Report on the
Tohoku Area
Pacific Offshore Earthquake

1. Introduction

Radionuclides were detected in the water of Tokyo in March, after the accident of Fukushima nuclear power plant. As a result, people became concerned about whether the water was safe. There are two kinds of people who concern: those who have no knowledge about nuclear, and those who have little knowledge and find out that "Japan's standard of radionuclides is 30 times higher than World Health Organization (WHO)'s!"

So in this paper, I would like to introduce how Japan's tentative standard for radioactive materials was made and compare it with other countries and organizations' standards.

In addition, the paper will only be focus on how Iodine-131's (short for I-131, which is a typical radioactive material threatens human beings' health) standard was made, since other standards can be analogized similarly.

2. Different Standard in different countries and organizations

Table 1 "different standards"(i

	JAPAN	FDA(ii,US	IAEA	WHO
I-131(Bq/kg)	300(100)(iii	170	3000(iv	10(v

It could be easily thought that "Japan's standard is 30 times higher than WHO's!"

However, it is not. Those standards are for different uses. Concretely, they are either for emergency case or for daily life. Apparently, Japan, FDA(US) and IAEA's standards are for emergency case and WHO's is for daily life.

How were they made? I would like to explain the decision-making process based on certain expressions.

3. Tentative standard making process, Japan

• Since it is "tentative" standard, there is no official standard until now.
• It was not made suddenly, however. It was made based on a guideline in 1998",(vi by Nuclear Safety Commission (NSC) of Japan.
• The number of 300(Bq/kg) (for I-131) is calculated based on the equation below.
  

  S=(ILD/G)/(F×W×Σfi×Si×((1-e(-λi×t))/λi))

  Where,

  S:

  tentative standard

  ILD:

  Intervention Level of Dose (ILD=50mSv×2/3(vii)

  G:

  Ratio of S's decreasing(viii (a fixed number=3 for I-131, which means taking the consideration of contamination spread, including water, milk, vegetable and fruits.)

  F:

  Ratio between the average concentration and the peak (F=1 for I-131 because for Iodine the half-life is short so average and the peak value can be thought to be similar)(ix

  W:

  Intake of water per day (W=1.65kg/day for adult)

  Fi(x:

  Premier abundance ratio(xi (specific abundance of isotope series when fi for I-131 is set to be 1)

  Si:

  conversion factor of radionuclides (to thyroid) (for example, si=4.3×10-4mSv/Bq for I-131, adult)

  λi:

  Decay constant (for example, λi=8.621×10-2/day for I-131)

  It is a complicated expression. Briefly, it contains several main points:

  Points

  • ILD - why 50 mSv?

    It was made by NSC based on the International Commission on Radiological Protection (ICRP). Briefly, social factors and some other cost must be taken into consideration when dealing with certain issues as the process of "optimization". Optimization is an idea for balancing the possibility of being exposure, individual's exposure dose and the amount of people who are exposure. The 50mSv is the balanced result.(xii

  • What does "(1-e(-λi×t))/λi" mean?

    The effect of radionuclides will decrease by time because of the half-life. Taking this into consideration, the standard was made for the maximum value right after the accident or similar situation, not the average value for the whole coming year. (That is the different point compared with other countries and organizations)

  • It seems that "300Bq/kg" cannot be calculated as the result of the expression based on the data above…

    That is true. The result is not 300Bq/kg based on the data above. Actually, there are different values of ILD, and other factors not only for adult but also for infants of ~3 years old and several months old. The result of different age groups is as follow:

    Table 2 Tentative standard of I-131 for the water in Tokyo by different age groups(xiii

    	Adults	Infants (under 3years)	Infants (several months)
    Tentative standard of I-131 (BQ/kg)	1270	424	322

    So it could be understood that "300Bq/kg" is conducted based on the most strict value among all the different ages.

4. Standard making process, United States (US)(xvi(xv

• Based on Guidance Levels for Radionuclides in Domestic and Imported Foods, revised in 2004, by Food and Drug Administration (FDA).
• This guidance document represents the FDA's current thinking on this topic. It does not create or confer any rights for or on any person and does not operate to bind FDA or the public.
• Food that is accidentally or intentionally contaminated with radionuclides are added in 2004. These changes were made to ensure that FDA staff has appropriate guidance to address an incident involving food accidentally or intentionally contaminated with radionuclides, whether in domestic interstate commerce or offered for import.
• The number of 170Bq/kg (for I-131) is calculated based on the equation below.
  

  DILs (Bq/kg)=(PAG(mSv))/(f×FI (kg)×DC (mSv/Bq))

  Where,

  DC:

  Dose Coefficient; the radiation dose received per unit of radionuclide activity ingested (DC=4.3×10-4mSv/Bq , for I-131, adult)

  f:

  Fraction of the food intake assumed to be contaminated (f=1 for I-131, adult)

  FI:

  Food Intake; the quantity of food consumed in an appropriate period of time (year) (average 250 kg/year (tap water) for US adults)

  The Protective Action Guides (PAGs) used are 5 mSv committed effective dose, equivalent, or 50 mSv committed dose equivalent to individual tissues and organs. (same as Japan)

As mentioned in the Japan’, similarly, “170Bq/kg” is conducted based on the most strict value among all the ages.

5. Comparison between the standard of Japan and US

Similarities:

• The basic form of equation
• The consideration of "50mSv" for I-131

Differences:

• The intake of water per year
• Whether taking consideration of the decrease of impact of radionuclides inside the human’s body. (Japan does while US does not)
• US divided more ages groups than Japan

For example,

Table 3 Tap water intake by age groups

	Age Group
Food Class	＜1	1~4	5~9	10~14	15~19	20~24	25~29	30~39	40~59	60&up
Tap water(l)	62.3	159	190	226	243	240	226	232	268

At the same time, IAEA made its Operation Intervention Level (OIL) for emergency case. The value comes to be 3000Bq/kg.

Here is the language explanation (descript) of OIL 6. (Cited from IAEA Safety Standard)

OIL6 plain language explanation

II36. Below OIL6: Locally Produced Food,milk and water have been screened, and all members of the public, including infants, children and pregnantwomen, can safely drink the milk and water and eat the food during the emergency phase.

II37. Above OIL6: Locally produced food,milk and water have been screened, and the measurements indicate that further investigation is neccessary before unrestricted general consumption of these items is allowed. however, if restriction of consumption is likely to result in severe malnutrition or dehydration, becaouse no replacement food, milk or water is available, then these items may be consumed for a short time until replacements are available.

II38.The analysis for OIL6 considers the most vulnerable members of the public(e.g. infants and pregnant women), and it assumes that all of the food, milk and water is contarminated. Exceeding the criteria therefore might not mean that the food, water or milk is unsuitable for consumption but might indicate that further investigation, including consideration of actual consumption rates and additional sceening is needed.

In one word, this standard is for huge emergency cases, to ensure that human beings' lives safety.

On the other hand, besides emergency cases, water-quality standard including criteria for radionuclides for daily life also exists, such as the WHO Guideline Level.

6. WHO Guideline Level

Citing a part of the guideline:

• The guidance levels for radionuclides in drinking-water were calculated by the following equation.
  

  GL=IDC/(hing×q)

  Where,

  GL:

  Guidance level of radionuclides in drinking-water (Bq/litre).

  IDC:

  Individual dose criterion, equal to 0.1mSv/year for this calculation.

  hing:

  Dose coefficient for ingestion by adults (mSv/Bq).

  q:

  Annual ingested volume of drinking-water, assumed to be 730 liters/year.

  Briefly, because the purpose is totally different from the emergency case, the values used are different. As a result, the value of standard is also different.(10Bq/kg)

7. Summarization

Table 4 Comparison of different equations for calculating standards

	JAPAN	US	IAEA	WHO
Equation	(ILD/G)/(F×W×Σfi× Si×((1-e(-λi×t))/λi))	(PAG(mSv))/(f×FI (kg)× DC (mSv/Bq))	IDC/(hing×q)	Not found
level of dose	ILD=50mSv	PAG=50mSv	IDC=0.1mSV/year	N/A
The consideration of intake besides drinking water (ex: fruits)	Yes(the "G")	Yes(the "f")	No(only drinking water)	No
Water-intake	W=1.65kg/day~adult	FI=62.3-268 l/year (depends on age)	q=730 liters/year	Not found
Consideration of dose coefficient(xvi	Σfi×Si× ((1-e(-λi×t))/λi)	DC	hing
Consideration fo half time(especially radionucliedes whose half-time is relatively long)	Yes (related to the formulation above)	No	No	N/A
Purpose	For emergency	For emergency	For daily life	For emergency

It is apparently that Japan and the US share the similar method to set the standard, because of some little differences which mentioned before, however, the final value turned to be different. While WHO and IAEA's are not unified with the two countries' for different purpose.

At last, the paper would be summarized as follows:

Table 5 True or false about the "different standard"

Truth	False
Radionuclides detected in the water in Tokyo	Japan decided the tentative standard for this accident suddenly.(based on the guideline in 1998)
Japan did not have standard on radionuclides for daily life water management, while some other countries or organizations, such as WHO, have.	Japan's standard is 30 times lower than WHO's (there are for different uses)
"Different standards" exist, for different uses, however.

As a result, according to the standard making process introduced above, whether the water is safe based on the tentative standard, or whether the standard is trustful, please think by yourself.

8. Reference

1. Sources are from the official site of certain department of each government and organization.

2. Food and Drug Administration

3. For infants

4. "IAEA Safety Standard"

5. "WHO Water Guideline"

6. 原子力安全委員会,「飲食物摂取制限に関する指標」；1998/3,

7. Left 1/3 is thought to be as reservation

8. 「食品群にまたがる場合のDIL低減比」

9. For most radionuclides, the half life is long. So hardly is it thought that the effect of certain nuclides could taken fully.

10. i=1 I-131; i=2 I-132; i=3 I-133; i=4 I-134; i=5 I-135; i=6 Te-132

11. 「初期存在比率」

12. 「最適化：それぞれの防護措置によって回避される放射線障害は、その措置によって達成される正味の便益が最大となるように、その措置の費用と他の損害に対してバランスを保つ必要がある。」

    http://www.nsc.go.jp/shinsashishin/pdf/history/59-15.pdf

13. Based on the data from the NSC

14. US.FDA：FDA/ORA CPG 7119.14 Sec. 560.750 Guidance Levels for Radionuclides in Domestic and Imported Foods (CPG 7119.14)

    http://www.fda.gov/Food/FoodSafety/FoodContaminantsAdulteration/ChemicalContaminants/Radionuclides/UCM078331

15. Supporting Document for Guidance Levels for Radionuclides in Domestic and Imported Foods

    http://www.fda.gov/OHRMS/DOCKETS/98fr/03d-0558-bkg0001.pdf

16. Obviously different values for different materials