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The level of radioactive cesium in food that is generally consumed in the rehydrated state can be calculated from measurements taken in the dried state using the specific weight change rate set by the Ministry of Health, Labour and Welfare. However, only a few dried foods have a specified weight change rate. Accurate specific weight change rates are critical in determining the compliance of a dried food item with Japanese maximum limits (JMLs) for radioactivity. We investigated the weight change rate of dried to rehydrated kotake mushrooms, which may contain relatively high concentrations of radioactive cesium and whose weight change rate has a large effect on the judgment of JML compliance. The average weight change rate of dried kotake mushrooms was 5.7 (range: 4.2 to 6.9), which was 1.4 times larger than the currently applied weight change rate of 4.0. Since the minimum weight change rate was 4.2 in this study, it was considered that the weight change rate currently applied to dried kotake mushrooms was a reasonable value. Further data is required in order to set specified weight change rates and to evaluate the validity of currently applied weight change rates in dried kotake mushroom.

To ensure food safety during emergency events such as nuclear disasters, we developed a practical rapid determination method for strontium-90 (Sr-90) in foods. Purification of Sr from foods was simplified using a commercial Sr-extraction column. We also reduced the waiting time to achieve radiative equilibrium between Sr-90 and Y-90. Finally, we developed a rapid determination method for Sr-90 that can be completed in about a week. Using the new method, stable Sr recoveries exceeded 85%. The trueness of the method ranged from 109 to 115% and the detection limit of Sr-90 was estimated to be 0.07 Bq/kg fresh weight according to a performance evaluation using standard materials. Sr-90 radioactivity concentrations in food samples determined by the new method were highly correlated and nearly equal to concentrations determined by the conventional method. The present study suggests that the new method offers highly sensitive and rapid detection of Sr-90 which are necessary attributes for food tests during emergency events.

Between fiscal years 2014 and 2016, we surveyed the concentration of radioactive cesium in commercial foods produced in areas where there is a risk of radiation contamination due to the Fukushima Daiichi nuclear disaster. The number of samples with a concentration of radioactive cesium that exceeded the regulatory limit （100 Bq/kg for general foods） was 9 out of 1,516 （0.6％） in fiscal 2014, 12 out of 900 （1.3％） in fiscal 2015, and 10 out of 654 （1.5％） in fiscal 2016. Even though some samples were expected to be contaminated with radioactive cesium, because wild mushrooms and edible wild plants were intentionally included in this survey, the percentage of samples that exceeded the regulatory limit was only around 1％. The surveillance results confirmed that the pre-shipment food monitoring conducted by local governments was properly and efficiently performed, although continuous monitoring of the concentration of radioactive cesium in cultivated and wild mushrooms, edible wild plants, and wild animal meats is still required.

We surveyed the concentration of radioactive cesium in foods purchased at markets in areas where possible contamination has been a concern after the Fukushima accident. In fiscal years 2012 and 2013, we surveyed 1,735 and 1,674 foods, respectively, using a NaI (Tl) scintillation spectrometer for the screening test and a γ-ray spectrometer with a germanium semiconductor detector for the final test. Only 3 and 4 samples (0.2% of our total samples) exceeded the regulatory limit (100 Bq/kg) for radioactive cesium in fiscal years 2012 and 2013, respectively. Our surveillance indicates that the pre-shipment monitoring of foods by local governments has been working effectively.

Radioactive contamination in foods is a matter of great concern after the Tokyo Electric Power Company's Fukushima Daiichi nuclear power plant disaster caused by the Great East Japan Earthquake. In order to estimate human intake and annual committed effective dose of radioactive materials, market basket and duplicate diet samples from various areas in Japan were analyzed for cesium-134 ((134)Cs), -137 ((137)Cs), and natural radionuclide potassium-40 ((40)K) by γ-ray spectroscopy. Dietary intake of radioactive cesium around Fukushima area was somewhat higher than in other areas. However, maximum committed effective doses obtained by the market basket and duplicate diet samples were 0.0094 and 0.027 mSv/year, respectively, which are much lower than the maximum permissible dose (1 mSv/year) in foods in Japan.

After the Fukushima No. 1 Nuclear Power Plant accident, high levels of radioactive cesium were detected in beef. Many prefectural governments decided to conduct blanket tests on meat from local beef cattle to prevent distribution of beef contaminated with radioactive cesium exceeding the provisional regulation value. In some cases, different concentrations of radioactive cesium were found in different cuts of beef from the same cows. These results raised questions about the reliability of the test results. Here, we investigated the reason for the differences in radioactive cesium concentration in different cuts of beef from the same cows. The concentrations of radioactive cesium in five different parts cuts of beef from three cows were negatively correlated with fat content, suggesting that the difference in radioactive cesium concentration is due to differences in fat content in the meat. In addition, our results showed that the concentration of radioactive cesium in muscle was more than 7-fold higher than that in fat in the same cow. These results suggested that it is necessary to use muscle for testing of radioactive cesium in cows.

It is important to obtain information about ways of removing radioactive cesium from foods in order to reduce internal radiation exposure from food and to ensure the safety and security of food. In this study, we investigated the change of radioactive cesium content in beef due to soaking in seasoning. Our results revealed that soaking beef in liquid seasoning (salt concentration: 8-10%) for 24 h or in miso seasoning (salt concentration: about 9%) for 7 days decreased the radioactive cesium content by about 20% and 55%, respectively, compared with that present in beef before soaking. Furthermore, soaking beef in 10% salt solution for 7 days while changing the salt solution every day or every three days decreased the radioactive cesium content by about 75%, compared with that present in beef before soaking. Because the seasoning is usually discarded after soaking, the procedure of soaking beef in seasoning is a useful method of reducing the burden of radioactive cesium.

We investigated the change of radioactive cesium content in food due to cooking in order to estimate the internal radiation exposure due to from radioactive materials in food. Our results revealed that soaking dry shiitake in water decreased the radioactive cesium content by about 50%, compared with that present in uncooked shiitake. Radioactive cesium in beef was decreased by about 10%, 12%, 60-65% and 80% by grilling, frying, boiling and stewing, respectively, compared to uncooked beef. For cooked beef, the decrease in the ratio of radioactive cesium was significantly different among the types of cooking. The decrease ratio of radioactive cesium in boiled and stewed beef was 8 times higher than that in grilled and fried beef.

We surveyed foods on the market from areas that had been exposed to radioactive materials contamination following the Fukushima accident. We used a NaI (Tl) scintillation spectrometer for the screening tests and a germanium semiconductor detector for the final tests. Test results from 1,427 samples showed that 6 samples (0.4%) exceeded the regulatory limit of 500 Bq/kg. Considering the detection rate of radioactive cesium in each food category, we suggest that it is necessary to continue monitoring fruits such as chestnuts and ginkgo nuts, mushrooms (especially raw wood-shiitake), mountain vegetables, and sea fish.

In Japan, seafood may be eaten raw or after having been cooked in diverse ways. Therefore, it is important to understand the effect of cooking on the extent of contamination with radioactive materials in order to avoid internal exposure to radioactive materials via seafood. In this study, we investigated the changes in radioactive cesium content in pond smelt cooked in four different ways: grilled, stewed (kanroni), fried and soaked (nanbanzuke). The radioactive cesium content in grilled, kanroni and fried pond smelt was almost unchanged compared with the uncooked state. In contrast, radioactive cesium content in nanbanzuke pond smelt was decreased by about 30%. Our result suggests that soaking cooked pond smelt in seasoning is an effective method of reducing the burden radioactive cesium.

Recently, it is concerned that nanomaterials induce undesirable biological responses (NanoTox) which is different from conventional materials attributed to their unique physicochemical properties in the world. Therefore, the movements to regulate the development and practical use of nanomaterials are accelerated in North America and Europe in corporation with Organisation for Economic Co-operation and Development (OECD). However, for our enjoying the benefits of nanomateirals, it is most important not to regulate nanomaterials in the blind way but to assure the security of nanomaterials and support the development of nanomaterial industries. These are duty of our country to be advanced country, technology-oriented nation and intellectual property nation. From these viewpoints, we are engaged on not NanoTox study but Nano-Safety Science study. That is, we try to research the relationship between physicochemical properties, biodistribution, intracellular localization, kinetics and biological responses (safety) of nanomaterials for the purpose of the collection and the transmission of safety information of nanomaterials based on scientific evidence lead to a support of nanomaterials' development. In this review, we would like to introduce our Nano-safety science study using mainly amorphous silica nanoparticles.

The Tokyo Electric Power Company's Fukushima Daiichi nuclear power plant disaster after the Great East Japan Earthquake has caused radioactive contamination in food. Using the market basket method, total diet samples in Tokyo, Miyagi prefecture and Fukushima prefecture were analyzed for cesium-134 and -137 (radioactive cesium) and naturally occurring potassium-40 (radioactive potassium) in order to estimate the committed effective doses of these radioactive materials from food. Doses were calculated on the assumption that "not detected" corresponded to zero or to half the limit of detection (values in brackets). The estimated doses of radioactive cesium in Tokyo, Miyagi and Fukushima were 0.0021 (0.0024), 0.017 (0.018) and 0.019 (0.019) mSv/year, respectively. Although the doses in Miyagi and Fukushima were more than 8 times the dose in Tokyo, they were significantly lower than the maximum permissible dose (1 mSv/year) determined by the Ministry of Health, Labour and Welfare, Japan. The estimated doses of naturally occurring radioactive potassium in these areas were in the range of 0.17-0.20 (0.18-0.20) mSv/year, and there were no significant differences between the areas.

With recent development of nanotechnology, nanomaterials (NMs) have been developed with innovative function and expected to cause a paradigm shift in various industry such as cosmetics, medicine and food. NMs begin to establish firm position in Japan as base of various industrials, in fact, a part of them have been already applied to various products. On the other hand, it is suggested that these innovative properties may induce unknown biological responses. It is concerned about the effect of these innovative properties to human health. Based on these situations, to evaluate risk of NMs, it is started to collect information about safety of NMs (Nano Safety Science). With this in mind, we analyzed the relationship between particle size and the in vitro effect of amorphous nanosilica (nSP) using human keratinocyte cells (HaCaT). Our results indicate that exposure to nSP of 70 nm diameter (nSP70) induced an elevated level of reactive oxygen species (ROS), leading to DNA damage. On the other hand, a markedly reduced response was observed using submicron-sized silica particles. Next, we investigate relationship between endocytosis, generation of ROS and DNA damage using endocytosis inhibitor, cytochalasin D (CytoD). As result, CytoD -treatment reduced nSP70-mediated ROS generation and DNA damage. This suggested that endocytosis is involved in nSP70-mediated cellular effects. Thus, particle size affects amorphous silica-induced ROS generation and DNA damage in HaCaT cells. We believe that clarification of the endocytosis pathway of nSP will provide useful information for hazard identification as well as the design of safer forms of nSP.

To clarify the whole picture of epidermal growth factor (EGF) signaling pathway, we identified proteins from the EGF-stimulated A431 cells by anti-phospho-tyrosine antibody column chromatography. Over 150 proteins were detected including previously unidentified proteins as well as well-studied proteins. Among these proteins, we picked up four proteins that had not been known in EGF signaling pathway and analyzed their functions. We report the functions of these proteins in this article. 1) CFBP interacts with CD2AP family proteins and functions as a key component in downregulation of EGF receptor protein level following EGF stimulation. 2) Ymer is found to be phosphorylated and ubiquitinated upon EGF stimulation, and functions as a regulator for the downregulation and endocytosis of EGF receptor. 3) CLPABP binds to mitochondria-specific phospholipids, cardiolipin, through its PH domain, and its complex includes various proteins related to mRNA metabolism. 4) GAREM is associated with Grb2 and Shp2. Each association affects the ERK activity. Finally, we discuss the possibilities that these proteins can be used as a novel biomarker protein for cancer and other diseases.

With recent development of the nanotechnology, nanomaterials have been successfully employed in various industrial applications such as medicine and cosmetics. Nanomaterials show the useful properties such as electronic reactivity and the tissue permeability that were not provided by micromaterials. Thus, nanomaterials are expected as innovative materials for the development of medicine and cosmetics. However, these innovative properties may show unknown biological responses that could not been detected by the conventional toxicity assay. For industrial development and affluent society establishment that enjoyed only a benefit of nanomaterials, it is urgent to gather information of the properties and the biological effects, and to establish the standard safety evaluation method of nanomaterials. So, we are analyzing association among property, biodistribution and biological effects of nanomaterials to search for the safety biomarker (functional-, molecular- and biochemical-biomarker) using nanosilicas (nSP) as a standard nanomaterial. Because nSP shows high uniform dispersibility and is already used in medicine, cosmetics and food additive, the results of this study are useful to extrapolate it to other nanomaterials and to make practicable as safety biomarker. In this report, we show the latest knowledge about the linkage information among property, biodistribution and biological effects of nSP by toxicokinetics and toxicoproteomics, and the search study of safety biomarker based on these basic information.

The recent development of nanotechnology has facilitated a dramatic reduction in the size of materials. Nanomaterials are nanometer-sized materials with specific physicochemical properties that are different from those of the bulk material of the same composition. Such properties make them very attractive for cosmetic and medical applications. However, nanoparticles can act on living cells or bodies at the nano-level resulting in biologically undesirable as well as desirable effects. Thus, reduction in particle size from the micro- to nano-scale not only provides benefits to diverse scientific fields but also poses potential risks to the environment and to human health. Although significant resources are aimed at exploiting the desirable properties of nanoparticles for applications in medicine or cosmetics there are only limited attempts to evaluate potentially undesirable effects in vivo. Thus, there is a pressing need for a careful consideration of the benefits and side effects to the use of nanoparticles in medicine and cosmetics. In recent years, the majority of toxic biological response induced by nanomaterials (Nanotoxicity) has focused on cell culture systems. However, data from these studies will require verification from in vivo experiments using animals. An understanding of Toxicokinetics (the relationship between the physical properties of the nanomaterials and their in vivo behavior) would provide a basis for evaluating undesirable effects. Moreover, toxicoproteomics may identify predictive bio-markers for examining nanotoxicity. In this review article, we describe the assumptions and challenges in the field of nanotoxicity and describe advances for studying nanotoxicity of nanosilicas using toxicokinetics/toxicoproteomics both in vivo and in vitro.