It is said that lines could be still made with silk as used to be done in Japan as a countermeasure against pollution by nylon fishing lines. However, it is not clear whether or not silk fishing lines would be decomposed biologically in marine environments. To answer this question, seawater was collected at six stations at the entrance of Tokyo Bay and sterile raw silk threads (27-denier) were added to these seawaters. The final concentrations of raw silk threads in the seawaters were 0.5%. The six seawaters with raw silk threads [silk-decomposing seawater media (SDS media)] were incubated for 2 months at 20°C. The tensile strengths of the raw silk threads in the three SDS media were clearly decreased at least after 2-month incubation. The degree of decomposition of the raw silk threads, which were observed visually, correlated approximately with the ammonia contents of the SDS media. When the incubated raw silk threads were examined microscopically, it was shown that the raw silk threads were split into more and finer filaments after 1-and 2-month incubation. These results suggest the possibility of decomposition of raw silk threads in marine environments.
