Deep-Sea Research,'Vol. 27A, pp. 1079 to 1082 0198-0149/80/1201-1079 $02.00/0 © Pergamon Press Lid 1980. Printed in Great Britain

N O T E

The determination of heavy metals in the Ligurian Sea. II. The geographical and vertical distribution of Cd, Cu, and Ni*

ROBERTO FRACHE~, FRANCA BAFFI t , ARDUINO DADONE~', GIUSEPPE SCARPONI t

a n d IGNAZIO DAGNINO3~

(Received 20 July 1979; in revised form 27 March 1980; accepted 27 May 1980)

Abstract--Cd, Cu, and Ni were determined in surface and deep-water samples from 15 stations in the Ligurian Sea. The samples were preconcentrated in chelating resins and quantitatively determined by atomic absorption spectrophotometry. The variability of the concentrations with depth was in general not significant compared with the variability of the analytical method, except at the station nearest the shore. Statistical analyses of the mean concentrations show also no significant regional variations in Cu, Ni, and Cd.

INTRODUCTION

As IN most parts of the Mediterranean, there are few data on the concentrations and vertical distributions of Cu, Cd, and Ni in the Ligurian Sea. FONSELIUS and KOROLEFF (1963) determined the vertical distribution of Cu and Zn down to 2250 m at a station near Monaco. FUKAI and HUYNH-NGOC (1976) determined Zn, Cd, and Cu at several depths at offshore stations in the northwestern Mediterranean. FONSELIUS (1970) determined Zn, Cu, and Cr at different depths at some stations in the Mediterranean, Red, and Arabian seas.

In this work we report data on the upper 200 m at 11 stations (Table 1) and on deeper waters at four stations (Table 2). The samples were collected in May 1975 and March 1976 from the R.V. Bannock and L.F. Marsili. Samples were collected by the same personnel and analyzed by the same methods. As in the previous work (FRACHE, BAFFI, DADONE and ZANICCHI, 1976) we used the analytical method suggested by LE MEUR and COURTOT- COUPEZ (1973) based on concentration of the metals by chelating resins (RILEY and TAYLOR, 1968), solvent extraction of the eluate, and quantitative determination by atomic absorption spectrophotometry.

EXPERIMENTAL

Sampling

The 10-1. samples were collected with polyvinylchloride van Dorn samplers and stored in polyethylene containers previously washed with 1 : 1 HC1 and deionized water.

* Contribution of the 'Gruppo Ricerca Oceanologica--Genova'. The research was carried out with a financial contribution of C.N.R. of Italy.

t Istituto di Chimica Generale ed Inorganica, Universit~i di Genova, Genova, Italia. ++ Istituto Geofisico e Geodetico, Universit/t di Genova, Genova, Italia.

1079

1080 ROBERTO FRACHE et al.

Resin

We used the resin Dowex A-1 (Fluka), 50 to 100 mesh, in hydrogen form. The resin beds were 12 mm in diameter and 60 mm high, in plexiglass columns.

Atomic absorption spectrophotometry

A Shandon Southern A 3400 atomic absorption spectrophotometer with a Kipp & Zonen 808 recorder was used. The analyses were carried out in an air-C2H 2 flame, using the resonance lines 324.7, 228.8, and 232.0 nm for Cu, Cd, and Ni, respectively.

Reagents

All the reagents, HC1, ammonium pyrrolidinedithiocarbammate (APDC), methyl iso- butyl ketone (MIBK), and buffer solution were reagent grade (Merk).

Method

Each sample was filtered through a 60-lam polyethylene filter and then through a 0.45- lam Millipore ® filter, both previously washed with 1:1 HCI and deionized water. The filtered seawater was allowed to flow directly into the resin bed at a 5 ml min-1 flow rate. The resin was washed with 250 ml of deionized water, eluted with 30 ml of 3N HCI and washed with 20 ml of deionized water. This preconcentration step was carried out on board, immediately after sample collection. In the laboratory, the eluate (50 ml) was quantitatively transferred to a separatory funnel, adjusted to pH 5.5 to 6.5 with NH4OH and acetate buffer. After addition of 0.1 g of APDC and 10 ml of MIBK, the sample was shaken vigorously for some minutes. The organic solution was analyzed with the atomic absorption spectrophotometer and the concentrations obtained from calibration curves. The method was checked with analyses of 10 aliquots of the same sample with the following precision: Cu 1.80 lag 1-1--SD 0.20; Ni 1.05 lag I-I--SD 0.13; Cd 0.20 lag 1 - 1 - SD 0.05.

The results with this technique refer to a fraction of the total element present in seawater, probably the ionic form of the element only. The metal not removed is probably associated to organic and inorganic colloids (FLORENCE and BATLEY, 1976) or bound in chelate compounds with high thermodynamic or kinetic stability. Nevertheless the technique allows for automatic preconcentration on board ship and thus minimizes contamination and possible alteration of the species in the sample.

RESULTS AND DISCUSSION

The results of the determinations are shown in Tables 1 and 2. For Stas 1 to 11 the results are expressed as mean values of the concentrations because,

except for Sta. 3 and some sporadic cases, the variability in the water columns is not significant compared with the variability of the analytical method (confidence limit 95~o). The variability of the concentrations with depth at Stas A to D is significant in only some cases.

Station 3 differs from the other coastal stations (1, 2, 4, 5, 6); Sta. 3 is nearer the coast (distance <2 miles) than the others (distance >15 miles). Table 3 shows higher con- centrations at Sta. 3¢ particularly of Cd and Ni, at depth. The deeper water may be contaminated by the sediments, which are highly polluted in this region. The con- tamination at Sta. 3 seems not to be widespread, because the nearby Stas 2 and 4 show no

The determination of heavy metals in the Ligurian Sea 1081

Table 1. Mean concentration (lag 1-1) and standard deviation of Cu, Ni, and Cd at the 1975 Stations. The means are the averages of five samples from depths of O, 25, 50, 100, and 200 m

Station Location Cu Ni Cd

1 43°50.10'N 1.725 0.79 0.05 s 08°06.30'E SD: 0.52 SD: 0.25 SD: 0.045

2 44 ° 15.20'N 1.025 1.05 0.05 08°31.20'E SD: 0.17 SD: 0.54 SD: 0.04

3 44°21.05'N 2.34 4.23 0.33 08°54.00'E SD: 1.29 SD: 2.64 SD: 0.28

4 44 ° 10.00'N 1.42 0.52 0.02 09° 18.02'E SD: 0.37 SD: 0.21 SD: 0.01

5 43°50.02'N 1.21 0.58 0.02 09°44.00'E SD: 0.08 SD: 0.08 SD: 0.01

6 43 ° 31.08'N 1.58 0.61 0.02 09°56.08'E SD: 0.31 SD: 0.30 SD: 0.01

7 43 ° 12.0YN 1.70 0.53 0.05 09°41.0YE SD: 0.33 SD: 0.24 SD: 0.03

8 43°20.03'N 2.13 0.55 0.09 09° 14.00'E SD: 0.36 SD: 0.20 SD: 0.04

9 43°30.01'N 1.60 0.80 0.06 08°46.20'E SD: 0.50 SD: 0.28 SD: 0.015

10 43°37.02'N 1.43 0.69 0.065 08°16.50'E SD: 0.34 SD: 0.25 SI): 0.02

11 43°45.02'N 1.34 0.57 0.10 08°11.50'E SD: 0.26 SD: 0.25 SD: 0.01

Table 2. Mean concentrations and standard deviations Cu, Ni, and Cd in the 1976 stations

Station Location Mean concentration (lag l - t )

A 43°33.05'N Cu: 1.19; SD: 0.12 08°05.05'E Ni: 0.81; SD: 0 . l l

Cd: 0.065; SD: 0.04

B Cu: 1.88; SD: 0.51 Ni: 0.73; SD: 0.22 Cd: 0,08; SD: 0.05

C Cu: 1.50; SD: 0.70 Ni: 0.68; SD: 0.27 Cd: 0.055; SD: 0.04

D Cu: 1.59; SD: 0.39 Ni: 0.53; SD: 0.36 Cd: 0.06; SD: 0.06

43°31.05'N 08°32.07'E

43°05.03'N 08°52.00'E

43°00.40'N 09°40.00'E

elevated concentrations. Probably, as noted by FUKA! and HUYNH-NGOC (1976), near the coast there are sources of contamination but also metal removal can take place by natural processes.

In Table 4 we compare the mean concentrations of Cu, Ni, and Cd in the near-shore stations, except Sta. 3, with those of the offshore stations. There is no significant difference among the values (t-test, 95% confidence limit), with the exception of the difference between the Cd mean values at Stas 7 to 11 and those at Stas 1 to 6.

It is concluded that at a distance >/5 miles from the coast, there is no significant regional or depth variation in Cu, Ni, and Cd. A possible exception is at Sta. 8, where the Cu and Cd concentrations differed significantly from the other offshore stations.

1082 ROBERTO FRACHE et aL

Table 3. Concentration ofCu, Ni, and Cd (lag 1 -l) at Sta. 3

Depth (m) Cu Ni Cd

0 0.64 3.50 0.06 25 1.93 3.10 0.19 50 3.93 1.00 0.39

100 1.93 5.55 0.19 200 3.28 8.00 0.80

Table 4. Mean concentration (lag 1-1), standard deviation, and number of samples for Cu, Ni, and Cd in near-shore and offshore stations

Stations Cu Ni Cd

Near-shore 1-6 1.39 0.71 0.03

(except 3) SD: 0.39 SD: 0.35 SD: 0.03 (1975) n = 25 n = 25 n = 25

Offshore 1.64 0.63 0.075 7-11 SD: 0.51 SD: 0.25 SD: 0.03

(1975) n = 25 n = 25 n = 25

Offshore 1.58 0.68 0.065 A D SD: 0.54 SD: 0.27 SD: 0.04

(1976) n = 33 n = 34 n = 30

C o n c e n t r a t i o n s at Sta . 3, ve ry n e a r t he coas t , i n d i ca t e c o a s t a l c o n t a m i n a t i o n t h a t

d i s a p p e a r s qu i ck ly in s p a c e o r in t ime . P r o b a b l y equ i l ib r i a w i th pa r t i c l e s p lay an

i m p o r t a n t p a r t in t he d i s a p p e a r a n c e .

Acknowledgements--The authors express their sincere thanks to the Masters, Captain SCOTTO and Captain MANCUSO, officers and crew of the R.V. Bannock and L.F. Marsili for their helpful cooperation and assistance in the collection of the samples. The authors thank also the C.N.R. (Italy) for financial support.

REFERENCES

FLORENCE T. M. and G. E. BATLEY (1976) Trace metals species in sea water. I. Removal of trace metals from sea water by chelating resins. Talanta, 23~ 176.

FONSELIUS S. (1970) Some trace metal analyses in the Mediterranean, the Red Sea and the Arabian Sea. Bulletin de l'Institut ocdanographique. Monaco, 69, 1407.

FONSELIUS S. and F. KOROLEFF (1963) Copper and zinc content of the water in the Ligurian Sea. Bulletin de l'lnstitut oc~anographique. Monaco, 61, 1281.

FRACHE R., F. BAFFI, A. DADONE and G. ZANICCm (1976) The determination of heavy metals in the Ligurian Sea. I. The distribution of Cu, Co, Ni and Cd in surface waters. Marine Chemistry, 4, 365.

FUKAI R. and L. HUYNH-NGOc (1976) Copper, zinc and cadmium in coastal waters of the N.W. Mediterranean. Marine Pollution Bulletin, 7, 9-13.

LE MEUR J. F. and J. COURTOT-COUPEZ (1973) Dosage de traces d'elements lourds dissous dans I'eau de met par spectrophotometrie d'absorption atomique et redissolution sur l'electrode d'argent amalgam6. Bulletin de la Sociitk Chimique de France, 929-935.

RILEY J. P. and D. TAYLOR (1968) Chelating resins for the concentration of trace elements from sea water and their analytical use in conjunction with atomic absorption spectrophotometry. Analytica Chimica Acta, 40, 479.