Senior ministry officials involved with antipollution policy agreed on a new pollutant reduction plan Thursday for Japan's three most contaminated bodies of water, the Environment Ministry said.

The plan will include nitrogen and phosphorous as new elements to be monitored in measuring the pollution in Tokyo Bay, Ise Bay and the Seto Inland Sea, in addition to the current and sole yardstick, chemical oxygen demand, ministry officials said.

Chemical oxygen demand denotes the amount of oxygen needed to completely oxidize an organic molecule.

The officials were attending a lower-level meeting of the Conference on Environmental Pollution Control, where the new policy was to be reported to participating Cabinet ministers Friday.

The antipollution plan will be introduced next month in 20 prefectures, including Tokyo and landlocked prefectures whose rives flow into the targeted bodies of water, the officials said.

A 7 percent reduction from fiscal 1999 chemical oxygen demand levels will be sought in the three bodies of water by the end of fiscal 2004.

A 4 percent reduction in nitrogen and a 7 percent cut in phosphorous content is also called for over the period.

Prefectures around the three bodies of water have set reduction targets in line with basic goals established by the government in December. They hope to attain them by improving sewage systems and upgrading water-treatment plants.

Some of the worst-affected prefectures include Hyogo, which has to cut its chemical oxygen demand levels by 20 percent, and Osaka, which must slash 10 percent from the nitrogen content. Aichi and Hyogo must cut phosphorous by 13 percent.

Nitrogen and phosphorous are included in the plan as new targets in line with a recommendation made by a ministry panel in 2000. The panel attributed the overabundance of nutrients to the two substances, which help phytoplankton grow beyond normal levels.