Because the agencies which are suppose to regulate such things have left it open, not closed.
Some where in the 1970's the US EPA decided that Dieldren, Aldrin and the chemical similar compounds were bad. They restricted the use of the organophosphates so they could not be used for agricultural products.
They also declared that the were carcinogens of a type.
In 1987 they banned all use of dieldren, but they did NOT regulate dieldren nor did they create a maximum contaminant level (MCL) for its presence in drinking water.
By now you are saying, "Huh?"
Well so am i. This of cource leads many others to question what was going on.
The US EPA is still on record as declaring dieldren a carcinogen, but they simply do not back it up.
now others start asessing the issue:
In 1987, the US Environmental Protection Agency(EPA) classified aldrin and dieldrin as category B2 carcinogens, i.e. probablehuman carcinogens, based largely on the increase in liver tumors in mice fedeither organochlorine insecticide. At that date, the relevant epidemiology wasdeemed inadequate to influence the cancer risk assessment.
There is more
There is no conclusive evidence that aldrin ordieldrin cause cancer in humans. Aldrin and dieldrin have shown to cause livercancer in mice. The International Agency for Research on Cancer (IARC) hasdetermined that aldrin and dieldrin are not classifiable as to humancarcinogenicity. The EPA has determined that aldrin and dieldrin are probablehuman carcinogens.
Okay so what is the big deal?
The US EPA has again failed.
With Radon they threw a lot of money to get all the states on board the issue, even thought there was evidence that this was not as big a deal as they made it. (National Science foundation really link the cancer to a serious issue for those who smoke). They did not do this with the pesticide, thus we have controversy.