USEPA (and OECD) provide guidelines for interpreting and applying the results from biodegradability tests (e.g., OECD 301 and 302 series studies). A “pass” for readily biodegradable is defined below. Based on this definition, and based upon the results of Menzies et al. (2022), do you believe that polyvinyl alcohol meets the criteria for passing?

Answer Explanations

• Yes

  Expert 5

  the 2 types of PVOHs in the Menzies paper passed the degradation requirements by EPA methods 301; they are water soluble, but to some degree sorptive.

• Yes

  Expert 3

  The results reported by Menzies et al. show that the criteria for passing the OECD biodegradation test, have been met in the tests performed and this was the case for both OECD 301 as well as OECD 302. For instance: the observed %ThOD exceeds the 60% threshold set by OECD.
  Overall the results thus suggest that polyvinyl alcohol indeed meets the criteria for passing. Also, given the chemical structure of PVA, it is highly unlikely that persistent degradation products at very low concentrations which are not included in the biomass, are being formed.

• Yes

  Expert 8

  Data reported in Menzies et al (2022) shows the four PVA tested (PVOH79, PVOH 4-88, PVOH 8-88 and PVOH 18-88) are readily biodegradable. Data on Figure 1 shows the four compounds produce more than 60% of theoretical carbon dioxide (ThCO2) production in less than 28 days, accomplishing the criteria considered in TG301B. These tests also appear to accomplish the additional requirement established in section (v) of EPA-HQ-OPPT-2009-0152-0002 about the 10 days period to move from 10 to 60% production of ThCO2:
  “(v) These pass levels have to be reached in a 10-day window within the 28-day period of the test. ... The 10-day window begins when the degree of biodegradation has reached 10% DOC removal, ThOD or ThCO2 and has to end before or at day 28 of the test. The pass levels of either 60% ThOD (or ThCO2) …”
  Data reported in Figure 2 and Table 1 for Test 302B shows the degradation can be even faster when working with higher biomass concentration in the tests. Table 1 shows results indicating that in 28 d only 3.2, 3.6, 3.7 and 4.5 % of DOC remain, which are more than the required 70%DOC removal, in fact more than 95%DOC is removed.

• Yes

  Expert 6

  All qualities of PVA/PVOH tested by Menzies et al. reach a level of >60 % biodegradation (based on ThCO2) within 28 days, and not a single replicate was below 60 % on Day 28. This provides conclusive evidence that, under the conditions of the 301B-based test(s) performed by Menzies et al., all qualities of PVA/PVOH tested satisfy the conditions to be labeled readily biodegradable without reservations.

• Yes

  Expert 7

  Background of ready biodegradability testing; The rationale behind the ready biodegradability tests is that any chemical passing these tests would be rapidly broken down in activated sludge plants and in most aerobic ecosystems. For such an approach to be valid, tests have to be extremely stringent. The stringency of the ready biodegradability tests is primarily ensured by precluding pre-exposure of the test item thereby preventing competent microorganisms to increase their numbers, and by minimizing the initial biomass concentration which delays the onset of biodegradation and limits the microbial diversity. Because of this stringency discrepancies in results obtained in individual OECD 301 tests with a single substance are common and inevitable. Conflicting results in ready biodegradability tests are therefore always treated by only considering positive results when the quality of these tests are well. This approach is also used by the competent authorities.
  Results found by Byrne et al (2021) and Menzies et al (2022) demonstrate that PVA meets the criterion of ⪂60% within 28 days. The results found by Byrne et al (2021) were disparate. The time window criterion of 10 days inserted within the 28 day period was not met. Byrne et al (2021) justly ignored this criterion because the time window is irrelevant due to PVA being a mixture of chemicals (Richterich and Steber (2001). PVA was therefore justly classified as readily biodegradable based on their results by Byrne et al (2021). All test results of Menzies et al (2022) allow classification of PVA as readily biodegradable.
  Gerike and Fischer (1979, 1981) demonstrated in a study with 44 chemicals that readily biodegradable substances are removed in activated sludge plants. Nearly all the chemicals which passed the screening tests were degraded in their simulation test of wastewater treatment plants. Based on their results and many other high removal percentages found by others, it is safe to assume high biodegradation percentages of PVA in properly operated and designed (SRT >10 days) activated sludge plants. The ⪂94% of EPA is in line with the science.
  Gerike P, Fischer, WK, (1979) A Correlation study of biodegradability determinations with various chemicals in various tests. Ecotox Environ Safety, 3, 159-173
  Gerike P, Fisher, WK, (1981) A correlation study of biodegradability determinations with various chemicals in various tests II Additional results and conclusions. Water Res., 5(1), 45-55.
  Richterich K and Steber J (2001) The time-window – an inadequate criterion for the ready biodegradability assessment of technical surfactants. Chemosphere 44 1649-1654.

• Yes

  Expert 1

  The experimental data presented by Menzies et al. (2022) show that the polyvinyl alcohol(PVA) that PVA meet the 60% theoretical carbon dioxide threshold before 28 days in the OECD 301B test (using activated sludge inoculum) and OECD 302B (Modified Zahn-Wellens) test.

  The polyvinyl alcohol meets the criteria passing because the authors (Menzies et al. 2022) have indicated that All PVOHs mineralized completely during the study reaching >75% ThCO2 by 28 d and >87% ThCO2 production at 60 d (Figure 1C) with negligible DOC remaining at study completion (<4.3% DOC), Table 1. Reproducibility was strong as evidenced by the low standard deviation among replicates.

• No

  Expert 2

  It very much depends on the receiving environment. It might qualify as a pass under certain circumstances, but for most environments I think the precautionary answer is no.

• Yes

  Expert 4

  Figures 1C and 2C in the peer-reviewed publication by Menzies et al. (2022) provide data that satisfies the definition of polymer biodegradability according to OECD. The data support the authors' conclusion that all PVOHs were mineralized completely in OECD 301B and 302B studies reaching >80 % biodegradation with negligible dissolved organic carbon remaining at study completion. I do think that the use of the terms "completion" and "negligible" in describing the conclusions over-extend interpretation of the data.