Tau told Pacific Waves the Pacific Ocean is already endangered and Japan's plan will have devastating impacts.
"We have a nuclear testing legacy in the Pacific. That continues to impact our people, our islands and our way of life, and it impacts the health of our people.
"Having this plan by Japan poses greater risks to the ocean which is already in a declining state.
"The health of our ocean has declined due to human endured stresses and having this could aggravate the current state of our region.
"And also, there are possible threats on the lives of our people as we clearly understand in this part of the world, the ocean is dear to us, it sustains us."
Tau said both the opposition in Vanuatu and the president of the Federated States of Micronesia have expressed serious concerns about Japan's plans, and the Pacific Islands Secretariat this year has appointed an international expert panel to advise the Forum Secretary-General and national leaders.
The Northern Marianas' House of Representatives has also condemned Japan's plan to dump nuclear waste.
Tau said the plans should not proceed without the Pacific people being able to voice their concerns and be better advised.
- RNZ