Due to population explosion, rural development, productivity gains in food and livestock production is important to food security and crucial to poverty alleviation.The Pakistan’s population has increased from 65 to 161 million over the past 3 decades and is forecast to increase to 234 million by 2025.It is widening the gap between supply and demand and increasing food insecurity problem in the country.To fill this gap, vegetable production is important to squeeze this problem. Horticultural crops contribute about 6% of country’s GDP and 22% of national food production.
More than 60 species of vegetables are cultivated in the country and are a rich and comparatively cheaper source of vitamins.A nationwide assessment showed that the direct use of untreated waste water for agriculture, particularly vegetable production, is common in most cities and suburbs.The use of sewage-contaminated municipal water for irrigation of crops is an old practice in many big cities of Pakistan. Since the wastewater is rich in nutrients, it increases crops yield substantially but at the cost of food quality.
Poor quality groundwater and lack of alternative water sources results in the use of untreated wastewater for local irrigation in urban, peri-urban and even rural agriculture, all across Pakistan. Municipal and wastewater from homes and different industries contains different harmful chemicals and heavy metals like Fe, Mn, Cu, Zn, Pb, Cd and Hg. Sourcesof these heavy metals other than wastewater includes manures, sewage sludge, fertilizers and pesticides applied to soils and crops.Latest estimates reveal that total quantity of wastewater produced in Pakistan is 962,335 million gallons (4.369 x 109 m3/yr). A recent nationwide wastewater assessment showed that total water supply is 4.6 x 106 m3/day, and about 30% of wastewater is used for irrigating an area of 32,500 hectares.It has also been estimated that 64% of total wastewater of Pakistan is disposed of either into rivers or into the Arabian Sea. Similarly, 400,000 m3/ day wastewater is additionally added to canals.
But, Sewage is not only hazardous in itself, but the use of acids in homes and chemicals in factories only make the water more dangerous. Ingestion of vegetables containing heavy metals is one of the main ways in which these elements enter the human body. Once entered, heavy metals are deposited in bone and fat tissues, overlapping noble minerals. Slowly released into the body, heavy metals can cause an array of diseases.Waste water should not be used for vegetable production because these chemicals are absorbed by the vegetables along with the water, and this affects health because use of sewage in vegetable production can cause hepatitis or cancer. The hazards posed by the consumption of heavy metal contaminated vegetables are summarized in the following table.
Table: Summary of Heavy Metals effects on Human and their Permissible Limits.
| Heavy Metal | Cu | Ni | Pb | Cd | Hg | As |
| Limits (mg/kg) | 0.001 | 0.001 | 0.1 | 0.05 | 0.1 | 0.010 |
| Effects on humans | Gastrointestinal distress, Liver and kidney damage.
| Carcinogenic, cardiovascular disease, neurological deficits, high blood pressure. | Delays in physical or mental development, Kidney problems, high blood pressure.
| Kidney damage, Carcinogenic. | Kidney damage, Neurotoxicity, Insomnia. | Skin damage, Problems with circulatory systems, Risk of cancer. |
Written By:
Zia Ur Rahman Farooqi
MSc. (Hons.) Environmental Science
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