Study On Bioaccumulation Characteristic And Toxic Effect Of Hexabromocyclododecane And Cadmium Combined In Soil-plant System

As an additive flame retardant,hexabromocyclododecane(HBCD)has bioaccumulative and biotoxic properties,and widely exists in various environmental media and organisms.HBCD can not only be accumulated by plants,but is also harmful to human and the ecological environment.At present,there are few studies on the tissue distribution of HBCD in the soilplant system,and the pollution of Cd in farmland is still serious in China.In agricultural land nearby typical areas such as e-waste dismantling sites,there is a combination of the two types of pollution.Therefore,it is significant to study the accumulation and distribution characteristics of Cd and HBCD in the soil-plant system.In this study,the effects of Cd and HBCD on the growth of wheat and pak choi and the accumulation and distribution of pollutants were investigated via indoor seedling trials and outdoor pot experiments.Furthermore,the influence of nutrient element absorption in edible parts of the two plants and the distribution of HBCD isomers in plant tissues were studied.The main conclusions are as follows:(1)In the seedling experiments,roots were strongly inhibited than shoots in treatments with 10 mg/kg Cd.Single HBCD treatments can significantly inhibit pak choi roots(inhibition ratio up to 50%),while 5～10 mg/kg HBCD can promote the photosynthesis of the leaves.High concentrations of HBCD can stimulate the growth of plant shoots to varying degrees.Under high concentrations of Cd,10 mg/kg HBCD can increase the content of photo synthetic pigments in wheat while inhibiting the photosynthesis of pak choi.The results of pot experiments showed that low concentrations of Cd and HBCD promote the growth of different wheat parts while high concentrations bring inhibition,and the promotion was the strongest at 0.5 mg/kg HBCD,and the inhibition was the greatest at 2 mg/kg HBCD.The degree of inhibition differs in pak choi roots at different HBCD concentrations.(2)The Cd concentration of wheat tissue in the experiments without adding Cd and with 1 mg/kg Cd followed the order of shoots>roots>grains,while the order changed to shoots>grains>roots with 10 mg/kg Cd.The Cd content in pak choi followed the order of roots>shoots generally.The Cd accumulation in wheat followed the sequence of shoots>grains>roots,and the proportion of Cd accumulation in the shoots of pak choi was higher than in the roots.The accumulation of Cd in the high-concentration Cd group was comparable to that in the low-concentration Cd group,but the Cd absorption rate of shoots was lower than roots.The bioconcentration factor(BCF)of the single HBCD treatments of the two plants was lower than that of the Cd-spiked groups while the tissue translocation factor(TF)was higher.Under 10 mg/kg Cd,the translocation of Cd into the edible part would be weakened,and the ability of pak choi to enrich Cd was stronger than wheat.(3)The HBCD content sequence in wheat and pak choi was roots>shoots>grains,roots>shoots respectively.Cd can affect the accumulation of HBCD in plants.Low concentration of Cd can promote the absorption of HBCD in pak choi roots,while high concentration of Cd reduced the content of HBCD in the roots.The HBCD accumulation in wheat was the highest in the shoots,followed by roots,while that mainly accumulated in pak choi roots.Compared with the HBCD control group,the accumulative amount of HBCD in the shoots of HBCD spiked groups decreased by 85%on average.The enrichment of HBCD in the roots of pak choi was stronger than that of wheat,but the TFs of pak choi were much lower than the latter.The increase of HBCD concentration in soil could reduce the BCF of pak choi.(4)The contents of Zn and Cu in the edible parts of the two plants were similar,and Cd could reduce the absorption of K,Ca,Zn and Cu in pak choi shoots and wheat grains.Compared with soil,the proportion of α-,β-HBCD increased and that of γ-HBCD decreased in plant tissues.The ratio of α-HBCD in wheat rhizosphere soil,roots,shoots and grains were 8%,39%,15%and 34%,respectively.In addition,the percentage of α-HBCD among pak choi rhizosphere soil,roots and shoots were 9%,16%and 11%respectively,indicating the selective absorption of HBCD isomers in different plant tissues.(5)According to the MOE method,the risk thresholds of wheat grains and pak choi shoots were 56.6 ng/g and 70.9 ng/g,respectively.The corresponding soil thresholds were 12 mg/kg and 13 mg/kg in red soil.