Refers to thick, muddy, often toxic sediment or waste, especially industrial or environmental sludge.
Sludge has built up on the riverbed.
Sludge from the factory flowed into the river.
Special equipment is needed to treat the sludge.
The factory regularly removes sludge from its drainage outlet.
In summer, the sludge in the pond gives off a foul smell.
Standard katakana spelling for this loanword.
Hiragana spelling; less common than katakana but still used.
Loanword from English 'sludge', adapted into Japanese as ヘドロ. The exact phonetic shift from 'sludge' to ヘドロ is uncertain, but it likely entered via early industrial or environmental terminology.