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thescienceofthc

Totrlt The Science of the Total Environment

197 (1997) 161-165

Accumulation of copper, nickel, lead and zinc by snail, Lunellu coronatus and pearl oyster, Pinctada radiata from the Kuwait coast before and after the gulf war oil spill A.H. Bu-Olayan *, M.N.V. Subrahmanyam Department

qf Chemistry,

Faculty

of Science.

Kuwait

Unioersity,

P.O.

Box

5969.

&fat

13060.

Kuwait

Received 7 September 1996; accepted 18 December 1996

Abstract This study investigated the contribution of the 1991 oil spill to heavy metal contamination in the marine environment of the Gulf in Kuwait by analyzing moleskin organisms (gastropod snail, Lunch coronatus and bivalve Pearl oyster, Pinctuda radiuta) for their heavy metal contents before and after the spill. Concentrations of copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were determined in the soft tissue of both snail and oyster samples from three coastal stations during 1990 and 1994. In the 1990 samples, the metal concentrations in snail and oysters from different sampling stations were between 0.35 and 0.67; 0.11 aid 2.29 pg/g for Cu, 1.50 and 4.50; 0.47 and 1.33 ,ug/g for Ni, 0.16 and 2.98; 0.44 and 0.69 pg/g for Pb and 19.94 and 54.79; 247.20 and 1204.40 fig/g for Zn, respectively. In the 1994 samples, the metal concentrations were between 11.24 and 55.00; 28.90 and 168.43 pg/g for Cu, 15.33 and 16.96; 0.08 and 1.54 pg/g for Ni, 0.37 and 0.57 pug/g; 0.07 and 0.44 pg/g for Pb and 28.86 and 486.61; 17.75 and 575.00 pg/g for Zn respectively. The 1994 samples have significantly higher mean concentrations of Cu, Ni and Zn than the 1990 samples, except Pb in the 1994 samples, which showed a slightly lower mean concentration. The difference in patterns of metal occurrence and the significant increase in the Cu, Ni, and Zn concentrations in the 1994 snail and oyster samples were due to a contribution from the 1991 Gulf War oil spill. 0 1997 Elsevier Science B.V. Ke,vwords: Accumulation; Heavy metals; Lunella

coronatus;

Pinctada

radiata;

Gulf War

1. Introduction

* Corresponding

author.

Gastropod and bivalve molluscs accumulate metals in their tissues in proportion to the degree of environmental contamination and can be used

004%9697/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII

SOO48-9697(97)05428-4

162

A.H. Bu-Olu.van, M.N. C’.Subrahtnan.vtrm ,’ The Science oj’ the Totul Ettoironmetlt 197 (1997) 16l- I65

as indicators of marine metallic pollution [1,2]. They are very appropriate as monitors in situ because they are sedentary, abundant, of relative longevity, large, easily collected and weighed [3]. However, the concentration of metal in the mollusts depends not only on the level of the element in the environment but also on other factors: size, age, speed of growth, sex and reproductive conditions of the molluscs, season, salinity, chemical species and interaction with other pollutants [4]. The 1991 Gulf War in Kuwait resulted in the release of 6-8 million barrels of crude oil into the marine environment, and emission of a vast amount of burnt and unburnt crude oil from the burning and gushing oil wells into the atmosphere [5]. Combustion products, together with unburned crude oil, were deposited onto terrestrial and marine areas. The 1991 event prompted various research activities in the effected regions of Kuwait. Most of the yet-unpublished studies have centered around the effects on communities and species levels atid on the chemical effects of the spill. Few, however, have considered inorganic aspects, although heavy metals are an integral component of any crude oil. Their concentrations vary, but a significant proportion of the total heavy metal input into marine environments occurs through the burning of fossil fuels.

nitric acid, 1% hydrochloric acid and 1% hydrofluoric acid for 48 h. The samples were then diluted to 50 ml with deionised water, and digested in an automatic microwave digestion system (SpectroPrep CEM). Both the energy delivered by a microwave’s magnetron to the cavity and the energy absorbed by the contents are critical factors in the development of a digestion program [6]. The digested sample solution was analyzed by Perkin Elmer 5100 atomic absorption spectrophotometer (AAS). Flameless HGA-600 graphite furnace techniques equipped with deuterium background techniques was used for the determination of Ni and Pb, while air-acetylene techniques was used for the determination of Cu and Zn. Blanks were treated similarly. All glassware was cleaned by refluxing with hot nitric acid and thoroughly rinsed with double-distilled water before use.

2. Materials and methods Snail and pearl oyster samples were collected from three locations off the coast of Kuwait (Fig. 1). Sample collection was undertaken twice; March-June 1990 and March-June 1994. The organisms (shell plus flesh) were placed in labeled plastic bags and stored at - 10°C until analysis for metal content. A composite sample of 15 animals from each station was defrosted, shucked, drained, removed from their shells, weighed in 150 ml. Beakers and their wet weights recorded and later dried to constant weight at 65°C. Coarse homogenization of each sample was done by crushing in a PVC pestle and mortar (particle size < 250 pm). A dried sample of 0.125 g was weighed into a 50 ml. Fisher brand disposable sterile centrifuge tubes and wet ashen in 10%

Fig.

1. Samplinglocationsalong the coast of Kuwait.

A.H.

Bu-Olavun,

M.N.

Table I Results of heavy metal concentrations material. Oyster tissue (SRM-I 566a)

V. Subrahmanyam

/ The Science

in standard reference

Metal

Certified values (fig/g)

Present study (I[ gig)

Recovery

CU Ni Pb Zn

66.3 2.25 0.371 830

65.1 2.21 0.362 832

98.6 100.5 98.2 99.1

The accuracy of the method was verified using (IO-replicate) by means of standard reference material oyster tissue (SRM-1566a) from the National Bureau of Standards. Recoveries were above 90% for all trace metals measured (Table 1). The reported results are the mean values of duplicate determinations and are expressed as fig/ g dry weight. Statistical analysis to study the difference between concentrations in the 1990 and 1994 samples from the different locations were studied by Students t-test. Statistical significance was considered when P < 0.01.

3. Results and discussion

The metal concentrations and standard deviations of trace metals in the snail Luneflu coronutus, and Pearl oyster Pinctada radiata, are presented in Table 3. The patterns of metal occurrences, in order of decreasing concentrations, were Cu >Pb >Ni>Zn>for L. coronatus and Pb > Cu > Ni > Zn > for P. radiata, in the 1990 samples from Stations A, B, and C; whereas metal occurrences changed in the order Pb > Ni > Cu > Zn > for both L. coronatus and P. radiata, in the 1994 samples from Stations A, B and C. In the 1990 samples, metal concentrations in snail samples from different sampling stations were between 0.35 and 0.67; pg/g for Cu, 1.50 and 4.50 flgjg for Ni, 0.16 and 2.98 pug/g for Pb and 19.94 and 54.79 pg/g for Zn; whereas in oyster samples, the metal concentrations from all the three sampling stations were between 0.11 and 2.29 fig/g for Cu, 0.47 and 1.33 pglg for Ni, 0.44 and 0.69 ,ug/g for Pb, and 247.20 and 1204.40 pg/g for Zn. In the 1994 samples, the concentrations in snail sam-

qf’the

Total

Enoironmeni

197 (1997)

IhL

t65

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ples were between 11.24 and 55.00 pg/g for Cu, 15.33 and 16.96 pug/g for Ni, 0.37 and 0.57 pg/g for Pb, and 28.86 and 486.61 ,ug/g for Zn. In oyster samples, the metal concentrations were between 28.90 and 168.43 pgig for Cu, 0.08 and 1.54 pgig for Ni, 0.07 and 0.44 /(g/g for Pb and 17.75 and 575.00 /lg/g for Zn. Maximum concentrations of Cu, Ni, Pb and Zn in the 1990 samples were found in Stations B, A, C and A, respectively; whereas maximum concentrations in the 1994 samples were found at Station B for all the 4 metals (Table 2). The 1992 samples have significantly (P < 0.01 by Student’s r-test) higher mean concentrations of Cu, Ni and Zn than the 1990 samples except Pb in the 1994 samples from Station A which showed a significantly (P < 0.01 by Student’s t-test) lower mean concentration. The 1994 samples from Station B exhibited the highest mean concentrations of Cu, Pb and Zn; whereas only Zn showed the highest concentration in the 1990 samples from Station B. Increases in metal concentrations in the 1994 samples varied among metals and sampling stations. Cu and Zn, the most potentially toxic of the studied metals and Ni showed increases in the 1994 samples from Stations B and C. The highest increases were observed with mean Cu and Zn concentrations in the 1994 samples which were many times greater than the 1990 samples from Stations A, B and C. The 1994 samples from Station B exhibited the highest mean Cu, Pb and Zn concentrations; while only Zn showed the highest mean concentrations in the 1990 samples from Station B. Because snails and oysters can be used as bioindicators for metal pollution these results suggest that a significant increase in Cu, Pb and Zn discharge occurred between 1990 and 1994. Elevated metal concentrations in oysters after increase in pollution discharge to the marine environment in Mexico were recently reported by Pdez-Osuna et al. [7]. Metal accumulation by clams and oysters have been studied by several investigators (Table 3). Fowler et al. [8] reported metal levels in different areas of the Arabian Gulf. It must be realized that, owing to variability in the quality of analytical data, sampling season, size and age of species. comparisons of the present results with those

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2

Starion wise mean Cu. Pb, Ni and Zn concentrations in the 1990 and 1994 snail and oyster samples (Values are i‘rlnebst*d 111,i,