The article never really explained that. I thought they were using a little more scientific method ie tracing the mercury through the sewer pipes.
What really amazed me is the quantity of "healing" cream and powder she brought back. How could any person need that much product for any treatment and how is it that she could bring 10 kilos of these mystery substances through customs?
The test the sewer lines. When the line comes up clean, they know they passed it and can narrow it down. Same thing here for chemical dumping.
What amazes me is how many people go to third-world countries and actually buy, use, or even believe some concocted remedy from there will heal all their ills. It's a third-world country for goodness sake, and India to boot. They don't even have proper sanitation yet she thought a bunch of cream and powder from there would give her a cure?