Use of shell

 https://furusatobussan.jp/?mode=f3

https://www.noukaweb.com/shell-fertilizer/

https://kappa-egg.com/?p=1296

http://umdb.um.u-tokyo.ac.jp/DKankoub/Publish_db/2002Shell/02/02100.html

https://www.sbbit.jp/article/cont1/37864

https://www.spf.org/opri/newsletter/515_2.html

https://smilekodomo.com/takaragai-polishh/

https://www.city.koto.lg.jp/381104/kurashi/gomi/genryo/72439.html