(The Gist of Science Reporter) Heavy Metal Toxicity: From Farm to Plate

[SEPTEMBER-2019]

Heavy Metal Toxicity: From Farm to Plate

VEGETABLES and foods are essential for a healthy diet. But does the environment they are grown is also affect the nutritional status of the vegetables and fruits?
A recent study conducted by CSIR-NEERI (National Environmental Engineering Research Institute), Nagpur, reveals that vegetables grown on the Yamuna river floodplain in Delhi contain toxic metals that could trigger serious human health diseases including cancer, organ malfunction, etc. These vegetables make their way to the largest markets in the city, risking the health of the consumers unknowingly feeding on toxins.
During the study, samples of seven vegetables including cabbage, spinach, fenugreek, cauliflower, radish, brinjal and coriander were collected from three different locations in east Delhi (Geeta Colony, Mayur Vihar and Usmanpur Khadar) and tested for heavy metal
contamination like Lead (Pb), Cadmium (Cd), Mercury (Hg) and Nickel (Ni).
The study stated that the level of lead exceeded the safe limits of FSSAI (Food Safety and Standards Authority of India) in coriander samples collected from Geeta Colony. As per FSSAI guidelines, in vegetables the permissible limit for Pb (lead) is 2.5 mg/kg but the level detected in vegetables ranges approximately from 2.8 mg/kg to 13.8 mg/kg. It is believed that vehicles, pesticides, paint, battery, polythene and units processing lead could be the possible sources for lead contamination.
Earlier studies had reported that vegetables grown near the Yamuna contain high quantities of lead, mercury and arsenic. The deviation from the permissible limits is shocking as it was found that the regular seasonal bottle gourd (ghiya) had 28.06 PPM (Parts per Million) of lead, 139.90 PPM of mercury and 318.70 PPM of arsenic whereas the safe limits as per Food Safety and Standards Regulation (FSSR) for lead and mercury are 0.1 PPM and 1.0 PPM respectively. Surprisingly there is no scale to measure arsenic since it was never thought that its contamination could be present in vegetables, therefore, FSSR did not map the chemical. It seems that Yamuna fed fresh veggies are serving poison to our bowls.

Sources of Heavy Metals

Although heavy metals exist naturally in the atmosphere, in recent times their biochemical and geochemical balance have been drastically altered due to indiscriminate anthropogenic
activities.
Industrial & Domestic Waste: Metal contaminated industrial waste has been the main reason for contamination of the soil and water in the last few decades with increasing mining and manufacturing industries. The industrial and domestic waste generated is not disposed the way it should be, inflicting far-reaching impacts on agriculture for many years to come.
There is an urgent need to introduce reliable strategies and stable treatment systems to address the issue of industrial and domestic wastes. In the last few decades construction industries (housing, roads, railways, etc.) have evolved into a million-dollar business and became one of the biggest contributors of heavy metals in the soil pollution.

Agricultural and Livestock Practices:

Arrival of modern fertilizers and pesticides has given a tremendous hike to chemical use. These chemicals are not natural and cannot be broken down easily; they seep down into the ground mixing with water and finally ending up in our diet.
Excessive use of chemicals, pesticides, fertilizers which have trace amounts of metals as micronutrients contaminate the groundwater, rivers and the soil, which accumulate in plant tissue and are passed to other animals and humans affecting the entire food chain and causing many
problems from short-term acute diseases like diarrhoea to long-term chronic ailments like cancer. For agriculture, adequate water resources are needed. Often sewage sludge and inadequately treated water is used in fields. The quality of crops grown in such fields cannot be guaranteed.

Transport Emissions:

During transportation, vehicles release emissions that find their way to soils by atmospheric
deposition and petrol spills. Similarly, traffic during rainfall and runoff may translocate heavy metal-rich particles from the corrosion of metal automobile parts, pavement abrasions and tires, etc. Effects of Heavy Metals Soils are important for maintaining the good quality of groundwater and food production by filtering, buffering and transforming inorganic and organic pollutants. However, soil pollution with heavy metals has toxic effects on soil biota and plants (Phytotoxicity).
Lead: Lead-contaminated food is one of the major sources of exposure for the general public. Studies have principally established that individuals exposed to elevated levels of lead for short-term may develop problems like brain damage, gastrointestinal symptoms, etc., whereas long-term exposure causes damage to the kidney, immune and reproductive system, etc. However, it is extremely toxic to young children even at low levels as it interrupts neurobehavioral development; with higher doses, it could be fatal. Lead can cross the placenta and have adverse effects on the developing foetus. The main sources of lead contamination are lead paint, car mining, foundry activities, automobile emissions, burning of coal, construction activities, smoking and agriculture activities e.g. chemicals, fertilizers, etc.

Safety Measures

There is a need to recognise the value of water bodies and soil for their productive capacities as they maintain a healthy ecosystem and contribute towards food security. On the occasion of the World Soil Day 2018, the Food and Agriculture Organisation (FAO) offered many recommendations to reduce the soil pollution at state, industrial and consumer level suggesting that up to 80% of garbage produced by evolving cities could be recycled. Realising the problem of e-waste generated every year affecting the soil, FAO urged to donate or recycle the old devices rather than throwing and also asked the governments to promote the sustainable management of agrochemicals.
The United Nations Environment Assembly (UNEA), in December 2017, tasked the WHO and FAO to carry out surveys and report on the extent of global soil contamination, monitor future trends and identify linked risks and impacts. The results will be presented in the fifth session of UNEA in 2021.
Phytoremediation or bioremediation is cost-effective, affordable, eco friendly and solar energy driven passive technology which can minimise the level of heavy metals in die soil With proper post-harvest management techniques, phytoremediation presents a solution to combat heavy metal contamination. Besides, an appropriate selection of crops can also help in overcoming the heavy metal stress because crops differ in their ability to uptake metals. For example, high level of heavy metals in the leafy and root vegetables has been observed; therefore, it would be a wise decision to avoid growing them in highly contaminated areas. Crop rotation is also a good way of influencing pollutant mobilisation and uptake by crops because of the residual impact of various organic acids in the roots of the plants. Growing non-edible plants like flowering plants in the contaminated area can be helpful to an extent. According to Dr B.S. Tomar, Head of the Vegetable Sciences Department at Indian Agricultural Research Institute (IARI) in Pusa, “Leafy vegetables such as spinach, vegetables that grow below the ground or close to the ground such as carrot, radish and turnip and vegetables that grow faster tend to absorb more metals from the soil and water. The government should ban growing any edible items in such soil and water. Ornamental plants, flowering plants or cash crops can be allowed to grow.” (Hindustan Times). There is also a need to cut down the use of pesticides as there are many other alternatives to control pests, for example, crop rotation, adequate and effective manure management, removal of the infected portion of a plant, plowing, biological controls (like useful mites that feed on mite pests in orchards), etc.
With increasing industrialisation, modern lifestyle and urbanisation, heavy metal accumulation is of great concern. The sad state of soil-water-crop system needs regular monitoring, assessment, guidelines, effective legislation with strategies and policies to control heavy metal toxicity. Otherwise, in the near future there will be severe complications imposed by heavy metal contamination.