οὐκ ἔστι γῆρας τοῦδε τοῦ μιάσματος → that pollution never wears out, that pollution can never grow old
ὀχῶν: «ὀχευτικῶς ἔχων. ἢ τροχῶν ἁρμάτων» Ἡσύχ.