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DETERMINATION OF ARSENIC, CHROMIUM, SELENIUM AND ZINC INSOME TROPICAL FISH BY NEUTRON ACTIVATION

VIEWS: 57 PAGES: 9

Determination of heavy metals in fish samples of Bangladesh is described

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									Journal of National Oceanographic, Atmospheric and Maritime Institute
©NOAMI, Eastern Plaza, Dhaka, Bangladesh
Vol.22, No.2, 1- 8, 2005
ISSN: 1027-2119




DETERMINATION OF ARSENIC, CHROMIUM, SELENIUM AND ZINC IN
SOME TROPICAL FISH BY NEUTRON ACTIVATION

A.K.M.Sharif
Bangladesh Atomic Energy Commission, Dhaka, Bangladesh

K.R.Krishnamoorti
Analytical Chemistry Division, Bhava Atomic Research Center, Trombay, India

M.Alamgir and Stanley A.Bajue
Department of Physical, Environmental and Computer Sciences
Medgar Evers College, CUNY, NY, USA
____________________________________________________________________________________________________________


ABSTRACT

Determination of arsenic, chromium, selenium and zinc in several commonly consumed
tropical marine fishes have been by neutron activation followed by radiochemical
separation to remove the interfering activities of sodium, potassium, bromine, and
phosphates, etc., in order to establish the baseline data and to measure the levels of
contamination, if any. The results of this study positively indicate that the marine fishes
of Bangladesh have concentrations much below permissible levels for these toxic levels
for these toxic elements. A radiochemical scheme for the separation of these trace
elements in biological materials is also presented in this paper.

Key words: Arsenic, Chromium, Selenium, Zinc, Tropical Fish, Tropical Fish, Bay of
Bengal, Bangladesh
_______________________________________________________________________

INTRODUCTION

Determination of essential and toxic trace elements in biological materials, especially
foodstuffs, has been become the need at this present time. Earlier workers [1-3] have
reported that trace metal contents of certain foods, especially fish can be contaminated
with industrial effluents and wastes discharged into oceans, lakes, coastal waters, etc.
Various species of fish [4-6] may uptake heavy metals in their tissue, which may in some
approach toxic levels.
                       J.Nat.O.A.M.Institute, Vol.22, No.2,1-8,2005

Some of the investigators [7-12] have reported significantly high levels of cadmium and
arsenic in some species of fish. However, the investigation of DE GOEIJ [13] and
GUINN [14] have shown that there is no significant difference of these levels of certain
trace elements, like arsenic, cadmium than those in unpolluted areas.

Whether or not fish will be contaminated will depend on the chemical form of the
element and its concentration in the surrounding medium, microbiological activity in the
marine environment, texture of the sediment, type and age of the fish, etc. However, there
are still insufficient data available in Bangladesh for toxic metals like arsenic, cadmium,
etc. It is strongly believed that this study will consequently be a great help for
Bangladesh’s economy in view of quality assurance for trade as well as the health, safety
and benefit of her people. This paper presents information on the concentration of
arsenic, chromium, selenium and zinc in some varieties of fish and also describes briefly
the chemical procedure followed.

The instrumental neutron activation analysis (INAA) of such elements as As, Cr, Cd, Zn
and Cu in animal organs and fish tissues is difficult because of the 24Na and 86Br
activities developed on irradiation. This is because the photopeaks of radioactive products
of these elements are masked, particularly by the Compton continuum of the high 24Na
matrix activity, thus posing problem not only in handling but also in the computation of
the peak areas from the γ-ray spectra. This problem has necessitated post-irradiation
chemical separation of isotopes of interest. This paper describes such a scheme for
determination of seven trace elements (As, Cr, Se and Zn) in biological materials.

EXPERIMENTAL

Samples collection and irradiation. Eight varieties of common marine fish, selected in
accordance with their public flavor for Bangladeshi (near coastal belt) in both taste and
cost, namely, Coilia neglecta, Cirrhinna reba,Johnius argantus, Harpondon nehereus,
Setipinna phasa and Lepturacanthus savala were collected from the coastal belt of the
Bay of Bengal and sun-dried after removal of their internal organs, head, skin, and tails.
The dried samples were then chopped into pieces with the aid of a stainless steel knife
(steam cleaned). Only the edible muscle tissue samples were used for analysis. The
sample pieces were dried at 105o-110oC in an oven until a constant weight was obtained
(dry weight).

The dried samples were ground, sieved and thoroughly mixed in a stainless steel rotating
drum for 100 hours to produce a homogeneous powder. The sample powder was finally
preserved in clean and dry polyethylene bottles. Portions of the samples (200-300 mg
each) were heat-sealed in polyethylene bags and irradiated along with a known amount of
MA-A-2 ™, the fish flesh homogenate standard of IAEA in the CIRUS reactor at Bhabha
Atomic Research Center, Trombay, Bombay, India, at a flux of about
(0.5 to 1) .1012 n. cm-2. s-1 for 20 hours.
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                        J.Nat.O.A.M. Institute,Vol.22(2),1-8,2005

Chemical reagents. (1) NH3, HCl, HNO3, HClO4 and acetic acid; (2) Na2SO3 solution:
4 mg/cm3 ; (3) NaOH pellets; (4) thioacetamide; (5) H2O2; (6) BaCl2 (=0.2M solution in
water; (7) NH4H2PO4= 1M solution; (8) hydroxylamine hydrochloride (NH2OH.HCl).

Dissolution. Each of the irradiated samples was allowed to “cool” for 4-5 days to enable
the decay of short-lived isotopes and also to reduce the 82Br and 24Na activities. About 10
mg carrier for each of the element was added to a 100 ml round-bottomed flask and the
irradiated sample was carefully opened and emptied into it. Then, the sample was
digested in Bethge’s apparatus with a mixture of 6 cm3 concentrated nitric acid and 2 cm3
of concentrated perchloric acid till a liquid remained in the flask.

Chemical separation and determination of metal

After the digestion was completed, the distillates were, evaporated to dryness on a sand
bath to remove nitric acid, and leached with conc. HCl (10 cm3) and preserved to be
combined with the filtrates from chromium and selenium precipitation.

   (1) Determination of chromium: 4 cm3 HClO4 was added to the residue in the flask
       and drops of conc. HCl added to the hot solution to distil of CrO2Cl2 . The
       distillate was collected in 10 ml sodium hydroxide solution (1N) . To this was 1.5
       cm3 BaCl2 solution followed by addition of 2-3 drops of H2O2. The pH was set at
       6. BaCrO4 was digested in a water bath and was filtered, dried and counted for
       51
         Cr. The filtrate was combined with the distillate from decomposition step.
              Cr is oxidized to Cr(VI) by HClO4
            H2Cr2O7 + 4 HCl → 2CrO2Cl2 + 2H2O(reddish vapor)
            CrO2Cl2 + 2NaOH →Na2CrO4 +2HCl (yellow distillate)
            Na2CrO4 + BaCl2 → BaCrO4 + 2 NaCl
   (2) Determination of selenium: To the residue remaining in the flask 20 ml of conc.
       HCl was added and the volume kept at 50 ml. To the warm solution 4-5 cm3
       Na2SO3 solution was added and digested in a water bath for 1 hour. The
       precipitated Se metal was filtered, dried and counted for 75Se. This filtrate also
       was combined with the distillate from the decomposition step.
             MCl2 + SO2 +2H2O → M (metal) + 2HCl + H2SO4
   (3) Determination of arsenic: The acidity of the first distillate, with the filtrates from
       chromium precipitation and selenium precipitation mixed together, was adjusted
       to 1M HCl and 1 ml of a 1% solution of thioacetamide was added to the boiling
       solution. This was digested in a water bath. Precipitates of sulfides of As were
       filtered off, washed, dried and counted 76As.
         CH3CSNH2 + H2O → CH3CONH4 + H2S
         CH3CONH2 + H2O→ CH3COONH4
            H2S + M+++ → MS + 2H+
          [M = As]
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                    J.Nat.O.A.M.Institute,Vol.22,No.2,1-8,2005

(4) Determination of zinc. The filtrate from (3) was evaporated to dryness in a boiling
    water bath followed by addition of drops of conc.HNO3 until the ammonium salts
    were completely destroyed. To this was added 1 cm3 1M NH4H4PO4 solution. The
    pH of the solution was then adjusted to 6 and it was heated for a few minutes. The
    mixture was then kept in a water bath for 1 hour. The precipitates obtained were
    filtered off, washed, dried and counted for 65Zn.
         ZnCl2 + NH4H2PO4 → ZnNH4PO4 + 2HCl [M= Zn]

Counting
The samples and the standards were counted on a 45 cm3 HPGe detector connected to
a 4096 channel pulse-height analyzer (Ortec PCA-MCA card). The energies (in keV)
chosen for the evaluation of the peak areas were: 76As(26.4 h), Eγ=657 keV (since,
the photopeaks of 122Sb (561keV) interfered with photopeak 76As at 559 keV, the 657
keV photopeak was chosen to measure 76As photopeak area) ; 51Cr(27.7 d),
Eγ=320.08keV; 75Se (119.77 d), Eγ = 264.66 keV; 65Zn (243.9 d), Eγ= 1115.5 keV.

Accuracy and precision
Experiments were initially carried out using radioactive tracers and the corresponding
carriers to evaluate the recoveries. The yields were in the range of 93% to 98%. The
accuracy of the method was evaluated by analyzing homogenate fish flesh (IAEA)
Standard Reference Material, MA-A-2™. Our results (values in μg/g) are in good
agreement with the IAEA certified values.

RESULTS AND DISCUSSION

The As, Se, Cr and Zn concentrations determined in the fish species are presented in
Table 1. The values are expressed in μg.g-1 dry weight. The range of concentrations
found in the fish samples are As (2.843-3.920), Se (2.961-6.274), Cr (0.498-1.8430),
and Zn (37.59-101.19). These variations are likely to be due to the migratory nature
and feeding habits of the different species of fish.

Normally, the levels of As (3 ng/ml), Se (0.09 ng/ml) and Zn (0.01 ng/ml) have been
found to be quite low in sea-water [15], but the levels of these metals as found in fish
samples under investigation are higher. This is due to the tendency of various species
of fish to concentrate certain elements in the tissue more than surrounding medium.
The mean concentrations of arsenic, selenium, chromium and zinc in fish are 3.234
μg/g, 4.385 μg/g, 1.007 μg/g and 59 μg/g, respectively.

Using neutron activation, HAMILTON AND MINSKI [16] reported the mean values
for As in fish as 2.0±0.08 μg fresh weight. Up to 174 ppm has been found in prawns
from the coastal waters of Britain [17] and 42 ppm in shrimp from the southeastern
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                   J.Nat.O.A.M.Institute,Vol.22,No.2,1-8,2005

coastal waters of the United States [18]. Fish flour for human consumption has been
reported [19] to contain 1.8 ppm Se and tuna meal median levels as high as 5.1 and
6.2 ppm (dry basis)[20]. High natural Se levels in tuna [21] and marine mammals [22]
have been reported. Open ocean water contains as little as 10 μg/l of Zn at the surface
[23] although coastal seawater usually contains 0.5-2 μg/l of Zn as a result of river
inputs and sewage outfalls [24-26].

                            Table 1
     Arsenic, selenium, chromium and zinc in different varieties of fish
                  (μg. g-1 dry weight basis)
Types of      Weight                                                         Organic
fish          Analyzed, Arsenic         Selenium Chromium Zinc               Matter,
                 g                                                           %
Colia         0.36220        3.025      4.751     1.843          80.48       79.75
neglectic
Cirrhina      0.31093        3.076      2.961     1.287          49.55       84.85
reba
Johnius       0.32212        3.920      3.856     0.550          37.59       83.45
argantus
Harpodon 0.27691             3.070      6.274     0.871          101.19      81.82
nehereus
Setipinna     0.31377        3.469      3.839     0.995          50.73       82.68
phasa
Leturacan- 0.36220           2.843      4.627     0.498          38.02       81.73
Thus
salala
Stromateus -                 2.52       -         -              51.0        -
sinensis
Rita rita        -           3.78       3.15        -             -           -
Mean             -           3.234      4.385     1.007          59.59       82.36
Range           -            2.843-     2.961-    0.498-         37.59-      79.75-
                             3.920      6.274     1.843          101.19      84.85



Taking 6 g of fish as the maximum consumption [27] per person per day for
Chittagong and coastal areas of Bangladesh, it is estimated that the average intake of
arsenic, selenium, chromium and zinc through fish is 3.881 μg, 5.262 μg 1.208 μg and
71.51 μg, respectively. The daily intake of arsenic is quite low[28]. Table 2. gives the
comparison of the levels of arsenic, selenium, chromium and zinc in fish by various
researchers in different countries.
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                   J.Nat.O.A.M.Institute, Vol.22,No.2,1-8,2005

CONCLUSIONS
The present study indicates that the radiochemical separation scheme should be used
for the isolation nuclides with mutually interfering γ-rays (e.g., 75Se, with 203Hg at
265 keV ) . In the case of 76As, due to the interference of 122Sb, at 559 keV, we have
chosen the less sensitive 657 keV peak for computation of arsenic.

Eight tropical marine fish species collected from the Bay of Bengal were analyzed in
order to assess the level of trace toxic elements in this food item consumed by the
                            Table 2
Trace element concentrations (mg. Kg-1 wet weight ) in muscle tissue of various
species of fish from different areas of the world
Source          Area           Cr        As        Se         Zn       Species
Bebbington Australia,            -         0.2-      -        4.24-    Commercial
Et al (1977) N.S.W                       2.2                 6.60      Species
[29]                                                                   including
                                                                       flathead,mullet
Roth and        Israel         2.8-4.9 -              -      14.9-
Harnung                                                      25.5
(1977) [30]
J.H.Powell      Papua            -       0.4-3.5     -       3.0-4.5 8 species
et al.          New                                                    including
[31]            Guinea                                                 sharks,travelly
Khan et.al      Dhaka,           -       2.52-     3.15      26.0-     6 species
(1987)          Bangladesh               5.53                93.8      including prawn,
[32]                                                                   rita,gar
                                                                       fish
Anand.S.J.S. Bombay,             -       0.069-      -         -       6 species
(1978)          India                    0.931                         (pampus
[33]                                                                   argentius,
                                                                       harpodon
                                                                       neherer etc.)
*Present        Bay of         0.50-     2.84-     2.96-     37.59-    6 species (coilia
study (on       Bengal,        1.84      3.92      6.27      101.19 neglecta,cirrhina
dry weight      Bangladesh                                             reba, johnius
basis)          (1998)                                                 argentus,
                                                                       harpodon
                                                                       nehereus,setipina
                                                                       fhasa and
                                                                       lepturacanthus
                                                                       savala)

*The present data were calculated on dry weight basis
                                         6
                     J.Nat.O.A.M.Institute,Vol.22,No.2,1-8,2005

population of Bangladesh. The results indicate that the concentrations of these
elements are much below the toxic levels.


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