All 57 drinks samples tested by the Centre for Science and Environment (CSE) contained residues of three to five different pesticides, the group said, calling for stricter standards to be enforced in India.
The findings, which were spread over 11 soft drinks brands, add to the public relations problems facing Coca-Cola and PepsiCo in India, and threaten to knock their sales in a soft drinks market growing by seven to eight per cent per year.
The new CSE report echoes a similar study by the same group in 2003, which also found soft drinks in Delhi contaminated with pesticides at levels above international standards.
Soft drinks firms questioned the study's accuracy, but it was endorsed by India's Parliament, which asked for standards to be set on pesticides in fizzy soft drinks.
These have now been drafted by the Bureau of Indian Standards, but continued debate and lobbying has kept them from being fully implemented.
"This is a grave public health scandal," said Sunita Narain, director of CSE. She said CSE's new findings were "clearly unacceptable as we know that pesticides are tiny toxins and impact our bodies over time".
CSE has warned consumers to avoid Coca-Cola and PepsiCo drinks. It claimed to have found one drink containing the neurotoxin Chlorpyrifos at 200 times above the proposed safety limit.
Soft drinks makers in India rejected the findings. "Consumer safety is paramount to us. The soft drinks manufactured in India comply with stringent international norms and all applicable national regulations," said the Indian Soft Drinks Manufacturers' Association.
The association said it had spent three years working with the government, scientists and campaign groups to establish "stricter norms" for pesticide traces in drinks that complied with international standards.
Coca-Cola has stated previously that its drinks in India were confirmed safe by the Ministry of Health and Family Welfare in 2003. "In India, as in the rest of the world, our plants use a multiple barrier system to remove potential contaminants and unwanted natural substances, including pesticides."
CSE, however, said it was "even more confident" about its findings this time because its lab was accredited by the international quality standard ISO 9001:2000.
The lab also contained GC-MS testing equipment, a detection method used by many food scientists including those at the US Food and Drug Administration.
The Bureau of Indian Standards has set provisional limits of 0.1 parts per billion for individual pesticides in fizzy drinks and 0.5 parts per billion for total pesticide content.