Why have some chemicals been banned from usage in agriculture/food production

okay so to tell the story short:

Explanation:

over the years farmers in agriculture businesses have decide to use safer chemicals. because since people have been getting food poisoning and been getting sick. but now farmer businesses now use some chemicals that have very low toxicity. When pesticides were first introduced, farmers were using chemicals that were very toxic. but then that's when they realised that the they had to be removed from the application and today they have been replaced with better and healthier ones just like (glyphosate.)

they are made of gases.

they have a spherical shape.

they make energy through fusion.

i'm pretty sure its b i might be wrong though!