When something is described as compostable an ordinary consumer would think it can be converted into compost, but the Standards for
this type of plastic(ASTM D6400, EN 13432 etc.) require it to convert into CO2 gas within 180 days. You cannot therefore make compost from
it - only greenhouse gas. This process contributes to climate change but does nothing for the soil, and it cannot be described as organic
recycling.

The Federal Trade Commission of the USA has said that it is not sufficient to show that a test item had complied with ASTM D6400 or D6868
[or EN13432 or the ISO equivalents].

"Compostable"(also loosely known as "bio-based plastics" or "bio plastics")and designed according to EN13432 or ASTM D6400 to biodegrade in the special condtions found in industrial or anaerobic digestion.
From Chris Packham

Oxo-biodegradables, Research has shown that moisture retards the oxidation process, delaying the potential onset of biodegradation.
In addition, for landfills, no data has been presented to support complete biodegration in anaerobic environments.

Data has shown that at high temperatures in conjunction with UV in arid condtions, that frag mentation can be achieved in 2 to 3 months.
However, fragmentation is not a sign of "biodegradation" and there is no data to show long these plastic fragments will persist in the soils
or marine environments.
From Biodegradable products institute

Oxo-biodegradable materials were not included in NOP petition, because they did not fulfill the two criteria proposed to address the concept
of "fully biodegradable plastics".
From Farmerpam

The NOP considers PLA to be synthetic because PLA is chemically polymerized(Briassoulis and Dejean,2010).
While the PHA polymer is made directly by microoranisms in the fermentation process (thereby considered "natural" by the NOP),
it is highly crystalline, making its end product more brittle, and less desirable, unless blended with PLA or other co-polymers (Hayeset al., 2012)

Some processes that are used to form biodegradable polymers utilize additives.
Some additives are derived from petroleum and/or are chemically processed, and are therefore considered synthetic material by National
Organic Program(NOP) standards(Hayes et al., 2012;NOS,2012), which has preventes their use in U.S. oragnic agriculture.
Thre environmental impact of many additives may be a major concern in organic as well as conventional corp production

In the U.S., organic corp producers have not been able to use currently biodegradable plastic mulch products because these products did not
conform to NOP standards. To be acceptable for organic production, biodegradable plastic mulch must be entirely composed of constituents derived fro, natural resources(bio-based), cannot contain synthetics such as petroleum-derives ingredients or additives, and cannot be
chemically modified during the manufacturing process(NOS, 2012; Corbin et al.,2013;Corbin et al.,2009). An additional requirement to meet
the organic standards is that feedstocks, such as corn, used to produce the polymer, must be free of genetically modified organism(GAOs).
Similary, any polymer made from microbial fermentation, such as PHA, must be producerd by organisms that have not been genetically
modified.

The Organic Standards are inconsistent, as 205.206(c)(1)permits "mulching with fully biodegradable materials " but 205.206(c)(6) requires that "plastic or other synthetic mulches... are removed from the field at the end of the growing or harvest season."