Population studies ofCavelerius saccharivorus Okajima (Heteroptera: Lygaeidae): A few findings on population interchange

Summary The change in population density ofCavelerius saccharivorus was studied in the sugar cane field and theMiscanthus habitats around it. This species spent 2 (or partly 3) generations a year. It was suggested that the density rose in the sugar cane field where the density had been low enough, when the population density increased in the nearby sugar cane fields. Likely, the density in theMiscanthus habitat increased with the density in the nearby sugar cane field. It seems that these are mainly due to flying movement of adults, and that the movement takes place in every season. It was found through the investigation in the sugar cane field that the percentage of long-winged adults increased with the population density. These adults seemed to emmigrate to the nearby sugar cane fields andMiscanthus habitats. The remarkable increase in the percentage of long-winged adults in the sugar cane field was probably due to the immigration into there. In theMiscanthus habitat the adult population was consisted mainly of long-winged ones. Through all the observations, it was suggested that the adult movement was associated with the population regulation and performed chiefly by long-winged adults.     

Theoretical studies on the role of food exploitation for the competition of scaamble type

Summary A model was made to clarify the basic processes of competition to occur among larvae by the exploitation as defined byBakker (1969). It was found that this model is applicable to the experimental results on the food exploitation amongDroshophila larvae obtained byBakker (1961). In the model the preimaginal stage is divided into two periods;T _f which is the time that a group of larvae spends in exhausting the food after hatching, andT _s which is the duration of the starvation period afterT _f .T _f and thenW _l (larval body weight) just after the end ofT _f are decided byF _s (amount of food supplied per larva at larval hatching) andF _c (amount of food consumed per larva).T _f affects on the onset ofT _s as well asR _l (rate of decrease in the individual body weight duringT _s ).W _a (weight of emerging adults) is gotten by a subtraction ofR _l fromW _l just after the end ofT _f ,R _e is affected directly by these components ofW _l andR _l . As a result,W _a andR _e are expressed by functions ofF _s . This model confirmed that the food exploitation lead to the competition of scramble type. Finally it was suggested that there exist some strategies which prevent ill-effects owing to the food exploitation.     

Methods for estimating the number of the Cryptomeria red mite, especially with the removal by solutions

Summary We compared the removal by solution, the represented count-area method and the beating, for the purpose of estimating the number of the Cryptomeria red mite. Among them the solution procedure provided the smallest standard error as per cent of the mean. 0.25 per cent unheated solution of sodium hydroxide is used for the summer generation, and also 0.25 per cent boiling one for the winter eggs. The mean proportion removed±standard error for the summer eggs and the winter eggs were 0.8770±0.0316 and 0.7920±0.0281 respectively, while 0.9894±0.0050 for the mites.     

Effect of Particle Size on Risk Assessment of Direct Soil Ingestion and Metals Adhered to Children's Hands at Playgrounds

The quantity of heavy metals in soil is measured after 2‐mm sieving in Japan for risk assessment of direct soil ingestion. A study was conducted on the relationship between the size of soil particles and quantity of heavy metals in soil, and the particle‐size distribution of soil adhered to children's hands, and the risks of direct intake of soil considering the particle sizes ingested were evaluated. The results showed that smaller particles had a tendency to contain more heavy metals than bigger ones, that the particle size of approximately 90% of the soil particles from playgrounds adhered to children's hands was less than 100 μm, and that 2‐mm sieving in preparation for measuring heavy metal content caused underestimation of the risk of direct soil intake. The amount of heavy metals on children's hands after playing outside was investigated. Various metals and soil were adhered to their hands, and the amount of soil adhered could be estimated from the concentration of metals. To develop accurate risk assessment, the particle‐size distribution of ingested soil and more detailed scenarios of soil intake are necessary.     

A Probabilistic Approach to Assess External Doses to the Public Considering Spatial Variability of Radioactive Contamination and Interpopulation Differences in Behavior Pattern

Dose assessment is an important issue from the viewpoints of protecting people from radiation exposure and managing postaccident situations adequately. However, the radiation doses received by people cannot be determined with complete accuracy because of the uncertainties and the variability associated with any process of defining individual characteristics and in the dose assessment process itself. In this study, a dose assessment model was developed based on measurements and surveys of individual doses and relevant contributors (i.e., ambient dose rates and behavior patterns) in Fukushima City for four population groups: Fukushima City Office staff, Senior Citizens’ Club, Contractors’ Association, and Agricultural Cooperative. In addition, probabilistic assessments were performed for these population groups by considering the spatial variability of contamination and interpopulation differences resulting from behavior patterns. As a result of comparison with the actual measurements, the assessment results for participants from the Fukushima City Office agreed with the measured values, thereby validating the model and the approach. Although the assessment results obtained for the Senior Citizens’ Club and the Agricultural Cooperative differ partly from the measured values, by addressing further considerations in terms of dose reduction effects due to decontamination and the impact of additional exposure sources in agricultural fields, these results can be improved. By contrast, the measurements obtained for the participants from the Contractors’ Association were not reproduced well in the present study. To assess the doses to this group, further investigations of association members’ work activities and the related dose reduction effects are needed.     

Methodology for setting risk-based concentrations of contaminants in soil and groundwater and application to a model contaminated site

In Japan, environmental standards for contaminants in groundwater and in leachate from soil are set with the assumption that they are used for drinking water over a human lifetime. Where there is neither a well nor groundwater used for drinking, the standard is thus too severe. Therefore, remediation based on these standards incurs excessive effort and cost. In contrast, the environmental-assessment procedure used in the United States and the Netherlands considers the site conditions (land use, existing wells, etc.); however, a risk assessment is required for each site. Therefore, this study proposes a new framework for judging contamination in Japan by considering the merits of the environmental standards used and a method for risk assessment. The framework involves setting risk-based concentrations that are attainable remediation goals for contaminants in soil and groundwater. The framework was then applied to a model contaminated site for risk management, and the results are discussed regarding the effectiveness and applicability of the new methodology.     

Bioaccessibility of Fukushima‐Accident‐Derived Cs in Soils and the Contribution of Soil Ingestion to Radiation Doses in Children

Ingestion of contaminated soil is one potential internal exposure pathway in areas contaminated by the Fukushima Daiichi Nuclear Power Plant accident. Doses from this pathway can be overestimated if the availability of radioactive nuclides in soils for the gastrointestinal tract is not considered. The concept of bioaccessibility has been adopted to evaluate this availability based on in vitro tests. This study evaluated the bioaccessibility of radioactive cesium from soils via the physiologically‐based extraction test (PBET) and the extractability of those via an extraction test with 1 mol/L of hydrochloric acid (HCl). The bioaccessibility obtained in the PBET was 5.3% ± 1%, and the extractability in the tests with HCl was 16% ± 3%. The bioaccessibility was strongly correlated with the extractability. This result indicates the possibility that the extractability in HCl can be used as a good predictor of the bioaccessibility with PBET. In addition, we assessed the doses to children from the ingestion of soil via hand‐to‐mouth activity based on our PBET results using a probabilistic approach considering the spatial distribution of radioactive cesium in Date City in Fukushima Prefecture and the interindividual differences in the surveyed amounts of soil ingestion in Japan. The results of this assessment indicate that even if children were to routinely ingest a large amount of soil with relatively high contamination, the radiation doses from this pathway are negligible compared with doses from external exposure owing to deposited radionuclides in Fukushima Prefecture.     

Benzene Risk Estimation Using Radiation Equivalent Coefficients

We estimated benzene risk using a novel framework of risk assessment that employed the measurement of radiation dose equivalents to benzene metabolites and a PBPK model. The highest risks for 1 μg/m³ and 3.2 mg/m³ life time exposure of benzene estimated with a linear regression were 5.4 × 10⁻⁷ and 1.3 × 10⁻³, respectively. Even though these estimates were based on in vitro chromosome aberration test data, they were about one-sixth to one-fourteenth that from other studies and represent a fairly good estimate by using radiation equivalent coefficient as an "internal standard."     

Population studies ofCavelerius saccharivorus Okajima (Heteroptera: Lygaeidae): Adult dispersal in relation to the density

Summary Two adjacent stations (H and L) were set up to study movement ofC. saccharivorus adults in sugarcane fields. At the beginning of the study the density ofC. saccharivorus including all stages of development was quite different between the two. The density of the first generation adult on Station H was about 5 times that on Station L. The number ofC. saccharivorus on both the stations became almost the same one month after the beginning of the study. At the beginning of the study macropterous adults were more numerous in Station H than in Station L. However percentage of macropterous adults on Station L increased after one month whereas that on Station H declined. About 2,000 marked adults were released on each station during the early period of the emergence of the first generation adult. Marked insects were recaptured on both the stations one month after the release. The adults released on the dense population (H) tended to disperse more actively than those on the scarce population (L). Marked macropterous adults moved more actively than brachypterous ones. The density related dispersal of adults was considered to be an important factor to regulate the population density.