Journal of Dairy & Veterinary sciences
Rapidly growing urbanization and increased
industrialization has led to introduction of numerous detrimental
toxicants into the environment. Such toxicants which are hazardous to
human health, ultimately become a part of our food chain and accumulate
in human body, in levels exceeding permissible limits. One of the most
common food toxicants is heavy metals out of which Arsenic ranks 1st in
the list of top 20 hazardous substances. Arsenic intake has been found
to induce skin, liver, bladder and lung cancers, disturb GIT, cause
fatigue, arrhythmia, bruising, nerve impairment, hyperkeratosis,
hyperpigmentation of skin, gangrene, cyanosis and black foot disease.
Milk and milk-based products from different milch animals that make up
one of the most nutritious categories of food are reported for being
contaminated with Arsenic, worldwide. Arsenic is introduced in milk from
human and other milk producing animals by the intake of arsenic
contaminated water or through their feed. On the other hand, breast
feeding is reducing day by day due to a false verdict that it is unsafe
for infants whereas infant formula milk is safer, as heavy metals like
arsenic become a part of human milk in areas with high arsenic content
in drinking waters. Therefore, this review highlights various studies
determining arsenic contamination in raw milk, infant milk formulas as
well as breast milk, in an attempt to create awareness regarding which
mode of infant nutrition is safest to choose
Keywords: Arsenic; Heavy Metals; Milk Contamination; Infant formulas; Breast feeding
From farm to fork, food is subjected to numerous
potential hazards of physical, chemical and microbiological nature,
making it quite a challenge to ensure that the food is not at all toxic
for human consumption [1,2].Toxicity is a condition when a micronutrient
or additive or any toxic compound exceeds its safety limit and causes
adverse health effects. The trace elements in different foods are of
significant interest because of their essential (as micronutrients) or
toxic nature. Although there are many potential toxins related to
foodstuff but heavy metals are quite common and abundant. Heavy metals
are the metals which have high density (more than 5 g/cm3) and are
dangerous for human consumption if exceeding their safety limits.
According to the list of “Top 20 Hazardous Substances” compiled by the
U.S. Environmental Protection Agency and the Agency for Toxic Substances
and Disease Registry (ATSDR), heavy metals including Arsenic (As), Lead
(Pb), Mercury (Hg), and Cadmium (Cd) stand on 1st, 2nd, 3rd and 4th
position, respectively. Arsenic is of prime importance as it is a common
yet potent water contaminant and from there it transfers to different
food by coming in contact directly or indirectly. This heavy metal has
been reported to pose multiple adverse effects on human health as well.
Milk and milk-based products make up one of the most
nutritious category of foods rich in protein and minerals, a great
source of calcium and magnesium, as well as trace amounts of essential
elements such as iron, copper and zinc. Since, the primary form of feed
at infant level to almost all ages is milk, therefore milk and
milk-based products have always been valued for their significant role
in body growth and development. Unfortunately, the rapidly increasing
urbanization and growing industrialization have immensely polluted the
environment and consequently milk and milk-based products have been
highly contaminated with several toxic substances particularly heavy
metals that may pose detrimental effects to human health [3]. Milk is
also being contaminated with arsenic. Arsenic is introduced in milk from
human and other milk producing animals by the intake of arsenic
contaminated water or through their feed. This is known to exceed the
safety limits i.e. 0.1 mg/ml. Breast feeding is reducing day by day due
to false consideration that it is not safe for infants whereas infant
formula milk is safer, as heavy metals like arsenic becomes a part of
human milk in areas with high arsenic content in drinking waters. This
review paper is written to shed some light on this issue and highlight
the studies that indicate the arsenic contamination in milk.
Heavy metals are the metals whose specific gravity
exceeds 5g/cm3 in their standard state. The most toxic heavy metals are
namely Arsenic, Lead, Mercury, and Cadmium ranked 1st, 2nd, 3rd,
and 4th in the list, respectively. Presence of these heavy metals
is to be measured in parts per million (ppm), and the obtained
values are to be compared to the Provisional Tolerable Weekly
Intake (PTWI) for toxic metals as set by the FAO. Heavy metals
that contaminate milk might originate from the milking utensils,
milking personnel, milk processing, contaminated water used for
agricultural purposes and animal fodder, as well as the immediate
surroundings of milch animal [2].
The toxicity of heavy metals results due to the longterm
exposure to low contamination sources in our environment,
including in the air we breathe, water and food we consume. Lead,
chromium, nickel, cadmium and cobalt are the common heavy
metals that might contaminate cows and other environments,
disrupt milk at different levels and cause numerous problems.
The contamination of milk products with heavy metals might be
a consequence of the contamination of the basic cow milk that
has been exposed to contaminated atmosphere including feed or
poor water source. Moreover, contamination of raw milk might
occur during its production. Cadmium, mercury and lead are
quite hazardous to human health therefore they are referred to
as a major menace to humans when consumed along with food
[2]. Another study named as “Lead and Mercury in Breast Milk”,
has reported the presence of Mercury in breast milk as well as
bovine milk in substantially higher amounts as compared to those
observed in common infant formulas. Whereas the Levels of lead
in breast milk are relatively lesser than that found in milk-based
infant formulas [4].
Heavy metals belong to a class of pervasive toxicants that
prevail everywhere in land, air and water. Among all the toxicants,
arsenic (As) and mercury (Hg) were considered to be unusual,
since they exist in a series of different chemical species with diverse
toxicities to human beings [5]. Heavy metals when accumulate in
the body might cause various diseases including nervous system
disorders, renal failure, genetic mutations, types of cancers,
neurological disorders, respiratory disorders, cardiovascular
diseases, immune system weakening and infertility. Lead causes
onset and development of various cancers, central nervous
system disorders, anemia, renal, hepatic and cardiac damage,
compromised immune system as well as weakened GIT tract.
Lead can also cause encephalitis and hepatitis. Whereas Cadmium
deposits in body tissues just like the liver and kidneys, causing
anemia, as well as elevated blood pressure. Cadmium is also a
potent carcinogen that can readily induce tumor development
particularly in the prostrate and lungs.
Arsenic toxicity has emerged as a worldwide health issue
that has affected masses of people because of its high prevalence
in land, air and water resources, as well as absorption in food
crops. The maximum permissible limit for arsenic in milk
established by European Union Commission is about 0.1 mg/
ml (European Union 2006). The organic forms of arsenic
such as monomethylarsenic (MMA), dimethylarsenic (DMA),
arsenobetaine and arsenocholinehave been observed to be
relatively nontoxic in comparison to its inorganic formsarsenite
(AsIII) and arsenate (AsV) that have been categorized as Type 1
carcinogens by the International Agency for Research on Cancer
(IARC) [6]. Comprehensive data is present to validate the oraltoxicity
of inorganic arsenic along with its various carcinogenic
and non-carcinogenic effects. Its intake has been reported to
cause generalized body fatigue, disturbed GIT, arrhythmia,
bruising and nerve impairment. The most distinctive effects that
are observed as a result of prolonged oral exposure of arsenic are
hyperpigmentation of the skin and hyperkeratosis. Other noncarcinogenic
effects might include peripheral vascular effects
such as gangrene, cyanosis, blackfoot disease and various other
cardiovascular effects including circulatory problems as well
as increased blood pressure. Oral exposure to inorganic arsenic
has also been observed to increase the risk of cancer in the skin,
liver, bladder and lungs [7]. Previous century witnessed a massive,
endemic disease just due to contamination of drinking water with
arsenic, called Hydroarsenism Chronic Regional Endemic that is
associated with a specific type of skin cancer.
A number of factors are responsible for severity of toxicity
of arsenic in humans. These factors include age, sex, nutritional
status, concentration, dose and duration of exposure to arsenic.
Arsenic exposure during gestation period has been observed
to pose detrimental effects on development of fetus through
irreversible faltering of thioredoxinreductase, methyltransferases
and DNA repair enzymes. Human arsenic toxicity has also been
associated with epigenetic changes like DNA methylation, histone
modification and RNA interference whereas chronic arsenic
exposure might result in an increased risk of diabetes mellitus.
Arsenic is the first metalloid which is directly associated with
adverse pregnancy outcomes (APO) and even induces lungs, skin
and urinary bladder cancers [8,9]. Long-term exposure to As might
result in arsenicosis-a term that refers to arsenic related health
effects including internal cancers (lung, kidney, bladder), skin
problems, skin cancers, diseases of the blood vessels of the legs
and feet, hyperkeratosis, hyperpigmentation, hair hypomelanosis
and mee’s lines [10]. The actual mechanism behind how arsenic
induces cancers is yet not completely understood. While certain
studies declare arsenic toxicity to be affective on child intelligence
(e.g., perceptual reasoning, verbal comprehension and working
memory) as well [11].
Mothers’ milk is the basic source of nutrition of the offspring;
therefore, it is indispensable to ensure that the composition of
human milk is safe enough for the infant. Lately, the presence of
lead, cadmium and mercury in human milk, has been reported
as well. Due to prevalence of arsenic rich bedrock in widespread areas of the world, ground water is often detected with high
concentration of arsenic and travels through the entire food
chain to ultimately become a part of mother’s milk as well. Native
Andeans living in a village at the northwest of Argentina have
been reported with high concentrations of arsenic (200μg/l) in
the drinking water. Whereas, low concentrations of arsenic were
detected in the breast milk and urine of the nursing babies in
relation to the high level of maternal exposure. This shows that
inorganic arsenic is not found in breast milk to a significant extent.
Therefore, there is a quite valid reason for long breast-feeding
periods for newborns [12].
A study revealed that in Izmir, breast milk was observed to be
considered toxic for suckling infants, but still less than the cow’s
milk. Therefore, the point to ponder is that arsenic contamination
through breast or cow’s milk is relatively higher in babies living
in areas with higher thermal activity or in regions where ground
water has higher arsenic concentration (Ulman, C. et al.,1998).
In another study atomic absorption spectrometry was used to
measure level of arsenic in 64 samples of breast milk collected
from Ankara, Turkey and the arsenic level appeared to be below
the limit of quantification (LOQ, 7.6μg/l) in all samples [13]. The
probable effects of arsenic contamination for nursing new-borns
and infants, were also analyzed by Sternowsky & Moser [14] with
a Perkin-Elmer Type 403 hydride-generation atomic absorption
spectrometer, equipped with an arsenic EDL-lamp using 36 breast
milk samples obtained from three different regions of Germany.
Arsenic was not detectable, i.e. below 0.3μg/l, in majority of
samples whereas the greatest concentration of 2.8μg/l was
obtained in a sample from the rural area. It was revealed that
Arsenic concentrations did not vary in samples obtained before
and after nursing nor with the age of the infant.
Khan & Ismail [15] also determined arsenic concentration in
breast milk samples collected from all over Pakistan. The results
of the study indicated the presence of arsenic in the mother
milk samples within the range of 0.092-1.240mg/L, while the
mean as level was 0.504 ppb. The concentration of arsenic in the
mother milk was found to be within the safe limits. Although,
Breastfeeding is the primary preventive measure that can be given
to the child at birth, the ratio of exclusively breast milk fed babies
for their first six months has dropped from about 20% in 1998 to
16% in 2003 [12].
Arsenic is considered as one of the inevitable contaminants for
human beings and is well known as a toxic element since ancient
times. Humans are exposed to many chemical forms of both
inorganic and organic arsenic but the highly stable organic forms
are apparently nontoxic. Arsenic content of foods is generally
less than 1 mg/kg, with the exception of seafood in which arsenic
is predominantly in the organic form [16]. Prolonged, chronic
exposure to inorganic arsenic through breathing, drinking or
ingestion has been linked to, skin, lungs and urinary bladder cancer
[17]. In past decade, almost 13,000 Japanese infants have been
afflicted with contaminated milk powder, majorly in the western
part of the country where industrialization was considerable.
Affected infants reported diarrhea, fever, skin pigmentation,
whereas more than 100 died from acute poisoning [4].
Carrera et al, 2004 also determined the concentration of
arsenic in cow milk samples collected from Cordoba. The arsenic
was found to be in the range of 0.3-10.5 ng/g. Dakeisi et al, 2006
analyzed the concentration of arsenic in milk powder as well.
The level of arsenic contamination in milk powder was found
to be in the range of 4-7mg/l. In 2005, ANTUNOVIĆ et al, used a
hybrid technique on an atomic absorption spectrophotometerto
determine the arsenic content of milk and the results revealed
that arsenic concentrations in ewe milk varied depending on the
lactation stage. Concentration of arsenic was lower in colostrum
at 2nd lactation day (As0.011mg/kg) as compared with milk
on the 10th (As: 0.025 mg/kg), 30th (As: 0.028 mg/kg) and
60th (As: 0.029mg/kg) lactation day. Licata & Trombetta [18]
assessed the milk from 40 cows bred on various farms in Calabria
to determine the load of heavy metal contamination in them.
Quantitative analyses performed using an atomic absorption
spectrophotometer with graphite furnace; followed by hot
vapor generation technique showed the mean concentration of
as in samples was about (37.90μg/kg). In 1999 arsenic levels
were determined in cow milk samples collected at the most
important dairy farms of the Comarca Lagunera in Coahuila
and Durango, Mexico, a region naturally rich in Arsenic. Arsenic
concentrations found in milk ranged from <0.9 to 27.4 ng g-1.
Using a pharmacokinetic approach, it was found that the cow’s
milk biotransfer factor for arsenic was up to 6 × 10-4 [19].
The concentration of Arsenic in Philippine’s infant formula
milk for 6-12 months old was also analyzed by Cruz, Din [20]
using Atomic Absorption Spectrophotometry and results were
compared with an existing standard for permissible quantities of
arsenic in food products as set by the World Health Organization.
All the infant formulas tested showed up to be negative for Arsenic.
Another study was conducted to determine arsenic concentration
in 32 raw cow milk samples collected from traditional and
industrial sites of Arak City, Markazi Province, Iran using an
atomic absorption spectrometer. The residual amounts of as were
found out to be lower than permissible limits established by Codex
Alimentarius [2].
Therefore, considering the stated previous studies, we cannot
conclude that all the infant formula milk available in markets
worldwide, contains toxic heavy metals or not. However, this study
can be further utilized as a reference or a foundation for future
in-depth analysis of heavy metal contamination in various foods.
This review can also help create awareness among consumers,
manufacturers, and the professionals in the health care system
because of its cumulative display of important statistics regarding
heavy metal contamination in foodstuff.
Milk is no doubt affected by the heavy metal contaminated
water sources, yet the above discussed studies showed that
human milk is still the safest of all, as arsenic levels do not vary
significantly even if one is taking arsenic contaminated water in
daily routine, however it may be a potent risk on a long term basis.
Furthermore, safety of milk obtained from different animals with
respect to arsenic contamination showed that if it is taken from a
sheep, it is least susceptible to Arsenic toxicity even from a place
with higher Arsenic content in water, but the cow milk is most
susceptible. In a nutshell the misconception of breast milk being
unsafe and infant formulas being safer is under question and the
studies show that breast milk is the safest among all other milk
sources.
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