They must be prosecuted, they are Absolutely Liable as expounded the Rule of Absolute Liability by Supreme Court in MC Mehta Vs Union of India.
Exemplary Punishment should be inflicted,
Its more dangerous than any kind of terrorism, it's not just killing humans slowly, but also the nature and the place of our living.
Think if we poison water of a house, we will be punished, even Attempt to murder, etc can be imposed, but if we poison the whole river then no case.
We need to reform our environment protection laws, enforcement is the key,