Rats are really a nuisance in my parents' home. We don't really get a lot of them, probably a couple in two weeks. But they are troublesome. They noisily run around our ceiling, disrupting our sleep. And they also eat our grocery items, linens, etc. Even wood. Whatever they can put their teeth on, they chew.
We only use one rat killer, and that is Racumin Rat Bait by Bayer. Racumin is very effective, It is a cereal-based rat poison that contains coumatetralyl. It effectively kills rats.
But there is a downside to it. When the rats (or mice) eat the bait, they don't die instantaneously. And they have to eat quiet some amount for the poison to be effective. The problem with this is, they go off somewhere before they die. When this happens, sometimes they are stuck in some compromising position that we know not of. Sometimes, we can trace the body, sometimes we can't. When the latter happens, we will have to endure the smell of a dead rat inside the home until it is fully decomposed. This problem really is for the home, that is why in my in-laws' home where rats also abound, we cannot use Racumin. Why? We live in a three-storey commercial building with a lot of doors and rooms and stairs and very few windows that we will probably have to tear the entire house down before being able to locate a dead rat.
But in the garden, the Racumin Rat Bait is very good. After all, the rats run around freely there and when they die, their dead bodies will just rot away into the ground.
In terms of being environmentally safe, I am not sure. But since it is made by Bayer, I believe Bayer has secured this problem already.
This rat poison is definitely a good buy for a box of something like $3.