80's animated films with dark themes
I remember living through an era where animated movies with dark themes to them were comon place. The Hobbit, The secret of Nimh, The last Unicorn, Wind in the Willows, all of them I vividly remember and recall the names of, however one such movie's name strongly eludes my memory, I remember in vivid detail that it starts, there is a Haz-mat truck crash, the truck spills a deadly gas from a rupture in it's trailer that seems into the nearby forest almost instantly killing anything it comes in contact with. During the movie the main character is trying to evade/find where the gas has not gone yet and where it is coming from/find a cure for someone close to them that was exposed to the gas. At one point in the movie you see people cleaning up the dead vegatation while trying to contain what remains of the leaked gas. I'm not sure if this is enough information about the movie or not to finger the film, but I know that it comes from the late 70's to the early 90's (no latter than 92) Is an animated movie (since the main characters were not people) and is possibly one of the "lost movies" from that erra that is just waiting to resurface much like a few of the others from then did. Any help would be very appreciated
