ASTM D7991-22

5.1Plastic is sometimes carried by rivers or accidentally discharged by ships into the sea; this plastic can then reach different parts of the marine environment. Tides and waves also frequently deliver plastic marine debris into the sandy tidal zones.

5.2This test method simulates the environmental conditions found in the tidal zone. Plastic debris that reaches the sandy tidal zone can settle there and become partially or totally buried by sand and kept wet by waves or tides. It is of interest to assess the biodegradation behavior of plastic materials under these conditions to predict the removal time of this waste in the environment.

5.3This test method is applied to determine the extent of biodegradation of a plastic exposed in the laboratory to a sandy sediment kept wet with seawater. Both sediment and seawater are collected from a sandy beach in the tidal zone. If the natural microbial population present in the sediment is able to biodegrade the plastic, there will be an evolution of CO₂ as a consequence of the aerobic microbial respiration. The level of biodegradation at any given time is the ratio between the cumulative amount of the evolved net carbon dioxide and the theoretical amount produced in the case of total conversion of the organic carbon present in the plastic into carbon dioxide.

5.4This test method does not measure the amount of organic carbon that is converted into biomass, but only the biodegradation that leads to mineralization (that is, the formation of CO₂).

1.1This test method determines the biodegradation level of plastic materials exposed to laboratory conditions that simulate the environment found in the sandy tidal zone.

1.2The tidal zone, that is, the part of the coast affected by the tides and movement of the waves, is the borderline between sea and land, frequently a sandy area that is kept constantly damp by the lapping of the waves. Stony and rocky shorelines also exist.

1.3Plastic marine debris is frequently washed up in this habitat where it must be removed in order to restore the original landscape.

1.4It is of interest to know the biodegradation behavior of plastics when exposed to conditions simulating this habitat, because this information can help in predicting the time needed for the biodegradation of the litter.

1.5Biodegradation is determined by measuring the CO_{1.6Marine fresh-water habitats (for example, those found in brackish waters and estuaries) are not considered by this standard.}

1.7Reports shall clearly state the percentage of net CO_{Note 1:There is no known ISO equivalent to this standard.}

1.8UnitsThe values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.9This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.10This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.