Blackspots across the city may be temporary in nature, but may leave behind a longer-lasting effect on the soil of Bengaluru.
Researchers from Bharathiar University (Tamil Nadu) and St. Joseph’s College (Autonomous) and Christ Deemed to be University in Bengaluru sampled seven dumpsites in the city and tested the soil on physiochemical parameters as well as on vegetation parameters. These figures were compared with similar tests on ‘undumped’ soil next to the dumpsites.
Researchers found that the soil in the dumpsites were more alkaline due to degrading organic waste, while the electrical conductivity was found to be 1.5-fold higher than that of non-dumpsites due to the leaching of sodium and potassium salts from the waste.
“Minerals such as nitrogen, nitrates, potassium, phosphorous, sulphates, sodium, calcium and magnesium content were found to be in slightly higher levels (up to 21% more) in dumpsite soils as compared to the non-dumpsite soils,” notes the study authored by Johny Joseph from the Department of Botany, Bharathiar University, Coimbatore. The study was published in the Journal of Applied and Natural Sciences recently.
More alarmingly, the concentration of heavy metals, such as cobalt, chromium and lead, were found to be 74% more in dumpsites than in adjacent non-dumpsites.
These become a cause of concern considering that there are hundreds of blackspots and areas of municipal dumping, which may be leaching into the soil or into waterbodies when it rains, says Jayarama Reddy, Department of Botany, St. Joseph’s Post Graduate Centre, and one of the authors of the study.
While the studied dumpsites have been used between 2.6 to 9 years, the toxic effects of the waste is discernible from the third year itself, he added. “The dumpsite will be cleaned and newer sites chosen, but the toxic effects will linger for long. The presence of batteries, old medicines and plastics contributes to the leachate that will percolate into the soil,” he says.
An analysis of plants at the dumpsites revealed that the soil harboured lesser plant diversity. There were 13 plants common across non-dumpsites while it was just six among dumpsites. The soils also allowed certain plants to thrive while others withered.
“The plants that thrive in the soil are better at absorbing heavy metals and other nutrients. They can be used for bio-remediation to reduce the toxicity of soil,” said Prof. Reddy.
However, these plants also point to bio-magnification of heavy metals where plants will have a higher amount of toxic chemicals, which will then be absorbed into the local ecosystem when smaller animals feed on them, he warns.
“There is a lot of research to be done, but there are concerns considering that garbage dumps are everywhere in the city,” he said.