Environmental Engineering Reference
In-Depth Information
22
Risk from Inhalation of the
Long-Lived Radionuclides
Uranium, Thorium, and Fallout
Plutonium in the Atmosphere
Isabel M. Fisenne
CONTENTS
22.1 Introduction ......................................................................................................................... 555
22.2 Similarities and Differences ............................................................................................... 556
22.3 Sampling ............................................................................................................................. 556
22.4 Uranium in Total Suspended Particulates........................................................................... 557
22.5 Thorium in Total Suspended Particulates ........................................................................... 557
22.6 Plutonium in Total Suspended Particulates ........................................................................ 557
22.7 Resuspension ....................................................................................................................... 560
22.8 Respirable Concentrations of U, Th, and Pu....................................................................... 561
22.9 Value of Long-Term Monitoring ......................................................................................... 561
22.10 Exposure Estimation of U, Th, and Pu ............................................................................... 563
References...................................................................................................................................... 563
22.1 INTRODUCTION
The global population is chronically exposed to naturally occurring and man-made radionuclides
by both inhalation and ingestion. The inhalation pathway is the principal focus of this chapter and
the ingestion pathway will only be touched upon as necessary.
All soil and rocks contain the uranium and thorium series, headed by
238
U (t
1/2
= 4.468 × 10
9
year)
and
232
Th (t
1/2
= 1.405 × 10
10
year), respectively. The natural forces of erosion and weathering reduce
the particle size of the host rock or soil and surface winds suspend the small particles. These are
removed from the atmosphere by the usual scavenging processes. It is known that “dust storms”
resulting from desertiication carry material for thousands of kilometers and in some instances
around the world. The distribution of uranium and thorium in the terrestrial environment is rela-
tively constant at 2-3 μg U g
−1
(25-36 mBq
238
U g
−1
) of soil and 10 μg Th g
−1
(4 mBq
232
Th g
−1
) of soil
(NCRP 1987; UNSCEAR 2000a). There are geographical areas that do have higher concentrations
and have had the deposits exploited for commercial purposes. The bulk of the atmospheric inventory
of uranium is soil derived from the earth's surface. Additional sources of uranium are emissions
from energy-generating plants (coal, oil, nuclear), fallout resuspension from atmospheric nuclear
weapons tests, satellite failures, and nuclear-related accidents (UNSCEAR 1988). Atmospheric
thorium also is derived from soil resuspension and to a lesser degree energy-related emissions.
Plutonium is a man-made element and like U and Th is an actinide element. The principal
source of terrestrial plutonium was atmospheric nuclear weapons testing. Plutonium is produced
555
Search WWH ::
Custom Search