Over ten thousands kinds of chemical substances have been widely used for manufacture, agriculture, household and other purposes in industrialised countries. Various unintended by-products are also generated in manufacturing processes and in combustion of fossil fuel. Some of these chemicals released to the environment, e.g. into air and water, are likely to be hazardous and pose a public health concern. Regulation by Chemical Substances Control Low and PRTR systems are important frame works for managing release of hazardous chemicals to the environment in Japan. Biological monitoring is a novel methodology for assessing the health risk of exposure to environmental chemicals. Mutation is one practical endpoint for biological monitoring, whereby exposure to mutagenic chemicals may result in DNA mutations, e.g. base substitutions. Therefore, our studies have been focused on development of a bio-assay method for estimating in vivo mutagenicity of environmental chemicals, especially in ambient air. The potency of urban air for DNA adduct formation was estimated using rats maintained in a small animal facility beside a road with heavy traffic. The amount of DNA adducts in the lung was significantly elevated after a 4-week exposure, indicating that mutagenicity of urban air should be further evaluated. Diesel exhaust, a major source of mutagens in urban areas, was evaluated for in vivo mutagenicity using transgenic animals (Big Blue rat and gpt delta mouse) developed for detecting mutagens. Mutant frequency in lung of Big Blue rat was significantly increased by exposure to diesel exhaust for 4 weeks at the concentration of 6 mg SPM/m³. For detecting mutagens in water, we have developed a transgenic zebrafish line; this project is also reviewed.

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The dioxin issue in Japanese paper industry has emerged October 1990 and the governmental organizations (i. e., Environment Agency and MITI) have taken immediate actions to investigate the current status of organochlorine compounds in paper mill effluents. The Japan Paper Association has created the Special Committee for measures against Dioxin Issue and announced on December 1990 the guideline for reducing AOX (Adsorbable organohalogen compounds) to 1.5 kg/ ton by the end of the year 1993.
The current dioxin issue is analyzed from a wider perspective of global environmental problems with particular emphasis on the government's action and the technological countermeasures by the Association.
The present status of dioxin research from chemical, toxicological and pharmacokinetical aspects are summarized. The recent advances of kraft pulping and oxygen bleaching technologies as countermeasures for reducing AOX in paper mill effluents are described.
The potential impacts of the current dioxin issue on recycled paper manufacture, environmental protection movements and consumer's movements are also described.

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ダイオキシン類に対する社会的な関心の高まりを受けて, 昨年, ダイオキシン類対策特別措置法が制定された。この法律は, 環境媒体間を移動し, 様々な経路から曝露されるというダイオキシン類の特性にあわせて, 大気, 水, 土壌などを一体に管理するものであり, 環境保全に係わるこれまでの法律にない特徴を有している。法律の施行に向けて各種基準の設定や排出抑制対策の検討が行われたが, 環境中の挙動を中心としてダイオキシン類に係る科学的知見が不足しており, 時間的制約もあったことから, 環境媒体間の移動を十分に反映させることができていない。これらの点については, 知見の整備を進めて早急に見直しを行う必要がある。しかし, この法律の施行によってダイオキシン類の環境排出量は一層削減されると考えられる。人への曝露を低減するには, 水生生物に濃縮されやすいコプラナーPCBの削減を図る必要があり, 回収・保管されているPCBの処理がとくに重要となっている。排出削減に続くのが, 土壌, 底質や最終処分場に蓄積しているダイオキシン類の除去対策であるが, これを実施するには膨大な経費が必要となる。過去のダイオキシン類の曝露量が現在よりも高かったことを踏まえた有害性評価を行うとともに, 蓄積しているダイオキシン類がどのようなリスクをもたらすかをサイト毎に評価してから判断する必要がある。

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