"In virtually all types of tissue in every animal species, dioxin induces the production of enzymes that are the organism's trying to metabolize, or render harmless, the chemical that is irritating it."

Although I understand that answer, but explanation says that 'chemical that is irritating it' or ' chemical irritating it' are grammatically correct but wordy. I think use of 'it' is ambiguous here and so grammatically incorrect. 'It' can not modify 'organism's' because 'organism's is a possessive noun and so can be followed by possessive pronouns only. Is 'it' modifying something else here?

Please explain.

Thanks.