA)and DNA damage(?-H2AX).In addition,stronger activities of antioxidant enzymes,such as superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD),were observed in tolerant maize cultivar than in sensitive cultivar,indicating that the difference between cultivars in antioxidant ability is one reason for the difference of toxicity effect among different maize cultivars.3.Developing nervous system is identified very sensitive to many exogenous substances,environmental contaminants can interfere key developing processes of nervous system,such as the proliferation,migration,differentiation of nerve cells,synapse formation,myelination,and apoptosis,lead to developmental neurotoxicity,and have adverse impacts on learning,behaviors and health.Previous epidemiological studies suggested that children who were contaminated in mining areas might experience cognitive development impairments compared to those in non-mining areas,which resulted in poorer academic performances.However,there are few studies on developmental neurotoxicity of village soils adjacent to coal gangue accumulation areas,especially relative toxicity mechanisms.In this chapter,we used zebrafish(Danio rerio)as a model,zebrafish embryos were exposed to village soil leachate(0,1:27,1:9,1:3 and 1:1)at 1 h postfertilization(1 hpf)until 24,48,72 hpf,quantitative reverse transcription-polymerase chain reaction(q RT-PCR)was used to clarify expressions of neurodevelopmentassociated genes during different developmental windows of zebrafish embryos.The locomotor activity of zebrafish larvae was monitored with a Video-Track system(Danio Vision),further investigated the change of village soil leachate on neurobehavioral function of zebrafish larvae.The results revealed that soil leachate can affect the key processes of early neurodevelopment in zebrafish at the critical windows,mainly including the alterations of cytoskeleton regulation(?1-tubulin),axon growth(gap43),neuronal myelination(mbp)and synapse formation(sypa,sypb and psd95),eventually leads to neurobehavioral damage in zebrafish larvae.4.Various environmental pollutants can disrupt thyroid homeostasis.Moreover,thyroid hormone system is closely related to early neurodevelopment.On a cellular level,effects of thyroid hormones have been shown to be involved in neuronal proliferation,migration,synaptogenesis,synaptic plasticity,and myelation processes.Epidemiological studies show that impaired psychomotor development and visuospatial processing have been revealed in children born to mothers with(subclinical)hypothyroidism.Studies on thyroid endocrine disrupting effects of village soils adjacent to coal gangue accumulation areas are rare,especially those related to toxicity mechanism.In this chapter,the zebrafish embryos were exposed to village soil leachates at 0,1:9,1:3,and 1:1 from 1 to 120 hpf,and the village soil leachate caused a dose-dependent increase in the mortality and malformation rate,and decrease in the heart rate,hatching rate and body length of zebrafish larvae.In addition,the type of malformation such as yolk sac edema(YE),pericardial edema(PE),spinal curvature(SC)was observed.Importantly,the soil leachate alleviated the whole-body triiodothyronine(T3)and thyroxine(T4)levels at higher concentrations,and altered the expression of the hypothalamic-pituitary-thyroid(HPT)axis-regulating genes(crh,trh,tsh?,nis,tg,nkx2.1,pax8,hhex,ttr,dio1,dio2,ugt1 ab,tra and tr?)and the heavy metal and PAH exposure-related genes(mt,ahr2 and cyp1a).Therefore,the village soil leachate may cause thyroid endocrine disorder by altering the expression of the HPT axis-regulating genes,and eventually lead to the growth and development of zebrafish larvae were inhibited at early development stage.At the same time,the thyroid endocrine disrupting effect caused by the village soil adjacent to coal gangue stacking area may be related to the heavy metals and PAHs in the soil samples.In this study,we first analyzed soil pollution characteristics of three typical coal gangue stacking areas in Shanxi Province,and established corresponding risk assessment models to analyze ecological health risks.Secondly,maize was used as a test plant to study phytotoxicity of soils in coal gangue stacking areas,in which maize cultivars tolerant to coal gangue accumulations were screened,and tolerance mechanisms were investigated.After that,a zebrafish embryo exposure model was established to explore toxicity effects and mechanisms of contaminated soils in gangue accumulation areas from perspectives of neurodevelopment and endocrine,so as to provide technical supports and scientific bases for managements and controls if soil ecological health risks in coal gangue stacking areas.