- Email: [email protected]
Chapter 11 Radon in Water
CHAPTER 11 RADONIN WATER The water in rivers, lakes and streams can be expected to contain radon in small amounts in view of the solubility of radon in water to the extent of almost 0.25 1 kg-‘ under standard conditions (see Table 3.1) and the wide distribution of uranium and thorium and their decay products in the soil and rocks of the Earth’s crust (Table 4.1). PUBLIC WATER SUPPLIES During the condensation and growth of rain drops minute quantities of radon from the air are included such that rain water contains only about 50 Bq m-’ (1.4 pci 1-’) and surface waters less than 2,000 Bq m-3. Water from underground aquifers where contact is made with rocks and soils containing normal quantities of uranium and radium will have an appreciable quantity of dissolved radon that may range from 20 to 44,000 Bq m-3 (ref. 1). A study of public ground water supplies that includes 3,318 samples from 42 states shows a geometric mean of 5,180 Bq m-’ with a geometric standard deviation of 3,530 Bq m-’ (from EPA reports 1979-1983). See ref. 2. In another survey Hess et al. (ref. 3) give a population-weighted average of 6,920 Bq m-’ geometric mean for water samples from 2,973 utilities across the United States 11.1
110
serving drinking water to some 59 million persons. The lifetime risk per person is 4 , 4 0 0 for the geometric mean with an overall lifetime risk of some 70 parts per million, a very small risk indeed. It is estimated that some 4 0 % of houses use water from private wells or similar sources having high radon content. Although domestic water use varies widely in the amount of radon released, some uses such as showers and dish washing release up to 98% of the radon in the water to indoor air. Of the 50 to 100 gallons of water used per day per person approximately 70% of the radon is released to the indoor environment. On this basis some 0.5 to 3 % of the approximately 4 0 Bq m-' mean radon concentration of radon in homes originates from the domestic water supply (ref. 1). From the above studies it can be concluded that radon does not constitute an appreciable hazard in water from public utilities. The interested reader is referred to I1SpecialIssue on Radioactivity in Drinking Water," Health Physics (ref. 4 ) for further information on this subject. SEA WATER Radium and "'Rn are found in near equilibrium amounts in the oceans at a level of about 4 Bq m-' ( 0 . 1 pCi 1-') only about lo-' of that found in domestic water supplies. A deficiency of "'Rn is found near the ocean surface due to escape through bubble formation and evaporation while an excess of "'Rn over its parent 226Raexists near the ocean floor where.minerals in the ocean floor add a small additional component. Since "'Rn atoms cannot escape readily from the water surface compared with the soil and rocks of continental areas, marine air masses contain only about 1% or less radon per unit volume than air over large land areas. 11.2
111
REFERENCES 1
2 3 4
NCRP 103, Control of Radon in Houses, National Council on Radiation Protection and Measurements, Bethesda,MD, 1989, p. 12. W.W. Nazaroff, S.M. Doyle, A.V. Nero and R.G. Sextro, Potable water as a source of airborne “‘Rn in U.S. dwellings: A review and assessment, Health Phys., 52(3) (1987) 281-295. C.T. Hess, J. Michel, T.R. Horton, H . M . Prichard and W.A. Coniglio, The occurrence of radioactivity in public water supplies intheunitedstates, HealthPhys.,48(5) (1985)553-586. C.R. Cothern and W.L. Lappenbusch, Guest Editors, Radioactivity in Drinking Water, Health Phys. , 48 (5) (1985) Pergamon Press, New York, NY, 529-716.
110
serving drinking water to some 59 million persons. The lifetime risk per person is 4 , 4 0 0 for the geometric mean with an overall lifetime risk of some 70 parts per million, a very small risk indeed. It is estimated that some 4 0 % of houses use water from private wells or similar sources having high radon content. Although domestic water use varies widely in the amount of radon released, some uses such as showers and dish washing release up to 98% of the radon in the water to indoor air. Of the 50 to 100 gallons of water used per day per person approximately 70% of the radon is released to the indoor environment. On this basis some 0.5 to 3 % of the approximately 4 0 Bq m-' mean radon concentration of radon in homes originates from the domestic water supply (ref. 1). From the above studies it can be concluded that radon does not constitute an appreciable hazard in water from public utilities. The interested reader is referred to I1SpecialIssue on Radioactivity in Drinking Water," Health Physics (ref. 4 ) for further information on this subject. SEA WATER Radium and "'Rn are found in near equilibrium amounts in the oceans at a level of about 4 Bq m-' ( 0 . 1 pCi 1-') only about lo-' of that found in domestic water supplies. A deficiency of "'Rn is found near the ocean surface due to escape through bubble formation and evaporation while an excess of "'Rn over its parent 226Raexists near the ocean floor where.minerals in the ocean floor add a small additional component. Since "'Rn atoms cannot escape readily from the water surface compared with the soil and rocks of continental areas, marine air masses contain only about 1% or less radon per unit volume than air over large land areas. 11.2
111
REFERENCES 1
2 3 4
NCRP 103, Control of Radon in Houses, National Council on Radiation Protection and Measurements, Bethesda,MD, 1989, p. 12. W.W. Nazaroff, S.M. Doyle, A.V. Nero and R.G. Sextro, Potable water as a source of airborne “‘Rn in U.S. dwellings: A review and assessment, Health Phys., 52(3) (1987) 281-295. C.T. Hess, J. Michel, T.R. Horton, H . M . Prichard and W.A. Coniglio, The occurrence of radioactivity in public water supplies intheunitedstates, HealthPhys.,48(5) (1985)553-586. C.R. Cothern and W.L. Lappenbusch, Guest Editors, Radioactivity in Drinking Water, Health Phys. , 48 (5) (1985) Pergamon Press, New York, NY, 529-716.