Modifiers matching dirt:

• organic,
• hydrophobic,
• visible,
• stubborn,
• difficult,
• off,
• persistent,
• industrial,
• dry,
• soluble,

Simple categories matching persistent:

• instability,
• disorder,
• condition,
• organophosphate,
• symptom,
• difficulty,
• affliction,
• disease,
• state,
• metal,
• infection,
• pesticide,
• problem,
• time,
• matter,
• material,
• aggression,
• information,
• event,
• contaminant,
• cause,
• bacteria,
• circumstances,
• volatile,
• discomfort,
• substance,
• insecticide,
• illness,
• organism,
• substrate,
• virus,
• herbicide,
• dirt,
• retrovirus,
• chemical,
• mineral,
• pathogen,
• pollutant,
• distress,
• complaint,
• consequence,
• lesion,
• abnormality,
• pain,
• headache,
• upset,
• compound,
• injury,