Selected Aquatic Vascular Plants as Biological Indicators for Heavy ...

Pertanika 7(1), 33 -47 (1984)

Selected Aquatic Vascular Plants as Biological Indicators for Heavy Metal Pollution

LOW KUN SHE, LEE CHNOONG KHENG and TAN SWEE HA1N C hem istry D epartm ent,

F acu lty o f Science and E n v iro n m en ta l S tu d ies U niversiti Pertanian Malaysia Serdang, Selangor, Malaysia

Key w ords: A quatic p lants; O ttelia alism odes; F im bristy lis pauciflora; B lyxa m alayana; F im bristy lis

K epekatan z in ku m , kuprum , kadm ium , p lu m b u m , nikel, fe ru m dan krom ium dalam lima tum buh- tum buhan terbenam telah d itu n ju kka n . Pertam bahan kandungan logam adalah bergantung kepada jenislogam.

Pengambilan kuprum , z in ku m , kadm ium , krom ium dan n ike l dari larutan berzat ya n g ber cam pur dengan logam-logam itu dengan m enggunakan O tte lia alism oides Pers., F im bristy lis pauciflo ra R . Br. dan Blyxa m alayana R id ley telah dikaji. Sem ua jenis tu m buhan m en u n ju kka n kebolehan m enyerap kuprum , z in ku m dan kadm ium dengan kadar ya n g lebih cepat dari krom ium dan nikel. Pertam bahan kandungan logam adalah bergantung kepada paras pendedahan dan jenis tum buhan.

Penggunaan yang m ungkin bagi O tte lia alism odes dan F im bristy lis pauciflo ra sebagai p e n u n ju k biologi terhadap pencem aran air juga dibincangkan.

C oncentra tions o f zinc, copper, cadm ium , lead, nickel, iron and chrom ium in fiv e subm erged plants are presented . M etal en richm en t was fo u n d to be d ep en d en t on the p la n t species and m eta l type.

The up ta ke o f copper, zinc, cadm ium , chrom ium and n icke l fro m n u tr ien t so lu tions enriched w ith these m etals using O ttelia alism oides Pers., F im bristy lis pauciflo ra FT. Br. and B lyxa m alayana R id ley was studied. A ll p lan ts dem onstra ted the ab ility to rem ove copper, z inc and cadm ium m ore rapidly than chrom ium and nickel. M etal accum ula tion was a direct fu n c tio n o f the exposure level and varied w ith the plant species.

The possib le use o f O ttelia alism odes and F im bristy lis pauciflo ra as biological indicators o f w ater po llu tion is also discussed.

SUMMARY

INTRODUCTION indigenous biota. The use of w ater analysis is expensive and laborious. M ultiple sam pling m ust be u n dertaken to elim inate variations in m etal co n cen tra tio n s w ith tim e, season, rainfall and flow speed. T he use of sed im en t is sub ject to som e errors; m etal co n te n t depends on sed im en ta tion rate and a m o u n t o f organic m a tte r presen t. The use o f biological ind ica to rs to define areas of po llu tion seem s m ost a ttrac tive , as they n o t only co n cen tra te m etals from w ater but also rep resen t a m oving tim e-average value for the relative biological availability o f the m etals at each site stud ied (Phillips, 1977).

E nvironm ental po llu tion by heavy m etals is of w idespread concern . These heavy m etals are constan tly being released to the aquatic environ­m en t th rough various industrial processes and hum ^n activities. This represen ts a serious w ater po llu tion problem due to the ex trem e tox ic ity of som e of the elem ents.

The elucidation of the e x te n t o f p o llu tion o f an aquatic area by heavy m etals is theo re tica lly possible by the analysis of w ater, sed im ents or

Key to a u th o rs ’ nam es; K.S Low, C.K. Lee and S.H. Tan.

33

K.S. LOW, C.K. LEE AND S.H. TAN

A ccording to Phillips (1977 ), a biological in d ica to r can generally be defined as an organism w hich m ay be used to quan tify relative levels of po llu tio n by the m easu rem en t o f the to x ican t c o n cen tra tio n in its tissues. E ither the entire organism or p a rt o f it, or a single tissue m ay be used. An im p o rta n t fea tu re o f biological ind ica to rs is th a t in m any instances, they can respond to a chem ical substance by accum ulating it in the am o u n t p ro p o rtio n a lly re lated to the am bien t level or supply rate. Hence, it m ay be m ore con ­venient and m ore in form ative to m easure the level o f th e chem ical substance c o n te n t in those associated b io ta whose concen tra tio n reflects am b ien t levels w hich are at various con cen tra tio n s (G oodm an e t a l , 1976).

P lants m ay ind ica te the quality of w ater in a wide v<yiety o f ways. T heir d is trib u tio n in tim e or space, chem ical com positions and m orphological characteristics m ay be used to d e tec t im p o rtan t fea tures o f th e w ater (W hitton , 1979). O f late, aqua tic p lan ts have been suggested as biological ind ica to rs to m o n ito r changes in m etal levels in the aqua tic env ironm ent. This is due to the ir ability to take up heavy m etals from th e su rro u n ­ding w ater and thus p roduce an in te rna l co n cen tra ­tion greater than the surroundings. This ability of the p lan ts can be m o n ito red e ith e r in the labo ra to ry or the field. A useful biological ind ica­to r m ust exh ib it a high to lerance to p o llu tan ts and have a high en richm en t capacity fo r these po llu tan ts. It m ust be rep resen tative of the area, be easily co llected and allow fo r id en tif ica tio n unequivocally (R ay and W hite, 1979).

Since S cu lthorpe (1 9 6 7 ) suggested th a t aquatic vascular p lan ts could be used as an indica­to r fo r po llu tio n m on ito ring , several stud ies have dem o n stra ted the capacity o f subm erged vascular p lants to accum ulate heavy m etals from the aquatic env ironm ent. The chem ical analysis of these p lan t tissues m ay give valuable in fo rm ation a b o u t the co n cen tra tio n s o f m etals in th e ir sur­roundings (A dam s e t a l, 1973; F ranzin and M cFarlane, 1980; Ray and W hite, 1979; A ulio and Salin, 1982). The m ost com m on p lants stud ied include Elodea, E qu ise tum , M yro p h y llu m and P otam ogeton .

H owever, Schierup and Larsen (1 9 8 1 ) found th a t the m etal concen tra tio n in aquatic p lants did n o t m irro r the co n cen tra tio n and to ta l c o n ten t of the su rround ing w ater and sedim ent. U ptake was greater in a n on -po llu ted lake than a sewage po llu ted lake. They suggested th a t this could possibly be due to th e cum ulative effec t of the

prevailing chem ical cond itions such as pH, cation exchange capacity and organic co n ten t.

The purpose o f the presen t study is to evaluate the use of several subm erged p lants as biological m o n ito rs o f heavy m etal po llu tion . It repo rts th e prelim inary observations on heavy m etal u p tak e o f six vascular p lants in the ir na tu ra l hab ita t. The p lants are H ydrostem m a m o tley i, O ttelia alism oides Pers., F im bristy lis acum inata V ahl., F im bristy lis pauciflora R. Br., B lyxa mala- yana Ridley and H ydrilla verticillata. Three p lants, O ttelia alism oides Pers., F im bristy lis acum inata V ahl and B lyxa m alayana R idley, were selected fo r fu rth e r study on the ir heavy m etal u p tak e u nder a con tro lled env ironm ent.

MATERIALS AND METHODS

S tu d y Area

The stream s tud ied has its source at the C hnoong Keow R ubber Estate and discharges in to a sm all lake near the F acu lty o f F isheries and Marine Science, Universiti P ertan ian Malaysia, Serdang, Selangor. It has been chosen fo r the study because o f its accessibility and aquatic flora.

Nine sites were chosen from upstream and dow nstream in o rder to give a good profile o f changing co n d itio n s dow n the main stream . D etails o f the sites are given in Figure 1 and of flora in Table 1.

Sam pling Program m e

W ater and p lan ts were co llected tw ice at an interval o f 10 weeks s ta rting on 2nd Ju ly 1982. Samples were taken at a d istance o f 10-m apart along the stream , term ed a reach (conven tion o f H olm es and W hitton , 1981). The num ber o f sites was reduced to 7 during the second sam pling due to destruc tion caused by co n struc tion o f a drainage system outside the UPM cam pus.

At each sam pling site, w ater sam ples were collected in acid-w ashed po lye thy lene bottles. M easurem ents fo r pH were com pleted in the labora to ry . A fte r filtra tion , w ater sam ples were analysed fo r seven elem ents, nam ely Zn, Cd, Pb, Cu, Ni, Fe, Cr by d irect aspiration using an in d u c­tively coupled plasm a emission sp ec tro m e te r (ICP).

W herever possible, 3 replicates o f the particu lar whole p lan t, to g e th e r w ith roo ts, were co llected from each site. Choice o f m aterials was restric ted to p lan ts th a t were fully subm erged and sub jected to the fastest cu rren t occuring w ith in the reach.

34

In the lab o ra to ry , the p lan t m aterials were rinsed tho rough ly in tap w ater, then transferred to deion ized w ater. W ithered and dam aged parts of the p lan ts were rem oved and only the green p a rt o f th e p lan ts was analysed as a w hole. The w et w eight o f the m aterials was determ ined a fte r12 hours d rying at room tem peratu re . F u rth e r drying to preserve the m aterial was carried o u t in the oven at 80° C for 48 hours before dry w eight was recorded . The dry m aterials w ere then dis­in teg ra ted by a stainless steel blender.

Sam ples fo r analysis w ere p repared by the w et-ashing m e th o d as rep o rted by L ittle and Martin (1972). D uplicate po rtio n s o f the ground p lan t m aterial, usually 1 gram , were digested w ith AR grade n itric and perchloric acids (4:1 by volum e) till fum es of N 0 2 w ere no longer visible and the liquid was m ore or less clear. The digests were m ade up to a final volum e of 25 cm 3 w ith \% d istilled n itric acid.

M etaI U ptake S tud ies

J tte lia alism oides, F im bristy lis pauciflora and B lyxa m alayana were co llected from the stream fo r lab o ra to ry m etal up tak e studies. They we.e tho rough ly w ashed in stream w ater and also ta > w ater, and dam aged parts o f the p lan ts were rem oved. The ‘c lean ’ m aterials were left overnight in plastic pails con ta in ing tap w ate r a t room tem p era tu re p rio r to experim en ta tion .

K nop’s so lu tion (Douglas, 1977) was used as a n u tr ie n t so lu tion fo r the cu ltivation o f plants. It was m ade up o f M gS 0 4 .H 20 (2g d m '3), K H 2 P 0 4

(2g d m '3). K.NO3 (2g d m '3), Ca ( N 0 3 ) 2 ( 8 g d m -3 ) and traces of F e S 0 4 . A series o f 2 lite r and 1 lite r pyrex beakers were filled w ith respective volum es of n u tr ien t so lu tion enriched w ith 5 jug c m '3 ,

AQUATIC VASCULAR PLANTS AS BIOLOGICAL INDICATORS FOR METAL POLLUTION

TABLE 1 Occurrence of plants at sites A -l

A B C D E F C, H I

Hydrostemma motleyi (Hook, f.) Mabberlay + + +

Ottelia alismoides Pers. + + +

Fimbristylis acuminata Vahl. + +

Fimbristylis pauciflora R. Br. + + +

Blyxa malayana Ridley + + + + +

Hydrilla verticillata + + + + + +

Fig. 1. S tu d y A rea show ing locations o f sam pling sites.

Only lush green p lants were co llected so th a t they were o f th e sam e viability.

The m aterial was first w ashed several tim es in stream w ater to rem ove the ad h eren t sed im en t and a tta ch ed invertebrates. It was then squeezed gently to rem ove the bulk of w ater and tran sp o rted back to th e lab o ra to ry in p o ly e thy lene bags. An ex tra lo t o f each p lan t species was k ep t in a separate p o ly e thy lene bag for iden tifica tion .

35

K.S. LOW, C.K. LEE AND S.H. TAN

10 p g c m '3 , 20 n g c m '3 , 50 p g cm ' 3 and 100 jug cm - 3 of Cu as C u (N 0 3)2. 3H 2 0 , Zn as ZnCl2 , Ni as NiCl2 .6H 20 , Cd as CdCl2 .2H 20 and Cr as C r 0 3 , e ith e r indiv idually or a m ix tu re o f three m etals. A fter rinsing w ith deionized w ater, the aquatic p lan ts, a round 80g w et w eight, were cu ltiva ted in each of the beakers. All plants were cu ltiva ted in 2 litre beakers. P lan t con tro l free o f heavy m etal and m eta l con tro l free of p lants w ere also estab lished fc r each set o f experi­m ents. No a tte m p t was m ade to co n tro l light in tensity and tem pera tu re .

T he co n cen tra tio n s of m etals in so lu tion were determ ined before the p lan ts were cultivated and at 24 h o u r intervals. A liquots o f 10 cm 3

so lu tion were rem oved and filtered . The sam ple so lu tions were s to red in a freezer un til fu r th e r analysis. pH m easurem ents and observation o f p lan t co n d itio n s were also reco rded a t the tim e o f sam pling. C orrection fo r evaporation was m ade daily by the add ition o f deionized w ater.

A t the end o f th e experim en t the p lan ts were washed w ith tap w ate r fo llow ed by deionized w ater.

The m ateria l was then oven dried at 80° C for 48 hours and ground. The dry m ateria l was then p repared fo r analysis o f heavy m etals acco r­ding to the m e th o d previously described.

Heavy m eta l analyses w ere co m p le ted by m eans o f ICP spec trom etry . The values recorded were the m eans o f th ree readings.

RESULTS

Field S tud ies

Water C hem istry. The heavy m etal c o n ten t of stream w ater only ind icates the qua lity pre­vailing at the tim e o f sam pling and n o t the average level over a long period . There was no great d ifference in th e concen tra tio n of the heavy m etals, w hich was generally low. The m etal co n cen tra tio n in the sites chosen was in the o rder of Fe > Ni > Zn > Cd > Cu > Cr.

Cr was n o t de tec ted in the w ater at all sam ­pling sites. Cu was sim ilarly n o t de tec ted excep t at sites A and B. The relatively higher levels o f Fe cou ld possibly be due to Fe rich sedim ents. pH o f the w ater sites was fo und to increase tow ards dow nstream (Table 2) and this could be due to househo ld w astew ater discharges.

Plant Sam ples. The d is tribu tion of the p lan t species in the stream stud ied is defin itely influenced

by various poorly u n d ers to o d variables since none of the species inhab it all the sam pling sites. An in te resting featu re is th a t O ttelia alism oides, F im bristylis acum inata, F im bristy lis pauciflora and H yd ro stem m a m o tle y i were res tric ted in the u p p e r stream while H ydrilla verticillata was the m ost com m on species grow ing in the low er stream (T able 1).

M etal co n cen tra tio n in H ydrostem m a m o tle y i w ith respect to sam pling sites are show n in Table 3.The results show th a t Fe and Zn were concen ­tra ted to a g reater ex ten t com pared to Cu, Pb,Ni and Cr. C o ncen tra tions o f Cd, Pb and Cr show ed little variations dow n the stream bu t vast variations were observed in the con cen tra tio n s of Fe, Zn, Cu and Ni.

The sam e tren d o f m etal en richm en t was also observed for O ttelia alism oides (Table 3). The concen tra tio n s of Zn, Pb, Cu, Cd, and Cr rem ained virtually c o n stan t while Fe and Ni show ed vast variations in three sam pling sites. The greater up take o f Fe and Zn com pared to o th e r m etals was also observed in F im bristylis acum inata (Table 3).

A nalytical da ta for F im bristy lis pauciflora (T able 3). The Zn c o n te n t d iffered greatly at m en t o f m etals. U nlike o th e r p lan ts, the heavy m etal c o n te n t of the p lan t varied greatly from site B to G. The high levels of Ni and Gr in F im bristy lis pauciflora ind ica te th a t the p lan t is a good accu­m u la to r o f these m etals in its na tu ra l env ironm ent.

F o r B lyxa m alayana, Fe and Zn w ere enriched to a larger e x te n t than Cu, Cd, Pb, Ni and Cr. R elatively high values o f Ni and high values o f Ni and Fe were recorded sites E and F. (Table 3).

H ydrilla verticillata appeared to be a good accum ula to r o f Zn in its natu ral env ironm ent (T able 3). The Zn c o n ten t d ifferen t greatly at d iffe ren t sites and the highest value was recorded a t site G. As in o th e r p lants, en richm en t o f Zn and Fe was generally higher than o th e r m etals. The low Cd c o n te n t ind ica tes th a t H ydrilla verticillata had a low affin ity fo r the m etal a t the sam pling sites.

I

L aboratory S tud ies

Copper. The rate o f up take o f Cu by various p lants under a 6 -day static bioassay is show n as con cen tra tio n o f Cu rem aining (pg cm -3 ) as a function o f tim e in Table 4.

In all cases, the greatest decrease occurred during the first tw o days. A fter the in itial de-

36

r

TABLE 2pH and concentration of heavy metals (/ig cm '3) in water

collected at sampling sites A -I

Samplingsites

pH Zn (x l0 ~J )

Cu Cd (x 1 0 ' 2 ) Pb Ni Fe Cr

A 4.81 ± 0.25 1.4 ± 0.2 2 . 2 ± 1 . 6 1 . 8 ± 0 . 1 0.17 ± 0.01 0.24 ± 0.0 0.26 ± 0 . 2 0 < D.L

B 4.85 ± 0.25 1.7 ± 0.2 1 . 2 ± 0 . 1 1.7 ± 0.1 0.17 ± 0.01 0.26 ± 0 . 0 0.07 ± 0.01 < D.L

C 5.38 ± 0.62 6.3 ± 0.5 < D.L 1.7 ± 0.1 0.16 ± 0 . 0 0.26 ± 0 . 0 0.66 ± 0.17 < D.L

D 5.98 ± 0.12 3.9 ± 2.7 < D.L 1.7 ± 0.1 0.17 ± 0.01 0.24 ± 0.03 1.23 ± 0.64 < D.L

E 6.03 ± 0.27 1.6 ± 0.3 < D.L 1 . 8 ± 0 . 1 0.17 ± 0.01 0.26 ± 0 . 0 1 2.21 ± 0.57 < D.L

F 6.23 ±0.23 4.6 ± 3.4 < D.L 1 . 6 ± 0 . 2 C.l< ± 0 . 0 0.26 ± 0 . 0 1 1.93 ± 0.53 < D.L

G 6.30 ± 0.15 3.4 ± 1.7 < D.L 1.5 ± 0.0 0.16 ± 0 . 0 0.26 ± 0 . 0 0.71 ± 0.69 < D.L

H 6 . 0 0 9.1 < D.L 1 . 6 0.16 0.27 1.72 < D.L

I 6 . 2 0 5.2 < D.L 1.5 0.16 0.26 0.93 < D.L

D.L. = detection limitD.L. for Cu and Cr arc 2 and 3 n g dm " 3 respectivelyAll readings are the means of 2 samplings except for H and 1

AQUATIC V

ASCU

LAR

PLANTS

AS BIO

LOG

ICAL

IND

ICATO

RS FOR

METAL

POLLU

TION

TABLE 3Concentration of heavy metals in aquatic plant samples

(/ig g" 1 dry weight)

Species/locality Zn Cu Cd Pb Ni Fe Cr

Hydrostemma motleyi

Site A 183 ± 14 25.6 ± 1.0 9.6 ± 1 . 0 42.5 ± 7.0 50.1 ± 6.4 8173 ± 173 10.43 ± 1.52B 83 ± 15 26.7 ± 3.1 9.30 ± 0.0 41.5 ± 3.3 45.5 ± 3.1 10509 ± 1448 8.51 ± 0.65C 210 ± 4 13.5 ± 0.5 8.3 ± 0.3 36.6 ± 0.1 79.4 ± 8.3 7043 ± 82 6.91 ± 0.06

Ottelia alismodes

Site A 398 ± 40 22.3 ± 1.1 19.5 ± 1.5 86.9 ± 6.1 53.2 ± 3.7 32079 ± 2219 15.6 ± 1.04B 394 ± 25 16.3 ± 1.4 17.3 ± 0.5 90.0 ± 0.5 196 ± 7.5 34442 ± 2008 14.04 ± 1.35C 403 ± 20 16.1 ± 2 . 2 9.3 ± 1.3 65.0 ± 1.1 82.2 ± 6.7 20564 ± 405 10.85 ± 0.44

Flimbristylis acuminata

Site A 164 ± 18 26 ± 3.3 1 0 . 0 ± 0 . 2 53.0 ± 4.7 40.9 ± 5.5 9933 ± 77880 13.41 ± 0.45B 183 ± 0 43 ± 2.3 26.3 ± 2.5 5.4 ± 0.1 48.4 ± 2.0 30241 ± 2193 16.13 ± 0.75

Flimbristylis pauciflora

Site B 402 ± 93 24.90 ± 4.6 1 1 . 8 ± 1.3 54.0 ±4.5 144.4 ± 15.9 17525 ± 198 18.75 ± 0.03C 192 ± 76 15.1 ±1.3 4.9 ± 0.4 28.1 ± 1 . 2 192.3 ± 21.2 6731 ± 299 41.15 ± 1.35D 390 ± 116 15.6 ± 1.6 1 1 . 0 ± 0.3 70.9 ± 13.1 436.6 ± 58.5 16810 ± 8 8 6 20.67 ± 3.92G 995 ± 106 22.4 ±1.2 7.8 ± 0 . 6 46.8 ± 6.3 57.2 ± 21.2 4503 ± 1195 14.37 ±4.30

Blyxa malayana

Site C 383 ± 21 18.6 ± 1 . 2 5.3 ± 0.5 32.0 ± 4.0 29.2 ± 5.8 6264 ± 841 25.63 ± 3.37D 412 ± 8 6 13.1 ± 2.0 5.9 ± 1.7 42.0 ± 15.5 45.7 ± 19.2 7156 ±499 15.43 ± 3.47E 441 ± 41 14.4 ±0.1 7.0 ± 0 . 8 54.2 ± 12.4 305.7 ± 14.9 15.25 ±492 12.23 ± 1.39F 465 ± 82 17.9 ± 1.1 9.3 ± 0 . 0 63.3 ± 6.5 338.7 ± 18.9 12255 ± 706 17.71 ± 0.98G 523 ± 174 17.8 ±2.6 7.3 ± 0 . 8 42.3 ± 4.8 33.3 ± 9.8 5243 ±903 34.58 ± 15.97

Hydrilla verticillata

Site D 386 ± 19 13.2 ±1.2 9.0 ± 0.5 56.1 ± 14.3 50.6 ± 5.6 6518 ± 2997 11.14 ± 1.04E 456 ±41 17.0 ± 1.0 8.4 ± 0 . 2 93.5 ±4.0 59.3 ± 3.7 17720 ± 372 19.60 ± 3.06F 571 ± 6 18.5 ±2.3 8.5 ± 2.3 527 ± 3.2 161.0 ± 4.0 8976 ± 568 17.32 ± 0.94G 684 ± 217 16.4 ±2.0 10.7 ± 0.7 57.1 ± 1.8 62.2 ± 6.4 8557 ± 582 14.44 ± 0.13H 508 14.7 7.3 36.8 198.4 6659 8.761 378 19.6 5.1 34.3 144.4 5579 7.61

All readings are the means of 2 samplings except for H and I.

K.S. LOW, C.K. LEE

AND S.H. TA

N

AQUATIC VASCULAR PLANTS AS BIOLOGICAL INDICATORS FOR METAL POLLUTION

TABLE 4Copper concentration (/ig cm '3) in single-metal solution

after treatment with aquatic plants.

Exposure time (Days) 0 1 2 3 4 5 6

iOttelia alim osdes 5.00 4.86 4.77 4.64 4.47 4.55

1 0 . 0 0 9.75 9.75 9.66 9.90 9.63 9.422 0 . 0 0 19.12 19.48 19.39 19.71 19.43 19.4950.00 49.83 48.43 47.87 48.53 48.07 48.00

1 0 0 . 0 0 99.00 98.95 99.64 99.61 97.84 94.32

Flimbristylis pauciflora 5.00 0.85 0.28 0.17 0.15 0 . 1 1 0.091 0 . 0 0 2.17 1.25 0.53 0.34 0.27 0.232 0 . 0 0 9.04 7.23 1.34 1 . 2 1 0.64 0.7650.00 31.33 26.00 20.77 7.51 3.50 1 . 6 8

1 0 0 . 0 0 66.25 63.17 53.17 52.04 41.11 40.71

Blyxa malayana 5.00 1.85 0.63 0.23 0.16 0.13 0 . 1 2

1 0 . 0 0 5.32 3.73 1.65 1 . 1 0 0.41 0.442 0 . 0 0 11.27 9.82 6.47 1.89 1.06 1.3650.00 32.47 27.64 27.97 13.35 8.28 4.83

1 0 0 . 0 0 69.14 63.02 63.73 43.07 40.93 52.05

crease, the co n cen tra tio n of Cu in so lu tion re­m ained relatively co n stan t. There was som e variation in the m etal u p take , depending on the p lan t species. T he o rder o f effectiveness o f the subm erged p lan ts in rem oving Cu from so lu tion was B lyxa m alayana > F im bris ty lis pauciflora > O ttelia alism oides.

O bservation of the exact re la tionsh ip betw een co ncen tra tion of Cu in the dry p lan t m aterial to the am b ien t Cu level, defined as en rich m en t fac to r (N akada e t al., 1979), is sum m arised in Table 5. The ratios decreased as the* co n cen tra tio n o f Cu increased fo r all p lants. These ratios ind ica te th a t during the 6 -day tre a tm en t period, the greatest up tak e o f Cu occurred w ith the 5 (Jig c m ' 3 for O ttelia a lism oides and F im bris ty lis pauciflora and 10 /ng cm ' 3 fo r B lyxa malayana.

A t th e end o f the tre a tm en t period, an apparen t release o f Cu at 100 ppm level by B lyxa m alayana to the so lu tion was ind ica ted by the increase in Cu level in the so lu tion . The release may have been re lated to the d isrup tion of the norm al physiological activities o f the cells, resul­ting in the efflux o f Cu (S u tto n and B lackburn, 1971).

Zinc. The en richm en t o f Zn appeared to be species specific. Zn co n ten t in dry p lan t m aterials

(T lble 6 ) was in the order o f F im bris ty lis pauci- flora > B lyxa m alayana > O ttelia alism oides. The high co n cen tra tio n o f Zn in th e first tw o p lan ts cou ld suggest the selectiv ity o f these p lan ts fo r this m etal in the ir na tu ra l env ironm ent.

The rate o f Zn up take by the p lan ts is show n in Table 6 . In all cases, the rate o f Zn u p tak e decreased rap id ly a fte r a 3-day exposure. This indicates th a t a 3-day du ra tion w ould p robably be th e o p tim u m period for the rem oval o f Zn if the p lan ts w ere used as biological filters. The co n cen tra tio n o f Zn in the so lu tions rem ained relatively co n stan t a fte r the in itial decrease. The en richm en t fac to rs (Table 5) suggest th a t the greatest u p tak e o f Zn occurred w ith the 5 n g e m ' 3

so lu tion for all p lants. Even though Zn was found to be less tox ic than Cu, the en rich m en t facto rs decreased as the co n cen tra tio n o f Zn in the cu ltivation m edia increased.

C adm ium . A fter a 6 -day exposure , Cd co n ten t in plants u n d er d ifferen t cond itions is show n in Table 7. The u p tak e increased as the exposure levels increased. Cd was also fo und to be as tox ic as Cu. The exposed p lan ts dem o n stra ted decay in p lan t tissues w hile no such tox ic e ffec t was no ted in the con tro ls. As observed w ith o th e r m etals, a fter the greatest in itial decrease, th e co n cen tra ­tion of Cd in the m edia rem ained relatively con-

39

TABLE 5Metal uptake (/ig g~‘ dry plant material) and enrichment factor

at the end of treatment period for aquatic plants.

Cu Zn Ni Cd Cr

Concentration of metal in solution ()Ltg cm '3) Metal

uptakeEnrichment

factorMetal

uptakeEnrichment

factorMetal

uptakeEnrichment

factorMetaluptake

Enrichmentfactor

Metaluptake

Enrichmentfactor

Ottelia alismodes

5.00 454 91 327 65 152 30 263 53 515 1031 0 . 0 0 872 87 656 6 6 244 25 522 52 921 922 0 . 0 0 1079 54 841 42 700 35 1751 8 8 1885 9450.00 2277 46 1962 39 1655 33 3250 65 3285 6 6

1 0 0 . 0 0 5547 56 2819 28 3290 33 3529 35 5572 56

4*.Flim bris tylis pauciflora

5.00 1236 248 1006 2 0 1 424 85 764 149 753 1511 0 . 0 0 2263 226 1372 137 623 62 1372 137 1257 1262 0 . 0 0 2947 147 2804 140 1613 81 3900 195 2225 1 1 1

50.00 6403 128 3578 72 2487 50 4406 8 8 4613 921 0 0 . 0 0 9996 1 0 0 4634 46 3573 36 8206 82 9694 97

Blyxa malayana

5.00 1308 262 8 6 6 173 543 109 684 139 206 411 0 . 0 0 3325 333 1488 140 903 90 1236 124 492 492 0 . 0 0 3585 179 3134 157 1483 74 1971 99 756 3850.00 7059 141 3685 74 3935 79 5812 1 16 2008 40

1 0 0 . 0 0 17341 174 4504 45 7583 76 9424 94 3941 39

, _ concentration of heavy metal in plant (Ug g _1)"Enrichment factor = --------------------------------------------------------------------

concentration of heavy metal in solution (fj.g cm '3)

K.S. LOW, C.K. LEE

AND S.H. TA

N

AQUATIC VASCULAR PLANTS AS BIOLOGICAL INDICATORS FOR METAL POLLUTION

TABLE 6

Zinc concentration (pig cm '3) in single-metal solutions after treatment with aquatic plants.

Exposure time (Days) 0 1 2 3 4 5 6 7 8 9

Ottelia alismodes 5.00 3.54 2.17 0.51 0.23 0.08 < D.L < D.L < D.L < D.Li

1 0 . 0 0 5.30 1.57 0.04 < D.L < D.L 0 . 0 2 0 . 1 1 0.29 0 . 1 1

2 0 . 0 0 14.20 10.96 5.31 1.45 0.54 0.32 0.14 0.08 0.1650.00 39.61 35.67 31.51 27.14 20.92 18.28 14.37 10.42 5.42

1 0 0 . 0 0 83.10 71.46 57.64 52.38 42.84 39.49 37.94 34.47 28.62

Fimbristylis pauciflora 5.00 3.52 1.92 0.71 0.29 0.07 0.04 < D.L < D.L < D.L1 0 . 0 0 5.38 1.07 0.35 < D.L < D.L < D.L < D.L 0.04 0.042 0 . 0 0 9.57 0 . 8 8 0.42 0.24 0.06 0 . 0 2 0 . 0 2 0 . 0 1 0 . 0 1

50.00 33.97 21.72 11.57 5.99 2.28 1.53 1 . 2 1 0 . 8 8 0.801 0 0 . 0 0 68.19 45.34 23.76 1 2 . 2 0 8.87 8.26 6.33 6 . 2 1 5.71

Blvxa malayana 5.00 3.22 2.46 1.42 0.91 0 . 6 6 0.06 0.07 0.05 0.041 0 . 0 0 7.24 6.40 4.70 : .84 1.06 0.54 0.30 < D.L 0 . 0 1

2 0 . 0 0 15.97 14.56 13.48 1 i.03 9.73 6.55 3.20 2.37 1.9150.00 41.99 35.75 26.25 21.26 15.60 11.30 5.67 3.28 2.15

1 0 0 . 0 0 84.02 80.03 69.69 S4.45 62.21 56.21 54.17 46.21 42.59

D.L. for Zn is I pig dm

stan t fo r all p lants stud ied . B lyxa m alayana and F im bristy lis pauciflora appeared to be m ore effective in th e rem oval of Cd th an O ttelia alis­m oides.

T he en rich m en t factors (Table 5) generally decreased w ith increasing co n cen tra tions o f Cd in the m edia.

C hrom ium . T he rate o f chrom ium u p tak e by the p lan ts is show n in Table 8 . It is ap p aren t th a t Cr u p tak e by B lyxa m alayana was low com pared to o th e r plants. The greatest u p tak e occurred during th e first tw o days fo r all exposed plants.

Again, Cr accum ulation increased as the exposure levels increased. As observed in o ther m etals, the en richm en t factors, decreased as the exposure levels increased. Values o f en richm en t factor (Table 5) at 5 pig cm ' 3 w ere the highest for all p lan ts w ith the excep tion o f B lyxa malayana during the 6 -day trea tm en t period. Cr was found to be as tox ic as Cd and Cu to all p lants.

N ickel. The rate o f Ni rem oval by the p lan ts was less rap id com pared to o th e r m etals stud ied

(T able 9) ind ica ting th a t th e p lan ts had low affin ity fo r th e m etal. O f the five elem ents stud ied , Ni show ed th e least ten d en cy to be abso rbed by all p lants, reflecting th e low affin ity of p lan ts in rem oving Ni from p o llu ted w aters.

The en rich m en t facto rs o f Ni (T able 5) show th a t the highest up tak e of Ni occurred w ith 5 pirn cm ' 3 fo r all the p lan ts. The to x ic ity o f Ni was fo und to be g reater than Zn b u t low er than Cu, Cr and Cd. This is based on the rate a t w hich decay developed in th e tissues o f exposed plants.

The rates o f rem oval o f Cu, Zn and Ni by O ttelia a lism oides in th e m ixed so lu tion are show n in Tables 10, 11 and 12. The accum ulation o f Cu was fo u n d to be enhanced in the p resence o f Ni and Zn. H ow ever, b o th Ni and Zn u p tak e in O ttelia alism oides was fo und to be an tagonized when O ttelia a lism oides was grow n in m edia en riched w ith these th ree m etals. Such an tagonis­tic and synergistic effects w ere fo u n d to be m ore p ro nounced fo r Zn than Cu or Ni>

F im bris ty lis pauciflora w as fo u n d to accum u­late less Cu, Zn and Ni w hen it was cu ltiva ted in

41

K.S. LOW, C.K. LEE AND S.H. TAN

TABLE 7Concentration of cadmium (MS cm '3) in single-metal solutions

after treatment with a aquatic plants.

Exposure time (Days) 0 1 2 3 4 5 6

Ottelia alismodes 5.00 1.96 1.14 1 . 1 0 0.04 0.04 0 . 0 1

1 0 . 0 0 2.84 1.05 0.17 0 . 0 2 0.03 0 . 1 2

2 0 . 0 0 9.49 3.97 0.42 0.27 0.06 0 . 1 0

50.00 38.16 22.40 12.44 3.36 2 . 1 1 0.901 0 0 . 0 0 72.33 62.35 54.74 39.84 23.91 12.75

Flimbristylis pauciflora 5.00 2.03 0.07 < D.L < D.L < D.L < D.L1 0 . 0 0 5.65 0.43 0.15 0.04 < D.L < D.L.2 0 . 0 0 10.25 1.30 0.37 0 . 1 0 0.15 0 . 0 1

50.00 34.04 23.79 1 2 . 1 2 3.73 2.73 2 . 1 2

1 0 0 . 0 0 74.08 43.63 28.94 15.02 9.45

Blyxa malayana 5.00 3.13 2.29 1.64 0 . 1 0 0 . 1 0 0 . 0 1

1 0 . 0 0 6.80 5.26 2.53 0.26 0 . 1 0 0.042 0 . 0 0 13.69 10.90 4.20 1 . 0 2 0 . 2 2 0.1750.00 34.48 15.86 5.74 0.41 0 . 2 0 0 . 1 1

1 0 0 . 0 0 75.93 57.69 28.04 1 2 . 1 2 6.54 2 . 8 8

D.L. for Cd is 2 [Jig dm

m edia en riched w ith these th ree m etals com pared to w hen th e m eta l was added singly to the m edia (Tables 1 0 ,1 1 and 12). The u p tak e o f Ni rem ained v irtually nil a t 1 0 0 [jg cm ' 3 so lu tion and the an tagonistic e ffec t was m ore ap p aren t fo r Zn than Cu o r Ni. T he sam e tren d was also n o ted for O ttelia alism oides.

The an tagonistic e ffec t o f Cu, Zn and Ni on each o th e r was also n o te d in B lyxa malayana (Tables 10, 11, 12). D espite the fact th a t Cu was the m o st tox ic am ong the th ree m etals, its accu­m u la tion was still g reater than the o th e r tw o m etals w hen B lyxa m alayana was grow n in the so lu tion enriched w ith these th ree m etals.

DISCUSSION

A nalytical data o f field sam ples show th a t m etal en rich m en t was d ependen t p rim arily on the p lan t species and specific selectivity . This was also n o ted earlier by Dietz (1 9 7 2 ) and A ulio and Salin (1982). The com paratively high degree o f p re­ferential ab so rp tion of a particu la r m etal by p lan ts is p robab ly a physiological characteristic o f the species and is regu la ted by env ironm enta l factors

(B oyd, 1970). Fe and Zn were found to be en­riched to a g rea ter e x te n t com pared to Ni, Pb, Cd, Cu and Cr. Even though Cr was n o t de tec tab le in w ater sam ples at the tim e o f p lan t sam pling, its en richm en t was fo und to be g reater than Cd. This could be due to in te rm itte n t discharges which w ere m issed at the tim e o f sam pling. H ence, in te rp re ta tio n o f en richm en t factors is com pli­cated and a definab le re la tionsh ip w ith Cr in w ater m ay be obscured by flu c tua tions in w ater chem istry b rough t a b o u t by in te rm itte n t dis­charges. Such an effec t is also tru e fo r the o ther six m etals as th e m etal levels in the w ate r only ind icate the quality prevailing a t the tim e of sam pling and n o t the average levels over a long term period.

As a resu lt o f the relatively lim ited nu m b er o f locations and sam ples invovled, the data have no t been sub jec ted to analysis o f variance fo r s ta tis­tical significance. Hence, no co rrelation cou ld be draw n betw een the m etal levels in p lan ts and in w ater a t the sam pling sites.

It seem s likely th a t m etal up take in p lants could have been a ffec ted by a n u m b er of en-

42

AQUATIC VASCULAR PLANTS AS BIOLOGICAL INDICATORS FOR METAL POLLUTION

TABLE 8

Concentration of chromium (/ig cm"3) in single-metal solution after treatment with aquatic plants

Exposure time (Days) 0 1 2 3 4 5 6

Ottelia alismodes 5.00 3.94 3.38 2.97 2.38 1.80 1 . 2 0

1 0 . 0 0 8.25 7.43 6.53 5.64 4.50 3.80i

2 0 . 0 0 17.21 15.81 14.84 13.54 12.43 11.2950.00 43.41 41.94 38.88 36.45 34.46 36.24

1 0 0 . 0 0 85.35 80.32 76.50 73.05 70.26 68.19

Flimbristylis pauciflora 5.00 3.74 3.27 2.85 2.52 2 . 2 2 1.961 0 . 0 0 7.92 6 . 8 8 6.24 5.77 5.32 4.862 0 . 0 0 14.97 13.17 11.96 10.91 1 0 . 0 2 9.2050.00 37.50 34.61 32.75 30.70 29.82 28.61

1 0 0 . 0 0 78.10 74.47 70.93 68.95 66.63 75.60

Blyxa malayana 5.00 4.19 3.72 3.02 2.55 2.08 1.901 0 . 0 0 8 25 7.48 7.15 6.47 6.08 5.742 0 . 0 0 16.79 16.20 15.33 14.82 14.30 13.9550.00 43.70 42.09 41.83 40.20 39.57 38.92

1 0 0 . 0 0 86.18 83.37 82.23 80.41 78.72 78.17

TABLE 9Nickel concentration (/ig cm '3) in single-metal solution

after treatment with aquatic plants

Exposure time (Days) 0 1 2 3 4 5 6 7

Ottelia alismodes 5.00 4.93 4.93 4.83 4.68 4.81 4.76 4.791 0 . 0 0 9.87 9.81 9.68 9.53 9.41 9.27 9.582 0 . 0 0 20.50 19.93 19.69 19.51 18.13 17.82 17.7050.00 49.27 48.41 47.99 47.57 47.53 46.40 46.32

1 0 0 . 0 0 98.92 96.97 96.54 94.33 94.45 91.98 91.92

Flimbristylis pauciflora 5.00 3.84 3.55 3.22 3.10 2.96 2.77 2.671 0 . 0 0 8.69 8.63 8.43 8.19 7.93 7.66 7.432 0 . 0 0 17.07 16.45 15.49 14.90 14.81 14.40 13.0250.00 45.48 44.78 43.80 43.18 42.58 41.83 41.83

1 0 0 . 0 0 95.69 93.96 92.36 91.91 90.87 8 8 . 1 1 90.81

Blyxa malayana 5.00 3.73 3.46 3.26 3.10 2.94 2.67 2.641 0 . 0 0 7.42 6.37 6.65 5.79 5.48 4.89 4.922 0 . 0 0 15.27 14.02 13.71 13.57 13.78 13.31 12.9250.00 43.31 40.73 40.32 39.40 37.68 36.99 36.33

1 0 0 . 0 0 89.62 86.90 84.78 82.20 79.52 74.65 68.07

43

K.S. LOW, C.K. LEE AND S.H. TAN

TABLE 10Copper concentration (/ig cm '3) in mixed-metal solutions

(Cu, Zn, Ni) after treatment with aquatic plants.

Exposure time (Days) 0 1 2 3 metal uptake (jUg g" 1 dry plant material)

Ottelia alimodes 5.00 0.80 0.29 0 . 2 1 4401 0 . 0 0 2.51 0.94 0.38 7802 0 . 0 0 7.30 4.66 3.39 159850.00 32.47 25.42 22.82 3008

1 0 0 . 0 0 74.54 67.50 62.75 4550

Flimbristylis pauciflora 5.00 0.84 0 . 1 1 0 . 1 0 10731 0 . 0 0 3.23 0.79 0.32 23112 0 . 0 0 9.42 7.48 3.48 312150.00 37.01 34.78 30.76 4567

1 0 0 . 0 0 87.08 86.82 83.85 5089

Blyxa malayana 5.00 2.74 1.44 0.24 13201 0 . 0 0 5.84 3.15 1.41 22522 0 . 0 0 13.24 11.28 9.37 393350.00 35.51 34.50 33.35 6430

1 0 0 . 0 0 78.72 74.75 71.19 12759

TABLE 11Zinc concentration (jug cm’3) in mixed-metal solution

(Zn, Cu, Ni) after treatment with aquatic plants.

Exposure time (Days) 0 1 2 3 metal uptake (jug g~‘ dry plant material)

Ottelia alimodes 5.00 3.44 2.17 1.27 2501 0 . 0 0 7.92 4.60 2 . 6 6 4352 0 . 0 0 16.89 14.27 11.63 70050.00 45.09 42.70 39.70 1004

1 0 0 . 0 0 91.28 8 8 . 0 0 83.91 1427

Flimbristylis pauciflora 5.00 4.37 0.09 0.03 7611 0 . 0 0 8.80 1.41 0.06 15812 0 . 0 0 18.93 17.04 15.77 165950.00 47.34 43.53 42.04 2068

1 0 0 . 0 0 98.42 94.52 94.82 2478

Blyxa malayana 5.00 4.47 3.47 0.53 7031 0 . 0 0 8.46 3.75 1 . 0 2 13172 0 . 0 0 16.89 15.70 13.19 212550.00 41.92 41.90 41.49 2887

1 0 0 . 0 0 89.81 89.34 86.99 3364

44

AQUATIC VASCULAR PLANTS AS BIOLOGICAL INDICATORS FOR METAL POLLUTION

TABLE 12Nickel concentration (/ig cm '3) in mixed-metal solutions

(Ni, Zn, Cu) treatment with aquatic plants.

Exposure time (Days) 0 1 2 3 metal uptake (/igg ' 1 dry plant material)

iOttelia alismodes 5.00 4.09 3.68 3.16 146

1 0 . 0 0 8.57 7.74 7.16 2322 0 . 0 0 .17.97 16.58 15.61 37050.00 46.80 45.38 43.93 735

1 0 0 . 0 0 93.63 90.00 85.31 1559

Flimbristylis pauciflora 5.00 4.92 3.31 3.31 4191 0 . 0 0 8.83 7.97 5.08 9442 0 . 0 0 18.45 17.88 16.38 148650.00 48.42 46.36 46.08 1815

1 0 0 . 0 0 97.58 95.92 94.28 2216

Blyxa malayana 5.00 4.21 3.84 2.34 31610.00 8.72 7.67 7.68 64420.00 17.58 17.25 16.21 118050.00 42.58 41.96 41.50 1978

100.00 89.92 88.10 87.71 2550

vironm ental variables such as hardness of w ater, n u tr ien t levels, age o f p lan ts and grow th (M ayers, 1977; M udroch and C apobianco , 1979; Low and Lee, 1981 , Schierup and Larsen, 1981). It is, therefo re , o f prim e im portance to establish the effect o f such env ironm ental variables on m etal up take. It is equally essential to establish the im portance o f seasonal variability and grow th form o f p lan ts so th a t in te rp re ta tio n of the data can yield reliable in fo rm ation regarding m etal up take in relation to the su rround ing level.

In the m etal up take stud ies, co n cen tra tio n of m etals in p lan ts was apparen tly regulated by both physiological and environm ental factors. Active u p tak e and accum ulation o f m etals against a co n cen tra tio n gradient was obvious, ind icating an active up take m echanism . The sam e tren d was no ted earlier by S u tto n and B lackburn (1 9 7 1 ) and E rnst and W erff (1978). In general, this up take is light-enhanced and requires m etabolic energy. It is also ap p aren t th a t the surface area to volum e relationsh ip of these aquatic plants is an im p o rtan t fac to r affecting m etal up take . Fleshy and heavily ro o ted p lan ts accum ulated metal m any tim es less than the profusely fo lia ted species.

It is in te resting to no te th a t en richm en t factors decrease w ith increasing co n cen tra tio n of m etals in th e cu ltiva tion m edia. This observation was n o ted earlier by S u tto n and B lackburn (1 9 7 1 ) and N akada e t al. (1979). The higher co n cen tra ­tion of m etals m ay have been m ore tox ic to the p lants, resu lting in a decline in the up tak e (S u tto n and B lackburn , 1971). The decrease cou ld also be due to th e im pairm en t o f physiological func­tion at the h igher levels o f m etals (C earley and C olem an. 1973).

In the p resen t s tu d y , som e heavy m etals w hich may occur as po llu tan ts were added to n u tr ien t m edia to observe the ir up take . The system involved is essentially a sta tic bioassay system . If the cu ltiva tion m edia used were m ade up o f w ater po llu ted w ith som e heavy m etals, the m etal u p tak e could be observed in a m anner as described herein. P referab ly , the system should be a co n tin u o u s flow system as rep o rted by Lin (1 9 7 7 ) fo r ben th ic d iatom s.

L abora to ry data show ed tha t co m p etitio n betw een m etals fo r b ind ing /adso rp tion sites w hich leads to an tagonistic and synergistic effec ts did occur for the p lan ts stud ied . Such effec ts w ould

45

K.S. LOW, C.K. LEE AND S.H. TAN

lead to u n d e r estim ation or over estim ation of p o llu tion by som e m etals in areas w here several m etals coexist in the w ate r colum n. Since such phen o m en a occurred in b o th low and high con­cen tra tio n s o f m etal, this m ay be the greatest prob lem concern ing the use o f subm erged p lan ts as ind ica to rs o f m etal po llu tion . This problem can n o t be overcom e by any sim ple m e thod , fo r exam ple, a change in sam pling techniques. The sam e prob lem was also suggested by Phillips(1 9 7 7 ) in th e use o f m acroalgae as biological ind ica to rs fo r m o n ito ring m eta l levels in estuaries and coastal waters.

In o u r search fo r possible ind ica to rs for m on ito ring po llu tion , Ottelia alismoides and Fimbristylis pauciflora appear to be prom ising. In this respect, the p lan ts m eet the basic requ ire­m ents of specific ity in m etal accum ulation and show a relatively high to lerance to all m etals tested . The p lan ts are easy to recognise w ith the naked eye, do n o t accum ulate silt or sed im en t and are easy to co llect and digest.

Fimbristylis pauciflora and Ottelia alismoides could be used as ind ica to rs in tw o ways. Due to the ir high en rich m en t capacity , they could be used as biological filters to rem ove m etal p o llu tan ts from co n tam in a ted w ater in the sam e m anner as Eichhorria crassipe (m art), Solm s for Cd and Ni (W olverton, 1976). T ransp lan ting o f Fimbristylis pauciflora and Ottelia alismoides cou ld yield valuable in fo rm atio n on po llu tion in s itua tions w here w ater co n tam in a tio n occurs periodically . In co n tras t to chem ical analysis o f w ater sam ples co llec ted a t one particu lar m o m en t, this m e th o d o f biological m on ito ring of w ater p o llu tion can reflect w ater quality over a period o f tim e.

N evertheless, m ore analysis is still needed to tes t th e constancy o f the en richm en t capacity in varying env ironm ental cond itions. More back­g round data on factors in fluencing accum ulation is also requ ired before any sta tistica l lim its can be p laced on th e significance o f analysis fo r ind icating co n tam ina tion levels. This should include m ore extensive sam pling, analysis o f w ater of varying pH, and n u tr ie n t levels. E qually essential is a deeper u n d ers tand ing o f the m echanism and m ode by w hich th e m etals are co n cen tra ted by the p lants.

CONCLUSION

The w ork rep o rted here d em onstra tes th a t m etal en richm en t varies w ith m etal type and the p lan t species. Iron and zinc were enriched to a

higher e x te n t than copper, cadm ium , lead, nickel and ch rom ium .

R esults o f m etal up tak e studies show th a t all p lants were able to rem ove copper, zinc and cadm ium m ore rapidly than chrom ium and nickel from th e cu ltiva tion m edia. The e ffec t o f the sim ultaneous presence o f several m etals on the up take o f any m etal was dependen t on th e p lan t species and m etals involved. It is p roposed th a t Ottelia alismoides and Fimbristylis pauciflora could be p o ten tia l biological ind ica to rs because of the ir relatively high degree o f to lerance to m etals and specific selectiv ity in m etal accum u­lation.

ACKNOWLEDGEMENTS

The au tho rs w ould like to express the ir thanks to Dr. R uth Kiew fo r the id en tif ica tio n o f the p lan t species and N oraini Abu Bakar fo r typ ing the m anuscrip t.

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AQUATIC VASCULAR PLANTS AS BIOLOGICAL INDICATORS FOR METAL POLLUTION

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(Received 2 June 1983)

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