( ( Hydrogen ( sulfide gas ) ) ( ( can ( be ( ( ( formed and ) released ) ( whenever ( ( waste ( containing sulfur ) ) ( is ( ( broken down ) ( by bacteria ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Hydrogen) (NN sulfide) (NN gas)) (VP (MD can) (VP (VB be) (VP (VBN formed) (CC and) (VBN released) (SBAR (WHADVP (WRB whenever)) (S (NP (NP (NN waste)) (VP (VBG containing) (NP (NN sulfur)))) (VP (VBZ is) (VP (VBN broken) (PRT (RP down)) (PP (IN by) (NP (NNS bacteria)))))))))) (. .)))
Hydrogen sulfide gas can be formed and released whenever waste containing sulfur is broken down by bacteria.
(ROOT (S (NP (NNP Hydrogen) (NNP sulfide)) (VP (VBZ is) (NP (NP (DT a) (ADJP (JJ noxious) (CC and) (JJ toxic)) (NN gas)) (VP (VBN produced) (PP (IN from) (S (VP (VBG decaying) (NP (JJ organic) (NN matter)))))) (SBAR (WHNP (WDT that)) (S (VP (VBZ contains) (NP (NN sulfur))))))) (. .)))