usually something can be found near a source in greater concentrations
level_of_exposure is scalar_quantity. exposure_to_liquid_phosgene is exposure_to_phosgene. exposure_to_gaseous_diphosgene is exposure_to_diphosgene. exposure_to_liquid_diphosgene is exposure_to_diphosgene. source_materials is source. find_inside is more_controlled_environment. source is facility. contamination is impurity. presence is proximity. fish is source_of_protein.