No...it's usually high density polyethylene which is one of the "safer" plastics when it comes to leaching.

In Tucson your biggest worry with it is probably going to be wind and sun breaking it down exposing tears (for the wind to whip) depending on how much is exposed during what time of year.

I love Tucson...my favorite place on the planet. It's a shame the winter rains weren't good enough for a heavy wildflower display this year. I generally try to get out there in good rainfall years in late March or early April to catch a piece of the bloom event.

What plastic degrades into depends somewhat on what that plastic was made of. Some plastics can degrade and leave behind toxins while others, biodegradable, do not appear to. However, the major problem is that many plastics stick around as small bits and pieces that birds and animals ingest.