Heavy metals in poultry eggs

The presence of heavy metals in poultry food has received considerable attention during recent years. Most of us ingest heavy metals via food in our daily diet, although the quantity of heavy metals varies from place to place depending on dietary habits, levels of environmental pollution and recycling of poultry food.
The eggs are one of the most common sources of protein in the diet of the population of Pakistan. Per capita eggs consumption increased significantly during the past few years. Even eggs are a source of metal exposure. Commercial poultry farmers now use inorganic materials in poultry feed for augmentation of health and production.
Metals of high specific gravity are called heavy metals. Metals are required for different life processes of animals and humans. The body requires substantial amounts of some metals like sodium and iron and has a high tolerance for their absorption. Other metals, such as the "micro-nutrients" copper and zinc, are required in much smaller amounts, and the body has a lower tolerance for them. There are metals which are not essential but are toxic to both man and other species even at lower levels.
The concentration of these metals increase, possibly due to human influence. Grains, such as maize, soyabeans and wheat which are the major components of feed, could also have picked up or bioaccumulated heavy metals directly from contaminated soil, depending on the location in which they were grown and the chemical nature of the soil there.
Excessive and improper use of inorganic or organic fertilizer could lead to the accumulation of metals in the soil (particularly) cadmium (Cd), chromium (Cr) and lead (Pb)), which would be biomagnified by plants and eventually end up in animal feed.
Traces of metals, such as Iron (Fe), Zinc (Zn), Copper (Cu) likely Cobalt (Co) are essential for normal functioning of the human body. Absence of these metals in food could result in stunted growth, poor vision, and inability to repair damaged tissues, especially in children; in high concentration, however, they are hazardous and injurious to the body. Lead (Pb), Chromium (Cr) and Cadmium (Cd) do not have any significant or useful nutritional value. High amounts of elements, like Copper (Cu), Lead (Pb), Zinc (Zn), Cadmium (Cd), and Mercury (Hg) is responsible for several diseases.
Cadmium is suspected for renal arterial hypertension, cancer and bone weakness. Chronic Lead toxicity produces anemia, paralysis and mental retardness. Mercury hazards are characterized by kidney damage, vomiting, inflammation of mouth and gums and muscle tremors. The concentration of lead (Pb), Chromium (Cr) and Cadmium (Cd) in eggs (in third-world countries) were reported slightly greater than the concentrations reported in eggs in many of the advanced countries, where the quality of animal feed and food items is monitored strictly.
Most Pakistani children between two to ten years of age consume one poultry egg daily, and the presence of heavy metals in their food is capable of producing subtle health hazards (e.g., deficit in intelligence quotient, mental retardation). The rates and methods of egg consumption vary among the people in Pakistan.
The rate of egg consumption depends on socioeconomic status, age group, and place of residence - either urban or rural. The rate of egg consumption among lower-class individuals and those residing in rural areas is very low.
Boiling and frying are the predominant ways of egg preparation among lower-class individuals, and their average intake is 4 eggs week (egg per capita: 3.7 kg; ie, the total weight of eggs consumed in a year calculated by multiplying the average weight of eggs taken per day by 365). The upper class, the rich, and the affluent consume more eggs prepared in several ways, in addition to the normal boiled and fried eggs.
These individuals eat more egg-containing cakes, homemade biscuits, drinks (eggovin), and salad than poorer individuals. Such behaviours could amount to an average intake of 3 eggs per day (egg per capita: 18.1 kg). On average, a middle-class individual (i.e., healthy urban inhabitant) consumes an average of 2 eggs per day (an egg per capita 12.1 kg.)