Cadmium in wheat: a threat to human being
The future prosperity and economic stability of Pakistan mainly depends upon the quantum of material resources and their judicious exploitation and utilization. The population of Pakistan is increasing at an alarming rate of 2.2% per annum. Therefore there is dire need for advanced planning and research to increase food production and improve quality in order to meet the needs of ever increasing population.
Wheat (Triticum aestivum L.) is an important cereal and the staple food crop in most parts of the world including Pakistan. It is a principle source of carbohydrates, fiber and iron (Fe), magnesium (Mg), zinc (Zn), niacin and gluten protein which is responsible for specific properties that helps in conversion of flour into dough further processed for making bread and other food products. It also provides essential amino acids, minerals, and vitamins and provides 56% carbohydrates and 21% of the calories consumed world-wide. Due to its immense and multi-purpose use in daily life there is no exaggeration in saying that prosperity and well being of bulk of world’s population primarily depends upon better harvest of wheat crop.
In 2003, 558 million tons (Mt) wheat was produced. Main countries which are producing wheat are china, Pakistan, Canada, Latin America and India. Wheat has no.1 position in cereals produced in Pakistan with respect to yield and grown on area of 8137 thousand hectares with an average yield of 2278 kg per acre but it is a dilemma that about 78% wheat production is obtained from cadmium contaminated soils. In this way, cadmium enters into the food chain and cause health hazards. All the reasons of this problem linked to soil contamination which is a major issue in developing countries since 1960’s. Soil is called to be contaminated when any undesired change in soil environment which have poor effects on human health and whole ambiance is detected or observed. There is another reason of soil contamination with cadmium that soils are being irrigated with contaminated water due to lack of irrigation water as a result of Kashmir dispute and electricity load-shedding, about 32580 ha soils receive cadmium contaminated water for irrigation. That application of sewage water causes accumulation of heavy metals like cadmium (Cd), chromium (Cr) and lead (Pb) in soils.
There are 20 major heavy metals which have bad effects on living things which includes plants, animals and humans from these 20 heavy metals, cadmium is categorized as carcinogenic heavy metal. When cadmium is accumulated in different crops, it enters into the food chain and ultimately, it is consumed by humans.
Sources of cadmium
Major source of cadmium in plants is irrigational water contaminated with cadmium and other hazardous heavy metals and this water normally called waste water produced by different industries like plastic industry, Ni-Cd (Nickel-Cadmium) batteries, pigments units and plating process. Other sources are over use of phosphate containing fertilizers, smelters, iron and steel production process and mining activities. From which, phosphate fertilizers, waste water and naturally occurring cadmium in soils is a cause of cadmium presence in food crops i.e. wheat.
Table 1: Heavy metal ranges occurring naturally in soils.
Effects of cadmium contaminated food consumption
When cadmium contained food is consumed, it cause carcinogenic effects as well as it effects on many human organs but main attacking site is kidney. It accumulates in it and remains in it for 10-30 years because it has 10-30 years range of biological half life. It also disturbs the metabolism of calcium, essential nutrients in human body and vertebrates and cause hypercalciurea which further develop into kidney stone. Occurrence of death due to excessive fluid loss; liver, bone, testes, immune system and cardiovascular system is also affected.
Ways to avoid cadmium in food
Weekly intake limit of cadmium is 7 μg/kg body weight described by World Health Organization (WHO) and to avoid the bad effects by consuming cadmium contaminated food and to keep cadmium away from soils as well as from our food, many methods can be adopted i.e. use of hyper accumulative plants to extract cadmium from soil (phytoextraction), removal of contaminated soil by excavation, stabilization of cadmium in soil, conversion of cadmium into secondary compounds which are less or not toxic and use of different soil amendments to stop cadmium accumulation in crops like silicon, zinc and biochar.
Zia Ur Rahman Farooqi.
Institute of Soil and Environmental Sciences,
University of Agriculture, Faisalabad Pakistan