Constitutional Court Reinforces Broad Environmental Liability for Property Owners and Possessors (Thailand)

Background of Constitutional Court Decision No. 6/2569

On 10 June 2026, the Constitutional Court issued Decision No. 6/2569 (2026) in Case No. 39/2568 (2025), addressing the definition of “having in possession” under Section 4 of the Hazardous Substances Act B.E. 2535 (1992) (the “Act”).

Facts

The landowner leased land to a lessee. Under the lease agreement, the lessee was required to construct two warehouses on the leased land, and the landowner was entitled to collect rental income from one of the warehouses.

Subsequently, the two warehouses were leased to a sublessee, who later brought industrial waste onto the premises.

The landowner demanded that the sublessee remove the industrial waste, and the lessee reported the matter to the police. The sublessee ultimately abandoned the industrial waste in the warehouses and on the land. Thereafter, the Department of Industrial Works (DIW) ordered the landowner, pursuant to Section 52, paragraph one and Section 52/1 of the Act, to cease the violation of the Act and to properly dispose of the hazardous substances found on the land. The landowner appealed the order. However, DIW rejected the appeal and issued a warning letter requiring compliance with the order. DIW further notified the landowner that, if the landowner failed to comply with the order, DIW could itself undertake the remediation or appoint a third party to do so, at an estimated initial cost of THB 42.5 million.

Argument

The landowner, as plaintiff, filed a case against DIW with the Central Administrative Court, and argued that, under Section 52, paragraphs two and four of the Act, DIW itself had a duty to dispose of the hazardous substances or, alternatively, to order the owner of the hazardous substances to dispose of them. The landowner also challenged the constitutionality of the definition of “having in possession” under the Act.

The landowner argued that it was inconsistent with the polluter-pays principle to impose liability on a landowner or possessor merely because hazardous substances were left or found on land in that person’s possession, in the same manner as on persons directly involved with and benefiting from the hazardous substances. The landowner further argued that landowners should not be liable for damage they did not cause, as they had neither consented to nor been directly involved in the conduct giving rise to the damage; and that, therefore, the definition of “having in possession” under the Act was unconstitutional.

The Central Administrative Court subsequently referred the constitutional issue to the Constitutional Court for determination.

Judgment of the Constitutional Court

The Constitutional Court rejected the arguments.

The Court held that, given the serious risks that hazardous substances pose to human health, property, and the environment, it is reasonable (i) to impose strict obligations, at every stage of the hazardous-substance distribution chain, on manufacturers, importers, exporters, transit operators, re-importers, re-exporters, and possessors of hazardous substances, and (ii) to require such persons to bear civil liability unless they have proved that the damage resulted from force majeure or the fault of the injured party.

In addition, the Court held that the said definition under the Act creates an irrebuttable presumption that owners or possessors of immovable property “possess” hazardous substances, even if they have no intention of possessing them for themselves or another person. This is because owners or possessors have a duty to ensure that their property does not create hazardous conditions, and to prevent others from committing legal violations on the property; and thus they bear joint liability for any resulting damage.

The Court considered the definition consistent with fundamental principles of environmental law, which emphasize the prevention of environmental harm and the allocation of environmental costs to persons likely to create risks that may affect public safety, even if they did not know of or benefit from the pollution.

The Court further held that, although the statutory definition of “having in possession” may restrict the rights of owners or possessors of immovable property where hazardous substances have been left or found on the premises, such a restriction is proportionate when balanced against the public interest.

However, the Court also noted that landowners or possessors retain the right to seek compensation from or pursue legal action against the person who actually brought the hazardous substances onto the property.

Our Insights: Key Takeaways for Businesses

Constitutional Court Decision No. 6/2569 was limited to determining the constitutionality of the definition of “having in possession” under the Act. It may therefore be premature to conclude that a landowner or possessor will be automatically liable whenever hazardous substances are left or found on its land. Liability will depend on the facts of each case and on any available defenses or exemptions under the relevant law. We understand that the case will now be remanded to the Central Administrative Court for consideration of the facts and determination of the remaining issues.

Moreover, given that the focus of the Constitutional Court was on the Act, as opposed to a civil claim for damages and recovery of environmental remediation costs under Sections 96 and 97 of the Act on Enhancement and Conservation of National Environmental Quality B.E. 2535 (1992) and Section 63 of the Act, a separate and additional court judgment by the competent court is required to determine whether the landowner will ultimately be held jointly liable for the hazardous-substance disposal costs, estimated by DIW at THB 42.5 million.

Nevertheless, Constitutional Court Decision No. 6/2569 highlights the rationale for imposing broader accountability throughout the hazardous-substance distribution chain, even on parties that are not direct polluters.

Factories, warehouses, and property owners should therefore strengthen their environmental due diligence and controls, recognizing that:

• Both hazardous substances and industrial waste found on land may create obligations for the landowner or possessor.
• Engaging a licensed waste management operator may not necessarily end a company’s responsibility if the hazardous substances and industrial waste are mishandled.

The decision also highlights the importance of environmental due diligence in land acquisitions and of including appropriate indemnification clauses in a land purchase agreement and/or a land lease agreement.