Chemically assisted phytoextraction of heavy metal contaminated soils using three plant species

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1 Plnt nd Soil (25) 276: Ó Springer 25 DOI 1.17/s Chemilly ssisted phytoextrtion of hevy metl ontminted soils using three plnt speies P. Zhung, Z.H. Ye, C.Y. Ln, Z.W. Xie & W.S. Shu 1 Shool of Life Sienes, nd Stte Key Lortory for Bioontrol, Sun Yt-sen (Zhongshn) University, Gungzhou, P.R. Chin. 1 Corresponding uthor* Reeived 6 Deemer 24. Aepted in revised form 15 Mrh 25 Key words: mmonium, EDTA, hevy metls, phytoextrtion, Rumex K-1 (Rumex ptienti R. timshmius), Vetiver ziznioides, Viol oshnensis Astrt Phytoextrtion is potentil, innovtive nd ost-effetive tehnology for non-destrutive remedition of hevy metl-ontminted soils. A field tril ws onduted to evlute the phytoextrtion effiienies of three plnts nd the effets of EDTA or mmonium ddition [(NH 4 ) 2 SO 4 nd NH 4 NO 3 ] for ssisting hevy metl (P, Zn, nd Cd) removl from ontminted soil. The tested plnts inlude Viol oshnensis, Vertiveri ziznioides, ndrumex K-1 (Rumex ptienti R. timshmius). The pplition of EDTA soil ws the most effiient to enhne the phytovilility of P nd Zn, ut did not hve signifint effet on Cd. Led phytoextrtion rtes of V. oshnensis, V. ziznioides nd Rumex K-1 were improved y 19-, 2-, nd 13-folds ompred with the ontrol tretment, respetively. The pplition of mmonium did not hve ovious effets on phytoextrtion of the three metls, exept tht the umultions of Zn nd Cd in shoot of V. oshnensis. Among the three tested plnts, V. oshnensis lwys umulted the highest onentrtions of P, Zn, nd Cd. The onentrtions of P, Zn, nd Cd in the shoots of V. oshnensis treted with EDTA were 624, 795, nd 25 mg kg )1, respetively, nd the phytoextrtion effiienies of this speies for P, Zn, nd Cd were lso the highest mong the three speies. Results presented here indited tht V. oshnensis hd gret potentil in phytoremedition of soils ontminted y multiple hevy metls, lthough the dry weight yield ws the lowest mong the three plnts. Introdution * FAX No: E-mil: ls53@zsu.edu.n The pddy soils ontminted with hevy metl hve posed mjor environmentl nd humn helth prolem round the world, due to mining tivities, industril proesses, the use of syntheti produt (e.g. pints) nd other nthropi tivities during the lst entury (Cmr et l., 1999; Dudk nd Adrino, 1997). Therefore, remedition opertions to remove hevy metls from ontminted soil re neessry (Bker et l., 1994; Geiger et l., 1993). Trditionl remedition methods involve exvtion nd uril, or wshing of polluted soils with strong ids nd heltors (Mihel nd Hung, 2; Steele nd Pihhel, 1998), however, they hve een losing puli eptne nd eonomi fvor, nd phytoremedition s n lterntive tehnology hs emerged (Glss, 2). Phytoextrtion of hevy metl-ontminted soil, defined s the use of living green plnts to trnsport nd onentrte metls from the soil into the ove-ground shoots, whih re hrvested with onventionl griulturl methods (Bker et l., 1994; Kumr et l., 1995; Rskin et l., 1994), represents novel, ost-effetive ÔgreenÕ remedition tehnology for lering up polluted-soils, nd hs gined ttention widely in lst dede (Blylok, 1999; Slt et l., 1995).

2 154 Erly phytoextrtion reserh minly foused on plnts known s hyperumultors, whose shoot prts or leves my ontin >1 mg kg )1 Cd, >1 mg kg )1 Ni nd Cu, or >1, mg kg )1 ZnndMn(dryweight)whengrownin nturl hitts (Bker nd Brooks, 1998). However, phytoremedition potentil my e limited y these plnts due to the slow growth rte, low iomss prodution, nd resonle time frme(e.g. 5 1 yers) y remedition with little known gronomi hrteristis (Cunninghn et l., 1995; Roger et l., 2). In ddition, the lower metl iovilility in the soil nd poor metl trnslotion from roots to shoots re mjor limiting ftors for phytoextrtion of metls from polluted-soils (Epstein et l., 1999; Hung et l., 1997). Therefore, severl plnts with higher iomss, suh s mize (Ze mys L.) nd sunflower (Helinthus nnuus L.), hve een lso tested for their phytoextrtion potentil (Liphdzi et l., 23; Lomi et l., 21). Together with the pplition of hemil mendments, inluding heltors, soil idifiers, orgni id, mmonium, these high iomss plnts ould prtilly eliminte these limiting steps s desried ove in metl phytoextrtion (Chney et l., 1997; Dushenkov et l., 1999; Slt et l., 1998). Mny studies hve een onduted using EDTA for phytoextrtion of P, Zn, nd Cd in ontminted soils (Blylok et l., 1997; Hung et l., 1997; Kyser et l., 2; Pushenreiter et l., 21). It hs een reognized tht EDTA is one of the most effiient hemils in enhning P phytovilility in soil nd susequent uptke nd trnslotion in shoots fter treting for few dys (Chen nd Cutright, 21; Hung et l., 1997). Up to now, however, no dt hs een reported tht EDTA ould enhne Cd uptke in the plnt ut ppered to stimulte the trnslotion of Cd from root to shoot (Jing et l., 23). It hs lso een reported tht the pplition of mmonium to soil signifintly enhned 137 Cs umultion in plnts (Lst et l., 1998), nd promote hevy metls phytovilility from the ontminted soil (P, Zn, Cu, Cd, Ni) of smelter (Pushenreiter et l., 21). However, not ll studies re enourging in terms of hevy metls extrtion rtes hieved y ddition of hemil mendments, suh s EDTA, HEDTA, orgni id, nd NTA (Cooper et l., 1999). Despite helte gents, suh s EDTA, hve een shown to enhne phytoextrtion of P from ontminted soil, some onerns hve een expressed regrding the lehing of metl-helte omplexes to groundwter, posing potentil risk during extended periods of time. Severl reports hve indited the possile thret of hevy metls to groundwter ontmintion (Copper et l., 1999; Grˇ mn et l., 21; Hung nd Cunninghm, 1996; Kos nd Leštn, 23), therefore phytoextrtion utilizing heltes must e designed properly to protet environmentl sfety. It hs een reognized tht seletion of pproprite plnt mterils nd ppreite hemil mendments is still very importnt even tody for promoting phytoremedition effiieny. The study on phytoextrtion initited in Chin sine the 199s, nd severl hevy metl hyperumultors hve een identified, of whih V. oshnensis is new speies elonging to Violeee (Shu et l., 23), nd hs een proved to e Cd hyperumultor sed on field investigtion nd hydroponi test (Liu et l., 24). Vetiver ziznioides, perennil grss elonging to grmineous plnt, hs een widely known for its rpid growth nd high iomss, nd high tolerne to hevy metls (Shu et l., 22; Truong nd Bker, 1998), nd ould e potentilly used for phytoremedition of soils ontminted y hevy metls (Chen nd Cutright, 21). Rumex K-1 (Rumex ptienti R. timshmius) is lso perennil grzing with high iomss nd used for wter erosion ontrol in North Chin, lthough the metl tolerne in this plnt hd not een studied, ut severl Rumex plnts hve een proved to e metl tolernt speies or P hyperumultors (Liu et l., 22). Therefore, field tril ws onduted to: (1) evlute the metl umultion pity nd phytoextrtion effiieny of V. oshnensis, V. ziznioides nd Rumex K-1 grown on pddy soil ontminted y P, Zn, nd Cd; nd (2) ssess the effets of different hemil mendments on the phytoextrtion effiieny of these plnts. Mterils nd methods Site desription The study site is frmlnd nery the Lehng led/zin (P/Zn) mine, whih is loted t out

3 155 4 km est of Lehng ity in the northern prt of Gungdong Provine, South Chin. The P/Zn mine, loted t ltitude 24 4 N nd longitude E, hs humid sutropil limte with n nnul verge temperture nd rinfll of 19.6 C nd 1522 mm, respetively. The minerls minly onsist of pyrite, sphleritem glen, nd mgnetite, with lite, qurtz nd musovite s minor minerls (Shu et l., 21). In the P/Zn mine re, pproximtely 25, tons of wste roks nd 3, tons tilings per yer re produed with totl dumping res of 8,3 nd 6, m 2, respetively (Shu et l., 21). Lol environment hs een polluted seriously y dishrge of P/Zn tilings effluent nd dispersion of dust sine the 195s, s result, the frmlnd round this mine re seriously ontminted y P, Zn, nd Cd (Yng et l., 24). Field experiment The experimentl frmlnd ner the Lehng P/ Zn mine, overing n re of.8 h nd onsisting of six onseutively retngle pddy plots, ws seleted for onduting field experiment of phytoremedition. A portion of the ontminted frmlnd ws set up to ondut the field experiment on April 1, 23. The split-plot design ws used in present field experiment, whih might id to overome heterogeneous ondition. Four plots (8 m 3 m) were set up within this re, nd eh plot ws further eqully divided into four suplots (2 m 3 m), nd eh suplot ws plnted with V. oshnensis, V. ziznioides, or Rumex K-1, respetively. Eh plnt speies ws plnted with the spe of 2 m 2 m for V. oshnensis, 4 m 4 m for V. ziznioides nd Rumex K-1. The experiment inluded four tretments with four replites: tretment A (EDTA); tretment B [(NH 4 ) 2 SO 4 ]; tretment C (NH 4 NO 3 ); nd tretment D (ontrol). The three plnts were ll trnsplnted synhronously t the experimentl frmlnd on April 1, 23. The tillers of V. ziznioides (out 2 m height), were olleted from South Chin Institute of Botny, Gungzhou, seedlings of V. oshnensis (out 3 m height) ws olleted from Hunn Provine. Seeds of Rumex K-1, purhsed from Beijing, were sown t the experiment field on Jnury 1, 23 nd out 1 m height seedings were trnsplnted on April 1, 23. During the experiment period, weeding, wtering, fertilizing nd loosening of the soil were done mnully s needed. The NPK fertilizer (1:1:1) ws dded t the rte of 75 kg N h )1. On July 2, 23, (NH 4 ) 2 SO 4 nd NH 4 NO 3 were pplied t onentrtion of 1 mmol kg )1, nd dissolved EDTA (N 2 EDTA) ws pplied t rte of 6 mmol kg )1 on August 2, 23, respetively. After pproximtely 14 dys of ultivtion, ll the plnts were hrvested 1 week fter the EDTA pplition, nd 4 weeks fter the pplition of (NH 4 ) 2 SO 4 nd NH 4 NO 3. Assoited soil smples from the study sites were lso olleted from root zone of plnts. Smple nlysis Soil smples were ir dried, nd ground to pss through 2-mm mesh sieve. The soil smples were nlyzed for the following prmeters: ph (wter: soil = 1:2), orgni mtter (K 2 Cr 2 O 7 + H 2 SO 4 ), totl metl (P, Zn, nd Cd) ontents (digested y 5:1:1 HNO 3, HCl, nd HClO 4 ), nd extrtle metl (P, Zn, nd Cd) ontents [extrted y diethylenetrimine penteti id (DTPA)]. Conentrtions of P, Zn, nd Cd were mesured y flme tomi sorption spetrometry (AAS) (Pge et l., 1982). Plnt smples were thoroughly wshed with de-ionized wter to remove surfe dust nd soil, divided into root nd shoot, dried t 8 C until ompletely dry, weighted nd then milled to pss through 2-mm mesh sieve. Eh smple (.5 g) ws digested with onentrted HNO 3 (16 mol L )1 ) nd HClO 4 (12 mol L )1 ) t the rtio of 5:1 (v/v), the onentrtions of P, Zn, nd Cd were determined y AAS (Allen, 1989). Qulity ontrol for soils nd plnts ws sed on the use of ertified smples (GBW 746 nd 762), smples from inter-lortory omprisons, internl ontrol smples nd duplites of the nlysis. Phytoextrtion rte The potentil for phytoremedition depends on four vriles: plnt iomss, plnt metl onentrtion, soil metl onentrtion, nd the soil mss in the rooting zone. The phytoextrtion rte of plnt ws lulted y the following eqution (Zho et l., 23):

4 156 % of soil metl removed y one rop ¼ (Plnt metl onentrtionbiomss) 1 (Soil metl onentrtion Soil mss in the rooting zone) It ws ssumed tht metl pollution ours only in the tive rooting zone, top 2-m soil lyer, whih gives totl soil mss of 26 t h )1 (ssuming soil ulk density of 1.3 t m )3 ). Sttistil nlysis Dt were exmined y one-wy ANOVA followed y LSD test s ville in the SPSS 11. sttistil pkge. Results Chemil properties of the soils ssoited with the three plnts The ph, orgni mtter, totl nd DTPAextrtle metl onentrtions of the soils re presented in Tle 1. The soils of V. oshnensis (ph = 6.28) nd V. ziznioides (ph = 6.9) were slightly idi, while the soil of Rumex K-1 ws neutrl (ph = 7.13). In generl, the soils ontined low onentrtion of totl orgni mtter, ut high onentrtions of totl nd DTPA-extrtle Zn, P, nd Cd. The soils ssoited with V. ziznioides ontined the highest onentrtions of totl P (278 mg kg )1 ) nd Zn (2472 mg kg )1 ), while the soils ssoited with V. oshnensis hd the highest onentrtion of Cd (9.8 mg kg )1 ). The onentrtions of hevy metls in plnts Tle 2 ompres the onentrtions of P, Zn, nd Cd in shoots nd roots of V. oshnensis, V. ziznioides, nd Rumex K-1 with different tretments. In generl, onentrtions of P, Zn, nd Cd in shoots were higher thn in roots of V. oshnensis with different tretments. It ws lso found tht the EDTA tretment signifintly inresed P onentrtions in shoots of V. oshnensis, V. ziznioides nd Rumex K-1 from 35 to 624 mg kg )1, 19 to 32 mg kg )1, nd 19 to 194 mg kg )1, respetively. With the pplition of (NH 4 ) 2 SO 4 nd NH 4 NO 3, the onentrtions of Zn in shoot of V. oshnensis signifintly enhned from 479 up to 799 nd 868 mg kg )1, respetively, nd Zn onentrtions in shoot of Rumex K-1 inresed from 114 to 18 mg kg )1 (P <.1) nd 147 mg kg )1, respetively. The pplition of oth (NH 4 ) 2 SO 4 nd NH 4 NO 3 did not hve signifint effet on uptke nd umultion of P nd Cd y the three plnt speies tested. Tle 1. Seleted hemil properties of the soils ssoited with Viol oshnensis, Vetiver ziznioides, nd Rumex K-1 (Rumex ptienti R. timshmius) (men ± se, n =4) Prmeter Unit V. oshnensis soil V. ziznioides soil Rumex K-1 soil ph (1:2) 6.3 ± ± ±.27 Orgni mtter %.64 ±.1.68 ±.2.62 ±.2 Totl P mg kg )1 975 ± ± ± 39 Extrtle P mg kg )1 63 ± ± ± 28 Totl Zn mg kg )1 924 ± ± ± 228 Extrtle Zn mg kg )1 42 ± ± ± 6.9 Totl Cd mg kg )1 9.8 ±.9 7. ± ±.73 Extrtle Cd mg kg )1.37 ±.3.29 ±.2.91 ±.1 Dt with different letters in the sme row indite signifint differene t p<.5 ording to the lest signifint differene (LSD) test.

5 157 Tle 2. Conentrtions of P, Zn, nd Cd (men ± se, n =4,mgkg )1 ) in shoots nd roots of Viol oshnensis, Vetiver ziznioides, nd Rumex K-1 (Rumex ptienti R. timshmius) grown on ontminted frmlnd with different tretments Speies Tretments P Zn Cd Shoot Root Shoot Root Shoot Root V. oshnensis A 624 ± ± ± ± ± ± 19 B 68 ± ± ± ± ± ± 5.1 C 56 ± ± ± ± ± ± 3.4 D 35 ± ± ± ± ± ± 3.4 V. ziznioides A 32 ± ± ± ± ± ± 1.1 B 16 ± ± ± ± ± ± 1.8 C 14 ± ± ± ± ±.29 1 ± 1. D 19 ± ± ± ± ± ± 1.8 Rumex K-1 A 194 ± ± ± ± ± ±.17 B 17 ± ± ± ± ± ±.5 C 29 ± ± ± ± ± ±.21 D 19 ± ± ± ± ± ±.16 Note: A: EDTA tretment; B: (NH 4 ) 2 SO 4 tretment; C: NH 4 NO 3 tretment; D: Control tretment. Dt with different letters in the sme speies, plnt tissues (shoot or root) nd metl indite signifint differene t P <.5 ording to LSD test. Totl mounts of hevy metls umulted in plnts nd phytoextrtion rte After 14 dysõ ultivtion, the totl dry weight yields of V. oshnensis, V. ziznioides, nd Rumex K-1 were 6.5, 3 nd 18 t h )1, respetively. The P, Zn, nd Cd uptke mounts (mg m )2 )in shoots of these three plnts re shown in Figure 1. In generl, V. oshnensis umulted the highest mounts of P nd Cd, in ll tretments exept P in outrol. The Zn nd Cd uptke mounts in shoot of ll the three plnts showed similr level under the sme tretment, while the pplition of EDTA hd signifintly enhned P umultion, while (NH 4 ) 2 SO 4 nd NH 4 NO 3 tretments slightly inresed Zn nd Cd uptke mounts in shoot of V. oshnensis. Phytoextrtion rtes of P, Zn, nd Cd y V. oshnensis, V. ziznioides, nd Rumex K-1 with different tretments re presented in Figure 2. In generl, V. oshnensis hd the highest phytoextrtion rte mong the three plnts, while there ws no signifint differene in V. ziznioides, nd Rumex K-1. The pplition of EDTA remrkly enhned P nd Zn phytoextrtion rtes of V. oshnensis from.1 to.19%, nd.17 to.26%, respetively. The ddition of (NH 4 ) 2 SO 4 nd NH 4 NO 3 inresed the Cd phytoextrtion rte of V. oshnensis from.66 to 1.24% nd.81%, respetively. Disussion It hs een reognized tht high umultion level of hevy metl nd high iomss prodution of plnt were of prmount importne for suessful phytoextrtion (Roger et l., 2). Up to now, more thn 4 metl hyperumultor speies hve een reported in the world (MGrth nd Zho, 23), ut only few of these hyperumultors hve een tested for phytoextrtion (Bker et l., 1994; Brown et l., 1994; Es et l., 1997). Field trils with seleted metl hyperumultors, suh s Thlspi erulesens, Alyssum ertolonii, nd other speies, illuminted tht these plnt speies umulted high levels of Cd nd Zn in shoot (Bker et l., 1994; Lomi et l., 21; Roinson et l., 1997). However, extensive reserhes hve een rried out to selet metl hyperumulting plnts from high iomss prodution speies (Kumr et l., 1995; Liphdzi et l., 23; Lomi et l., 21). It hs demonstrted tht metl hyperumultion ould e hieved with seleted high iomss gronomi rops in onjuntion with soil mendments pplition to the ontminted soils (Roger et l., 2). It ws ommonly known tht signifintly high mount of plnt iomss resulted in umulting high hevy metl mount, nd then n importnt quntity of metl n e removed

6 () P Uptke mount in shoot (mg m -2 ) () Zn () Cd EDTA NH 4 NO 3 (NH 4 ) 2 SO 4 Control V. oshnensis V. ziznioides Rumex K-1 Figure 1. The uptke mounts of P (), Zn (), nd Cd () in the shoots of V. oshnensis, V. ziznioides, nd Rumex K-1 (Rumex ptienti R. timshmius) with different tretments for period of 14 dys. Different letters in the sme tretment indite signifint differene t P <.5 ording to the LSD test. form the soil vi plnt umultion (Blylok nd Hung, 2). High-iomss trees suh s willows or poplrs hve lso een demonstrted hve gret potentil to further efforts to develop phytoextrtion (Liphdzi et l., 23; Verveke et l., 23). Field investigtion nd hydroponi experiment hve proved tht V. oshnensis is hyperumultor of Cd (Liu et l., 24). Their results hve showed tht the onentrtion of Cd in shoot of V. oshnensis is 1168 mg kg )1 under nturl ondition nd the Cd onentrtion in shoot/root quotient ws greter thn 1 under oth field nd hydroponi onditions. The results presented here further demonstrted tht the plnt hd exeptionl umultion pity for Cd, nd the shoot of the speies ould umulted 3 mg kg )1 Cd from the soil with low onentrtions of Cd (totl: 9.8 mg kg )1, DTPA:.3 mg kg )1 ), ws out 8 1 folds higher thn the other two plnts. Despite the onentrtion of Cd in shoot ould not hieve the riterion for Cd hyperumultor (>1 mg kg )1 ), whih might due to the reltively low onentrtion of totl Cd (9.8 mg kg )1 ) nd DTPA extrtle Cd (.3 mg kg )1 ) in soil, Cd onentrtion in shoot of V. oshnensis ws lso signifintly higher thn tht in the root nd soil. The field experiment here indited tht the Cd phytoextrtion rte of this speies rehed 1.24 nd.81% with the pplitions of NH 4 NO 3 nd (NH 4 ) 2 SO 4, respetively, nd the EDTA tretment inresed P nd Zn phytoextrtion rtes of this speies y.19 nd.26%, respetively. P, Zn nd Cd phytoextrtion rtes nd umultion mounts y V. ziznioides nd Rumex K-1 were lso

7 159 Phytoextrtion rte (%) () P () Zn signifintly less thn those y V. oshnensis (Figures 1 nd 2). The present results suggested, tht the reltive low iomss hyperumultor, V. oshnensis, hd signifintly higher effiieny in phytoextrtion of P, Zn, nd Cd thn high-iomss plnt. Blylok et l. (1997) nd Hung et l. (1997) hve ompred five syntheti heltes (EDTA, DTPA, HEDTA, CDTA, nd EGTA), nd indited tht the pplition of EDTA signifintly enhned the onentrtion of P in plnt shoots. Es nd Kohin (1998) reported tht there ws no signifint differene in Zn onentrtion nd uptke mount in the shoots of ot nd whet grss y ddition of EDTA. The () Cd V. oshnensis V. ziznioides Rumex k-1 EDTA NH 4 NO 3 (NH 4 ) 2 SO 4 Control Figure 2. The phytoextrtion rtes of P (), Zn (), nd Cd () y V. oshnensis, V. ziznioides, nd Rumex K-1 (Rumex ptienti R. timshmius) with different tretments for period of 14 dys. Different letters in the sme tretment indite signifint differene t P <.5 ording to the LSD test. mmonium slts pplied to ssist phytoextrtion in the metl ontminted soil hve een rried out y Lst et l. (1998) nd Dushenkov et l. (1999), nd suggested tht the mmonium slt tretments inresed the onentrtion of 137 Cs in plnts. In the present study, we deteted tht the EDTA tretment inresed the P phytoextrtion rte of V. oshnensis, V. ziznioides nd Rumex K-1 y 19-, 2- nd 13- folds ompred with the ontrol tretments (Figure 2). Those results were in line with the view tht EDTA is the most effiient heltor in inresing P umultion in plnt shoots (Blylok et l., 1997; Hung et l., 1997), while Zn nd Cd umultion nd uptke mount hd no remrkle response to the pplition of EDTA (Figures 1 nd 2). The pplition of (NH 4 ) 2 SO 4 nd NH 4 NO 3 hd slightly enhned the uptke mounts of Zn nd Cd in shoots of V. oshnensis, V. ziznioides nd Rumex K-1. It is generlly noted tht Thlspi erulesens is the suitle ndidte plnt for phytoremedition opertion, whih hs lower nnul iomss ut umulte very high Zn nd Cd onentrtions in the shoot (Brown et l., 1994, 1995; MGrth et l., 1993). It ws lso reported tht three suessive ropping of T. erulesens remove pproximtely 2 nd 8mgkg )1 of Zn nd Cd for period of 391 dys from the soil industrilly ontminted with Zn (292 mg kg )1 ) nd Cd (19 mg kg )1 ) (Lomi et l., 21). In present study, one ropping of V. oshnensis grown over 14 dys removed pproximtely 2, 268 nd 15 mg kg )1 for P, Zn nd Cd from the ontminted frmlnd without ny tretment, respetively (Figure 1). Espeilly, the uptke mounts of P, Zn nd Cd were 349, 445 nd 14 mg y one rop with the pplition of EDTA, respetively, suggested tht V. oshnensis ws n importnt ndidte for phytoremedition of soil ontminted y hevy metls. Furthermore, V. oshnensis lso hd n dvntge to phytoremedite the ontminted soil with multi-metls, due to the plnts ould strongly umulte three elements (P, Zn nd Cd) t the sme time. The more extensive use of V. oshnensis stnds in phytoextrtion looks very promising through the suessive ropping, due to this speies is perennil plnt with iomss prodution of 6.5 t h )1.

8 16 Hevy metl onentrtion in soil (mg kg -1 ) () P t h () Zn 6.5 t h -1 Although V. oshnensis hd high potentil for phytoremedition, it ws long wy for using the plnt for phytoremedition in prtie, for exmple, sed on the dt of present tril (Figure 3). It would tke 56 roppings of V. oshnensis (14 yers) to redue soil Cd from the initil onentrtion of 9.8 mg kg )1 to 3 mg kg )1 with 6.5 t h )1 iomss produe y the NH 4 NO 3 tretment. And 256 nd 26 roppings of V. oshnensis (64 nd 65 yers, respetively) would e required to hieve the initil P nd Zn onentrtion of 975 nd 924 to 5 nd 3 mg kg ) Time (yer) Time (yer) () Cd 6.5 t h -1 Zn in soil (mg kg -1 ) P in soil (mg kg -1 ) Cd in soil (mg kg -1 ) Time (yer) Crop numer Figure 3. The onentrtions of P (), Zn (), nd Cd () in soil fter suessive roppings of V. oshnensis with 6.5 t h )1 iomss or during phytoremediting time frme. Horizontl lines represent the trgets for phytoremedition. 1 soil P nd Zn trget with 6.5 t h )1 iomss y the EDTA tretment, respetively. It ppered tht phytoremedition using V. oshnensis is more fesile when soil ontminted y low levels of Cd thn tht of P nd Zn (the ritil vlues of P, Zn, nd Cd re 5, 3, nd 3mgkg )1 of soil respetively). The previous reports nd present results show the limittions of phytoremedition only using hyperumultor, suh s V. oshnensis or T. erulesens. Given these severe limittions of helte-ssisted phytoextrtion nd low phytoextrtion rte of hyperumultor plnts, further efforts to develop phytoextrtion should fous on trnsporting genes tehnology or optimized gronomi methods. Therefore, further explortions re neessry for improving phytoextrtion rte of V. oshnensis. Aknowledgements This work ws supported y the Ntionl 863 Projet of Chin (No. 21AA6451-3) nd the Ntionl Nturl Siene Foundtion of Chin (No nd No ). Referenes Allen S E 1989 Chemil Anlysis of Eologil Mterils. 2nd Edn. Blkwell Sientifi Pulitions, Oxford. Bker A J M nd Brooks R R 1998 Terrestril higher plnts whih hyperumulte metli elements review of their distriution, eology nd phytohemistry. Bioreovery 1, Bker A J M, MGrth S P, Sidoli C M D nd Reeves R D 1994 The possiility of in situ hevy metl deontmintion of polluted soils using rops of metl-umulting plnts. Res. Conserv. Rey. 11, Blylok M J, Slt D E, Dushenkov S, Zkhrov O, Gussmn C, Kpulnik Y, Ensley B D nd Rskin I 1997 I. Enhned umultion of P in Indin mustrd y soil-pplied heltion gents. Environ. Si. Tehnol. 31, Blylok M J 1999 Field demonstrtions of phytoremedition of led ontminted soils. In Phytoremedition of Tre Elements. Ed. G S. Bnuelos. & N E. Terry. Ann Aror Press, Ann Aror, MI. Blylok M J nd Hung J W 2 Phytoextrtion of metls. In Phytoremedition of Toxi Metls Using Plnts to Clen up the Environment. Eds. I Rskin. & B D Ensley. pp John Wiley & Sons, In., New York. Brown S L, Chney R L, Angle J S nd Bker A J M 1994 Phytoremedition potentil of Thlspi erulesens nd ldder mpion for zin- nd dmium-ontminted soils. J. Environ. Qul. 23,

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