“…after researching for over an hour, I haven’t been able to locate any information or even studies on the actual impact assessment of the ‘biodegraded’ plastic. While I get that it can’t be deemed ‘compostable’ for a few reasons, I don’t see anything anywhere about the soil quality after having bio-plastics degrade in it or the impact on the micro-organisms that constitute the final phase of the degradation. If there are any studies available I would be very interested in reading them. Thanks.”
The comment was accidently deleted so in response to the question:
Bioplastics that are certified as compostable undergo tests that adhere strictly to the EN 13432 norm on compostability of packaging materials (EN = European norm) or ASTM D.6400 on compostability of plastics (comparable to ASTM D.6868 on compostability of coated paper). All norms are very similar to one another.
For certification bioplastics undergo the following tests:
1) Chemical analyses
3) Disintegration piolot-scale
4) Plant ecotoxicity test
Your question makes reference to the last point, which relates to compost obtained at the end of the composting cycle. For EN 13432 the ecotoxicity tests comprise 2 plant tests, namely the summer barley and the cress test. Both tests include germination and growth. The procedures followed are those prescribed in the German RAL GZ 251 and OECD #208 guidelines.
For more info I’d recommend contacting compostability certification bodies responsible for these studies.