HEAVY METAL RESIDUES IN MILK AND PUBLIC HEALTH CONCERNS
Prasana Kumar Rath
Assistant Professor
Department of Veterinary Pathology, C.V.Sc & A.H., OUAT, Bhubaneswar-751003, Odisha
ABSTRACT
The rapid industrialization & enhanced agricultural activities have resulted in an increase in levels of many heavy metals in air, water and soil. These harmful metals get enter into the body of the animals through grazing on the contaminated pasture lands, through drinking of polluted water and also through inhalation of the contaminated air. The non-biodegradability and persistence nature of the heavy metals in the body of the animals lead its excretion through milk. Consumers suffer from various health disorders by getting exposure to the heavy metals through consumption of milk. Initiatives should be taken at both government as well as at producer levels for prevention and control of these residues in milk and dairy products. Effective quality assurance programme like Good Manufacturing Practices (GMP), Total Quality Management (TQM) and the Hazard Analysis & Critical Control Points (HACCP) approach can be followed in each and every step of production chain either to prevent or to reduce the level of metal residues in milk and milk products.
Introduction
Milk is an ideal source of many high biological proteins, essential minerals, vitamins and energy rich lactose and milk fat. It is rich in bone forming salts like calcium and phosphorous. So, milk is considered as an important food for all sections of the people starting from children to old aged persons. Milk is, however a potential ready source for various disease-causing agents and other chemical and biological contaminants. Most of the livestock products act as a source of many harmful residues such as antibiotics, pesticides and heavy metals (Khaniki, 2007). The residues are those substances which are having a definite pharmacological action and are likely to be harmful to human health.
Even if, milk is an important source of many macro and micro elements, toxic heavy metals may pave their way into milk and dairy products and impart adverse effects on human health (Qin et al., 2009). Metal residues in milk are of particular concern because milk is largely consumed by infants and children. The rate of absorption of heavy metals in infants and children are more due to the incipient development of the digestive tract in them. Heavy metals get bio accumulated in tissues of dairy animals and usually found in milk (Meli et al., 2015). Consumers get the symptoms of heavy metals when they get exposed to levels more than the maximum residue level as prescribed by Prevention of Food Adulteration (PFA) act.
Heavy metals
Metals with density greater than 5g/cm3 (Eskandari & Pakfetrat, 2014), atomic weight 63.546 to 200.590 and a specific gravity more than 4.0 are generally considered as heavy metals. The metals such as lead, cadmium, cobalt, nickel, arsenic and tin have significant adverse effect on humam length (Mahmoudi et al., 2015). These six heavy metals have high degree of toxic impact on the human health. These metals can induce multiple organ damage, even at very low levels. Milk and milk products may also contain other toxic trace metals like selenium, sulphur, iodine, zinc and cyanide (Ahmad et al., 2016). These metals are non-biodegradable and can get bio-accumulated and bio-magnified in animal as well as human being. Heavy metal get excreted to milk and enters into the body of the recipient individuals through consumption of milk and other dairy products. At present there is no specific limit/ standard available for milk and milk products for heavy metals in India. The feed materials, environmental conditions and the genetic makeup of the individual animal has a significant effect on the level of trace metal contents in milk (Ayar et al., 2009).
Sources of heavy metal contaminants
Heavy metals come to the environment from natural weathering of the earth’s crust, mining, soil erosion, solid waste disposal, application of sludge, waste water irrigation, industrial wastes, sewage effluents and air pollution fallouts. Environmental contamination increased to some significant level due to various industrial activities and advanced technologies. Contamination during handling, exposure and processing leads to increase in the level of heavy metal in milk and milk products. Metals may get leached from the processing containers such as steel or aluminium-ware during boiling or frying process into the milk and milk products (Onianwa et al., 1996). Lead soldered cans can act as a source of metallic lead to the raw milk. Hazardous element can also migrate from the packaging materials into the milk products.
Heavy metals get transmitted to animals by grazing over the pasture lands contaminated with industrial and agricultural wastes and pastures grown on soils irrigated with domestic and municipal waste water. Primarily, milk get contaminated before milking, may be from the feed of cattle, from sources used during the processing of milk as well as improper handling of the milk during the pre- and post-processing period. Milk and milk products may also get contaminated with metal residues when animals used to graze in pastures contaminated with industrial wastes (Younus et al., 2016). Heavy metals may enter the milk that is coming from coal burning plants, smelters and other industries. Through food chain, metals may enter to animal body by grazing of animals on pastures irrigated with contaminated industrial waste water or by drinking water from water source contaminated with industrial wastes. Plants and grass can uptake heavy metals from the contaminated soil and helps in transferring it to animal body through grazing. From animals these toxic residues can get transferred to consumers through consumption of milk obtained from those animals.
The wide variation in heavy metal content in milk might be due to several reasons such as variations between species, properties of the manufacturing processes and probable contamination from the equipment used during the processing, manufacturing and packaging also. Also, contamination of milk with heavy metals may occur during storage, marketing and leaching from processing and packaging containers.
Public health concerns
Metal ions usually interact with cell DNA and nuclear proteins and cause damage of DNA and structural changes which may lead to modulation of cell cycle, carcinogenesis or cell death. It has been found that children are highly susceptible to exposure of these toxic substances because of their immature renal systems and exhibit a very narrow tolerance to these trace elements. Heavy metals generally cause nervous disorder, kidney disorders, toxic effect on foetus and teratogenicity in humans. It may result in impairment of cardiovascular system, altered detoxification pathways and abnormality in hormonal functions.
Arsenic is having long retention time inside the body and therefore, many physiological functions of the body get affected by it. Aluminium is a potent neurotoxin; and long-term feeding of Aluminium containing foods to young one causes impaired mental development. Copper gets deposited in liver and brain of the consumers when they get exposure to excess amount of copper through food. Excess amount of lead in body causes decreased synthesis of haemoglobin which decreases the oxygen supply of the body. These events alter functions of bone-marrow, liver, kidneys and male gonads and may lead to gastrointestinal effects, encephalopathy, peripheral neuropathy, chronic irreversible nephropathy, aggressive behavior & wrist drop. Fe catalyses the lipid oxidation reaction with development of unpleasant odour in milk and milk products. The organic forms of mercury such as methyl mercury causes severe abnormality in the development of the brain and intellectual behaviour in young children. Cadmium is known as one of the important factors in development of bladder and prostate cancer.
Heavy metal contaminants prevention and control
Governments should take necessary steps for framing various regulations for giving protection to the consumers against adverse consequences arising from exposure to heavy metals through dairy products. The regulation for unethical residues in foods is a combined action of Food Safety and Inspection Services, Food and Drug Administration and Environmental protection Agency. The veterinary drug residues are regulated through Maximum Residues Levels (MRLs) which are present in milk and dairy products on sale. The maximum permissible levels of metals recommended by International Dairy Federation Standard are 0.037 µg/g for Fe, 0.328 µg/g for Zn, 0.02 µg/g for Pb,0.01 µg/g for Cu and 0.0026 µg/g for Cd. Preventive steps must be taken at each stage of production process to ensure quality of milk and milk products. The level of these contaminants can get reduced to a great extent in the milk and processed milk products by organizing public awareness programme and controlling manufacturing processes. To be effective, both farmers and company workers as well as managerial staffs should well aware about these issues. Metals may get migrated from the milk containers to milk. Therefore, containers used for milk must be free from those toxic metals, or those containers must be prepared with appropriate materials. Advanced techniques and technologies must be used by Dairy plants. The milk and dairy products must be allowed to sell only with approved packaged containers and not in open or loose form. Above and all, an effective food safety strategic plan such as HACCP can be imposed by government which may play an important role in the prevention of contamination of milk and dairy products with these metals. There is a need to set legal regulatory limits for all types of heavy metal residues in milk and its products. Appropriate risk communication and mitigation strategies should be followed for all farms that are situated near to wastewater drainage. Regular monitoring and testing of samples for presence as well as for detection of their level in milk and milk products should be done by using appropriate standard techniques. Feed in the polluted area should be controlled.
Conclusion
As these toxic metals get accumulated inside the body and imparts various adverse health effects, it is highly necessary to control their levels in milk and milk products so as to protect public health. Routine surveillance of dairy products must be carried out by taking samples from potentially contaminated areas followed by laboratory analysis to determine their levels in the sample. The public sector can play a very important role through conducting awareness programmes, educating to dairy farmers and milk processors about the harmful effect of heavy metals, such as cadmium, lead, mercury, arsenic and their preventive steps to control the occurrence of such health hazards by the consumption of milk and milk products.
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https://pubmed.ncbi.nlm.nih.gov/33152470/
