Modes of Entry into the Body - STD-1128-98master0043

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

the ICRP 48 model yielding the lesser value. Factors affecting radiobiological effects include the

mode of entry of plutonium into the body, its distribution in the body, and its transfer to a fetus.

2.4.1

Modes of Entry into the Body

Radioactive material can enter the body by four different pathways: by inhalation,

through a wound, by ingestion, or by absorption through intact skin. These pathways

may occur singly or in any combination.

Inhalation is probably the most prevalent mode for occupational intake of

plutonium. It also provides a generally conservative assumption of intake for

designing bioassay programs.

Wounds are potentially the most serious mode of intake because of the high

dose-per-unit uptake of plutonium. Wounds can result from direct penetration by

an object (i.e., a puncture or cut), from abrasion, or from burning by an acid,

caustic, or thermal source.

Occupational ingestion of plutonium poses a relatively small risk because the

uptake factor from the GI tract to the blood is quite small and because most of the

alpha energy from transformations within the GI tract is absorbed by the contents

of the GI tract, rather than by the target tissues of the tract itself.

Absorption of plutonium through intact skin is, for practical purposes, almost

nonexistent. However, when removing skin contamination, care must be taken to

ensure that the skin integrity is not damaged by rough or extensive

decontamination procedures. If the skin integrity is damaged, the result can be

considered a wound, regardless of how it occurred.

2.4.2

Distribution Within the Body

Three commonly encountered biokinetic models have been promulgated by the ICRP for

the internal distribution and retention of plutonium. These models are identified by the

ICRP publications in which they were first reported: ICRP 30, Part 1 (1979), ICRP 48

(1986), and ICRP 30, Part 4 (1988b). The models are similar with regard to the organs of

significance, but differ with regard to the fraction of uptake deposited in the organ and its

respective retention (or clearance) half-time in the organ. The three models represent the

ones most widely used in dosimetry and in commercially available computer codes. In

all three ICRP models, once plutonium has reached the bloodstream, it is translocated

primarily to the liver and skeleton. In the skeleton, it is deposited primarily on the

endosteal surfaces of mineral bone, from which it is gradually redistributed throughout

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