1. 2) www.env.go.jp/water/marine_litter/2016.html
2. 3) www.env.go.jp/water/marine_litter/conf/c01-07/mat04_1-1-1.pdf
3. 4) www.spf.org/opri-j/projects/133th_Summary.pdf
4. 5) www.unic.or.jp/activities/economic_social_development/sustainable_development/2030agenda/sdgs_report/