Aquatic plants bioremediation to groundwater contaminated by mines in karst areas

ZHANG Liankai; QIN Xiaoqun; HUANG Qibo; LIU Pengyu; SHAN Xiaojing

doi:10.11932/karst2017y47

Abstract：The karst regions in southwest China is an important producing area of nonferrous metals.Long-term extensive mining and waste residue accumulation have made the local environment seriously polluted by heavy metals.Many heavy metal elements enter the underground through surface runoffs and leaching,pol-luting groundwater aquifers,and pose a significant impact on the vulnerable karst environment.The leachate from the tailings reservoirs enters the groundwater system through karst pipelines and has a serious impact on the downstream ecological in a lead-zinc mine environment.In order to study the treatment technology of heavy metal pollution in karst groundwater and improve the quality of groundwater of this area,H ydrilla verticillata and Spirogyra communis grown in tailing reservoir leachate were selected as the sorbents of heavy metal.Hydrochemistry and enrichment factor analyses were conducted to examine the adsorption ca-pacity of heavy metals of these two aquatic plants.Meanwhile,their heavy metal adsorption mechanism was explored and the feasibility of using these two aquatic plants to control karst groundwater pollution was dis-cussed.Results show that,(1)The contents of heavy metals in these two aquatic plants lived in the mining area are high and the plants are well growing with large biomasses,suggesting these two kinds of aquatic plants have a certain avoidance or resistance to the heavy metals;(2)The bio-concentration factors (BCF)to elements in H ydrilla verticillata are relatively high,with value order as Pb > As > Co > Mn > Cu > Cd> Zn > Ni > Cr > Hg.The BCFs in Spirogyra communis are higher than those in H ydrilla verticillata but their value order is the same as that in H ydrilla verticillata .Although the contents of heavy metals do not reach the critical value of hyper-accumulators,the enrichment coefficients of Cu,Pb,Zn,Cd,Co,Ni, Mn and As in these two kinds of plants are much larger than 1,consistent with the hyper-accumulator en-richment characteristics,showing a co-enrichment feature;(3)Compared with non-karst areas,the content and BCF of heavy metals in these two aquatic plants in karst areas are much higher.Three main enrichment mechanisms of heavy metals in H ydrilla verticillata are suggested,which are enhancement of antioxidant enzyme activity under the stimulating of heavy metals,passive absorption,and ion exchange effect.For Spi-rogyra communis ,its special molecular structure is important for its heavy metal adsorption.As the H ydrilla verticillata and Spirogyra communis are widely distributed in karst areas of southern China,u-sing these two planes as the heavy metal remediation plants in karst polluted water will have a good pros-pect.