Abandonment
noun, する verb
Something you throw out and abandon has been sent to the realm of abandonment.
とうき
This is a jukugo word that uses the on'yomi readings of the kanji. You learned the on'yomi for 投 when you learned 投資 a long time ago.
それが不法投棄になるとは知らなかったんです。
I didn’t know it would be unlawful dumping.