In deep seabed mineral resource development, environmental impact assessments (EIAs) are essential to balancing development and environmental protection, and their implementation is mandatory under international law. This paper provides an overview of the EIA procedures established by the International Seabed Authority (ISA), the international organization overseeing deep seabed mineral resource development. It also briefly examines the potential impact of the BBNJ Agreement on EIAs for deep seabed mineral resource development.

Under the United Nations Convention on the Law of the Sea (UNCLOS), the area defined as the deep seabed under international law (the Area) refers to the seabed and subsoil beyond the outer limits of the continental shelf, and is designated as the “common heritage of mankind.” Based on this legal status, coastal states do not exercise sovereignty or exclusive jurisdiction over the Area, and the development of deep seabed resources is conducted under the management of the ISA^*1, an international organization.
In recent years, interest in deep seabed mineral resource development has been growing among nations due to factors such as increased demand for rare earth elements. However, deep seabed mineral resource development can have significant impacts on the marine environment. Therefore, resource development projects are required to minimize their impact on the natural environment as much as possible.
To respond to such demands, it is essential to conduct EIAs, a procedure that investigates and predicts the potential environmental effects of a project in advance, and considers either suspending the project or modifying its plan accordingly. From this perspective, this paper aims to provide an overview of the current state of international law regarding EIAs in the context of deep seabed mineral resource development.

The general method for implementing an EIA is roughly as follows. First, “screening” is conducted to examine the necessity of implementing an EIA, and “scoping” is performed to narrow down the matters to be examined in the EIA. Subsequently, core investigations and examinations of the EIA are conducted, including environmental baseline studies to clarify the current situation, prediction and assessment of environmental impacts from the project, examination of alternative measures, and consideration of mitigation measures to reduce impacts. The results are published as an Environmental Impact Statement (EIS) and become subject to review. Furthermore, after the launch of the project, continuous monitoring of its impact will be carried out.
The implementation of EIA is considered an obligation under customary international law, and under the Convention on Biological Diversity (CBD) state parties are obligated to carry out EIAs for numerous treaties. UNCLOS also stipulates obligations for EIA in Articles 204 and 206, and these obligations apply to deep seabed mineral resource development as well. In fact, the Agreement relating to the Implementation of Part XI of UNCLOS,concerning the deep seabed regime, stipulates that when contractors (a State or enterprises sponsored by a State) submit a plan of work to the ISA, it must be accompanied by a description related to the EIA (Annex I, Section 7of the Agreement).
However, the Agreement relating to the Implementation of Part XI and UNCLOS only generally stipulate the obligation to conduct EIAs without specifying detailed procedures for implementation. This gap is filled by the “Mining Code”^*2 developed by the ISA. The Mining Code is the collective term for the documents that set out procedures for deep seabed mineral resource development, and it also stipulates the methods for conducting EIAs. In the following section, an overview of the EIA obligations under the Mining Code will be provided.

The Mining Code comprises regulations adopted by the Council, which consists of 36 countries elected from ISA member states (state parties to UNCLOS), and recommendations issued by the Legal and Technical Commission (LTC), a body of the Council. Additionally, the Mining Code is classified into those relating to exploration of seabed mineral resources and those relating to exploitation.
As part of the Mining Code related to resource exploration, regulations (Exploration Regulations) have been adopted for the exploration of polymetallic nodules (formulated in 2000, revised in 2013), polymetallic sulphides (2010), and cobalt-rich ferromanganese crusts (2012). These regulations stipulate the procedures for conducting EIAs that contractors must follow at the time of submitting a plan of work and after its approval. Furthermore, these Exploration Regulations require reference to the recommendations adopted by the LTC regarding the specific procedures for conducting EIAs, such as the items to be investigated in baseline environmental surveys and the types of activities for which an EIA is required. In 2013, the Legal and Technical Commission (LTC) adopted recommendations that apply uniformly to the exploration of all three types of mineral resources mentioned above, and the revised version from 2023 (ISBA/25/LTC/6.Rev.3) is currently in effect.
On the other hand, as of July 2025, neither regulations nor recommendations related to resource exploitation under the Mining Code have been adopted. However, the draft exploitation regulations, which were made public in 2016 and are currently under negotiation by the ISA Council for the purpose of adoption, already contain provisions related to EIA. In addition, in 2022, a draft guideline was prepared (ISBA/27/C/4, etc.) that specifies detailed procedures for conducting EIAs, from screening to monitoring. If the exploitation regulations are adopted, it is expected that this guideline will be applied, although it may be subject to future revisions.

Finally, I would like to touch upon the relationship with the BBNJ Agreement^*3 adopted in 2023. By definition, the deep seabed falls under areas beyond national jurisdiction and is therefore subject to the application of the BBNJ Agreement. Consequently, the relationship with existing legal systems concerning the deep seabed may become an issue.
The BBNJ Agreement stipulates, in Article 29 (4), that if a State Party conducts an EIA "equivalent" to an EIA under the Agreement, it is not required to conduct an additional EIA under the Agreement. Therefore, if the EIA conducted under the Mining Code is considered “equivalent” in this context, the entry into force of the BBNJ Agreement would not immediately affect deep seabed mineral resource development.
Nevertheless, long-term impacts seem unavoidable. An EIA under the BBNJ Agreement is more stringent than an EIA based on the Mining Code in many respects. For example, the BBNJ Agreement stipulates that at the scoping stage, not only environmental impacts but also social, cultural, and human health impacts should be considered (Article 31, paragraph 1(b)), whereas the Mining Code only partially mentions these elements. In recent years, environmental concerns have been growing even more, with calls for a moratorium on deep seabed mineral resource development on environmental protection grounds. Considering this current situation, there is a sufficient possibility that EIAs under the Mining Code will become more stringent in the future under the influence of the BBNJ Agreement.

*1 International Seabed Authority (ISA) https://www.isa.org.jm/
*2 The Mining Code https://www.isa.org.jm/the-mining-code/
*3 The official name is the “Agreement on Marine Biological Diversity of Areas beyond National Jurisdiction.” The Japanese translation is “海洋法に関する国際連合条約に基づくいずれの国の管轄にも属さない区域における海洋の生物の多様性の保全及び持続可能な利用に関する協定” (Agreement on the Conservation and Sustainable Use of Marine Biological Diversity in Areas Beyond National Jurisdiction under UNCLOS). As of the time of writing, 51 countries, including Japan, have ratified the agreement, but it has not yet entered into force (it will enter into force 120 days after it is ratified by 60 countries).