KARACHI: Vegetables being grown and sold in certain parts of the city contain very high levels of toxic metal content — lead, iron, copper and cadmium — posing a serious health risk to consumers, according to the findings of a three-year research work.

Besides, the study also found elevated levels of metal contamination in tap water.

Samples of beet, carrot, radish, turnip, potato and sweet potato and their leaves collected from SITE (Shershah), Malir and Saddar (Empress Market) over a period of three years were irrigated with the Indus River supply or industrial effluents, according to the study, Effect of Industrial Waste on the Cultivation of Root Vegetables.

The vegetable samples were examined for trace metal content (cadmium, copper, chromium, iron, manganese, nickel, lead and zinc).

Samples of sand, industrial wastewater and tap water were also tested to ascertain the level of acidity, total dissolved salts, alkalinity, hardness, sulphate, chloride, dissolved oxygen, biological oxygen demand, chemical oxygen demand and trace metal contents.

The research was conducted at the chemistry department of Federal Urdu University of Arts, Science and Technology by Dr Kousar Yasmeen, who earned a doctorate on the basis of her research and currently teaches at the university, under the supervision of Dr Qamrul Haq and Dr Mohammad Ali Versiani.

According to the study findings, the concentration of all metals, except zinc, crossed the threshold limits in all samples of root vegetables irrigated with industrial wastewater but comparatively less in those collected from Empress Market, Saddar.

Root vegetables and the soil irrigated with industrial wastewater in Malir had elevated levels of cadmium, cobalt, copper, chromium, iron, manganese and nickel, the three-year research showed.

The maximum concentration of iron was found in radish and beet leaves, with 0.875 ppm (parts per million) in 2007 and 0.932 ppm in 2008 in radish leaves and 1.957 ppm in beet leaves in 2009.

The samples of industrial wastewater and tap water also had higher concentration of metals that exceeded the WHO permissible limits.

In tap water samples taken from Gulshan-i-Iqbal, average concentration of metals was 3.279ppm (2007), 3.890ppm (2008) and 5.090ppm (2009).

Iron retained its highest level in the industrial wastewater in Malir in three years, while iron and lead were dominant metals in the industrial wastewater in the SITE area.

The results showed that a linear correlation exists within free metal availability in water source, soil composition and its metal retention and exchange capacity and the selective absorption behaviour of vegetables.

There was also a significant increase in the biological and chemical oxygen demand and a decrease in the total dissolved oxygen in industrial wastewater and treated water due to nutrients of organic matter brought in by urban sewage.

“The concentration level of metals showed an increase in water, sand and vegetable samples over the past three years as the levels of oxygen dropped. The metal contamination was seen more in vegetables that grow under the soil,” said Dr Kousar Yasmeen while speaking to Dawn.

Wastewater use for cultivation

The research also highlighted the fact the use of industrial wastewater for cultivation was on the rise as Pakistan faced shortage of water, she added.

According to her, the relation between contaminated food chain and various diseases is well documented and there is dire need for awareness as well as action on part of the government to take steps to discourage the use of industrial wastewater for cultivation.

“High levels of cadmium, copper, chromium, iron and manganese have been linked to kidney failure, weakened bones, cancer, goitre, diarrhoea, vomiting, stomach cramps, fatigue, loss of weight, high blood pressure while excess of lead and zinc may cause disruption in the nervous system, anaemia, brain damage, miscarriage, increase in cholesterol level and reduction in the metabolism of copper and iron,” she said.

Citing some statistics, Dr Yasmeen said that food was the second major cause of cancer after tobacco and one third of cancer cases could be prevented by eating uncontaminated vegetables.

“The three-year study initiated as a PhD in 2007 focusing on few areas in the city has now been taken to a larger scale and a research team at the university is collecting vegetable samples from across the city as well as from different parts of the country to check metal contamination,” she said.