Animal Experiment Studies On Non-Thermal Effects Of Static Electric Field

With the development of extra-high voltage direct current(UHVDC)transmission technology and increase in transmission voltage,the issue of environmental static electric field(SEF)pollution is standing out and its possible health effects have caused much public attention.At present,there are no international or national standards to provide relevant limits for SEF exposure,which results in difficulty in handling SEF complaints.In view of China’s leading position in the field of UHVDC transmission technology and the large engineering volume,the World Health Organization(WHO)and the International Electrotechnical Commission(IEC)have both proposed on different occasions that China should take the lead in proposing the standard limit of SEF.According to some relevant guidelines on setting electromagnetic environmental standards,animal experiment basis is one of the indispensable bases for formulating SEF standards.However,studies on non-thermal effects of SEF are still lacking.Hence,in order to promote the work of setting SEF standards,it is necessary to further conduct some relevant animal experiments.In this study,animal experiments on non-thermal effects of SEF were carried out both under± 800 kV UHVDC transmission lines and under controlled conditions in the laboratory.According to the SEF exposure characteristics and environmental characteristics,the methods of animal experiments on non-thermal effects of SEF under both conditions were studied and proposed respectively,which provides experimental design reference for the subsequent researches from the perspective of methodology.Based on the proposed methods and focused on the laboratory research,the latent non-thermal effects of chronic SEF exposure with different intensities(nominal 80 kV/m、50 kV/m、40 kV/m)and durations(7d、14d、21d、35d、49d)on growth,behavior,blood,liver,kidney,and reproductive capacity of male mice were investigated.Furthermore,RNA sequencing was used to explore the biological mechanisms of non-thermal effects of SEF from the perspective of molecular biology.The main conclusions are as follows:(1)Results of hematology test showed that the number of white blood cells(WBC)in the exposed group was significantly reduced under SEF exposure of nominal 80 kV/m(actual 55.3 ±2.7 kV/m),resulting in an inhibition on immune function of mice.The mechanism may be related to neuroendocrine dysfunction caused by long-term stress.To be specific,SEF is one of the abnormal stress factors in the external environment that could cause stress response in mice,which resulted in an activation of the hypothalamic-pituitary-adrenal axis(HPA axis)and an increasement in corticosterone secretion.Since corticosterone could cause apoptosis of lymphocytes,the number of white blood cells was eventually decreased.Moreover,nominal 50 kV/m(actual 34.1 ± 1.7kV/m)and 40 kV/m(actual 27.1 ± 1.4kV/m)SEF exposure had no effect on the number of white blood cells of mice,indicating that the effect of SEF on immune function was closely related to exposure intensity.(2)Effects of SEF exposure on liver showed that short-term exposure resulted in impaired hepatic function,and it was intensity related.The main manifestations were significant increases in liver function indicators,accompanied with abnormal liver oxidative stress indicators,suggesting that disrupting redox equilibrium may be one of the important mechanisms of the non-thermal effects of SEF on liver.However,with the exposure time increasing,impaired hepatic function could gradually recover,indicating that mice can adapt to the external SEF after a certain period,which may be related to the self-regulatory mechanism of the body.(3)Effects of SEF exposure on kidney showed that nominal 80 kV/m SEF exposure will affect kidney function of mice.Results showed that the serum creatinine(CREA)content in the exposed group increased significantly after 35-day exposure,and electron microscopy revealed that the foot process of glomeruli in the exposed group were partially fused into slices with occasional basement membrane hyperplasia,which indicated that high intensity SEF exposure may affect glomerular filtration of mice.(4)Effects of SEF exposure on male reproductive capacity showed that nominal 80 kV/m SEF exposure resulted in cristae losses in mitochondria of spermatogenic cells.Nevertheless,the mitochondria injury did not affect sperm motility,which might be explained from the perspective of energy supply,that is,most of the energy required for sperm movement is generated by glycolysis which occurs in the cytoplasm rather than oxidative phosphorylation which occurs in mitochondria.(5)Results of transcriptome sequencing showed that after nominal 80 kV/m SEF exposure for 49 days,there were 198 and 174 differentially expressed genes(DEGs)identified in liver and testis respectively between the exposed group and control group.Moreover,it was found that liver and testis shared 20 common DEGs,indicating a general involvement of these genes in the mechanisms of non-thermal effects of SEF.KEGG analysis showed that effects on substance transfer processes related to vesicle cycle and immune responses mediated by major histocompatibility complex(MHC)are likely to be two intrinsic biological mechanisms of non-thermal effects of SEF,which could explain the fact that WBC declined under SEF exposue to some extent.This study closely focused on the rapid development of UHVDC transmission technology and the fact that international or national exposure limits of SEF have not yet been established,and explored the non-thermal effects of long-term exposure to SEF and their mechanisms,which aims to provide animal experiment basis for formulating SEF exposure limit of UHVDC transmission lines.