48. Comparison of Stable Cesium and Radiocesium on Dietary Intakes in Japanese Subjects Using 18 Food Categories

Kunio Shiraishi, Tadaaki Ban-nai, Yasuyuki Muramastu and Masayoshi Yamamoto* (*Kanazawa Univ.)

Keywords: dietary intakes, ¹³⁷Cs, Cs, Japanese, mar bet basket study

The assessment of radiation doses in humans from man-made sources is important because artificial radiation is the largest contributor to committed internal doses in a nuclear emergency. Dietary intake of radioactive Cs has been studied since nuclear weapons testing began. Although analyses of many kinds of foodstuffs have been started, most results for Japanese subjects were obtained for total diet samples by duplicate portion studies. Furthermore, information on dietary element intakes ts umportant from the viewpoints of not only radiation protectuon, but also public hygiene and nutrition. It is also of interest to know the relationships for both radioactive and non-radioactive nuclides in food chains. Recently, inductively coupled plasma mass spec trometry (ICP-MS) has become a valuable instrumental method for trace element detection because of its wide dynamic range and capability for multi element analyses. In this report, stable Cs in 18 food categories was determined using a market basket study to clarify the food pathways of ¹³⁷Cs in Japanese subjects.

Three hundred and thirty-six foodstuffs were purchased from markets during 1994-1995. Total fresh weight treated was about 120 kg. Statistical consumption data of 1989-1991 (The Report of National Nutrition Survey) was used for collection of the food samples. Food categories are shown in Fig 15 The 18 categories were: 1) rice; 2) cereals, exclud ing rice; 3) nuts and seeds; 4) potatoes; 5) sugars and confectioneries' 6) fats and oils; 7) bean products; 8) fruits; 9) green vegetables; 10) other vegetables' 11) mushrooms; 12) seaweeds; 13) seasonings and beverages; 14) fishes and shellfishes; 15) meats; 16) eggs; 17) milk and milk products; and 18) cooked meals. Each food group was homogenized and freeze-dried. The obtained dry matter (approxi mately 5OOg) was incinerated in a muffle furnace at a final temperature of 40OC. Most of the ashed parts obtained were first used for -ray measurements using a Ge-detector coupled to a multichannel analyzer. A O.25g aliquot of ash sample was digested repeatedly with a mixture of nitric acid, perchloric acid, and hydrofluoric acid. Stable Cs was defer mined by ICP-MS.

The Cs concentrations in the 18 food categories were found range from 0.123 to 35.9ng per g-fresh. Five food categories, i.e. mushrooms (35.9ng), nuts and seeds (33.6ng), meats (26.8ng), fishes and shellfishes (21.6ng), and potatoes (19.2ng), were remarkably higher compared with other food groups. The groups of low Cs concentration were fats and oils (0.l23ng) and rice (0.737ng). The total daily Cs intake (9.12O.11 g per person) was estimated from the daily intakes of the 18 food categories.

¹³⁷Cs concentrations (mBq per kg-fresh) of the 18 food categories are shown in Fig 15. They were in the range of 0.022 (non-detectable; N.0.) and 1.7 Bq per kg-fresh. One category, mushrooms, as the highest at 1.7 Bq, was significant among the food groups. The next highest groups were nuts and seeds (O.23Bq), fishes and shellfishes (0.16Bq), meats (0.13Bq), potatoes(O.11Bq), and seaweeds (O.O92Bq) The groups with low ¹³⁷Cs contents were rice (<0.02bq), fruits (<0.02bcl), green vegetables (<0.03 bq), seasonings and beverages (<0.04 bq) and other vegetables (<0.05 bq). the total daily ¹³⁷Cs intake (<0.10 bq per person) was estimated from the daily intakes of the 18 food categories. the total of the values, excluding n.0. values, was 0.061 bq per person.

In conclusion, daily Cs and ¹³⁷Cs intake for Japanese were estimated to be 9.1 ng and 61mBq per person using a market basket study, respectively Mushrooms, fishes and shellfishes, milk and milk products, meats, potatoes, and nuts and seeds were found to be key food categories of Cs and ¹³⁷Cs intake in Japanese. Dietary intake studies by using eighteen or more food categories should be an effective procedure to resolve critical foods and critical pathways for Japanese. Critical pathways of radionuclides could be estimated more effectively by the analyses of stable isotopes using highly sensitive analytical methods.

Fig.15. Comparison of concentrations between 137cs and stable Cs in 18 categories for Japanese.

Publication:
Shiraishi, K., Ban-nai, T., Muramastu, Y. and Yamamoto M.: J. Radioanal. Nucl. Chem. 242, 687 692 1999.