ARTICLES

 

Concentrations of metal residues in domestically produced and imported milk in Kosovo

 

 

B. Dragusha^I; H. Aliu^{I, #}; S. Dizman^II

^IFaculty of Agriculture and Veterinary, University of Pristina, 10000 Pristina, Kosovo
^IIFaculty of Arts and Sciences, Recep Tayyip Erdogan University, 53 100 Rize, Turkey

 

 

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ABSTRACT

The aim of this study was to investigate the concentration of metal residues in cows' milk and the health risks to humans from its consumption. In total 37 milk samples were analysed, namely 32 raw milk samples from domestic rural milk collection centres, and 5 imported sterilized milk samples from markets. The concentrations of chromium (Cr), manganese (Mn), nickel (Ni), and copper (Cu) in the milk samples were from 0.06 to 20.3 [g/kg, 4.7 to 64.8 [g/kg, 2.16 to 65.99 [g/kg and 0.21 to 44.7 [g/kg, respectively. Concentrations of iron (Fe), zinc (Zn), arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) ranged from 157.52 to 989.95 [g/kg, 1429.63 to 5718.71 [g/kg, 0.12 to 2.01 [g/kg, 0.22 to 2.28 [g/kg, 0.00 to 0.29 ig/kg, and 0.17 to 4.29 [g/kg, respectively. The concentrations of Mg, Fe and Zn were slightly higher in domestic milk samples than in imported milk. The concentrations of Cr, Ni, Cu, As, Cd, Hg, and Pb were higher in imported milk samples than in the samples of domestic milk. Overall concentrations of minor elements had good nutritional values and the levels of the heavy toxic metals including As, Cd, Hg, and Pb were lower than the recommended limits and did not pose any threat to consumers.

Keywords: health metals, milk, toxicity

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Introduction

Milk and milk products are high-value foodstuffs that are important in the human diet. Milk is a source of proteins, fats, vitamins, and minerals in well-balanced proportions and is considered a valuable source of nutrients for humans.

Milk is also an indicator of environmental contamination (Enb et al., 2009; Qin et al., 2009; Yüzbasi et al., 2009). Milk and milk products made from may contain heavy metals as chemical contaminants. Heavy metals are commonly defined as those metals that have a specific density of more than 5 g/cm³. The main threats to human health from heavy metals are associated with exposure to Cd, Pb, Hg, and As (Järup, 2003). Obviously, the human body needs a certain amount of metal elements for regular function, as long as they are not present in overly large amounts (Singh et al., 2011).

Industry, agriculture, domestic effluents, combustion, decomposition of chemical fertilizers, and pesticides are some of the main sources of heavy metal pollution. Contamination of water resources and agricultural lands with heavy metals has increased around the world as a result of rapid economic development and remains a critical environmental issue that affects plants, animals, and human health negatively (Fang et al., 2016; Rezania et al., 2016). Heavy metals are not biodegradable in the environment, but accumulate in the food chain through biotransformation and bioaccumulation (Aslam et al., 2011).

The frequent occurrence of heavy metals in dairy products may be attributed to the contamination of milk, which results from cows consuming contaminated hay, grain, and water. Keeping in mind that milk is a route for the passage of heavy metals from soil to humans, the concentration of heavy metals in milk represents a concern for the health of consumers (Boudebbouz et al., 2021). The continuous intake of heavy metals from consuming contaminated milk can disrupt many biological and biochemical processes in humans (Balkhair & Ashraf, 2016).

Heavy metals such as Cr, Mn, Fe, Ni, Cu, and Zn are essential to metabolic activity in living organisms. Deficiency in any of these metal nutrients will result in the onset of characteristic clinical symptoms. Other metals such as As, Cd, Hg, and Pb are not essential and have no biological function. Even with the essential heavy metals there is a narrow gap between the concentration at which they are required and the concentration at which they are deemed toxic (Belete et al., 2014; Higham & Tomkins, 1993). The toxicity of heavy metals depends on their speciation and soluble metal species are generally the most toxic (de Paiva Magalhães et al., 2015)

Heavy metals such as As, Cd, Hg, and Pb are highly toxic, with infants and children being most vulnerable. Depending on the amount and duration of exposure, these metals can affect the nervous system, hormonal system, cardiovascular system, liver, kidneys, and the reproductive system (Meshref et al., 2014). Chronic exposure to Pb and Hg may cause anaemia, hypertension, kidney disease, autoimmune diseases such as rheumatoid arthritis, damage to the foetal brain, tremors, anxiety, restlessness, depression, and sleep disturbances (Barakat, 2011; Järup, 2003). Lead is nephrotoxic, even at levels lower than 5 mg/dL, especially in patients with diabetes, hypertension and kidney problems (Ekong et al., 2006). Exposure to inorganic metals such as As can cause cancer in various organs of the human body, whereas intake of Cd may cause nausea, vomiting and kidney damage (Järup, 2003; Ng et al., 2003). Numerous studies demonstrated that low dose exposure to As, Cd, Hg, and Pb interactions in mixtures was synergistic and these metals showed higher toxicities than individual heavy metals (Cobbina et al., 2015).

Therefore, it is essential to analyse the level of heavy metals in milk and to suggest possible pathways by which they migrate from soil to the human populace. To address this concern, the first intention of this study was to analyse milk produced in the territory of Kosovo and to compare its heavy metal content with that of imported milk.

 

Material and Methods

In 2018 and 2019, a total of 37 milk samples were collected across Kosovo. The first 32 raw milk samples were taken from rural milk collection centres and five additional sterilized imported milk samples were selected from various markets. Each sample of 1000 mL was placed in a labelled polyethylene bottle. Afterwards, each sample was kept in an ice cooled box at 2 - 8 °C, and transported to the laboratory for analysis. A portable GPS was used to record the geographical coordinates at which each milk sample was collected. Heavy metal concentrations in milk samples were measured with inductively coupled plasma mass spectrometry in high sensitivity mode (Bruker 820, Karlsruhe, Germany), which has been used successfully to determine the concentrations of multiple elements in an assay (Herrero-Latorre et al., 2017). The instrument was set to measure plasma flow at 18.00 l/min, auxiliary flow at 1.80 l/min, sheath gas flow at 0.20 l/min, nebulizer flow at 1.01 l/min, sampling depth at 6.50 mm, power at 1.40 kW, pump rate at 4 rpm, and stabilization delay 10 seconds. The method validation and calibrations for measuring heavy elements in milk samples are described below (Herrero-Latorre et al., 2017).

For the quantitative analysis, an external calibration technique and quality control was used for the ten heavy elements under scrutiny. First, for the background measurement, a blank sample was recorded. Then, the calibration for heavy metals such as Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Hg, and Pb was performed at five levels from 10 to 500 ppb. For quality control of measuring system, a standard with various heavy metals concentrations was used. Calibration curves and QC for cadmium and lead are presented in Figure 1. The same procedures were applied to the other heavy metals.

Concentrations of the heavy metals were reported as mean ± relative standard deviation. One way analysis of variance was used for comparisons of datasets of milks that originated from rural collection centres and imported milk samples, with significance level P <0.05. The statistical calculations were carried out with MS Excel (Microsoft Inc., Redmond, Washington, USA).

To find the estimated daily intake (EDI), the method of Cano-Sancho et al. (2010) was used. The EDI depends on the quantity of milk consumed and the concentration of heavy metals in the milk. The body mass of humans can influence their tolerance of contamination. The following formula was used to calculate EDI in μglkg bodyweight (BW)/day):

where: M_Intake is the daily average of milk intake (L/day),

C_metal represents the average of specific heavy metals in milk μg/L), and

individual represents the average body mass of a person.

The average daily consumption of milk per adult person was regarded as 0.2 L and the average mass for an adult person as 60 kg BW (AI-Ashmawy, 2011). The daily intake of heavy metals was compared with the recommended dietary allowance (RDA) values (Institute of Medicine, 2001).

 

Results and Discussions

This section reports findings for 10 heavy metals in 37 milk samples, 32 taken from rural fresh milk collection centres and 5 from markets as imported milk. The heavy metals assayed in this study and descriptive statistics characterizing their distributions for samples from the domestic marketplaces are reported in Table 1. Similar characterizations of the heavy metals found in the samples of imported milk are shown in Table 2. Residues of Zn, Fe, Mn, Cu and Cr were detected in all of the milk samples analysed in this study. The average concentrations indicated Zn > Fe > Mn > Cu > Cr. The elements Ni, As, Cd, and Pb were present in 40% to 60% of the samples. Mercury was usually detected only in trace amounts and was encountered only in three samples that were obtained domestically. The ratio of metal concentrations in the samples from domestic milk collection centres to those in imported milk was from 0.01 to 1.7 (Table 2). The average concentrations of Hg, Mn, Fe, and Zn from domestic milk were higher compared with the imported milk, whereas the concentrations of As, Pb, Cd, Ni, Cr, and Cu were higher in the imported milk than in domestic milk. The differences between milk samples from these sources were significant for Cr, Fe, As, and Cd.

Manganese was slightly more concentrated in the imported samples, whereas Cr, Ni and Cu were much more concentrated in the domestic milk samples. Similar results were reported for Cr, Mn and Cr concentrations in raw milk samples (Dobrzanski et al., 2005; Yasotha et al., 2020). Graphically, the whisker plots in Figure 2 illustrate the distributions for Ni, Cr, Mn, Cu, Fe and Zn for all samples combined. Higher average concentrations for Fe and Zn were detected in domestic milk in contrast to imported milk, with a ratio 1.74 and 1.04, respectively. High levels of Zn in dairy products had been observed (Khan et al., 2014).

Arsenic is among the most toxic elements with cumulative effects on the human body. The presence of As has been connected with certain types of cancer in humans, including lung, liver, skin and bladder cancer (Martinez et al., 2011). Also, non-carcinogenic effects of chronic As exposure include neurobehavioral and neuropathic effects (Kapaj et al., 2006). In the present study, As was encountered on 41% of domestic milk samples in the range between 0.12 and 1.11 μg/kg, whereas its presence in the imported milk samples was from 0.65 to 2.01 μg/kg. Nonetheless, the mean of As levels observed in the current study was lower than had been reported in milk samples from Croatia (Bilandzic et al., 2011). The maximum permissible limit for As in milk established by the European Commission is 10 μg/l or approximately 10 μg/kg (Commission Regulation (EC) No. 1881, 2006).

Cadmium is another highly toxic element that affects primarily the skeleton system, kidneys and liver (IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2006). The limit for Cd of 2.6 in milk has been proposed by the International Dairy Federation (Hitchins, 1996). This limit remains the only documented maximum limit of Cd level in milk. The mean level of Cd in the domestic and imported milk samples from this study was between 1.25 and 2.08 μς/kQ, respectively.

Exposure to Hg, even in small amounts, is a danger to humans and animals (Ye et al., 2016). In the current study, Hg residues were found only in 8% of domestic milk samples, with a mean of 0.002 μς/kQ, and it was not detected in any of the imported milk samples. Similar results were reported for Italian domestic milk with an average level of 0.002 (Caggiano et al., 2005).

Lead was present in 41% of domestic and 60% of imported samples. The EU regulation for Pb in unheated and heat-treated milk is 20 (Commission Regulation (EC) No. 1881, 2006). Pollution of the environment with heavy metals such as Pb continues to be a worldwide problem (Enb et al., 2009).

 

Conclusions

The present study provided important information about heavy metal concentrations in imported and domestic milk in Kosovo. On average, none of the heavy metal residues in the milk samples that were assayed in this study reached internationally established safety limits and EDI values were within acceptable ranges. The current study was the first presentation of heavy metal concentrations in milk sampled from the whole of Kosovo. It could be used by policy makers to manage potential health risks.

 

Acknowledgements

The authors received no specific funding for this work.

Author' Contributions

Conceptualization: HA, formal analysis: SD, methodology: SD and BD, software: SD and HA, validation: SD, investigation: BD, writing original draft: HA, writing, review and editing: BD, SD, and HA

Conflict of Interest Declaration

The authors declare that they have no conflicts of interest.

 

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Submitted 15 March 2021
Accepted 24 July 2021
Published 19 October 2021

 

 

# Corresponding author: hamdi.aliu@uni-pr.edu