Levels of metals (Cd, Pb, Cu and Fe) in cow’s milk, dairy products and hen’s eggs from the West Bank, Palestine

Abstract

Heavy metal contents in 160 samples of commercially available cow's milk (powder and liquid), dairy products (yoghurt, labaneh and white cheese) and hen' eggs (conventional farms and courtyard farms) were investigated using GAAS. Mean concentrations of metals (µg/g) in milk and dairy samples analyzed ranged between 0.022-0.057 for Cd, ND-0.93 for Pb, 0.62-0.85 for Cu and 3.2-12.91 for Fe. Results indicated high concentrations of Pb and Cd especially in powder milk samples. The lowest concentrations of metals were found in white cheese followed by liquid milk. Mean metal concentrations (µg/g) in hen's eggs were 0.021-0.049 for Cd, 0.06-0.48 for Pb, 2.29-3.26 for Cu and 15.25-33.52 for Fe. Hen's eggs were found to contain significantly more Fe and Cu than milk or dairy products but generally less Pb and Cd. Finally, further investigations are needed to identify the cause of elevated Pb and Cd levels especially in milk and dairy products.

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*Corresponding author.
Email: kswaileh@birzeit.edu
International Food Research Journal 19 (3): 1089-1094 (2012)
Abdulkhaliq, A., *Swaileh, K. M., Hussein , R. M. and Matani, M.
Department of Biology and Biochemistry, Birzeit University, P. O. Box 14, West
Bank-Palestine
Levels of metals (Cd, Pb, Cu and Fe) in cow’s milk, dairy products
and hen’s eggs from the West Bank, Palestine
Abstract: Heavy metal contents in 160 samples of commercially available cow’s milk (powder and liquid),
dairy products (yoghurt, labaneh and white cheese) and hen’ eggs (conventional farms and courtyard farms)
were investigated using GAAS. Mean concentrations of metals (µg/g) in milk and dairy samples analyzed ranged
between 0.022-0.057 for Cd, ND-0.93 for Pb, 0.62-0.85 for Cu and 3.2-12.91 for Fe. Results indicated high
concentrations of Pb and Cd especially in powder milk samples. The lowest concentrations of metals were found
in white cheese followed by liquid milk. Mean metal concentrations (µg/g) in hen’s eggs were 0.021-0.049 for
Cd, 0.06-0.48 for Pb, 2.29-3.26 for Cu and 15.25-33.52 for Fe. Hen’s eggs were found to contain signicantly
more Fe and Cu than milk or dairy products but generally less Pb and Cd. Finally, further investigations are
needed to identify the cause of elevated Pb and Cd levels especially in milk and dairy products.
Keywords: Heavy metals, milk, dairy products, hen’s eggs, Palestine
Introduction
Heavy metals are persistent contaminants in the
environment that can cause serious environmental
and health hazards. They are released into the
environment from natural as well as man-made
activities. Some heavy metals (like Cu and Fe) are
essential to maintain proper metabolic activity in living
organisms; others (like Pb and Cd) are non-essential
and have no biological role (Ayar et al., 2009; Qin et
al., 2009). However, at high concentrations, they can
cause toxicity to living organisms (Li et al, 2005).
Milk is a complex, bioactive substance that
promotes growth and development of mammalian
infants. It is considered as a nearly complete food
since it is a good source of proteins, fats, sugars
vitamins and minerals. Therefore, milk and dairy
products are important components of human
diets that are widely consumed by human children
and adults especially elderly people around the
World (Buldini et al., 2002; Enb et al., 2009; Qin
et al., 2009). Although, milk is an ideal source of
macroelement (Ca, K and P) and microelemts (Cu,
Fe, Zn, Se), addition amounts of contaminant metals
might enter milk and dairy products reaching levels
that are harmful to humans (Qin et al., 2009). Milk
and dairy products become contaminated with heavy
metals either through food stuff and water or through
manufacturing and packaging processes (Anastasio et
al., 2006; Ayar et al., 2009). Bakircioglu et al. (2011)
investigated the concentrations of Cd, Co, Cr, Cu,
Mn, Ni, Pb, Se and Zn in cheese samples packaged
in plastic and tin containers. They found that there
were considerable differences among of the studied
element contents of cheese samples packaged in tin
and plastic containers. They concluded that, cheese
types and packaging materials play a key role in the
content of trace metal.
Hen’s eggs are considered as a highly-nutritious
food that is of great importance for human health
(Surai and Sparks, 2001). However, eggs might
contain elevated levels of heavy metals that originate
mainly from food and water. Knowledge of the
mineral content of eggs is becoming increasingly
important for many reasons that are related to health
and nutritional value of eggs, the consequences of
egg metals on its embryonic development and the
use of eggs as bioindicators for environmental metal
pollution (Surai and Sparks, 2001; Sparks, 2006;
Pappas et al., 2006). Altogether, milk, dairy products
and chicken eggs constitute a major food source
around the World. Therefore, monitoring heavy metal
levels in milk, dairy products and chicken eggs is of
great importance for nutritional, toxicological and
environmental purposes.
In the West Bank, studies concerning heavy
metal levels in milk, dairy products and chicken eggs
are completely lacking, although these products are
typical food stuff that is largely consumed in the in

1090 Abdulkhaliq, A., Swaileh, K. M., Hussein , R. M. and Matani, M.
International Food Research Journal 19(3): 1089-1094
the Palestine. Therefore, The present study aimed
at evaluating the heavy metal quality of cow’s milk
(liquid and dry), 3 dairy products (yoghurt, white
cheese and labaneh) and hen’s eggs (farms and
organic) consumed in the West Bank. Levels of two
essential metals (Cu and Fe) and two nonessential
metals (Pb and Cd) were determined using atomic
absorption spectrophotometer.
Materials and Methods
Sample collection
A total of 160 samples of commercially available
cow’s milk (liquid and dry), dairy products (yoghurt,
white cheese, and labaneh) and hen’s eggs (from
conventional farms and small scale courtyard farms)
were purchased from supermarkets in Ramallah
City in the West Bank. Samples were belonging
to 21 different brands 14 of which were local and
the remaining 7 were foreign companies. Sample
collection took place twice during 2009. The name
of each brand was substituted by an alphabet from
A-U. Names were followed by either L meaning the
product belongs to a local company, or F meaning
that the product belongs to a foreign company.
Sample analysis
Samples of different dairy products were kept in
their original packages and transferred to the lab in
an ice box. Subsamples of from each products were
oven-dreid at 60oC till constant weights were reached.
Thereafter, dry samples were ground to powder using
a grinder with stainless steel knife, then stored in
clean glass vials for later analysis.
Duplicate sub-samples (about 0.2 g ne powder)
from each product were digested in a mixture of 1:1
nitric: perchloric acids (Suprapur, Merck) using a
heating block (Swaileh et al. 2009). At the end of
digestion, mixture volumes were adjusted to 10 ml
using double distilled water. Blanks and reference
material (Skim Milk Powder, BCR®-151 provided
by the European Commission, Joint Research Centre-
Institute for Reference Materials and Measurements,
Brussels, Belgium) were run with the samples.
Finally, concentrations of Cu, Cd, Pb and Fe were
measured by a graphite furnace atomic absorption
spectrophotometer (Perkin-Elmer, AAnalyst 600).
The pyrolysis-atomization temperatures used were
500-1500, 1200-2000, 1400-2100, and 850-1600
oC for Cd, Cu, Fe and Pb, respectively. All accepted
recoveries were between 97.5% and 101% (Table 1).
Statistical analysis
Data were analysed using Statistix 9.0 software
(Analytical Software, Tallahassee, FL, 2008).
Statistical differences between the same product from
different brands were tested using one way ANOVA.
Where signicant differences were observed,
Tukey HSD paiwise comparison test was applied.
Differences were considered signicant at p values
≤ 0.05.
Results and Discussion
Metal contents of cow’s milk, dairy products
and hen’s eggs are summarized in Tables 2-5. In all
samples analyzed, concentrations of Fe were the
highest and those of Cd were the lowest. Table 2
shows metal concentrations in milk powder from 6
foreign brands. Cd and Fe levels indicated signicant
differences between brands however; Cu and Pb levels
were similar in powder milk from the 6 brands. Mean
Table 1. Mean certied metal concentration (µg/g dry weight) in
the reference material (Skim Milk Powder, BCR®-151) used in the
present study, mean obtained values and percentage recovery obtained
for each metal measured
*: ng/g
Table 2. Concentrations of metals (Means ± SE) in
powder and liquid milk consumed in the West Bank,
Palestine. Minimum and maximum values are shown
between brackets. Samples were collected during 2009
and 4 samples were analyzed/each brand. F: Foreign, L:
Local.
Values with different letters within a column are signicantly different at p≤0.05

Metals in dairy products from Palestine 1091
International Food Research Journal 19(3): 1089-1094
Cd levels in powdered milk from one brand (D-F)
was signicantly higher those from other brands and
mean Fe levels in powdered milk from one brand
(B-F) was signicantly higher than other brands. The
mean levels of metals were: 12.91, 0.93, 0.66 µg/g
and 53.7 ng/g for Fe, Pb, Cu and Cd, respectively.
Metal concentrations had the following order: Fe>Pb>
Cu>Cd. The high concentration of Fe is caused by the
enrichment of powder milk with iron that is practiced
by most companies. Lead concentrations in powder
milk were found to exceed the maximum allowed
limit for Pb in milk powder and cheese that was set as
0.2 µg/g (Ayar, 2009). However, Cd concentrations
were below the maximum allowed limit of 0.5 µg/g
Cd in powder milk (Ayar, 2009).
Metal concentrations in liquid milk from 7
commercial brands are summarized in Table 2. No
statistically signicant differences between liquid
milk brands were observed for Cu, Pb and Fe. The
only signicant difference was observed for Cd
concentrations, where liquid milk from one brand
(G-L) contained signicantly higher Cd content (102.0
ng/g) than other brands. The mean concentrations of
metals in different liquid milk samples were: 8.23,
0.62, 0.20 µg/g and 35.71 ng/g for Fe, Cu, Pb and
Cd respectively. Levels of metals in liquid milk were
having the following order: Fe>Cu>Pb>Cd and were
less than those measured in powder milk. However,
mean Pb and Cd concentrations in liquid milk exceed
the maximum allowed limits of 0.02 and 0.01 µg/g for
Pb and Cd in liquid milk respectively (Ayar, 2009).
Concentrations of the four metals in yoghurt
and labaneh (a form of drained yoghurt) are shown
in Table 3. No statistical differences in Cd, Pb and
Fe concentrations were observed for yoghurt from
all brands. Signicant differences were observed for
Cu concentration where yoghurt from I-L company
contained the highest level of Cu. According to their
concentrations in yoghurt, metals were having the
following order: Fe>Pb> Cu>Cd. Concentrations
of metals in labaneh were generally less than those
in yoghurt. This may be caused by the loss of some
metals by the drainage process. Statistical differences
were observed for Cd and Pb concentrations in
labaneh from different brands. The order of metals
was Fe>Cu> Pb>Cd.
White cheese is the main and traditional form of
cheese made and consumed in the West Bank (CHF,
2011). Other types of cheese are less commonly
consumed and are imported from neighboring
countries like Turkey. Results of elemental white
cheese analysis from 7 local brands are summarized
in Table 4. Generally, cheese is characterized by
low concentrations of metals except Cu. Compared
to all products analyzed in the present study, white
cheese contained the lowest concentrations of Fe and
Pb (below detection limits) and the second lowest
Cd concentration. With regard to Cu, white cheese
comes second among dairy products after labaneh
which was found to have the highest levels of Cu. As
the two products undergo drainage during processing,
this indicates that the drainage process causes a
Table 3. Concentrations of metals (Means ± SE) in dairy products
(Yoghurt and Labaneh) consumed in the West Bank, Palestine.
Minimum and maximum values are shown between brackets. Samples
were collected during 2009 and 4 samples were analyzed/each brand.
F: Foreign, L: Local.
Values with different letters within a column are signicantly different at p≤0.05
Table 4. Concentrations of metals (Means ± SE) in white cheese
consumed in the West Bank, Palestine. Minimum and maximum values
are shown between brackets. Samples were collected during 2009 and 4
samples were analyzed/each brand. L: Local.
Values with different letters within a column are signicantly different at p≤0.05

1092 Abdulkhaliq, A., Swaileh, K. M., Hussein , R. M. and Matani, M.
International Food Research Journal 19(3): 1089-1094
signicant decrease in Fe, Cd, and Pb concentrations
but an increase in Cu levels.
Hen’s eggs are considered as an important source
of nutrients, including micro minerals (Surai and
Sparks, 2001) and are consumed largely in the West
Bank. Eggs were collected from conventional poultry
farms (S-L and U-L) and from a courtyard small scale
farm (T-L). Eggs were found to contain high levels of
Fe and Cu (essential metals) and much less levels of
Cd and Pb (non essential metals) (Table 5). Actually,
levels of Fe and Cu in eggs were signicantly higher
than those in milk or dairy products. Eggs from
courtyard were containing signicantly higher levels
of Fe than those obtained from conventional farms.
Metal concentrations in eggs were ordered as Fe>Cu>
Pb>Cd. Fakayode and Olu-Owolabi (2003) studied
levels of metals in chicken eggs from Nigeria. The
overall average concentrations for Pb, Cd, Cu and
Fe were 0.59, 0.07, 0.78, 23.2 µg/g, respectively.
Khan and Naeem (2006) investigated elemental
composition of Chicken eggs from Pakistan. The
average concentrations of Pb, Cd, Cu and Fe ranged
between 0.52-0.63, 0.07-0.08, 0.74-0.82 and 21.8-
24.1 µg/g. These results are comparable to results of
the present study.
Figure 1 shows the overall mean concentrations
of the four metals in all samples analyzed for each
product regardless of the brand name. The Figure
indicates that eggs are of great nutritional value
especially when it comes to the essential metals Fe and
Cu. Powder milk contains the highest concentration
of Pb and the second highest concentration of Cd
among all products analyzed. Powder milk is an
imported product that is not manufactured locally.
Ranking biological samples according to metal
concentration gives a clear idea about metal richness
(Swaileh et al., 2009). When ranked according to
metal concentrations (Table 6), eggs and milk powder
were found to have the highest total rank score and
Table 5. Concentrations of metals (Means ± SE) in Hen’s eggs
consumed in the West Bank, Palestine. Minimum and maximum
values are shown between brackets. Samples were collected during
2009 and 4 samples were analyzed/each brand. L: Local.
Values with different letters within a column are signicantly different at p≤0.05
Table 6. Cow’s milk, dairy products and Hen’s eggs ranked
according to their metal richness. TRS: Total Rank Score.
Table 7. Concentrations of metals (µg/g) in Cow’s milk from different
countries compared to those of the present study.
Figure 1. Overall mean (±SE) concentrations of metals in cow’s milk,
dairy products and hen’s eggs consumed in the West Bank, Palestine.

Metals in dairy products from Palestine 1093
International Food Research Journal 19(3): 1089-1094
cheese the lowest. The 6 products examined had the
following decreasing order in total rank score powder
milk, eggs>yoghurt> labaneh>liquid milk>cheese.
Milk is the raw material for all other dairy products
and the nal concentration of metals in any dairy product
is affected by the concentration of metals in the milk used
and the industrial processing. Table 7 shows a comparison
between milk metal concentrations in the present study and
those reported from other countries. The results indicate that
milk in the present study contains higher levels of metals
than most other countries. This is obvious especially in
the case of Pb. Although Palestine is not an industrialized
country, leaded fuel is still largely used which might be
one reason for the high Pb levels recorded. In addition,
processing and packaging of milk and dairy products may
lead to an elevation in metal concentrations.
Conclusions
Concentrations of Cd, Pb, Cu and Fe in milk,
dairy products and eggs consumed in the West Bank
showed little variability with brand. Generally, Pb and
Cd concentrations in milk and dairy products (except
white cheese) exceeded the maximum allowed values.
The elevated levels could be related to contamination
during industry processing and environmental
pollution. Powder milk was found to be the richest in
metals while white cheese was found to be the poorest.
Among the four metals studied, Fe concentrations
were always the highest and Cd concentrations
were always the lowest. Hen’s eggs were found to
have obviously higher concentrations of Fe and Cu
than milk or dairy products. This emphasizes its
nutritional value as a source of essential elements. No
clear differences were observed between metals in
eggs from conventional farms and courtyard farms.
Comparing results of the present study with those
of other studies revealed higher levels of metals,
especially Pb, in milk and dairy products investigated
in the present study. Results of hen’s eggs analysis are
comparable to those reported from other countries.
Finally, the elevated levels of heavy metals (Pb and
Cd) need further investigations to identify the cause
of these elevated levels.
Acknowledgement
The authors would like to thank Birzeit University
for the nancial support of the project.
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