The Environment Ministry will determine assessment methods by the summer and begin an examination of land where beer bottles containing toxic gas were found buried recently in Kanagawa Prefecture.
The site, where construction work is currently under way, belonged to a former Imperial Japanese Navy facility involved in research on toxic gas before and during World War II.
The ministry has yet to establish an assessment method for low-level toxic pollution over a long period of time, although the ministry does have methods to measure high-level contamination caused by terrorist attacks or chemical accidents.
Earlier this month, three construction workers became ill after sniffing three bottles that were unearthed at the site, leading Kanagawa Prefectural Police to dispatch a chemical squad to investigate.
The site is about 3.5 km northeast of the Sagami naval works, where construction workers building a road last September found 11 old beer bottles containing the residue of mustard gas and other agents. Eleven of the workers suffered injuries such as skin irritation.
The Sagami naval works is believed to have been involved in the production of chemical weapons before and during World War II.
Kanagawa Prefecture is constructing a government building on the site of the former chemical research facility, about 1.3 km from JR Hiratsuka station.