Indian Jurnal f Marine Sciences Vl. 28., December 1999, pp. 365-369 A cmparative study f atmic absrptin spectrphtmetry and andic stripping vltammetry fr the determinatin f trace metals Zn, Cd, Pb and Cu in castal waters f Visakhapatnam, east cast f India P V S.Prabhakara Murty & D Satyanarayana Schl f Chemistry, Andhra University, Visakhapatnam 03, AP, India Received 19 JUli e 1998; revised 12 August 1999 Cncentratin levels f sme f the disslved trace metals like Zn,.Cd, Pb and Cu have been determined in the castal waters alng three transects (Gangavaram, Harbur and Rushi hill) near Visakhapatnam. Estimatins. made hy andic stripping vltammetry in the present study are in gd agreement with the reprted values by atmic ahsrptin spectrphtmetry. Vertical distributin f disslved Zn, Cd and Cu shwed an increasing trend frm the surface waters t bttm. Surface depletin and bttm enrichment f these elements resembling thse f the di stributin pattern f nutrients are attributed t their invlvement in bi-gechemical cycles. Disslved Pb shwed enrichment in surface cmpared t bttm waters indicating anthrpgenic input. Disslved Zn, Cd and Cu shwed signiticant psitive crrelatins amng themselves and with nutrients indicating their cmmn assciatin and surce f ccurrence. The atmic ratis f Zn Si and Cd t N were fund t be higher while, that f Cd t P was lwer when cmpared with thse f the ffshre waters f the Bay f Bengal. This was attributed t the differences in the bilgical uptake f these metals. Determinatin f trace metals in marine envirnment has received cnsiderable attentin in recent years. During the last tw decades, sensitive and accurate methds such as atmic absrptin spectrphtmetry (AAS), andic stripping vltammetry (ASV) and neutrn activatin analysis (NAA) have been develped fr their determinatin in a variety f matrices. Amng them, AAS and ASV methds are mst cmmnly emplyed fr the estimatin f trace metals in seawater l - 13 _ Hwever, sufficient infrmatin is nt available n the intercmparisn f these tw methds. Further, the distributin f trace metals in castal waters and the prcesses cntrlling their distributin are nt wellstudied. In the present wrk a detailed study f the distributin f elements like Zn, Cd, Pb and Cu and their speciatin have been undertaken using ASV technique and the results were cmpared with the AAS data reprted earlier l 3. The pssible interrelatins f these elements with nutrients (nitrate, phsphate and silicate) have als been discussed. Materials and Methds Seawater samples were cllected with Niskin water *Occupatinal Health Ser ~iees & Research Center, Steel Plant, Visakhapatnam 5 031, India, samplers at mnthly intervals ver a perid f ne year (September 1986 t August 1987) alng three transects at Gangavaram (G), Harbur (H) and Ru shi hill (R) situated n Visakhapatnam cast (Fig. I). The hrizntal distance f each statin frm the cast alng the transects G(G I, G2 and G3), H(H I, H2 and H3) and R(R I, R2 and R3) is shwn in Table I. Seawater samples were filtered thrugh a preweighed acid cleaned membrane (0.45 11m pre size) t separate di sslved and particulate fractins. Nutrients (nitrate, phsphate and si licate) were determined phtmetrically using standard methds 14. An aliqut (800 ml) f seawater sample was acidified t ph 3-4, and the trace metals (Zn, Cd, Pb and Cu) were determined by andic stripping vltammetry in differential pulse mde. EG & G, PAR mdel 264A, in cmbinatin with a cell having three electrde assembly (mdel 3A), cnsisting f a hangi ng mercury drp as wrking electrde, Ag / AgCI as reference electrde and a Pt wire as cunter electrde. X-Y recrder RE 0089 was emplyed fr btaining current-vltage curves. Acetate buffer (0. 1 M, ph 4.5) was used as a supprting electrlyte. Abut ml f seawater sample (PH 3-4) mixed with ml buffer in the cell, was purged with pure nitrgen gas t expel the disslved xygen cmpletely, The electrlytic depsitin f metals was then carried ut
366 INDIAN I. MAR. SCI., VOL., 28. DECEMBER 1999 Fig. I-Transects lcat~ alng Visakhapatnam cast fr a fixed tiitief 6 min by hlding the ptential at -1.V while stirring the slutin thrughut. The slutin was allwed t attain equilibrium fr 1 min 'while discntinuing stirring. Stripping f metals was then nted by' andic scan at 5 mv/s with a pulse height f m\l..l'j:1~ resulting current - vltage plt was recrded at a' current sensiti vity f JlA. An. <;tliqut,f the slutin cntaining a knwn cncentratin f mixture Zn, Cd, Pb and Cu was added t the'seawater samples using a micr syringe. The electrlysis and stripping were repeated under identical cnditins f instrumental setting in all the cases. The peak heights crrespnding t the additin were cmputed at the peak ptentials - 0.98, - 0.63, - 0.42 and - 0.19 V crrespnding t the xidatin f Zn, Cd, Pb and Cu respectively. Cncentratins f these trace metals in the seawater were cmputed using the equatin : C m = i, v Cs / i2 V + (h - i, ) V where C m = cncentratin f metal IS seawater, i, = riginal peak height, i2 = spiked peak height, 0' Table I-Annual average cncentratin levels f disslved trace metals (lig. 1-') and nutrients (lim!. 1-') in castal waters f Visakhapatnam Trace metal/vertical Nutrient Zn Cd Pb Cu NO,-N POcP distance (m) JO JO 22.1 0 15.70 14.90 *Values given in parentheses are hrizntal distance (km) frm the cast. G ( 0-8) 7.90 8.57.45 12.80 12.70 0.67 0.87 1. 1.33 1.40 8. 6.63 5.95 3.80 3. 3.87 3.85 4.35 4. 6.70 7.43 7.60 8.55 1).40 0.68 0.86 0.91 1.16 1. 11.60 14.00 16. 18.60 Transects" H (0-9) 9.70 11. 13.60 14. 0.73 0.92 I. 03 1. 1.25 7.77 6.60 6.25 5.45 3.73 4.13 4.45 4.75 8.03 8.33 8.65 9.40. 1.02 1.09 1.24 1.47 1.70 11.57 11.73 12.45 13.80 R (0 - II) 8.80 9.77 11. 13.00 0.61 0.75 0.96 1.08 1.15 5.93 5.77 4.85 4.40 4.00 2.43 2.83 2.65 3. 15 3.00 4.27 4.97 5.60 6.90 7.90 0.36 0.52 0.56 0.74 0.97 11.97 11.95 13.80 v = vlume f standard slutin added, V = vlume f seawater taken, and Cs = cncentratin f standard slutin used fr spiking. The prcedure was repeated thrice fr its reprducibility III each case and
MURTY & SAY ANARA Y ANA: AAS & ASV FOR DETERMINATION OF TRACE METALS 367 ) calculated the percentage f deviatin as ± 8, ± 6, ± 12 and ± loin case f Zn, Cd, Pb and Cu, respectively. Results and Discussin The annual averages f disslved trace metals (Zn, Cd, Pb and Cu) and nutrients (N0 3 - N, P0 4 - P and Si0 4 - Si) present in the seawaters f the three transects f Visakhapatnam cast are depicted in Table 1. Typical vertical prfiles f these cnstituents at m depth are shwn in Fig. 2. Nutrients and trace metals (Pb and Cu) at surface waters revealed in general, a decreasing trend frm cast t ffshre. This can be attributed t the impact f land run ff and its gradual dilutin and dispersin twards ffshre. Zinc-The vertical distributin pattern, in general, resembles thse f nutrients (N0 3 - N, P0 4 - P and Si0 4 - Si). It revealed an increasing trend frm surface t bttm (Fig. 2), which can be attributed t its regeneratin in the water clumn. This is als evident frm the significant psitive crrelatins bserved between Zn and nutrients (nitrate, phsphate and silicate) in the present study (Table 2). Surface depletin and bttm enrichment f Zn can be attributed t its uptake by rganisms at surface and subsequent regeneratin f it frm sinking bilgical matter at bttm waters. Since phytplanktn is knwn t cncentrate large amunts f Zn, it is pssible that diatms may play an imprtant rle in bi-gechemical cycling. Similar vertical di stributin f disslved Zn was reprted earlier in castal waters TRACE METAL CONCENTRATION ().1g.(1 ) Zn Cd Pb Cu 5 15 0 1 2 3 6 9 0 3 6... >-r-..., r----1;)r---,...,---,...-j::t., r--cim-----' NUTRIENTS ( }lml'.. [-I) Si0 4 - Si 2 15. ' 25 -«1 0 2' 0.,. ~O 5 0 Vl 0 llj n:: I- LU ~ z ( H ) :r: 40 I- a.. LU Cl 0 1 0 ( R) 3 0-4 0 5 0 Fig. 2-Vertical prfiles f trace metals and nutrients at the three transects G. H and R
368 INDIAN 1. MAR. SCI., VOL., 28, DECEMBER 1999 f Visakhapatnam 7, and in the castal and ffshre waters f Bay f Bengal" )) which was attributed t its regeneratin frm rganisms. The atmic rati f Zn t Si (5.16 x -') derived frm the regressin equatin fr the castal waters f Visakhapatnam was fund t be higher than reprted value (l.40 x -') fr the ffshre waters f Bay f Bengal)). The cncentratin levels (range and average) f Zn (Table 3) are in gd agreement with the earlier values btained by AAS. Bth f them indicated a relatively higher cncentratin f Zn at Harbur than that at Gangavaram and Rushi hill transects. This may be attributed t anthrpgenic input f Zn in the Visakhapatnam harbur and its subsequent dispersin int the castal regins particularly alng Harbur transect. Cadmium - Vertical distributin f disslved Cd resembles that f Zn (Fig. 2), which is als evident frm significant psitive crrelatin (r = 0.84, P = 99%) btained between them (Table 2). Vertical prfiles f disslved Cd shwed relatively higher cncentratin in bttm when cmpared t surface waters (Fig. 2) similar t thse f nutrients. This is als evident frm the significant psitive crrelatins bserved between Cd and nutrients. This can be explained by the remval f Cd in the surface waters n t the particulate rgal1lc tissues and its subsequent regeneratin via xidative prcesses. Since Cd has n physilgical rle, it is prbably adsrbed n the surface f planktn debris r faecal pellets during its transprt t bttm waters '5. Based n the regressin equatin, the atmic rati f Cd t N (4.73xlO-4) btained is higher than the reprted value fr ffshre waters f Bay f Bengal" (2.8xlO-4). Hwever, the rati f Cd t P (2.73xI0-') is iwer than the reprted value (6.x - 3 ) ". This may prbably be due t differences in its bilgical uptake and ther physic-chemical prcesses. The Cd levels fund alng the three transects f Visakhapatnam cast are in gd agreement with the AAS data reprted earlier" (Table 3). Further, bth the data indicated high cncentratins at Gangavaram than ther tw transects. Lead - Unlike Zn and Cd, the cncentratin levels f disslved Pb shwed relatively high at surface as cmpared t bttm waters (Table I). Cncentratin depth prfiles (Fig. 2) als indicated similar trend suggesting its distributin cntrlled thrugh atmspheric input. Hwever, it wa~; attributed earlier 7,1J t its anthrpgenic input. Sanzgiri & Braganca 4 bserved higher cncentratin f Pb at surface waters when cmpared t bttm waters f Zn(nM) Cd(nM) Pb(nM) Cu(nM) Table 2-Crrelatin matrix amng disslved trace metals and between nutrients and disslved trace metab in castal waters f Visakhapatnam Cd(nM) Pb(nM) Cu(nM) N03-N(IlM) P0 4 - P(IlM) SiOrSi(IlM) 0.84-0.61 0.36-0.45 0.55 0.43* -0.56 0.3 1-- 0.39-0.46 06~ Number f samples (n) analysed in each case is 33; the level f significance (P) is >99%; - P.> 95% ; -- P> 90 % ; ----- nt significant. Table 3-Cmparisn f range and average cncentratin levels f disslved trace metals (Ilg. 1-1) with the reprted data (ref. 13) in the castal waters f V isakhapatnam Trace Transect Remarks metal G H R Zn 3. - 18.00(9.90) 5. - 19.(11.70) 4.00-18.00(.) Present study ND - 22.80(12.70) ND-21.90(13.) ND - 21.(11.70) Reprted I.' Cd 0.25-2.00(0.99) 0.34-1.95(0.95) 0. -1.80(0.84) Present study 0.11-2.11(1.03) 0. 11-2.11 (0.99) 0.11-2.32(1.01 ) Reprted I, Pb 4.00-11.00(6.40) -12.(6.) 3.80 -.00(5.2 1) Present study 0.16-11.(2.97) 0.31-11.(3.00) 0.31-7.90(2.24) Reprted I ) Cu 2.00-6.00(3.78) 2. -7.(3.44) 2: -4.(2.76) Present study 0.09-6.59( 1.80) ND -8.88( 1.82) 0.18-6.59(1.57) Reprted I.' ND = Nt detected ; Values in parentheses are annual averages 0.87 0.90-0.51 0.42' )...
MURTY & SAY ANARA Y ANA: AAS & ASV FOR DETERMINA non OF TRACE METALS 369 Andaman Sea. Disslved Pb shwed significant negative crrelatins with nutrients unlike ther trace metals (Table 2) indicating its nn-assciatin with them. The present data has cmparatively higher values than the reprted by AAS (Table 3). Hwever, bth f them shwed, a similar distributin f Pb with relatively high cncentratin at Harbur cmpared t Gangavaram and Rushi hill transects, which can be attributed t its anthrpgenic input. Cpper - Vertical prfiles f disslved Cu at all the three statins revealed an increasing trend with depth indicating its depletin at the surface and enrichment at the bttm waters. Its distributin in castal waters was same as thse f Zn and Cd and nutrients. This is evident frm the significant psitive crrelatins (Table 2) which further indicates their cmmn assciatin and surce f ccurrence in seawater. This can be attributed t its (i) rembilisatin frm shelf sediments and subsequent diffusin int the verlying waters, and (ii) release frm rganisms during degradatin and decay. Studies 3 n the distributin f trace metals in castal and ffshre waters f Bay f Bengal revealed enrichment f disslved Cu in the bttm water layers cinciding with the minimum levels f disslved xygen. The enrichment f Cu in bth disslved and particulate frms at the bttm layers f water near Harbur and castal areas f Visakhapatnam 7 was attributed t its release during the decmpsitin f the rganisms. Cmparisn f the cncentratin levels f Cu btained in the present study bradly agrees with thse values reprted by AAS (Table 3). Hwever, the average cncentratin f Cu btained by the ASV methd is relatively high in Gangavaram while it is almst same in Gangavaram and Harbur waters as btained by AAS technique. In cnclusin, values f trace metal cncentratins reprted in the present study using ASV technique bradly agree with thse reprted by AAS technique (Table 3). Hwever, ASV technique has several advantages ver AAS fr trace metal analysis particularly in seawater. These include (i) simple and reliable, (ii) multi element technique, (iii) n need f pre-cncentratin prir t analysis and (iv) relatively free frm interference. Acknwledgement Authrs wish t express their gratitude t the Defence Research and Develpment Organisatin, Gvt. f India fr spnsring this wrk. References I Sen Gupta R, Singbal S Y S & Sanzgiri S, Illdiall J Mar Sci, 7 (1978) 295. 2 Sanzgiri S & Mraes C, indiall J Mar Sci, g (1979) 254. 3 Braganca A & Sanzgiri S, indian J Mar Sci, 9 (1980) 283. 4 Sanzgiri S & Braganca A, indiall J Mar Sci, ( 1981 ) 23g. 5 Rajendran A, De Susa S N & Reddy C V G, Illdiall.I Mar Sci, II (1982) 43. 6 Gerge M D, Sawkar K & Reddy C V G, Illdiall J Mar Sci. \3 (1984) 64. 7 Satyanarayana D, Ra I M & Reddy B P R, Illdiall J Mar Sci, 14 (1985) 139. 8 Gerge M D, Indiall J Mar Sci, 15 (1986) 271. 9 Satyanarayana D, Prasada Reddy B, Dileep Kumar M & Ramesh A, in Cntributins in marine sciellces, edited by T S S Ra, R Natarajan, B N Desai, C Narayanaswami & S R Bhat, (Dr S Z Qasim Sastyabdapurti Felicitatins Cmmittee, NIO, Ga) 1987,329. Gerge M D, indian J Mar Sci, 17 (1988) I I I. II Satyanarayana D, Prabhakara Murty P V S & Sarma V V, Indian J Mar Sci, 19 (1990) 6. 12 Satyanarayana D, Prabhakara Murty P V S & Sanna V V, Mahasagar, 23 (1990) 3. 13 Pr"bhakara Murty P V S & Satyanarayana D. Illdiall JEll\! Prtec, (1990) 919. 14 Grashff K, Methds f seawater analysis, (Verlag Chemie, Weinheim) 1976, pp 7. 15 Kremling K, Pinze I, Brckel V K & Wng C S, Mar Bii, 48 (1978) I.