Japan said on Tuesday it would start releasing more than a million metric tons of treated radioactive water from the wrecked Fukushima nuclear power plant into the sea on Thursday, going ahead with a plan heavily criticised by China.
Japan has said the water release is safe.
The International Atomic Energy Agency (IAEA), the United Nations nuclear watchdog, approved the plan in July, saying it met international standards and the impact it would have on people and the environment was "negligible".
The IAEA travelled to the Cook Islands in July to present its findings to the Pacific Islands Forum - a regional bloc of 18 nations, whose combined exclusive economic zones span 40 million square kilometres of the Pacific Ocean, where half the global tuna catch is found.
"I believe that the discharge meets international safety standards," Brown said in a statement on Wednesday.
He said the IAEA would continue to monitor the water during the discharge process.
Not all Pacific leaders had the same position and the Pacific Islands Forum might not reach a collective position, he said.
In a region that had suffered from the effects of nuclear weapons testing by outside powers, it was a "complex issue", he said.
The United States conducted nuclear tests in the Pacific Islands in the 1940s and 1950s, and France between 1966 and 1996.
"This is a demanding situation for all of us and we need to assess the science," he said.
A Pacific Nuclear Free Zone was established in 1985 under a treaty that prevents the dumping of radioactive materials.
Fijian Prime Minister Sitiveni Rabuka said in a speech on Monday he supported the discharge, based on the IAEA report, and it was "fear-mongering" to connect the controlled release of water across 30 years to the nuclear weapons tested in the Pacific.
The Fukushima discharge will be discussed at a meeting of the five-nation Melanesian Spearhead Group - Papua New Guinea, Fiji, Vanuatu, Solomon Islands and New Caledonia's ruling FLNKS party - on Thursday.
