Investigating the Residual Heavy Metals Lead, Cadmium, Chromium, Arsenic and Nickel in Milk and Body Tissues of Holstien Dairy Cows

Environmental pollution, including pollution caused by urban and industrial sewage, factories and vehicles, causes pollution of natural resources in the environment, including water and fodder. The entry of these elements into the body of animals and their accumulation increases their concentration in products and enters the human food chain. Contamination of milk, meat and other edible tissues of animals with heavy metals is also a worrying issue and threatens food hygiene and human health because these elements are not naturally present in edible tissues and even very small amounts of them can be cause severe side effects. Scientists have mentioned the main cause of contamination of meat and animal tissues is feeding them from contaminated fodder sources or rearing them near contaminated areas. In the studies conducted in different countries, the amounts of heavy elements were more than allowed. In order to investigate the amounts of heavy metals including lead, cadmium, chromium, arsenic and nickel in milk and body tissues of dairy cows in North Khorasan province, two experiments were conducted in three regions and the amounts of heavy metals in milk and body tissues of dairy cows using the device Inductively coupled plasma-atomic diffusion (ICP) was measured, and studied.In the first experiment, three dairy cattle farms were selected from three regions, two farms were located in two regions at equal distances from large industries, and the third region was selected as a control region far from large industries. In each of the farms, 10 dairy cows (5 first lactation and 5 second lactation and above) was sampled and the amounts of elements were measured. In the second experiment, muscle, heart, liver, kidney and lung tissues were sampled from 5 dairy cows from each region that were removed and sent to the slaughterhouse for reasons such as mastitis and reproductive problems. Heavy metals, including lead, cadmium, chromium, arsenic and nickel, were measured in the tissues by an inductively coupled atomic diffusion plasma (ICP) device. The initial experiment's findings indicate that the levels of arsenic, cadmium, and lead in the milk of Holstein cows remained unaffected by varying regions. However, there were significant regional impacts on the levels of chromium and nickel in the milk of Holstein cows. Furthermore, the concentrations of arsenic, cadmium, nickel, and lead in the milk of Holstein cows were not influenced by the age of the cows or the interaction between region and age. In contrast, the concentration of chromium exhibited sensitivity to age and the interaction between region and age. These nuanced insights highlight the diverse influences on trace metal concentrations in Holstein cow milk, providing valuable information for understanding regional and age-related variations. The amount of arsenic, cadmium and lead metals in the thigh muscle tissue of Holstein cows in different regions was not significantly affected by regions. However, the amount of chromium and nickel in the thigh muscle tissue was significantly affected in different areas. The amount of arsenic, chromium, nickel and lead in the heart tissue was not significant in any of the regions (Shirvan, Esfrayen and Bojnoord). The amount of cadmium in the heart tissue of Holstein cows was significantly affected by different regions. Thus, the highest amount of cadmium in heart tissue was observed in Bojnord region and the lowest in Esfrayen region. The amount of chromium, nickel and lead in the tissue of all Holstein cows in different regions was not affected. However, the amount of arsenic and cadmium in the kidney tissue was significantly affected in different areas (Shirvan, Esfrayen and Bojnoord). Based on the obtained results, there was no significant difference in the amount of arsenic, cadmium and lead in lung tissue in different regions. However, the amount of chromium and nickel in the lung tissue of Holstein cows was significantly affected in different regions. Chromium enters various environmental sources (air, water and soil) from a wide range of natural and human sources, the most of which is emitted from industrial activities. When heavy metals are present in the air, feed and water of animals, they eventually accumulate in their tissues. While the levels of heavy metals did not exhibit significant differences across many investigated areas, it is noteworthy that the concentrations surpassed the standard values established for these metals in products like milk. The elevated concentrations raise concerns about the potential health implications associated with consuming products containing such heightened metal levels. An interesting observation emerges from the examination of elemental concentrations in tissues, irrespective of regions and distances. The lead element, in particular, demonstrated the highest concentrations, with the liver exhibiting the most notable accumulation compared to other tissues. This underscores the need for strategic interventions, and the consideration of solutions such as the application of absorbents to mitigate metal concentrations in dairy cattle products emerges as a viable recommendation. Implementing such measures could play a crucial role in ensuring the safety and compliance of dairy products with established standards.