You travel on a road in Chennai. You notice smoke from other vehicles and a mound of unsegregated solid waste on the side of the road. Maybe you are in a hurry to reach your destination, and you may not process these scenes. But next time, take in those sights. They are polluting Chennai’s soil with heavy metals.
Heavy metals are those metals that have greater atomic weight in the periodic table of elements. Moreover, in higher quantities, these metals can become toxic. Examples of heavy metals include Lead, Cadmium and Mercury.
Soil pollution due to heavy metals studied in Chennai
A group of researchers from Bharathidasan University in Tiruchirappalli studied the soil in Chennai to assess the extent of heavy metal contamination. They took 155 samples of soil across the extent of the region that comes under the Greater Chennai Corporation for this study. Cadmium, Chromium, Lead, Zinc and Copper were the five metals considered for the study.
“These five metals were more predominant in the samples than the other metals across the study area,” says G Kannan, one of the authors of the study and a Chennai-based IT professional pursuing PhD at Bharathidasan University.
The researchers initially took samples from the coastal areas of Chennai from Uthandi in the south to Ennore in the north of the city. Then, they planned to cover the interiors of Chennai, studying the soil in marshlands, industrial areas, hospitals, educational institutions and public parks, says Kannan.
Out of the 155 sample locations, 122 locations were found to have a very high degree of soil contamination due to heavy metals.
Trends and extent of heavy metal contamination
| Source of soil pollution | Heavy metal(s) generated | The area affected in Chennai |
| Large and small-scale industries | Cadmium, Lead, Copper and Zinc | Central and North Chennai |
| Over usage of vehicles and emissions | Zinc, Lead, Chromium and Copper | Almost all areas in Chennai |
| Unsegregated solid waste disposal | Cadmium, Lead, Zinc and Copper | Almost all areas in Chennai |
| Hi-tech computer industries and tourist boat activities | Zinc | South Chennai |
| Thermal power plant and fishing activities | Lead, Copper and Zinc | North Chennai |
The table above highlights the anthropogenic sources of metals that contaminate the soil in different areas in Chennai.
Lead, Copper and Zinc have very high contamination in 13 locations, near Adyar, Valasaravakkam, Velachery, Anna Nagar, and Ennore where small- and large-scale industries are present, found the study.
Cadmium pollution has been found in the soil across the city and Chromium has the lowest levels of contamination.
Cadmium > Copper > Lead > Zinc > Chromium: This is the decreasing order of metals contaminating the soil in Chennai, as per the study.
“Moreover, Cadmium is present all over the GCC region, and not specific to one or few parts of the city. The major cause of this metal polluting the soil is improper solid waste disposal,” says Sajimol Sundar, another author of the study and a Project Scientist at the National Centre for Coastal Research in Chennai.
Causes of metal-induced pollution
“Vehicular pollution caused due to wearing of tires and leakage of motor oil gives rise to heavy metals like Copper, Zinc and Lead,” says Sajimol. “In North Chennai where the seashore is close to the roads. So the vehicular emissions may enter the sea easily.”
“There is a greater presence of e-waste in South Chennai, which also contributes to the increase in heavy metals in soil,” says Kannan, talking about the influence of IT industries in the area.
For instance, improper disposal of batteries can contaminate the soil with Cadmium, says Sajimol.
Kannan also says that North Chennai faces more soil pollution due to these metals compared to other parts of Chennai due to the activities mentioned in the table above. For instance, the levels of Lead in the soil is greater in the northern part of the city, owing to the presence of many industries and the thermal power plant.
“The burning of fossil fuels in these industries also contributes to high levels of Lead,” says Sajimol.
In the soil in other parts of Chennai, the presence of Lead is relatively less due to the ban on leaded petrol in the country, illustrates the study.
Soil pollution is not a standalone issue. Water, air and soil pollution are connected, say the experts.
“The surface and interior sediments in the soil consist of particles from air and water too,” says Sajimol.
For instance, during monsoon, the run-off water from roads may contain heavy metal particles due to vehicular emissions, that will enter stormwater drains. This water will find its way into other major drains and the sea. Moreover, if there are recharge wells or pits, then the rainwater from the road may get recharged. Therefore, the groundwater may also contain heavy metal substances.
Garbage dumping happens in marshlands, due to which, the metals may even enter the sea.
“If solid waste is discarded in a dump yard, the metals may leach into the soil via stagnated water also,” says Shyamala Lionel, an Assistant Professor of Chemistry at Madras Christian College who has researched heavy metals.
Read more: Why I segregate waste at source despite a broken waste management system in Chennai
Effect of heavy metals on health
“If these metal substances enter the sea, then phytoplanktons may take them up. The fish in the sea may eat those phytoplanktons. When a human eats those fish, the metal substances may enter their bodies,” says Kannan.
Another way is for people to inhale the heavy metal particles that are suspended in the air or consume polluted groundwater.
“Cows may eat grass that could have grown on polluted soil. Drinking the milk of those cows can also lead to heavy metals entering the bodies,” says Shyamala. “This is called bioaccumulation, where heavy metals build up in living beings without releasing them. When the concentration of heavy metals crosses the lethal level in a living being, we may experience adverse health effects. That lethal level is different for different metals.”
The ecological risk due to greater levels of Cadmium is higher than that of the other four metals. Cadmium may cause might lead to cardiovascular diseases, developmental abnormalities, hearing loss, and cancer, notes the study.
“Lead could reach the food chain and could get into human bodies. Lead can replace Calcium in the body. Also, if pregnant women accumulate Lead in their bodies, their babies may be affected by phocomelia, a genetic disorder,” says Shyamala.
Heavy metals polluting the soil can have grave health effects. “It can almost affect every part of the body, including the nucleic acid in the DNA,” says Dr Sudharshini Subramaniam, public health expert.
“Since North Chennai is relatively more polluted, the residents of the region are highly susceptible to cardiovascular diseases, respiratory problems, eye irritation and carcinogenic issues due to high levels of Cadmium,” says Kannan.
“Metal-induced pollution may not seem like a serious problem now. But in few decades, the environment will not be livable and sustainable in Chennai if we let this issue go unchecked,” says Kannan.
Flora and fauna are also affected due to heavy metals contaminating natural resources.
“For instance, in an area which is supposed to support ten trees, one may find only two trees due to heavy metals polluting the soil,” says Kannan.
Read more: Can climate change influence tuberculosis cases in Chennai?
Remediating soil pollution
Awareness: Before finding ways to remediate soil pollution caused due to heavy metals, one should understand the causes and effects of the pollution.
“PET (polyethylene terephthalate) bottles, liquor bottles and worn-out vehicle tires, apart from industrial waste are dumped in the city which contributes to metal pollution,” says Kannan.
“The public must become aware of the ramifications of heavy metal pollution in the soil. The industry owners must make sure they do not indiscriminately dump waste in the land and waterbodies,” says Kannan.
Bioremediation: “To reduce the impact of heavy metals in soil and water, bioremediation is a solution,” says Sajimol. “This will reduce the toxicity from the metals.”
Shyamala talks about how certain plants can be used for bioremediation. “For heavy metals, we can choose appropriate plants that can either store the toxic contents of the heavy metals or process the toxic substances to relatively non-toxic components,” she says. “In some years, the toxicity of the soil will reduce.”
But there is a caveat. “Such plants must not be consumed by any animal or human, as they could enter the food chain.”
Ultimately, prevention is better than cure for soil pollution. The issue of rampant heavy metal pollution reinforces calls for Chennai to take garbage dumping, vehicular emissions and industrial pollution seriously.