Studies On Distribution, Uptake And Accumulation Progress Of Hexachlorobenzene In Plants

Hexachlorobenzene (HCB) is a representative persistent organic pollutant known for its carcinogenetic and mutagenic propertie. HCB presents in soil, water, and air may be taken up by palnts, which is the major pathways into the food chain. Since plants form the basis of human and animal food webs, potentially harmful HCB could find its way into human and animal populations via this route. Clearly, increasd understanding of how palnts take up and accumulate HCB from the enviroment, especially, the distribution of HCB in plants and the process and mechanism of the uptake of HCB by plants as well as the establishing of prediction model, will have connsierable benefits for risk assement purposesand and the phytoremediation of HCB-contaminated soil. The distributions characteristics of HCB in 12 plants in the contamination conduit,nearby river and cropland around a chemical plant in Wuhan city were studied and impact factors were also discussd in this paper. Uptake of HCB by ryegrass from water and soil was carried out in laboratory and the partition-limited mode for ryegrass uptake of HCB from water and soil was applicated. The uptake process and mechanism of ryegrass uptake of HCB were discussed.Both plants and soil were contaminated to some degree by HCB in the sampling area. The concentrations of HCB were determined from 4.45 to 1189.89μg/kg(d.w.) in plants while 27.93 to 3480.71μg/kg(d.w.) in rhizosphere soil. The concentrations of HCB in plants and rhizosphere soil in contamination conduit and nearby river were comparatively higher than those in cropland. Ryegrass uptake and distribution have shown to be dependent on the characteristics of the soil, and the plant species and physiology inluding properties such as lipid contents and transpiration rates.A strong sorption ability of HCB by the root and shoot of ryegrass were observed in sorption experiments. The partition coefficients of root and shoot of ryegrass were respectively 14019.81L/kg and 67697.22L/kg. The sorption ability of ryegrass was mainly affected by lipid content. Comparing the values of lipid prediction model to those of sorption experiment, the values for fat prediction model silmulation were clearly much lower than those for sorption experiments. This is due to that Kow value as parameter in lipid model is much lower than Klip value obtained from sorption experiments. Lipid model remains limited for predicting effectively the contamination levels.The uptake of HCB by ryegrass root from solution and the uptake of HCB by ryegrass shoot from transpiration stream had the same transference trend in uptake experiments. The uptake concentrations of HCB by ryegrass root and shoot were increased first and then decreased with uptake time. Moreover, the uptake rate and degree of root were much higher than shoot. e.g., the highest concentration were obtained 1274.18μg/kgand 18.46μg/kg respectively in root and shoot at 4h and 336h,. The max. of root concentration factors(RCF) of HCB from solution and the shoot concentration factors from transpiration stream(SCFtr) were respectively 1921.93L/kg and 24555.4L/kg, which both much less than the corresponding partition coefficients (14019.81L/kg and 67697.22L/kg respectively). The discrepancy was possibly caused by evaporation, plant metabolism and growth dilution of HCB.Partition-limited model was effectively for predicting the concentration levels of HCB in ryegrass. application of the model for ryegrass root and shoot uptake of HCB, the uptake rates of predicting errors were less than 41.97% and 55.06% respectively. the predicting values for shoot uptake of HCB from soil or water were much lower than those for root uptake. This was possibly due to the leaf and shoot uptake from air occurs by wet and/or dry depositioon on the above-ground parts.