Steve, thanks for your thought on polyethylene - maybe feelings can be checked out or trouble avoided. I too have heard that polycarbonate is the best material for water (mineral water is sold in that or glass), and can still remember polyethylene water containers used to impart a characteristic odour to the contents! Home brew kits in UK still use 5 gallon polyethylene containers, and I have carried a lot of water in those.
This would be my favorite material for an environmentally friendly container - a simple, relatively inert starting substance producing a product with useful properties. Most other starting materials for polymers are inherently more toxic - Vinyl Chloride, Styrene, Butadiene, Acrylic and Methacrylic esters, Amides, and the base for polycarbonate (which I cannot remember, but is another to be avoided if possible!), etc.
I do not know what materials are used in production apart from ethylene (a gas), except iron is probably used as a catalyst in the polymerisation. The product would be substances with increasing molecular size and inertness as polymerisation proceeded but I suppose that these could contain a 'reactive' double bond, and ethylene itself does have the (physiological) effect of ripening fruit (and flowers).
My other thought is that squid might not avoid physical contact so easily with something 'softer' or less dense than rock?
Sorry if this is getting technical - I don't know if it is helpful in a forum like this but it is at least making me think, and where else do the finer details of our effects on life come from?