Toxicity of materials
It used to be the pigments (white lead, cadmium yellow, etc.) which caused problems in life, but these have been superseded and eliminated. Now the things that cause concern are additives and contaminants. Brittle polymers like PVC require large proportions of plasticisers to make them usefully flexible (particularly as tubing). 30 years ago phthalate plasticisers were causing concern in cling film for human food use, and I don't suppose vinyl chloride monomer (a carcinogen ) levels were monitored as carefully as they are now.
I did try asking Eheim what materials they used but they informed me that they do not disclose this type of information - it might have worked better if I had asked specific questions (eg. if they still use phthalate plasticisers in tubing?). It is likely that producers have moved away from butyl esters (which have caused harm to terrestrial plants in commerce) towards iso-octyl esters as concern increased, but many plastics have characteristic odours which are only chemicals being released to the atmosphere - who knows the effect in the aquatic environment?
There are many other chemicals used - eg. flow modifiers and stabilisers - to help processing, and some of these used to include tin compounds. There is a tin compound [TBT tri-butyl tin (??)] which was used as an anti-fouling agent on boats until it was found to be causing feminisation of molluscs (whelks?) in the sea.
There was a feeling that squid are even more difficult to keep in polyethylene (polythene) containers (for more see - Tank setup and maintenance - fiberglass screen - topic)
All we can do is be careful what we use and learn from what we observe.