Nausicaä of the Valley of the Wind1984

Yupa:
"Nausicaa! What are you doing here? This chamber is filled with toxic plants."

Nausicaä:
"I collected the spores and grew them down here myself. Don't worry the plants aren't poisonous."

Yupa:
"Not poisonous? Its true, the air is pure in here. But I know these plants from the jungle. These are some of the most lethal."

Nausicaä:
"I irrigated this chamber using water drawn from deep underground by the castle windmill. I used soil drawn from there as well. I found that with clean water and soil, the plants from the toxic jungle aren't poisonous. All the poison is in the soil. Even the topsoil in our valley is polluted. But...I don't understand. Who could have polluted the entire earth?"