ASTM D5988-18 Determining Aerobic Biodegradation of Plastic Materials in Soil

Scope:

ASTM D5988-18 is intended to be used with any plastic material that does not restrict the growth of bacteria and fungus in the soil. This test technique evaluates the degree of aerobic biodegradation as soil is a valuable source of inoculum for testing the biodegradability of plastics in the environment since it contains so many different species.

Procedure:

ASTM D5988-18 consists of the selection of plastic material for the determination of aerobic biodegradability, obtaining soil as a matrix and source of inoculum, exposing the plastic material to the soil, measuring the carbon dioxide evolved by the microorganisms as a function of time, and assessing the degree of biodegradability. The CO₂ production measured for a material, expressed as a fraction of the measured or calculated carbon content, is reported with respect to time, from which the degree of biodegradability is assessed. The level of biodegradation expressed in percent is determined by comparing the BOD with the theoretical oxygen demand (ThOD). In using this alternative approach, however, the influence of possible nitrification processes on the BOD must be considered.

Data:

Proportion of biodegradation’s standard error Se is calculated, as follows:
S_e = SQRT [(S² test /n1) + (S2 blank /n2)] ×100/C_i
Where:
n1 and n2= number of replicate test and blank digesters respectfully
S= standard deviation of gaseous carbon
95 % confidence limits (CL) calculated by
95 % CL = % biodegradation ± (t × S_e)
t = t-distribution value for 95 % probability with (n1 + n2 − 2) degrees of freedom
thus n = 3 + 3 − 2 = 4.