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Evaluation of some toxic metals in selected milk products sold in Nigerian market.


The issue of pollution is central in man's quest to develop himself. Industrial activities result in redistribution of mineral substances from their natural deposits into foods and beverages (1). Many of these mineral elements or substances undergo chemical changes and are transformed either in solution or in finely dispersed form through many channels to the food chain. High levels of these materials in the environment facilitate their entry into the food chain thereby increasing their possibility of having toxic effects on humans and animals.

The problems posed by heavy metals found in food and beverages have been a topic of much discussion and debate and several studies (2-8) have been conducted in that respect. The presence of these metals in dairy products may be attributed to contamination of the original raw animal milk resulting from exposure of lactating animal to environmental pollution or consumption of feedstuff and water (8). However, processed dairy products way also be contaminated in the Industry through many routes (9).

Although the amount of heavy metals in uncontaminated milk is admittedly low, their concentration may be significantly altered and magnified through manufacturing and packaging processes (10).

Various techniques have been applied in determination of metals in dairy products such as Flame Atomic absorption spectroscopy (11,12); Capillary zone electrophoresis (13); ICP-AES (14); differential pulse anodic stripping voltametry (15); flow injection spectrometric methods (16), Atomic fluorescence spectroscopy (17) and Strip potentiometer (18). Many reports from such examinations indicated the presence of toxic heavy metals in milk (19, 20, 21). The presence of Pb, Cd, Hg, residue, in milk are of particular concern because milk is largely consumed by infants and children.

Metallic toxicants in diary products which find their way into the human body become poisonous either through inhibition of enzymatic activities (22), 23) or attack cell membrane and receptor or interference with essential cations or action on the artery (24). Various dairy food companies in Nigeria produce an market many brands of dried instant Cow milk powders and liquid tinned ones. Also, a whole lot of brands are being imported into the country from many places. These products are available in a wide range of satehets, or tins to meet the needs of low and high income earners. In many instances, the manufacturers state specifications with regards to chemical composition and additives to the products. However, the actual composition of the individual mineral elements is often not indicated on the product labels of these products (12).

This work was conducted to assay the toxic heavy metals present in selected milk samples sold in Nigerian market and at which levels they occur. Comparison of the levels with the regulating agencies set maximum limit was also done.


Sampling and Sample Pretreatment

A total of ten brands of diary products (milk) were collected from Nsukka and Onitsha Market based on their popularity with consumers. The samples were individually heated at a temperature of 70[degrees]C until a constant weight were obtained.


All reagents used are of analytical grade. Analytical procedure was carried out as cited in literature (13,14) using Atomic Absorption Spectroscopy, Buck Scientific. Model 210 VGP.

Results and Discussions

The results of the experimental analysis of the samples of processed milk products for heavy toxic metals are presented in table 1 below.

The Table 1 above shows the concentration levels of the determined toxic metals in milk samples. The concentration of Arsenic ranged from 0.08 to 0.85mg/l in eight of the brand samples but was below detection level in two samples. In these samples, which indicated As, levels were higher than the recommended level of 0.15mg/l set by Joint Expert Committed in Food Additives (JECFA) (25). Arsenic, which finds its way into dairy products through contamination of animals' drinking water or fodder is toxic whose effects on health ranges from headache, diarrhea, vomiting, muscle cramps, hair loss to death. The concentration of Cadmium as shown in the table above ranged from 0.09 to 0.51mg/l in eight of the brand sample but was not detected in two brands. Again, the levels of the cadmium are higher that the allowable limit by JECFA and FAO/WHO (26).

Increased consumption of cadmium which is carcinogenic can lead to chills, fever, pnuemonites, pulmonary edema, kidney damage and finally death. The highest level of chromium was found in brand H (0.35mg/l) and least in brand E but was not detected in brands A and B. In some brands, the level was higher that the recommended limit thereby posing danger to consumers of such products.

The concentration of Iron in the table above showed higher than recommended limit in six brands (A, B, D, G, H, I). The concentration of Cobalt was highest in brand F. The levels of lead ranged from 0.05 to 0.07mg/l in five brands but was not detected in the other five brands. The levels were above the recommended limit of 0.025mg/l by JECFA and European. Union; Lead is a cumulative poison when ingested. Nickel was detected in only four brand samples (A, E, F, I) and were all above the set limit 0.02mg/l. Exposure to high levels of Nickel can affect the cardiovascular and respiratory system. An earlier study (27) conducted to determine the levels of heavy metals in and infant milk products in Nigeria some fifteen years ago indicated their presence in these products. It is today a cause of great concern that the levels of these toxic metals are in steady increase in our milks.


The levels of metallic contaminants in food and beverages are known to be on unacceptable status and this is attributable to a general degradation of our environment. Contamination of milk products is of special concern because children and infants are the greatest consumers of milk. Regulating agencies should increase the pre and post manufacturing supervision of milk products and also place stringent sanctions on producers of unwholesome milk products to save our future generation.


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[2] Abdullah, M. I. N (2002). Evaluation of some Heavy Metals Residues in whole milk powder used at confectionary plants Regarding their Public Health Significance. Agric Research Centre, Report Egypt. 22pp.

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(1) * Nwachukwu R. Ekere and (2) Chinedu N.B.

(1) Department of Pure and Industrial Chemistry, University of Nigeria, Nsukka.

(2) Department of Industrial Chemistry, Renaissance University, Ugbawka, Enugu, Enugu State

Table 1: Mean Concentrations (PPM) and Standard Deviations of the
Heavy Metals in Sampled Milk Products. Metals

Sample As Cd
 X [+ or -] sd X [+ or -] sd
A 0.8 [+ or -] 008 0.29 [+ or -] 0.018
B 0.07 [+ or -] .016 0.09 [+ or -] 0.030
D .08 [+ or -] 0.014 0.21 [+ or -] 0.008
E 0.6 [+ or -] 0.022 0.30 [+ or -] 0.020
F 0.85 [+ or -] 0.0.12 0.07 [+ or -] 0.001
G 0.72 [+ or -] ..005 .45 [+ or -] 0.012
H 0.44 [+ or -] .002 0.51 [+ or -] 0.013
I 0.30 [+ or -] 0.001 0.42 [+ or -] 0.003

Sample Cr Fe
 X [+ or -]sd X [+ or -] sd
A ND 0.00 [+ or -] 0.011
B ND 0.50 [+ or -] 0.011
C 0.04 [+ or -] 0.020 0.20 [+ or -] 0.010
D 0.02 [+ or -] 0.006 0.70 [+ or -] 0.010
E 0.22 [+ or -] 0:010 0 ND
F 0.26 [+ or -] 0.006 0.10 [+ or -] 0.006
G 0.30 [+ or -] 0.003 0.65 [+ or -] 0.008
H 0.35 [+ or -] 0.020 0.75 [+ or -] 0.007
I 0.35 [+ or -] 0.004 0.55 [+ or -] 0.003
J 0.10 [+ or -] 0.005 0.20 [+ or -] 0.004

Sample Ni Co Pb
 X [+ or -] sd X [+ or -] sd X [+ or -] sd
A .05 [+ or -] 0.11 0.01 [+ or -] 0.000 .05 [+ or -] 0.010
B ND 0.01 [+ or -] 000 0.70 [+ or -] 0.008
D ND ND 0.50 [+ or -] 0.220
E 0.82 [+ or -] 0.008 ND ND
F 0.20 [+ or -] 0.011 0.03 [+ or -] 0.030 0.60 [+ or -] 0.011
G ND 0.04 [+ or -] 0.010 ND
H ND ND 0.50 [+ or -] 0.220
I 0.30 [+ or -] 0.010 0.02 [+ or -] 0.003 ND

X = Mean

sd = Standard Deviation

ND = Not detected.
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Author:Ekere, Nwachukwu R.; N.B., Chinedu
Publication:International Journal of Applied Environmental Sciences
Geographic Code:6NIGR
Date:Sep 1, 2012
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