Japan's Environment Ministry has put out for public comment the missing half of its Tokyo Bay oxygen standard: how many monitoring points in each zone must meet it, and by when. The draft amendment to a 2009 ministry notice sets attainment targets for eight of nine zones and leaves the innermost one undecided.
What the draft sets
The standard covers bottom-layer dissolved oxygen, graded at 4.0, 3.0 or 2.0 mg/L depending on how tolerant the local marine life is of low oxygen. Zones are judged by the share of monitoring points that pass, not point by point, because a temporary, local dip is thought unlikely to threaten a whole population.
Each zone gets one of three timelines: immediate attainment, attainment "as soon as possible" within five to ten years, or an interim goal within about ten years.
| Zone | Standard (mg/L) | Target rate | Ten-year rate | Timeline |
|---|---|---|---|---|
| Bay mouth | 4.0 | 100% | none set | Immediately |
| Central zone 2 | 4.0 | 71% | 64% | Interim goal within about 10 years |
| Kawasaki and Yokohama ports | 3.0 | 100% | none set | Within 5 to 10 years, as soon as possible |
| Inner bay zone 1 | 3.0 | 85% | 14% | Interim goal within about 10 years |
| Central zone 1 | 3.0 | 50% | 33% | Interim goal within about 10 years |
| Tokyo port | 2.0 | 100% | 50% | Interim goal within about 10 years |
| Chiba port | 2.0 | 100% | none set | Within 5 to 10 years, as soon as possible |
| Kisarazu port | 2.0 | 100% | none set | Immediately |
| Inner bay zone 2 | 2.0 | not set | not set | No timeline set |
The mouth of the bay and Kisarazu port have to hit 100% at once because every point there already passes. The inner bay is different. In the first inner-bay zone, the 85% target counts six of seven points, including a new station to be added, yet none of the six other stations met the standard over the decade to March 2024 on the report's classification. The report counts them because they rank as important habitat, and sets the interim goal at one point, St-8.
Where the draft stops
The second inner-bay zone gets no target or deadline. Its five points failed throughout the period, and the report says bottom oxygen there was already below 2.0 mg/L and 3.0 mg/L in the early 1950s. The ministry says current data do not allow a target and that it will decide after further measurements.
Chiba port shows a gap the other way: its 100% target rests on one new monitoring point, which replaces existing stations that never met the standard in the period.
Caveats in the report
The report concedes that science does not yet show what attainment rate keeps each species going. It warns that climate change may push summer oxygen lower, and that nutrient-management changes could worsen bottom oxygen. Targets may be revised, and a mid-term review is advised where deadlines approach ten years.
Timetable
Comments, in Japanese, are open from 30 September to 29 October 2026 via e-Gov or post to the Environment Ministry's Environmental Management Division. Promulgation and entry into force are both planned for November to December 2026.