Work Item
ASTM WK80360

Revision of D7991-15 Standard Test Method for Determining Aerobic Biodegradation of Plastics Buried in Sandy Marine Sediment under Controlled Laboratory Conditions


The current D 7991-15 requires the use of filter paper as the reference material (clause 7.6). This is a suitable reference material. However, also microcrystalline cellulose (widely used in many other standard test methods as a reference material), cotton can be applied as a reference material, especially when the test material is tested as a powder. It is proposed to also include microcrystalline cellulose as a reference material.

7.6 Reference Material—A cellulose filter paper for laboratory purposes, or microcrystalline cellulose , or cotton . Determine the carbon content as described in 7.5.

The current D 7991-15 suggests the use of a technical control as an option, with three replicates (clause 9.1). The technical controls are empty reactors that contain only the absorbing solution and no sediment. Considering that this test can last a long time (even two years), in order to identify potential problems due to the reduced gas permeability of the equipment, at least a technical control should be mandatory.

9.1 Test Set-up—Prepare at least the following number of reactors (6.1): a) three reactors for the test material; b) three reactors for the reference material; c) three reactors for negative control (optional); d) at least one reactor for the technical control; and (e) three reactors for the blank.


The current D 7991-15 contains some text that points to wrong equations. These typos must be amended.

The pH shifts of reactions (Eq 8) and (Eq 9) are superimposed and cannot be distinguished. Only a single end point in the range of pH between 7 and 8, corresponding to the two reactions, can be identified by using a suitable indicator.
The adsorbed CO2 can be determined by subtracting from the H+ equivalents needed to neutralize the original KOH solution and the H+ equivalents needed to neutralize the reactions (Eq 8) and (Eq 9). In practice:
mmol CO2 = [mL HCl consumed (Eq. 7)
- mL HCl consumed in (Eq. 8)
- mL HCl consumed in (Eq. 9) end point]*N HCl

where N is the normality of the HCl solution.
If an endpoint titrator is available the mmol of CO2 can be determined, without using an indicator, with a further reaction. A further addition of HCl makes HCl react with KHCO3, produced with reaction (Eq 9):

KHCO3 + HCl?H2CO3 + KCl at pH 4 (11)

The number of equivalent consumed in reaction (Eq 11), and therefore in reaction (Eq 9), corresponds to the K2CO3 produced during reaction (Eq 6) that in turn corresponds to the absorbed CO2. Consequently, 1 mole of KHCO3 corresponds to 1 mole of CO2 reacted in (Eq 6):


Developed by Subcommittee: D20.96

Committee: D20

Staff Manager: Alyson Fick

Work Item Status

Date Initiated: 01-04-2022

Technical Contact: Francesco Degli Innocenti

Item: 023

Ballot: D20 (22-03)

Status: Ballot Item Approved

Item: 002

Ballot: D20.96 (22-01)

Status: Will Reballot Item

Item: 001

Ballot: D20.96 (22-01)

Status: Will Reballot Item