Difenacoum is a coumarin

Coumarin

Coumarin is a fragrant chemical compound in the benzopyrone chemical class, found in many plants, notably in high concentration in the tonka bean , vanilla grass , sweet woodruff , mullein , sweet grass , cassia cinnamon and sweet clover...

 derivative. It has anticoagulant

Anticoagulant

An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...

 effects and is used as a rodenticide.

Uses

Difenacoum is sold as blue-green pellets intended to be ingested by pests such as rats and mice.

Safety and toxicity

Because other species of mammals and birds may prey upon affected rodents, there is a risk of secondary or tertiary exposure.
Using radiolabled isotopes, difenacoum (and/or its metabolites) has been shown to be distributed across many organ tissues upon oral ingestion, with the highest concentrations occurring in the liver and pancreas.

Difenacoum has been shown to be highly toxic to some species of freshwater fish and green algae despite the fact that difenacoum is weakly soluble in aqueous solutions.