This time around, they've come out with lab tests that show their pesticide residues are within limits and, while they continue to say the CSE testing protocol is wrong, they've announced their readiness to accept standards for their colas provided the testing protocols are properly defined, something the health ministry is working on right now.

Given that two government laboratories got very different results while testing Diet Pepsis from the same batch after the first CSE cola report, the testing protocol argument may have some merit.

• Soft drinks, hard truths

There is also a lot more purchase for their other argument that, if there are a lot more pesticides in milk and vegetables, why are they safe while colas are unsafe? One financial daily lead with a story titled "A handful of rice=34,180 colas", and then went on to say that two apples equal 30,200 colas ... You get the drift? Essentially, the CSE's targeting the colas because they're MNC (multinational corporations) products - why not expose the pesticide residues in milk and rice?

Before we get to the merits/demerits of this, it's worth knowing what Pepsi did after the CSE's allegations about the pesticide levels in its bottled water and soft drinks three years ago.

It changed the specifications of the carbon filter that the water was passed through, to make it more porous so as to be better able to trap the pesticides, and today the pesticide residue in the water is below 0.1 parts per billion - the CSE's report had said its bottled water's residue was 0.6 ppb.

As for the soft drinks, the time the sugar solution is passed through the carbon filters was doubled, from 7.5 minutes to 15, with the same result. None of this, Pepsi says, cost much - in which case, if pesticide residues have been reduced at no great cost, what's the problem?

The crux, as the financial daily pointed out, is the amount of pesticides we're ingesting through the food we eat. So, when it's argued we can drink 34,180 colas and still not have a problem, it's right, provided we're willing to forego that handful of rice. If we have both, we'll have ingested 68,360 colas' equivalent of pesticides.

This Acceptable Daily Intake of pesticide, that we can ingest every day of our lives without damaging our health, is set by various people - the World Health Organisation says it's okay to ingest 0.005 mg of DDT per kilogram of an individual's body weight, the Australians say 0.002 mg/kg's okay while the US says 0.0005 mg's the right amount - there's a different ADI for each pesticide.

Alongside this process, each time pesticide is sprayed on a crop, the Maximum Residue Limit, or the amount of pesticide that remains in the crop, is measured - this MRL for the same pesticide is different for each crop.

This MRL is then multiplied by the amount of food eaten in an average daily diet to get the theoretical exposure, or the Theoretical Maximum Daily Intake.

Add up all the TMDI, across all foods in the diet, and if this exceeds the ADI for that pesticide, you have to either stop using the pesticide for some of the foods eaten or simply drop the foods from your diet.

So, for instance, if your diet consists of only rice and colas, both of which have malathion residues, and the combined TMDI of malathion is greater than the ADI allowed for malathion, you have to give up either the cola or the rice.

Indeed, when the CSE did the TMDIs for various pesticides such as DDT, it found it was higher than WHO's ADI by 376 per cent; for monocroptophos it was 300 per cent higher, the list goes on.

Hence, the CSE argued it was time to stop drinking colas since we clearly can't do without the rice or other vital parts of the diet. Again, there's a dispute here as Pepsi says TMDI is a maximum whereas the actual is more likely to be around a third of this - its contention is India's pesticide intake is well below the maximum ADI, and cites some government studies to back this.

The CSE, in turn, cites other government studies that show the pesticide ingestion is greater than the ADI for certain pesticides! And though the government here does not take samples of all the food in a person's diet to test the actual pesticide residue in them, unlike in the case of countries like the US, the CSE cites private researchers who did a similar exercise in Kanpur and found the ADI had been exceeded.

This is the CSE's real contribution. Till it first blew the whistle three years ago, the MRLs for just 40 per cent of the 180-odd pesticides used in the country were notified (if you don't have the MRL, you can't even begin to calculate the TMDI!).

In many cases, while the pesticide is approved for use on various crops, the MRL has been checked and notified for just one of the crops. Indeed, in March this year, the health secretary himself admitted that, in the case of the 24 pesticides required for (just) sugarcane, MRLs still had to be fixed for 12!