Fish Chemicals

Fish Chemicals

What fish have less chemicals in them Ocean/bay, river, or lake fish?

I want to know which fish are less risky to eat. Ocean water fish, river/running water fish, or lake fish? WHich ones have less PBC's, Mercury, etc?

For the most part, ocean fish are cleaner, since there is far more water to dilute the chemicals. However, nonmigratory bottom-feeding inshore fish can pick up a lot of pollutants if they live near storm drains or other sources of pollution. The white croaker in Santa Monica Bay fit that description, and there are warning signs about eating them on piers in the area. However, other fish in the same waters have been tested and are fine to eat, probably since they eat free-swimming baitfish rather than worms in the muddy bottom.

One other concern might be the age of a fish -- the longer it's been alive, the more time it's had to accumulate pollutants. The Japanese like to eat big old fish because they think it will help them live to a ripe old age, but I'd rather eat a 20 pound tuna than a 200 pounder. By that standard, something like dorado (mahi-mahi) might be one of the best to eat, since they're one of the fastest growing fish out there.

Lakes can get very polluted, since there's relatively little change in the water... but then if it's a high mountain lake with no pollution sources on shore or upstream, there won't be a problem. Same with rivers and streams - it depends what's upstream.

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

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.

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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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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 51Cr. 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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(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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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].

Two Table 1 and 2 are deleted.

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

About the Author

 

REFERENCES

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20. M.L.Scoll, J.N. Thomson, Poultry Sci., 50 (1971) 1742.
21. H.E.Ganther, C.Gondie, M.L.Sunde, M.J.Kopecky, P.Wagnar, S. HOH, W.G.Hoekstra,Science, 175 (1975) 1122.
22. J.H.Koeman, W.H.M.Peeters, C.H.M.Koudstahl-Hol, S.P.Tjive, J.J.M.De Goeij, Nature (London), 245 (1973) 385.
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