Lesson 30. OCCURRENCE OF RADIO NUCLIDES IN MILK PRODUCTS

Module 11. Molecular spectroscopy

Lesson 30
OCCURRENCE OF RADIO NUCLIDES IN MILK PRODUCTS

30.1 Introduction

Utilization of nuclear energy for beneficial purpose has become more common in the recent past. Radio nuclides are often secreted into the milk by the consumption of contaminated feed and water and are ultimately found in milk and milk products.

30.2 Source of Radio Nuclides in Milk

There are different pathways through which radionuclides enter the human body. A general path of such contamination could be diagrammatically represented as below

Fig. 30.1 Typical set of path ways through the environment from radiation

Greatest contamination would occur during nuclear fallout periods when cows graze ingesting grass from contaminated soil. Even if they are kept indoors, contamination of milk may occur by inhalation of radio-nuclides or ingesting them through contaminated drinking water and feed. Milk from goat and sheep, should be checked periodically over a longer period because of their ranch system of grazing.

Environmental radionuclide contamination is primarily man made. Nuclear explosions, manufacture and processing of nuclear fuel, accidents and or operation of nuclear reactors, increasing use of nuclear and disposal of radioactive waste will discharge radionuclide elements into the biosphere. This will further result in the contaminate the natural resources like soil, plants and water.

30.2

Fig. 30.2 157C5 incorporation cycle diagram in nature

Fig. 30.2 diagrammatically shows the incorporation of 137Cs in the nature. Vegetation when decomposed will result in the entry of radionuclides into the soil. Erosion of soil by rain, rivers etc., would result in the contamination of water. Sediments from contaminated water will in turn contaminate the soil. The plants growing in such a soil absorb the radionuclides.

30.3 Common Radio Nuclides Found in Milk

The most important radionuclides associated to internal radiation exposure (due to ingestion of contaminated water and food by the animal) and the contamination of the environment, are 134Cs, 137Cs, 137mBa, 131I, 89Sr, 90Sr, 238Pu, 239Pu, 241Am, 242Cm and tritium. With regard to milk, radionuclides of specific interest are 134Cs, 137Cs, 131I, 89Sr, 90Sr . As they decay at different rates, the doses from these elements and other radionuclides are delivered in different manners.

Table 30.1 Distribution of radio-nuclides in milk and their half life

Tab 30.1

(Source: Dairy chemistry and Physics, Walstra and Jenness, 1984)

  • Physical half life is the period needed to reduce the concentration/ amount of radioactive emission by an isotope to half of its original level, outside the biological system (i.e in-vitro).
  • Biological half life is the time taken for a radioactive isotope to be reduced to half of the amount in the body of after ingestion by an animal/ person.
Strontium accumulates in bone and remains there for a long time.90Sr uptake causes a prolonged exposure to harmful radiation as it has a long physical half life. It is distributed in milk in much similar way to calcium. However, strontium phosphate in milk is less soluble than calcium phosphate and a greater proportion of it associated with the casein micelles.

Barium behaves more nearly like calcium. Iodine accumulates in the thyroid gland where it attains high concentration and radioactive isotopes of 131I are considered hazardous as they produce intense radiation. Small portions of 131I are being strongly bound to protein while about 2% of it is found in the fat globules. Cesium chemically behaves like Na+ and K+ ions.

Atomic Energy Regulation Board (AERB) standards for radio activity are based on an annual exposure of 10 mrem when all items of food are contaminated to the recommended levels and intake is throughout the year. From milk and milk products alone exposure would be 1.6 MR/year which is quite small compared to the natural and other radiation exposure that is received during the day to day activities.

Radio nuclides in milk and milk products observed in different countries are invariably lower than that of recommended limits in those countries. Presence of radio nuclides in milk and milk products varies from country to country.

40K is some what more hazardous due to higher energy of radiation compared to 137Cs. Natural radioactivity due to 40K present in milk powder is in the range of 600 – 800 Bq/kg while in liquid milk in the range of 30-40 Bq / l in Indian milk and 50-80 Bq/l in foreign milk. It has also been reported that cow milk contains 44 Bq/l and buffalo milk contains 38Bq/l. Since potassium salts are very soluble 40K being retained in liquid phase in the preparation of butter and it contains only 1.3Bq/kg. Cheddar cheese is reported to have 41Bq/kg of 40K.

The ratio of 90Sr/ 137Cs in European milk is 1.8 while it is 0.5 – 1.58 in Indian milk. The mean value for 90Sr is reported to be 3.9 pCi / l

In India 137Cs has been reported to be 0.02 Bq/ l in milk and 0.6 Bq/l kg in milk powder which is far below than the prescribed levels of 30Bq/l in milk and 210 Bq/l kg in milk powder. Most of the dairy products in general contain 137Cs to the extent of 40Bq/1 kg. 131I present in milk is to an extent of 20 Bq/l.

Last modified: Thursday, 8 November 2012, 6:52 AM