I spit toxic waste
Toxic Waste is a liquid waste material that can cause death, injury or birth defects to living creatures.
Spitting is a term that simply means to rap.
So Cassidy is using a simile to say the lines he spits are deadly (figuratively) like toxic waste (literally).
To help improve the quality of the lyrics, visit “11 Minute Freestyle on Hot 97” by Cassidy Lyrics and leave a suggestion at the bottom of the page