Not one of the 31 lakes in Bangalore has water that is fit for bathing, let alone drinking, going by the official rules for classification laid down by the Central Pollution Control Board. But last week, after five days of festivities as part of Ganesh Chaturthi, samples collected from the lakes indicated that the water bodies had slipped from Class C and D to E.
The Pollution Control Board collected samples from all water bodies one day before immersions commenced and on the sixth day of the festival. According to CPCB guidelines for classifying inland surface water, water classified as E has pH between 6.0 and 8.5, and can only be used for “irrigation, industrial cooling and controlled waste disposal”.
Puja debris
Interestingly, the parameters that have spiked when the samples are compared indicate that the real culprit is organic waste, that is mainly puja materials immersed along with the Ganesh idols.
In all four lakes that the Karnataka State Pollution Control Board — Sankey, Lalbagh, Yediyur and Shivapura lakes — released data for the dissolved oxygen values and biochemical oxygen demand (BOD), showed significant changes. Dissolved oxygen values saw a decrease by around 25 per cent. For instance, in Yediyur lake the values fell from 10.3 milligrams/litre (mg/l) to 2.5 (minimum permissible limit is 4). Similarly, another critical parameter, BOD increased from around 4 mg/l to 14 (when permissible limit is 3).
Aquatic life hit
All these figures indicate that water quality deteriorated significantly, and aquatic life in the lakes has been affected.
However, both these changes are attributed to puja material, rather than the paint on the idols. Successive campaigns on ecofriendly Ganesh idols have focussed on dissuading people from using painted Ganesh idols, but these numbers indicate that dumping of material used in pujas — such as plantain leaves, flowers, curd and ghee — have led to greater deterioration of water quality.
Other indicators
The pH value of the water (indicative of its alkalinity) increased by around 7 to 8 per cent for all the lakes after immersions: this owes to plaster of paris, adhesive materials and paints. Metallic content remained undetected for most samples, barring Lalbagh lake where 0.001 mg/l of mercury was detected after immersions. Iron content increased in almost all surface water samples (increased significantly in Lalbagh and Shivapura lakes). Lake sediment analysis, however, showed huge increase in ferrous (iron) content, and small increases in mercury traces too.
Encouraging statistic
An encouraging statistic this year is that around 20 per cent of the idols immersed in immersion tanks were made of clay. “This is encouraging. This means that people are realising that painted idols are ecologically damaging and are becoming sensitive. Now, we need to create awareness on dumping of puja material and convince people to reduce the size of the idols they use,” said Karnataka State Pollution Control Board Chairperson Vaman Acharya.
