This document specifies a test method for determination of the aerobic biodegradation of plastic materials exposed in seawater using accelerated conditions in laboratory. This document specifies the general requirements of the apparatus, and the procedures for using the test methods described. Biodegradation is determined by measuring oxygen demand in a closed respirometer or CO2 evolved from plastic materials when exposed to seawater. This test method is designed to give an early indication of the potential biodegradability of plastic materials. In addition, a method for analyzing resin-derived organic components in the test flask is further described as a determination method of the aerobic biodegradation of plastic materials instead of O2 and/or CO2 analysis. This document is not suitable for the assessment of disintegration caused by heat or light exposure.