You know those roles of black plastic you can get at Home Depot? What does the plastic have to be made of to be safe for lining a garden bed?
What if the plastic is exposed to sunlight - what plastic is still safe to grow edible vegetables from?
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Landscape fabrics are made of woven polypropylene which is considered to be stable, or safe, for organic gardens. As it is woven it will allow water through it. Cheap landscape fabric is not UV stable and tears like tissue paper after a while. I can't find anything about decay products even though manufacturers of commercial grade products describe them as "resistant" not impervious.
The commercial grade products I have used in retaining walls look good even after ten + years in close contact with the soil.
Given the short life cycle of vegetables any commercial grade fabric will do the job.Replace the fabric every ten years and you should be guaranteed not to have any contaminants.
Probably this is not safe. I found a PRODUCT SAFETY DATA SHEET for Polyethylene Sheeting, which includes the Husky brand sold at big box stores. It says:
This product is not FDA, CPSC or NSF compliant. It is unsuitable for use in applications such as direct or indirect food contact, toys, medical device or pharmaceutical applications or for potable water application.