We propose using loss of life expectancy (LLE) as a measure of risk due to exposure to chemicals including carcinogens. The advantages of using LLE are that the age at which cancer deaths occur can be taken into account and that LLE can be estimated also for noncancer effects. The LLE due to exposure to carcinogens at a lifetime cancer risk level of 10-5 was estimated and the estimation method was explained. The relationship between exposure to carcinogens and increase in cancer death rate was modeled based on a reported survey on radiation-induced cancer . In order to verify the model, several alternative models constructed by altering assumptions were also examined. Lifetime exposure and exposure from age 20 to 49 to carcinogens at a lifetime cancer risk level of 10^-5 were estimated to result in LLE of 66 minutes and 12 minutes, respectively. The LLE of an average Japanese as a result of one-year exposure to the same level of carcinogens was estimated to be 0.83 minutes .

View full abstract

In order to obtain baseline data for the development of diagnostic methods for forest decline based on chemical analyses, partitioning of metallic elements into liquid and solid phases (0.1M HCl soluble and insoluble fractions) from needles of Japanese cedar (Cryptomeria japonica) in the Kanto Plain of Japan and the distribution of elements in needles of different ages were examined. The results showed that most of the K, Mg and Mn in needles are present in their liquid phase while the greater parts of Ca, Al and Fe are contained in their solid phase. It was found that the significant proportions of Al and Fe were present in the form of soil particles (0.1M HCl insoluble fraction of solid phase) deposited on the surface of needles which can not be physically separeted for analysis. Also, the selective extracting technique using 0.1M HCl solution proved to be useful for evaluation of the amounts of Al and Fe supplied to needles through transpiration current. K, Mg, P and N were significantly enriched in current year needles, suggesting the occurrence of retranslocation of those elements from old needles. For K and Mg, concentration change by retranslocation from 1-year-old needles to current year needles could be analysed by a simplified mathematical model. On the other hand, higher concentrations of Ca, Al and Fe were observed in older needles, probably because those elements transported to needles through transpiration current were fixated into the tissue and accumulated with increase of needle age.

View full abstract

The effect of heavy metal pollution on soil, in terms cellulose decomposition, were investigated, through the field survey of 3 areas (Toyama, Ohta, Tsushima) in Japan. The decomposition of cellulose was examined by measuring β-glucosidase activity, a component of cellulase complexes. The results obtained are as follows. 1)β-Glucosidase activity was decreased with increasing the heavy metal content in all of 3 areas. Especially, a negative coralation between β-glucosidase activity and heavy metal content was observed with Ohta soils, since the soils were sampled from a paddy field with samll variability. 2) It was found that β-glucosidase activity was more sensitive than exo-cellulase activity to heavy metal polluted soil. 3) The extraction way of heavy metals (exchangeable, total) made no difference on the relation to the β-glucisidase activity. 4) Even a high concentrations (10, 000 ppm) of Cd, Zn and Cu, the β-glucosidase and exo-cellulase activity do not decline. This fact states that cadmium, zinc and copper do not directly affect cellulase. Thus, it can be setimated that heavy metals are incorporated into microbes, to disorder their metabolism, thereby affecting the biomass quantitatively, which in turn affects soil cellulase.

View full abstract

The food supply system in Japan was investigated from the concept of nitrogen balance. It is estimated that the amount of nitrogen fixed naturally in arable land in Japan is 1.5x10⁵ ton year^-1. The amount of nitrogen in industrial fertilizer, in catch of fish and in imported food or feed were 6.1x10⁵ and 2.6x10⁵ and 8.3x10⁵ ton year^-1 respectively in 1992. The nitrogen accompanied with the food supply system that provides sufficient food to 1.2x10⁸ people changes the natural nitrogen cycle and this is the cause of eutrophication in bays and lakes in Japan. It is necessary to use excreta from man for manure and to import meat instead of chemical fertilizer and feed imports in order to construct the society that does not disturb the natural nitrogen cycle.

View full abstract

The ready biodegradability test method 301C for chemical substances based on the "DECD Guidelines for Testing of Chemicals" is operated by demand as the biodegrada tion test under the "Chemical Substances Control Law" in Japan. Activated sludge subjected to the biodegradation test as seed was a mixture of environmental waters and returned sludges from sewage treatment plants at various places in Japan, and was cultivated in a uniform condition. When we attempted to measure bacteria selectively with anililne degradation activity in activated sludge by use of the Most Probable Number (MPN) method, we were able to assess the number of bacteria correctly. The relation between the number of bacteria with aniline degradation activity by this method and the lag period of aniline degradation by measurement of BOD in the activated sludge was shown. Moreover, the obtained results suggested the existence of at least more than two kinds of aniline degradable bacteria in the activated sludge. We attempted to isolate the bacteria from cultured solution under the condition of biode gradation test. So that, we were able to isolate two strains inferred to Arthrobacter sp. It is confirmed that these two strains showed good aniline degradation activity under the coexistence of activated sludge. These results were applicable to the investigation of a stable culture method for the activated sludge.

View full abstract

Three rice cultivars, Koshihikari, Suwon 258 and IR 74, were grown in environmentally-controlled glass chambers with three levels of biologically effective ultraviolet-B (UV-B_BE) radiation [daily dose : 0.0 (No UV-B), 6.5 (Low UV-B) and 11.3 (High UV-B) kJm^-2, UV-B_BE] for 4 weeks of the early growth period. UV-B radiation significantly depressed plant dry weight and height in different extent among the cultivars. Suwon 258 was relatively less sensitive and IR 74 was most susceptible to UV-B with Koshihikari being between the two cultivars. Leaf area of all the cultivars was reduced by UV-B. Specific leaf weight, index of leaf thickness, of Suwon 258 was significantly increased by UV-B, while that of Koshihikari and IR 74 did not change significantly. Total chlorophyll content of Koshihikari and IR 74 was de creased, but that of Suwon 258 was not affected. Amount of UV-absorbing compounds on leaf area basis was increased for all the cultivars with both Low and High UV-B treatments. In Suwon 258 and IR 74, more negative natural abundance of ¹³C (δ¹³C) was observed with high UV-B treatment. These results indicate that rice plants may be affected by UV-B radiation in the amount of present-day sunlight and that intraspecific variation in the leaf thickenss response may primarily contribute to the differences among the cultivars in susceptibility to UV-B enhancement.

View full abstract

To know interspecific difference in protection mechanisms against high ultraviolet-B radiation in plants, cucumber, a sensitive species, and rice, a less sensitive species, were grown in sun-lit glass chambers under enhanced UV-B with 11.3 kJ m^-2day^-1 biologically effective ultraviolet-B (UV-B_BE) for cucumber and 11.7 kJm^-2day^-1(UV-B_BE) for rice, while UV-B was almost nonexistent in the No UV-B treatment. Foliar damage occurred only in cucumber. The growth depression by the UV-B enhancement was also severer in cucumber than in rice. In rice, the content of ascorbic acid in the leaves was much higher than dehydroascorbic acid, whereas, in cucumber, the dehydroascorbic acid content was higher than ascorbic acid. The foliar damage in cucumber may be due to the shortage of ascorbic acid. The enhanced UV-B radiation increased the ascorbic acid and glutathione contents as well as the dehydroascorbate/ascorbate ratios in the leaves of both species. All the enzyme activities investigated (superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehy droascorbate reductase, glutathione reductase and guaiacol peroxidase) in both species were increased by the UV-B enhancement with greater increases in monodehydroas corbate reductase and guaiacol peroxidase in cucumber leaves than in rice leaves.

View full abstract

The Amaya′s (1981) method of measuring atmospheric NO₂, a simplified shortterm exposure method, was applied to examine the precision and accuracy in the measurement of atmospheric NO₂ concentration. When the NO₂ concentration was relatively small (<7 ppb), the variation coefficients were significantly different among five capsules installed in the plural sites. In the case of the NO2 concentration higher than 7 ppb, however, the variation coefficients were relatively stable, and the values were smaller than 13 %. It was also found that the exposure over 24 hours led to increase the variation coefficiency and to decrease the absorption efficiency. In order to examine the precision and accuracy, this method was carried out at a public monitoring station. As a result, the NO₂ concentration by this method (x) had a good correlation (r=0.82) with the station data (y), and the relationship was described as follows :y=0.73 x+0.14.However, it seems that some cases of measuring showed the decrease of absorption effiency, depending on the meteorological conditions.

View full abstract

The ascorbate/glutathione cycle in the leaves of rice (Oryza sativa L . cv. Koshihikari) plants was investigated under field conditions to study the protection mechanisms against ultraviolet-B (UV-B) radiation. Rice plants were grown and irradiated with the enhanced UV-B for almost a whole growing season in a paddy field at Tsukuba, Japan (36°01<N, 140°07<E). The UV-B enhancement simulated a 38 % depletion of stratospheric ozone at Tsukuba. The results showed no UV-B effects on plant height, numbers of tillers and panicles and dry weight of the plant parts. The ascorbic acid content was decreased, and dehydroascorbic acid content was increased in the flag leaves with the enhanced UV-B radiation. However, no significant effect of enhanced UV-B was observed on the glutathione content. Enhanced UV-B did not induce apparent changes in the activities of any of six antioxidative enzymes investigated.

View full abstract