INTRODUCTION
Well-known
as minor elements, heavy metals are common environmental substances that can
have natural (such as volcanic) and anthropogenic (such as industry) sources.
Therefore, increased industrialization is directly connected with rising levels
of environmental contamination (Stanovič
et al., 2016).
Heavy
metals, as toxic metals in the environment, have recently been discovered all
over the world (Rafiq et al., 2022). Generally, the name "heavy
metals" depicts a class of micro-metals, metalloids, and their derivatives
that have a high density and are toxic at even small concentrations (Sonone et al.,
2020).
Due to their toxicity, persistence, and bioaccumulation issues, heavy metals
have recently become one of the more harmful contaminants in the human
environment (Ariyaee et al.,
2015).
The majority of heavy metals can be hazardous to all life forms, including
bacteria, plants, animals, and humans in large quantities, although some of
them are necessary to trace elements (Abdullah et al., 2019; Alnabi et
al., 2022).
According
to their effectiveness and intoxication, heavy elements are divided into two
classes. Some of them are toxic even with low concentrations which are directly
hazardous to living things like As, Cd, Cr, Hg, and Pb. Meanwhile, Cu, Fe, Mn,
Ni, and Zn are important elements that living organisms must have in modest quantities
and their insufficient consumption results in deficient symptoms. However, in
greater quantities, they might cause poisoning (Khan et al., 2019). Substantial
quantities of heavy metals could be transported from polluted land, water
bodies, and ambient to plants and meadows, resulting in the cumulative levels
of these metals in pasturing livestock and their subsequent conveyance to the
food chain through the milk and the meat. Consequently, the buildup of serious
metals in livestock not just results in harmful impacts on the productivity of cattle,
but causes sanitary hazards to people too, particularly those who consume milk
and meat that were spoiled with the toxic metals (Gupta et al.,
2021).
Recently,
the contamination of milk by heavy metals is considered a public health concern
that has a detrimental impact on the community's health, particularly that of
children (Chirinos-Peinado & Castro-Bedriñana,
2020; Rafiq et al., 2022). It is generally recognized that increasing
urbanization and industrialization have contributed to higher concentrations of
heavy metals, which eventually find their way into milk and dairy products with
different pathways for instance, through the contaminated feed of animals and
industrial effluents surrounding regions where animals are being fed (Iftikhar
et al., 2014; Chandrakar et al., 2018).
Previously,
several investigations were undertaken by several researchers such as Ogabiela,
et al., (2011) in Nigeria, Lutfullah et al., (2014) in Pakistan, Rezaei et al.,
(2014) in Iran, and Abdel Khalek, et al., (2015) in Egypt who found a range of
toxic metals in milk, most of which were much above allowable levels.
Milk
is a key ingredient in the manufacture of numerous food items. Moreover, it is
essential nutrition for the child, it must be an acceptable quality and heavy
metal levels should be carefully controlled. Therefore, this study aimed to determine
the concentration of several heavy metals in Awassi ewe milk collected from a farm
in the Kwashe industrial area (KIA) to estimate the impact of these heavy
metals on public health.
RESULTS AND
DISCUSSION
The levels
of trace metals in the samples analyzed are demonstrated in Table (1). The
heavy metals concentration was compared to the acceptable limits in the milk of
farm animals according to WHO/FAO, (1999). The levels of heavy metals in the
results were in the following magnitude order: Zn=Pb > Ni>Fe > Cu >
Cd> Cr>Co (max to min). The maximum amount of heavy metals contained in
Awassi sheep milk is due to their direct dependence on heavily contaminated
industrial effluents as the main source of drinking water that flows in
Sulaivany grazed plain without any kind of handling or treatment, as well as
the grown forage in contaminated soil by these effluents. Large quantities of
heavy metals were found in milk along with other various dairy products in
contaminated soil (Kazi et al., 2009; Soylak et al., 2005).
As displayed
in Table (1), the Pb concentrated in milk ranged from 3.64 to 4.27 mg/L with a
mean value was 3.99 mg/L. The acceptable amount of Pb in milk is 0.02 mg/L of
fresh milk. It could be noticed that Pb concentrations in the present work were
10-fold over the allowable limit as illustrated in Fig. (2). Therefore, the
consumption of this milk by a human should be banned as it is associated with
high carcinogenic risks, particularly in children. Additionally, Pb poisoning
is a toxic condition created from Pb probation. In both children and adults, Pb
intoxication preliminary influences the digestive system and central nervous
system (Engwa et al., 2019). Pb
residues in water and animal feed are the most frequently reported source of Pb
contamination in milk. The Pb concentration in present milk was greater than
was found by Póti et al. (2021).
Furthermore, Pb concentration in milk from the industrial area was shown
to be statistically higher than in milk from a location supposed to be non-industrial
pollutants by Dobrzaski et al. (2009).
Fig (2):
the concentration of Pb in milk samples in comparison to the standard value
The
minimum level of Cd was 0.12 mg/L and the maximum level was 1.46 mg/L while the
mean average Cd concentration in milk was (0.75 mg/L). It is obvious from
obtained data that all samples of raw sheep milk had Cd concentration above the
allowable limit (0.01 mg/L) as recommended by WHO/FAO, (1999) (Fig. 3). Consumers
are at risk in this circumstance, especially children as Cd is an active
carcinogenic agent as Pb. Furthermore, studies on humans and animals showed
that Cd can cause osteoporosis (skeletal deterioration), which can lead to bone
mineralization (Engwa et al., 2019).
The existing findings were greater than the findings of other studies
undertaken in highly contaminated regions of other nations such as the peak amounts
of Cd in milk confirmed in Ecuador, Egypt, Italy, Mexico, Pakistan, and Romania
were 0.46, 0.11, 0.02, 0.29, 0.06 and 0.01 mg/L, successively (Chirinos-Peinado, and Castro-Bedriñana, 2020).
Moreover, the amount of Cd (52.9µg.kg-1) was found in the sheep milk from the Poráč
area in a study conducted by Stanovič
et al. (2016). The primary
source of Cd contamination in the study environment is a particulate matter
from the metal smelting that enters wet and pasturing areas mostly during the wet
season, travels to meadows, then enters the animal blood and milk where it
binds with lipids and proteins including casein and whey proteins (Chirinos-Peinado & Castro-Bedriñana, 2020).
Fig (3): Concentration of Cd in milk sample samples in
comparison to the standard value
Fig (4): the concentration of Cr in samples in comparison to the
standard value
The minimum and maximums Cr levels in the present
study were (0.24 and 0.29 mg/L) respectively, while the mean
concentration was (0.27 mg/L).
A similar value of Cr 0.29 in sheep milk was proved by Póti et al. (2021).
The Cr quantity in the current work was within the permissible level (0.3) (Fig.
4). It is conclusive that concerning the Cr concentration, consuming this sheep's
milk is entirely safe without creating a health risk.
Fig (5): the concentration of Cu in samples in comparison to the
standard value
The
appropriate amount of Cu and Zn in meals is desired because they are generally
considered necessary micronutrients and act as enzyme cofactors in metabolism.
Comparatively low quantities of Cu, as compared to Zn, were found in the examined
milk samples. The mean average value of the Cu content was 0.79 mg/L as this
value was above the limited value of 0.03 mg/l WHO/FAO, (1999) (Fig. 5).
Similarly, higher concentrations of various heavy metals were found in milk and
cheese samples gathered from the metal-affected site, it was discovered that
the Cu concentration in the milk samples on the roadside was importantly bigger
than in areas secured from pollution (Rasheed et al., 2022). In addition, El-Badry and Raslan (2016) recorded 0.43 mg/L
of Cu in sheep milk. Generally,
agriculture and various mining and smelting operations are the main causes of
contamination of the area with Cu. Among the heavy metals in the current
study, the Zn was the highest value recorded (4.99 mg/L) and it exceeded the
limited value (Fig. 6). Current findings were consistent with those confirmed
in Poland (5.53 mg/L) (Stanovič
et al. 2016) and in Turkey (5.02 mg/L) (Paksoy et al., 2018) and greater than values reported in
Pakistan (Khan et al., 2006) and Croatia (Antunović et al., 2016).
Fig (6): the mean concentration of Zn in milk
samples in
comparison to the standard value
The
concentration of Co in the present work varied from 0.01 to 0.09 with a mean
range was (0.038 mg/L). Current values exceeded the permissible range
(0.001-0.008) as recommended by FAO/WHO (1999) (Fig. 7). This finding agreed
with the finding of Safonov (2020). The higher heavy metal content in milk
samples is ascribed to the utilization of metal-polluted grazing land, water
resource, and livestock pastured on metal-contained lands.
Fig (7): the concentration of Co in milk samples in comparison to the
standard value
The
level of Ni in the current research was ranging from 0.89 to 0.99 with a mean level
of 0.948 mg/L. These data were higher than the recommended safe levels (0.1mg/L)
as shown in Fig. 8. This result is higher than the findings of Saber and El Hofy (2018), who found
0.038 mg/l of Ni in sheep milk. Ahmad et al. (2016) indicated that the mean average
value of Fe and Ni in examined milk were 0.592±0.321 and 0.34±0.001 mg/L, successively.
Animal species, geographic location, maternal age, health state, lactation
stage, and external factors including environment, diet, and season can affect
the element concentrations in milk samples (Paksoy et al., 2018).
Fig (8): the concentration of Ni in milk samples in comparison to the
standard value
The Fe value in the current study was (0.89-0.94)
with a mean level was (0.91 mg/L) were
exceeded the recommended level (Fig. 9). The current result was higher
than the concentration observed in previous findings of 0.85 mg/L (Miedico et
al., 2016) and 0.46 mg/L (Zhou et al., 2016). However, this average value was
lower than that displayed by Paksoy
et al. (2018), who observed that the Fe value presented within the milk
samples was ranging from 2.83 to 4.72 with a mean value of 3.49 mg/L. The
samples were collected during outdoor breeding and grazing. Thus, seasonality,
atmospheric factors, and feed ratio fluctuation can all have a significant
impact on the amount of Fe present in the sheep milk samples (Rahimi, 2013). The
toxicity of iron encompasses four phases, first phase symptoms, starting six
hours post-iron overdose, include nausea, vomiting, diarrhea, and bleeding in
the gastrointestinal tract. The second phase develops 6–24 hours after an
overdose, and this period is regarded as a chronic phase of obvious physiological
improvement. The third phase commences from 12 to 96 hours following the outbreak
of clinical signs and is marked by hypotension, shocks, drowsiness, hepatic
necrosis, tachycardia, and lactic alkalosis, and may occasionally result in
death. The last stage happens between 2-6 weeks after an overdose of iron. This
phase is characterized by the emergence of gastrointestinal ulcerations and
strictures (Engwa et al., 2019).
It is shown from Table (1), some measured heavy metals such as (Pb, Co, Ni, and
Fe) are differed significantly (p<0.01) between the milk of the studied ewe
samples and the global standard range or values. This means that such milk from
these toxic metals possess health risks to consumers and should be treated from
the mentioned heavy metal, because it may cause fatal diseases.
.
e
Fig (9): the concentration of Fe in milk samples in comparison to the
standard value
CONCLUSION
This
study concluded that the concentration of all heavy metals in the milk of
Awassi sheep grazed in the contaminated area with the oil refinery was higher
than the limits allowed by international standards, except Cr which was below the
standard level. It is possible to claim that consuming sheep milk in the present
study's area is a health danger due to the heavy metal concentration. It could bring
about long-term health hazards associated with consuming this sheep's milk.
Consequently, it is essential to continuously monitor and control the feed and
water of sheep to reduce the pollutants in milk in KIA.
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