A new study conducted in Sri Lanka found that the leafy vegetables found in the market are highly contaminated with heavy metals. So, it is not healthier to eat the leafy vegetable you buy from the market unless they are organic. Most of the leafy vegetables that we can buy are non-organic and mostly harvested from nearby drainages and pack and sell in the market.
Since the past, leafy vegetables took the main role in Sri Lankan’s dietary habit hence those are good sources of vitamins, minerals, dietary fiber, and anti-oxidants. “Mukunuwenna” (Alternanthera sessilis), “Kangkung” (Ipomoea aquatica), “Thampala” (Amaranthus viridis), “Kohila leaves” (Lasia spinosa), “Nivithi”/spinach (Basella alba), “Gotukola” (Centella asiatica) are common examples for highly consumed leafy vegetable in Sri Lanka. Most of these plants are typically grown well related to aquatic environments like drainage lines, irrigation channels, or water-retaining lands.
For more than a century that the synthetic pesticides of conventional farming leave heavy metals in the ground and washed out to water bodies. The special case related to leafy vegetables is their high ability to absorb heavy metals from that contaminated soil, irrigation water sources as well from polluted air. In here, nickel (Ni), chromium (Cr), lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), and cobalt (Co) came into the topic, on account of their solubility in water and soil solutions as well ability insolubilization by root exudates. Although plants need a certain amount of these heavy metals as micronutrients to complete their biological activities.
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| Image by S. Hermann & F. Richter from Pixabay ( Free Commercial Use ) |
Recently, a number of studies have shown that a considerable number of market fruits and vegetables are highly contaminated with heavy metals than the preferred dosage for human consumption. The University of Sri Jayawardhanapura collaborating with the Sabaragamuwa University of Sri Lanka conducted a study around the Colombo district (Wellampitiya, Kolonnawa, Kottawa, Piliyandala, Bandaragama, and Kahathuduwa) and subjected to research on main three metals (nickel (Ni), cadmium (Cd), and copper (Cu)) for their analysis. Samples were collected as leafy vegetables, irrigation water, and soil in the leafy vegetable cultivated areas and tested using atomic absorption spectrometry. The confusing results showed that the average concentration of Ni, Cd, and Cu in cultivated soil were 51.5 ± 45.5, 1.4 ± 1.1, and 66.5 ± 59.5 mg kg−1, respectively. But the above-mentioned research was detected the highest concentration of Ni in irrigation water in the Wellampitiya area (2.02 mg L−1) which was higher than the FAO permissible amount (0.2 mg L−1). In leafy vegetable samples, the mean concentrations (mg kg−1, dry weight basis) of heavy metals were measured as 0.23 for Cd, 12.6 for Cu, and 7.62 for Ni. The highest contamination of Ni, Cu, Cd was found in the Kollonnawa area than FAO/WHO defined permissible maximum level of above heavy metals intake per day. According to those researches, they found out “Kohila leaf” is the highest accumulator among all other leafy vegetables.
Unfortunately, recently conducted several studies related to leafy vegetables from urban and suburban markets areas gave considerably high amounts of each and every previously called heavy metals with market available vegetables including leafy vegetables. But still, the researchers trying to figure out the exact reason for the high amount of contamination of heavy metals in natural foods.
The considerable levels of heavy metals found in leafy vegetables might be closely related to the contaminated soils and irrigation water, fertilizer, and pesticides, or due to the atmospheric deposition of metals on plant surfaces during their production, transportation, and marketing. Some countries like Nigeria has found that their vegetables, fruits, and leafy vegetables are contaminated with heavy metals with polluted air in town areas.
However, long-term intake of heavy metals contaminated leafy vegetables in high amounts can cause numerous health hazards in the human body other than it is an organic food product. Thus, the studies/ researches related to leafy vegetables and heavy metals highlights the potential risks involved with the consumption of leafy vegetables cultivated in contaminated areas which may adversely contribute to the food quality and safety.
So that researchers worked on this heavy metal contamination until finding a key to a way out of this issue. Even though there are several techniques to reduce the metal content in vegetables and fruits which listed as cooking, boiling, washing and soaking, frying, roasting, or grilling, etc. cannot be applicable with leafy vegetables. Soaking and washing, pre-boiling are the least relevant which is not much effective and less practicable with leafy vegetables. But another study conducted by the Sabaragamuwa University of Sri Lanka was tried to figure out these processing techniques for leafy vegetables. There were three main processing methods were tried as raw, cooked, and stir-fried, and traced the elements using atomic absorption spectrophotometry. Then data were analyzed. According to the results of the study, there was no significant difference with the above-selected processing methods for heavy metal reduction in leafy vegetables. Some research studies have found that,
So, the most precise solution would be the detection method for heavy metals in fast technique and prevention of soil, air, and water pollution by reducing heavy metal added pesticides, herbicides, and fertilizers.
What we can do as Sri Lankans is controlling to pollution of water bodies, soil, or the air as much as we can. Limiting chemical fertilizer use, instead of organic fertilizer which we can freely available, proper purification of drainage water from industries, and monitoring regularly water quality, functioning of food standers and regulations to avoid contaminated food marketing as well regular consultation of normal people about what they sell and what they buy from the market and future effects on long term exposes to heavy metal contaminate foods like leafy vegetables. This is very important work that should strengthen the long-term prevention and short-term prevention methods too. If not, all we have to live in a poisoned world with unhealthy food, air-water, or soil. The main target of this article was to show the recently immerged critical problem in our country related to food. Because we have to overcome this situation before our young generation gets weak in the near future.
Article by Yashmi Jayaweera
( BSc. Agriculture, RUSL )
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