Since the pollution of underground water by chemical substances, which are harmful to man, was found, some chemical substances such as pesticides and organic solvents have been added as control subjects of the Japanese environmental standard. The plasticizers and fire retardants of plastics were also detected in the underground water surrounding the landfill site and the safety evaluation of leachate became a public concern. Therefore, we selected a mutagen test as the detection method of harmful chemical substances, especially carcinogens, and researched the mutagenicity of leachate to clear the production process of mutagen in the landfill site.
The mutagenic activities of leachate from four lysimeters which have a different landfill type and organic content were measured for 6 years. The results from this research are summarized as follows ;
The more the landfill type is aerobic, the earlier the mutagen is produced. Moreover, the production of mutagens accompanied the biological nitrification and chemical reduction of nitrate. A positive sample of Ames assay withSalmonella typhimuriumstrain TA 98 and TA 100, which is a leachate sample taken from Lysimeter B after 2 months, also showed the mutagenic activities of YG 1021, YG 1024, YG 1026 YG 1029, YG 1041 and YG 1042, which were extremely sensitive to the mutagenic action of nitroarenes and aromatic amines. It suggests that one of the mutagens in leachate detected on the chemical reduction of nitrate in solid waste may be nitroarenes and aromatic amines.

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In Japan, there is an urgent need to promote waste paper recycling at business establishments. Particularly in Tokyo's 23 wards, the recovery rate of waste paper from large-scale businesses is sufficiently high. On the contrary, the rate from medium and small-scale businesses is low. The objective of this study is to make a cost analysis of waste paper collection systems for medium and small-scale businesses considering collection efficiency and“indirect cost”. Costs of waste paper collection systems are analyzed by using GIS software, which can detect the shortest route. 3 kinds of“shadow costs” are also analyzed, such as“carrying work cost”, “occupation cost of floor space”, and“sorting work cost”. In case of“1F collection”, total costs of the waste paper collection system and carrying work are higher than the waste disposal fee regardless of the number of participating businesses. In the case of“floor collection”, costs of waste paper collection systems are higher than those of 1F collection because of lower collection efficiency, but the difference decreased according to the increase of the number of participating businesses. The container's cost and the occupation cost of floor space also decreased according to the increase in the amount of collected waste paper from each business.

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There is an increasing potential of heavy metal pollution from landfill sites in which the incinerator ash with high heavy metal content is disposed. However, elution of heavy metals from landfill sites has rarely been detected. The purpose of this study is to investigate heavy metal insolubilization in the landfill site, by batch and column experiments, using incinerator ash under semi-aerobic and anaerobic conditions. Under both conditions, sulfate reduction and subsequent heavy metal insolubilization by sulfide did not take place, while heavy metal precipitation in the form of hydroxide, as well as complex salt, and also coprecipitation with Ca ²⁺, were observed.

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Acase study of food waste treatment was conducted to compare the impacts of four scenarios: incineration, incineration after biogasification, biogasification followed by composting, and composting. Potential contributions to climate change, acidification, consumption of landfill and humantoxicity were assessed. Characterization of human toxicity caused by heavy metals and dioxins wasperformed by three multimedia fate models. Scenarios incorporating the biogasification processshowed lower impact on climate change and human toxicity. Compared to incineration, compostingcauses larger emission of green house gases (GHGs), but its lower consumption of landfill more thancompensates for the GHGs emission. The ranking of the four scenarios on human toxicity varieddepending on the characterization models applied. The steady state models placed high priority onemission of heavy metals in farmland, whereas the dynamic model (time horizon 100 years) estimatedthe emission of dioxins from the incineration process as more significant.

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Recently, PET bottles are circulating voluminously as beverage containers. However, it is difficult to say that the recycling of PET bottles is succeeding. Regarding the recycling of PET bottles, since the containers and packaging recycling law was implemented in 1997, it has operated full scale, although it remains now at about 20% of the collection rate of 1999. We want to carry out a comprehensive evaluation using the social cost benefit analysis regarding tackling of recycling of PET bottles in local governments. The social net benefit, including the external benefit, is increased by the decrease of environmental load in all 3 case study cities, but obtained the result of minus value. The recycling of PET bottles is becoming a big economic burden in local governments and it is requested to reform the recycling policy based on the beneficiary pay principle by the adjustment of the producer's responsibility.

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