Chinese Mystery Snail in the Sydenham

On friday I found snail shells I had not seen before.  There were a many snail shells on the mud flats under the bridge where in the previous year I only observed native mussel shells. I put some in my pocket and looked up the species when I got back to the office.  Turns out that this invasive Chinese Mystery Snail that I found competes with our native snails. 

Shells that I found on the clay/mud flats of the Upper East Sydenham.

Bummed out by my discovery, I  read a little more.  According to the Indiana Department of Natural Resources"Chinese mystery snails can serve as vectors for the transmission of parasites and diseases.  Some of the parasites and diseases that the Chinese mystery snail has been known to play host to can infect humans.  Their shells will clog the screens of water intake pipes inhibiting the flow of water.  Also, they naturally compete with our native snails for food and space. "

Is it too late to use copper sulphate?  http://www.mailtribune.com/apps/pbcs.dll/article?AID=/20100812/LIFE/8120306/-1/NEWSMAP  How would this treatment effect native species? Most importantly: Why are invasive species, plants and animals, still sold at places such as pet stores, nurseries, kijiji, and live at food marts (by the bag full)?

Chinese Mystery Snail - internet photo

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