Japan's Nuclear and Industrial Safety Agency said Tuesday that to cool down the reactors remain top priority to prevent further damage to the fuel rods.

"The coolant water injection is still the No.1 priority for us, " said Hidehiko Nishiyama, a spokesman for the agency, at a news conference. "If we fail to cool down the reactors, various kinds of radioactive substances will be discharged into the environment. "

Workers are facing the need to balance two urgent but difficult tasks -- the coolant water injection and the removal of leaked radioactive water. The radioactive water leak may be linked to operations to pour massive amounts of water to prevent reactors and spent nuclear fuel pools from overheating.

He emphasized radioactive water from the damaged Fukushima Daiichi nuclear power plant had not been confirmed to have leaked into the Pacific Ocean from the plant's underground drainage system.

Regarding the highly toxic plutonium detected on Monday, Nishiyama maintained the density is equivalent to that in the soil under normal environmental conditions and poses no major impact on human health.

Plutonium emits alpha radiation and low-energy x-rays which are easily absorbed by human tissue.

Roughly 80 percent of the plutonium that enters the bloodstream goes either to the liver, bone or bone marrow, where it is retained for years, damaging tissue nearby and possibly resulting in cancer.