Total dioxin emissions in Japan in 1998 were reduced to less than half of 1997 levels, but they were still far larger than in other developed countries, the Environment Agency said Friday.

Japan emitted 2.9 kg of the toxic substance last year, far less than the 6.3 to 6.4 kg released the previous year, the agency said.

But the 1998 figure was still nine times that of Germany and six times that of the Netherlands, according to the latest information available, it added.

Japan hopes to cut annual emissions to around 600 grams within four years by tightening controls, officials said.

The emissions data were obtained from waste disposal plants, steel mills and other dioxin emission sources, and the agency estimated that the reduction seen in 1998 levels was brought about by the introduction of new dioxin emissions regulations for incinerators.

Although the new tolerable daily intake of 4 picograms per kilogram of body weight, announced Monday by the Environment Agency and approved by a Cabinet-level committee Friday, includes coplanar PCBs (polychlorinated biphenyls), the inventory does not. Coplanar PCBs structurally resemble dioxin and have similar toxicological effects. A picogram is one-trillionth of a gram.

Officials said they initially hoped to include coplanar PCBs in the tabulation, but a lack of data made it impossible. However, the agency is working to complete a coplanar PCB inventory to add to the total sometime next year. Agency officials estimate this may increase the aggregate emissions estimate by about 10 percent.

Waste incineration was the largest contributor to dioxin emissions for both years, accounting for more than 90 percent in 1997 and slightly less in 1998. Municipal waste incineration alone accounted for nearly 68 percent of the total in 1997 and roughly 45 percent in 1998.

The new tabulation of dioxin emissions will provide concrete information for the government to gauge progress toward its goal of reducing emissions by almost 90 percent of 1997 levels by 2002, as dictated by the ministerial group appointed in February to oversee national dioxin policy.

In its basic policy outline released at the end of March for the reduction of dioxin, the committee called for the inventory to be compiled by the end of this month.

The new inventory replaces a piecemeal estimate that used emissions information from the United States to fill in gaps in domestic data. First compiled in 1990 by Kyoto University Professor Masakatsu Hiraoka, more recent estimates using the same method put total emissions for 1997 at around 5.3 kg.

Agency officials say the 1 kg rise in the new inventory compared with the earlier method is due to an underestimation of the amount of dioxin released by industrial waste incinerators. The new inventory means that for the government to reach its goal of a 90 percent reduction from 1997 levels, it will have to reduce emissions to 630 to 640 grams rather than 530 grams as previously estimated.

An additional consideration concerns "small-scale incinerators" — those that burn less than 200 kg of garbage per hour and are not regulated under current law. The number being operated throughout the country is estimated at about 16,500. Though these incinerators do not burn much, their large number has caused the Environment Agency to look into tightening regulations so they apply to incinerators capable of burning more than 50 kg per hour.

This promises to be a major theme in debates over more accurate assessments of dioxin emissions and reductions in emissions from currently unregulated sources.

The new study relies on data from three government bodies: the Environment Agency, the Health and Welfare Ministry, and the Ministry of International Trade and Industry.

Dioxin emission sources are divided into eight categories, including municipal and waste incineration, crematories, industry, tobacco and automobiles. The only category estimated to have seen an increase in dioxin emissions in 1998 levels is tobacco.