Toxicological Effects And Mechanism Of Hexabromocyclododecane(HBCD)on Caenorhabditis Elegans

Hexabromocyclododecane(HBCD),the third most widely used brominated flame retardants,is primarily used in polystyrene insulation foam boards,textile products,and electronic products.Due to its widespread use,HBCD has been found ubiquitously in various environmental media including water,sediments,soil,and even in human milk.Moreover,HBCD has multiple toxic effects,such as developmental toxicity,neurotoxicity,reproductive toxicity,etc.Currently many toxicological study of HBCD have been performed on aquatic organisms and terrestrial species.However,the toxicological effects of HBCD on soil nematodes is largely unknown.In order to understand toxicological effects along with the changes of stress response by HBCD exposure,the animal model Caenorhabditis elegans was chosen for toxicity study.The nematode Caenorhabditis elegans,a free living nematode,plays an important role in soil ecosystem.The Caenorhabditis elegans is a excellent model animal in environmental toxicology research,due to its translucent body,ease of cultivation,short life cycle,and sensitivity to toxicants.Toxicological effects of HBCD were conducted using C.elegans at the physiological,biochemical,and molecular levels,to assess the acute and prolong exposures and chronic exposure exposure.The main results are as follows:(1)Acute and prolong exposures to HBCD at concentrations of 200 nM significantly influence the body length,locomotion behaviours and brood size in C.elegans.Acute exposures to 20 nM of HBCD significantly decrease locomotion behaviours,and prolong exposures to 2 nM of HBCD also significantly decrease locomotion behaviours.It suggested that locomotion behaviours was the most sensitive endpoint,and prolonged exposure to HBCD resulted in more severe toxicity than acute exposure in C.elegans.Acute and prolong exposures to HBCD at concentrations of 200 nM could significantly increase ROS production and degree of cell apoptosis.Thus,HBCD exposure may induced oxidative stress and cell apoptosis,which resulted in the HBCD-induced toxicity on nematodes.The integrated gene expression profiles visually revealed that exposure to HBCD at concentrations of 200 nM resulted in obvious change of stress-related gene expressions,and the hsp-16.2 and sod-3 gene expressions were significantly correlated with HBCD-induced toxicity by the Pearson correlation test.Therefore,the hsp-16.2 and sod-3 genes played importance roles in HBCD-induced toxicity.(2)Prolonged exposure to HBCD at concentrations of 200 nM only caused adverse physiological effects in parental generation(F0),and the significant reduction of locomotion behaviours were also observed in the offspring under HBCD-free conditions(F1).HBCD-induced toxicities could be transferred from the parental to offspring.Exposure to 200 nM of HBCD could significantly increase ROS production and degree of cell apoptosis in the and F1 generation.The integrated gene expression profiles visually revealed that exposure to HBCD at concentrations of 200 nM resulted in obvious change of stress-related gene expressions,and the gene expressions of the F0 generation were more obviously increased than the F1 generation.The increased expressions were pronounced in several genes related to oxidative stress and cell apoptotic,e.g.,hsp-16.2,hsp-16.48,sod-1,sod-3 and cep-1 gene.Therefore,it was speculated that HBCD exposure induced oxidative stress and cell apoptosis,which resulted in the adverse physiological effects.(3)Chronic exposure to 20 nM of HBCD would significantly influence growth,locomotion behaviors,ROS formation,lipofuscin accumulation,and cell apoptosis on nematodes.The endpoint of head thrash was most sensitive among the physiological endpoints,and toxicity was observed at concentration of 2 nM.Treatment with antioxidants of ascorbate and N-acetyl-l-cysteine(NAC)suppressed induction of ROS production,degree of cell apoptosis,and decrease of locomotion behaviors induced by HBCD.The integrated gene expression profiles visually showed that chronic exposure to 20 nM of HBCD significantly increased expression level of stress-related gene,e.g.,hsp-16.2,hsp-16.48,sod-1,sod-3 and cep-1 gene.The mutations of sod-3(tm760)and cep-1(gk138)induced more severe toxicity compared with wild-type nematodes.Therefore,HBCD exposure induced oxidative stress by ROS accumulation and cell apoptosis,which resulted in the HBCD-induced toxicity on nematodes,and sod-3 and cep-1 genes played importance roles in protecting nematodes against HBCD-induced toxicity.