Police are trying to determine the origin of 13 large bags of aluminium dross found dumped at a Samut Sakhon roadside.
Nearby residents reported a foul smell and complained of eye and nose irritation.
Aluminium dross, a residue from processing, is classified as a hazardous material.
It’s believed the bags were dumped late Friday night in the vacant, overgrown property at the side of Lat Si-Yokkabat Road in Ban Phaeo district.
Heavy rain on Sunday could have triggered a chemical reaction that began afflicting neighbours.
Police, soldiers and district and Tambon Lak Ha municipal officials inspected the site at 5.30pm on Sunday.
The landowner was to be questioned and provincial offices handling industries, natural resources and the environment were expected to send experts.
The bags have meanwhile been covered with waterproof canvas and sealed within a police cordon.