relative importance of inhalation and ingestion as sources of uptake of 210pb from the environment

Relative importance of inhalation and ingestion as sources of

uptake of 210Pb from the environment.

Salmon P. L.1, Berkovsky V. I.

2 and Henshaw D. L.

3

1. Royal Veterinary College, VBS Bone unit, Royal College Street, London NW1 0TU;

[email protected]

Tel. 0171 468 5263

Fax. 0171 388 1027

2. Radiation Protection Institute, 53 Melnikova, Kiev 254050, Ukraine.

[email protected]

3. H. H. Wills Physics Laboratory, Bristol University, Tyndall Ave., Bristol BS8 1TL;

[email protected]

Running title:

Sources of human 210

Pb uptake

Salmon et al. 6/23/2015 Sources of human 210

Pb uptake

2

Relative importance of inhalation and ingestion as sources of

uptake of 210Pb from the environment.

Salmon P. L., Berkovsky V. I. and Henshaw D. L.

Abstract

Dietary intake of 210

Pb is generally higher than inhalation intake, but fractional uptake

to blood is higher from inhalation. In this study publications are reviewed in which

both inhalation and ingestion intake of 210

Pb are measured. Concentrations of 210

Pb in

bone are also given, where available. Up to date biokinetic information on Pb is used

to evaluate fractional uptake from inhalation and ingestion, including consideration of

the effect of aerosol particle size. Estimates are also given of 210

Pb uptake from

domestic radon, alcoholic beverages and smoking. The difficulty in obtaining precise

estimates of 210

Pb uptake is emphasised. On average, atmospheric inhalation, diet and

domestic radon contribute 12, 86 and 2 % of total 210

Pb uptake respectively. Alcoholic

beverages and cigarettes can add a further 75%. Average committed effective dose

from one year of 210

Pb intake to adults is 37 µSv, while committed dose equivalents to

organs range widely from 380 µSv for bone surfaces to 5 µSv for most soft tissue

reflecting heterogeneous tissue distribution of Pb.


Pb uptake

3

Introduction

A number of authors have evaluated the sources of body burdens of 210

Pb in the

population (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)

. The two most significant intake routes are diet and

inhalation of 210

Pb, although some 210

Pb is formed by decay of 222

Rn and 226

Ra in the

body. In some of these publications the relative contributions of inhalation and

ingestion have been distorted by failure to account for the difference in fractional

systemic uptake between the two routes. This results in underestimation of the

significance of inhaled 210

Pb, due to the higher fractional systemic uptake from

inhalation than from ingestion in adults. In the present paper the difference between

210Pb intake (entrance into the body) and uptake (entrance into systemic blood

circulation) is stressed. The above mentioned studies will be briefly reviewed below.

Some of these studies included measurements of 210

Pb concentration in bone, which is

a representative index of cumulative 210

Pb uptake. Updated estimates of the

significance of routes of 210

Pb uptake, and resulting radiation doses from 210

Pb, will

then be derived for several countries, focusing on countries or locations where good

published measurements exist for both dietary and inhaled 210

Pb. Exceptional 210

Pb

intakes from sources such as radon in dwellings, certain foods, smoking and alcoholic

beverages will also be considered.

Review of published evaluations of human intake of 210

Pb from the environment.

Holtzman (1)

measured 210

Po, 210

Pb and 226

Ra in autopsy bone samples from 128

individuals in Illinois, USA, and estimated the magnitude of the main sources of

human intake of 210

Pb. The mean concentration of 210

Pb in wet bone was 1.5 Bq kg-1

,

and for 226

Ra 0.38 Bq kg-1

. A higher concentration of 210

Pb was found in trabecular


Pb uptake

4

than cortical bone, 1.9 and 1.1 Bq kg-1

respectively, a trend also found by Fisenne (12)

which may reflect enhanced concentration of 210

Pb at bone surfaces (13, 14, 15)

, although

other studies have shown higher 210

Pb in cortical bone (e.g. 4, 16)

. Holtzman’s evaluation

of the environmental sources of 210

Pb in bone was: 226

Ra in bones - 2.6%; radon

(222

Rn) short-lived daughter inhalation - 2.6%; 222

Rn dissolved in the body - 4.5%;

diet - 43%; inhalation of 210

Pb - 47%. High concentration of 210

Pb found in water from

some sources, such as wells, could add a further 14%.

A comprehensive review of 210

Pb in the environment and in human tissues was

undertaken by Jaworowski (2)

. He concluded that 210

Pb associated with common lead

(0.81 ± 0.74 Bq g-1

), for instance in vehicle emissions, was insignificant as a source of

airborne 210

Pb compared to airborne radon. Natural production of 222

Rn and 210

Pb in

the atmosphere was estimated, and the study listed a large number of measurements of

airborne 210

Pb concentrations in many countries. Global production of 210

Pb from

exhalation of 222

Rn was estimated at 2.3 × 1016

Bq y-1

, the atmospheric content of

210Pb at 1.9 × 10

15 Bq and the mean residence time of

210Pb 29 days. The atmospheric

content of 210

Pb as measured in glacial ice samples was reported to have been

temporarily increased by 45-60 % during 1959-1963 due to 210

Pb formed by

atmospheric nuclear bomb detonations. A relatively rapid falloff in atmospheric 210

Pb

occurred subsequently, consistent with estimates of atmospheric residence times for

210Pb of 10-50 days.

210Pb is formed in thermonuclear detonations when stable Pb is

used in construction of the bomb, the reaction is 208

Pb (2n, gamma) 210

Pb. Some of

the Soviet bombs exploded in the Arctic during 1959-1962 contained large amounts

of lead, which reduces overall fission product yield. There were some very big

detonations in this test series including the world record of over 50 megatons

exploded on Novaya Zemlya. Measured activity concentrations of 210

Pb were


Pb uptake

5

reviewed for water, food and the body organs of humans and animals. Jaworowski

estimated the relative magnitude of sources of 210

Pb uptake to blood: air 20%,

drinking water 1% and diet 79%. Human bone was found to contain 70% of the body

burden of 210

Pb at concentrations about an order of magnitude higher than soft tissues.

Taking an average concentration of 1.5 Bq kg-1

in bone, dose equivalent rate to bone

marrow (within 40 µm of bone surfaces) was calculated to be 70 µSv/y (taking Q for

alpha particles to be 20).

Dietary 210

Pb intake in residents of New York was assessed by Morse and Welford (3)

and found to be about 44 mBq day-1

. Airborne 210

Pb concentration was measured at

about 0.52 mBq m-3

. Uptake to blood was estimated to be equal for inhalation and diet

at about 3.7 mBq day-1

(assuming a daily breathed volume of 20 m3 in an adult).

These authors drew attention to the greater fractional uptake to blood from inhaled

compared to ingested 210

Pb, and employed coefficients of 0.29 and 0.08 respectively.

Ladinskaya et al. (4)

made a thorough study of the environmental sources and human

biokinetics of 210

Po and 210

Pb, based on measurements in Rostov-on-Don, Russia. The

concentration of 210

Pb in air was 0.63 ± 0.17 mBq m-3

, and the residence time of 210

Pb

in air was calculated as 45 days, derived from the 210

Po/210

Pb ratio in air of 0.21. Daily

inhalation and dietary intake of 210

Pb were estimated at 13 and 230 mBq respectively,

but these values were not converted into daily uptake to blood, which would add

relatively greater weight to the inhalation route. Human bone contained 2.7 Bq kg-1

(wet weight), the highest concentration found in any study in this review. Dose

equivalent rates to tissues were calculated for 210

Po and were highest in bone, liver

and kidney at 420-1000 µSv/y; in bone all 210

Po is supported by 210

Pb (15)

. For both


Pb uptake

6

210Po and

210Pb the measured excretion was 14-15 times greater through faeces than

urine.

[Table 1]

A metabolic balance study of 210

Po and 210

Pb in humans at natural levels was

undertaken by Spencer et al. (5)

. Balance studies are costly but may be the best way of

obtaining precise biokinetic data (17)

. Twelve adult males aged 41-63 received a

strictly controlled diet for several weeks prior to the study period of 18-24 days in

which 210

Po and 210

Pb balances were measured. The daily values of intake and output

are shown in table 1. Considering the error and variation associated with the values in

table 1, the measured input and output of 210

Po and 210

Pb are essentially in balance.

The large intake of 210

Pb from smoking is striking, at about twice the magnitude of

210Pb inhalation from ambient air. It should be noted that the value for diet is intake

only, and fractional uptake from gut to blood is not quantified. Thus much of the diet

intake goes through the gut unaffected to leave the body in the faeces. By contrast the

value for inhalation is the systemic uptake value, taking account of fractional

deposition (estimated at 0.5). For this reason the high ratio of faecal to urinary output

- 5.5 - is not a reflection of systemic excretion. The same can be said of the faecal-to-

urinary ratio of 14-15 quoted by Ladinskaya et al. (4)

.

If we take a value of fractional gut uptake (f1) for Pb of 0.15 (17)

, we can then compare

systemic uptake from diet and inhalation, and also systemic excretion by urine and

faeces, using the data of Spencer et al. (5)

. Both uptake and excretion turn out to be

almost equally divided into the two respective routes. Dietary and inhalation uptake of

210Pb are found to be 7.6 and 8.6 mBq day

-1, and urinary and faecal excretion of

210Pb

are 9.3 and 8.6 mBq d-1

respectively. However these estimates need some caution


Pb uptake

7

since, as is discussed later, substantial uncertainty exists concerning the value of f1 for

Pb.

Watson (6)

published another literature review of measurements of intake of 210

Po and

210Pb in foodstuffs and tobacco smoke. Inhalation from air was not included and the

biokinetics of uptake from diet and inhalation were not considered. Estimates were

made of radiation doses resulting from 210

Pb in diet and in cigarette smoke, using

published dose conversion factors (18)

. At 21 locations in the USA, Europe and India

(most in the USA) published values of 210

Pb intake in the daily diet gave a mean of 96

±48 mBq/d (excluding water and beverages). Higher intake of 210

Pb in Japan and the

Arctic was attributed to a higher dietary proportion of fish and shellfish. Whole body

committed effective doses from one year of the quoted dietary intakes were 7-70 µSv

in Europe and USA, but reached maximum values of 140 and 250 µSv in Japan and

the Arctic. The estimated daily inhalation of 210

Pb with tobacco smoke was 34 ± 27

mBq, or 1.7 mBq / cigarette assuming a 20-a-day habit. The associated value of whole

body committed effective dose from 210

Pb arising from one year of smoking was in

the range 30-550 µSv.

The 210

Pb body burden in Japanese citizens was measured by Takizawa et al. (7)

and

this study included a brief review of measurements of 210

Pb inhalation and dietary

intake in Japan. The mean concentration of 210

Pb in sternum bone from 15 adults

(male and female) was 1.27 ± 0.54 Bq kg-1

. The ratio of 210

Po/210

Pb was 0.9 ± 0.1. A

mean concentration of 210

Pb in air in two Japanese prefectures was 0.63 mBq m-3

, and

mean dietary intake of 210

Pb taken from several publications including Kametami et

al. (19)

was 430 mBq/d.


Pb uptake

8

Bennett and Sandalls (8)

reviewed human intake of 210

Pb and 210

Po. This study focused

on dietary intake with inhalation receiving less attention, although intake from

smoking was evaluated. Table 2 shows summarised measurements from Bennett and

Sandalls’ review of daily dietary 210

Pb content in four categories: USA, West Europe,

Central-Eastern Europe and a category for countries with exceptionally high 210

Pb

dietary intakes. The latter included Finland (Arctic reindeer consumption), Japan and

Alaska (seafood consumption).

[Table 2]

The most recent and thorough comparison of 210

Pb systemic uptake by diet and

inhalation, for a specific locality, is the study by Carvalho (9)

based on the Portuguese

population. Numerous measurements of 210

Pb in dietary foodstuffs were made, which

for Portugal included a large fraction of seafood which increased significantly the

dietary content of 210

Pb. (High seafood intake increases the intake of 210

Po by a

greater factor). Dietary intake was combined with an f1 value of 0.08 in common with

earlier studies (e.g. 2, 20, 21, 22)

giving daily systemic uptake of 210

Pb of 38 mBq. A study

of airborne radionuclides around Lisbon by the same author (23)

included a measured

210Pb concentration of 0.18 mBq m

-3. Taking fractional inhalation uptake as 0.19 and

a daily breathed volume of 20 m3, daily

210Pb uptake was 0.69 mBq. Thus uptake

from food was more than 50 times higher than from inhalation. As this review will

discuss later, this ratio is exceptionally high compared to other countries, due to high

210Pb intake from food items including seafood and low

210Pb concentration of north-

eastern Atlantic air. Carvalho identified two other significant sources of 210

Pb uptake,

alcoholic beverages and tobacco smoke, which accounted for 9% and 6% of total

uptake respectively.


Pb uptake

9

Linsalata (10)

reviewed the foodchain transfer to humans and animals of natural

radionuclides in the uranium and thorium series. 210

Po and 210

Pb were shown by

Linsalata to have particular significance to agriculture due to the higher measured

transfer from soil to plants of 210

Po and 210

Pb compared to Ra, Th and U. Particularly

efficient transfer of 210

Po and 210

Pb to forage and hay was found, due in part to weaker

affinity for soil sorption in these two nuclides compared to Ra, Th and U. Cattle have

been found to have concentrations of 210

Pb in bone 2-5 times higher than in human

bone (12)

. Plant based foods were estimated to contribute 70% of human dietary intake

of 210

Pb, and animal based foods the remaining 30%. The efficient transfer of 210

Po

and 210

Pb to plant tissue from soil, both by root absorption and by deposition on leaf

surfaces, in the case of tobacco results in substantial activity of both nuclides in

cigarette smoke (24)

.

Pietrzak-Flis et al. (1997, reference 11) made detailed measurements of 210

Pb and

210Po content in dietary items of residents of several regions in Poland. The daily

intake of both nuclides at Nowe Miasto is shown in table 3. The largest sources of

210Pb were meat and flour. By contrast the highest

210Po contribution was from fish, in

which the ratio 210

Po/210

Pb was about 10. These trends reflect differences in the

chemical binding of Pb and Po to biological tissue. Annual effective dose equivalent

in adults from the measured intake of 210

Pb and 210

Po was 54 µSv. Table 3 gives a

general indication of the relative contributions of food types to dietary intake of 210

Pb

and 210

Po, but these contributions differ between countries due to differences in diet.

Measurements of concentrations of both nuclides in many food types are presented in

several references (2, 6, 8, 9, 10, 11)

.

[Table 3]


Pb uptake

10

[Table 4]

A summary of several previous estimates of the relative magnitude of sources of 210

Pb

uptake, from the studies reviewed above, is given in table 4. Since the earlier of the

above studies were published, more work has been done on measurement of fractional

systemic uptake of Pb from various forms of inhaled and ingested Pb. Physical and

chemical parameters of inhaled and ingested Pb cause wide variation in fractional

systemic uptake, and therefore it is impossible to derive precise general fractional

uptake factors. However, by applying currently available data on Pb biokinetics from

recent studies (e.g. 17, 25, 26, 27)

it is possible to obtain revised estimates of the relative

magnitude of inhalation and ingestion as uptake routes for 210

Pb. Estimates are given

here for several countries from which sufficient data has been published on airborne

and dietary 210

Pb to allow a comparison of intake routes. The relative intakes from

inhalation and ingestion differ between countries under the influence of factors such

as meteorology and diet.

Systemic uptake of Pb from inhalation and ingestion.

Two recent publications by the International Commission on Radiological Protection

(ICRP) summarise the experimental data to date on radionuclide fractional uptake

from ingestion and inhalation (26, 27)

. The data used by the ICRP for biokinetics of Pb

were summarised from extensive data provided in a model for Pb by Leggett (17)

.

These three papers are the principal sources of the biokinetic parameters for Pb in this

study, in which 210

Pb uptake will be calculated for adults only for simplicity.


Pb uptake

11

Fractional systemic Pb uptake from inhalation in relation to aerosol particle size

The uptake of Pb from airborne particles to the human bloodstream can be considered

as a process with several stages, such as fractional deposition of particles in the lung,

fractional clearance of particles from lung to the stomach, and uptake from lung-

deposited particles to blood. The ICRP 66 respiratory tract model (27)

embraces the

complex dynamics of particles in different parts of the respiratory tract by assigning

different parameters for fractional particle deposition in nine compartments, from the

extrathoracic region (the nasal and buccal cavities, compartments ET1 and ET2)

through the bronchiolar compartments to the alveoli. For each of these compartments,

fractional deposition is separately defined for 15 particle diameters (Aerodynamic

mean aerosol diameter, AMAD) from 0.0006 to 5 µm. Fractional parameters for

transfer of Pb from particles to lung to blood from ICRP 66 are shown in table 5 for

particles from 0.001 to 5 µm AMAD. The relevant value of fractional particle

deposition is the total value excluding ET1, the deposition in the anterior nasal

passage, since little uptake to blood occurs in this region. A small fraction of

particulate 210

Pb is cleared from lung to lymph nodes, about 0.7% for the lung and

0.05% for nasal passages and upper trachea (27)

. Within the respiratory tract model,

elements bound to aerosol particles are characterised as having fast, moderate or slow

transfer from particle to blood; in this respect Pb transfer to blood is fast.

[Table 5]

Chamberlain et al. (28)

made a thorough study of inhalation of car exhaust tagged with

203Pb; they showed that exposure of aerosols to strong sunlight significantly reduced

both lung clearance rate and systemic uptake of Pb, indicating the importance of


Pb uptake

12

photo-chemical transformations in Pb-containing aerosols. The factor of sunlight will

not be considered in the present study owing to the difficulty in quantifying its effect.

Outdoor atmospheric 210

Pb is mostly particle-associated, showing a strong correlation

with concentration of atmospheric dust (29)

. The selection effect of faster removal from

the atmosphere of larger particles, by settling and rainfall washout, ensures that a

significant part of atmospheric 210

Pb is attached to the smallest aerosol particles. It is

clear from table 5 that particle size can affect Pb fractional uptake from the lung by a

factor of 2 or more. In the next section published data on the distribution of airborne

Pb between particle size fractions is examined, allowing a nominal distribution to be

assumed for the purpose of the quantitative estimates of fractional inhalation uptake in

this study.

The level of physical activity and age strongly affect inhaled volume, so some

estimate of patterns of daily activity at different ages is required in order to estimate

average daily inhaled volume. Table 6 shows the time spent at different activity

levels, from sleep to heavy exercise, at different ages, and breathing rates at each

activity level (27)

. For this study the mean value quoted for adults of 22 m3 day

-1 will

be adopted for calculations of intake, but the variation on the basis of physical activity

and age should be noted. A study by Layton (30)

produced lower daily inhaled volumes

ranging from 10-18 m2. Layton calculated inhaled volume on the basis of a

biochemical calculation of oxygen consumption, using data on diet and other energy

expenditure such as exercise. This study pointed to the biochemical energy link that

exists between inhalation and diet - the digestion of food requires energy which

necessitates oxygen inhalation. But in principle a direct measurement of inhaled

volume is preferable to an indirect calculation.


Pb uptake

13

[Table 6]

Distribution of airborne Pb between particle size fractions.

Horvath et al. (31)

used rotating cascade impactors to measure the distribution of

several contaminant elements in relation to size fractions of atmospheric aerosols, in

suburban and city centre air around Vienna. Lead and other elements were measured

by proton induced x-ray emission (PIXE). The proportion of atmospheric Pb by mass

found in three aerosol size fractions is shown in table 7. There was more Pb in the

1µm - 60 nm fraction near the city centre than at the suburban site, which could have

arisen from vehicle exhaust. The identical measured fraction of Pb at both locations

attached to particles less than 60 nm in diameter - 10% - probably reflects long

atmospheric lifetime and good mixing of these particles.

[Table 7]

The physical characteristics of aerosol particles in Los Angeles, USA, were studied by

Hinds (32)

. The author showed the distribution of particles according to volume,

surface area and number. The fraction of the smallest submicron particles increases

sharply over these three respective dimensions. Thus most particle volume is

accounted for by the diameter range 0.1 - 10 µm, most particle surface area is in the

range 0.05-0.5 µm, and particle numbers are dominated by the range 0.005-0.05 µm

diameter. Of the three parameters, surface area correlates most closely to the

distribution of particle-bound Pb. Table 7 shows that the distribution of particle

surface area and the distribution of Pb by mass are in approximate agreement.

If we assume that the distribution of airborne 210

Pb by aerosol diameter is

approximately the same as for stable Pb, then we can use the data of Horvath et al. (31)


Pb uptake

14

and Hinds (32)

to specify a distribution of 210

Pb by activity into the particle diameters

(AMAD) which are considered in the lung model in ICRP 66, listed in table 5. We

will assume the following distribution by activity of airborne 210

Pb by particle

AMAD: 5 µ - 5%; 1 µm - 30%; 0.1 µm - 55%; 0.01 µm - 10%. When these fractions

are multiplied by the fractional inhalation uptake fractions from table 5 (last column,

total uptake) then a weighted mean fractional uptake fraction of 0.34 is obtained,

which will be employed in this study. We also assume that all airborne 210

Pb is

particle-associated (29)

.

Several studies have shown that the distribution of attached radon daughters by

particle size is broadly similar indoors to that reported by Horvath et al. (30)

for

outdoor Pb; again the daughter activity follows particle surface area (33, 34, 35)

.

One further factor must be considered in calculating inhalation uptake of 210

Pb.

Particles bearing 210

Pb deposit on surfaces more rapidly indoors than outdoors, and

this decreases the indoor concentration of 210

Pb compared to outdoor air. The

dynamics of particle deposition were described by Porstendorfer (36)

and will be

discussed below in the section on indoor radon. If the indoor rate of surface deposition

for attached 210

Pb, qa = 0.17 hr

-1 (36)

and the ventilation lifetime of indoor air is 2

hours, and for a house occupancy of 0.6, deposition in houses decreases total

inhalation uptake of 210

Pb by 15%.

Fractional systemic Pb uptake from ingestion

Several factors exert a strong influence on fractional uptake of Pb to blood from the

gastro-intestinal tract (GIT), including the concentration in the GIT of calcium,

phosphorus, zinc, iron and vitamin D, and fasting (17)

. Fractional uptake to the GIT is


Pb uptake

15

given the parameter name f1 in ICRP publications (e.g. publication 67 (26)

). The

published values for fractional systemic uptake of Pb from the GIT vary even more

widely than the values for fractional uptake of inhaled Pb, and values of f1 between

0.01 and 0.8 have been measured (17)

. However, balance studies assess Pb uptake over

a period of time and smooth some of the variation caused by the above factors. The

average f1 value obtained by Leggett (17)

for Pb fractional uptake from balance studies

is 0.15 for adults, and this value will be used here. However to indicate the wide range

of measured values for f1 of Pb, minimum and maximum values of 0.03 and 0.5 will

be considered, corresponding roughly to the 95% confidence intervals of a log-normal

distribution.

In infants and children fractional uptake of Pb from the GIT is much higher than in

adults. The f1 for Pb decreases from 0.5 in the first year to the adult value of 0.08 by

age 10 in the model of O’Flaherty (25)

and from 0.45 at birth to the adult value of 0.15

by age 25 in Leggett’s model (17)

. The balance studies in children from which these

values are derived have also produced highly variable results, so that elevated f1 for

Pb in children cannot be quantified with confidence. The f1 value in early life has an

important bearing on the monitoring of 210

Pb in children’s teeth as a measure of

environmental uptake of 210

Pb (37, 38)

, since these are generally deciduous teeth taken

from children aged 10-13, and if f1 is significantly raised at this age compared to adult

f1, then inhalation uptake will be a correspondingly smaller fraction of total uptake.


Pb uptake

16

Sources of additional or exceptional Pb-210 intakes

Radon in dwellings.

Inhaled radon (222

Rn) is also a source of 210

Pb in the body. Radon dissolved in body

tissues results in a component of 210

Pb uptake. Also, virtually all short-lived radon

daughters inhaled will decay into 210

Pb in the body. Following diffusion of radon from

soil and building materials into dwellings, the airborne short-lived daughters are

subject to complex processes involving diffusion and settlement onto particles and

surfaces. These processes have an important bearing on the amount of radon daughter

activity available for inhalation and uptake, and were comprehensively reviewed by

Porstendorfer (36)

. The two key processes which remove daughters from indoor air are

deposition on surfaces and removal by ventilation. These will be considered here

briefly in turn in order to calculate the concentration of radon daughters available for

inhalation, and the resultant 210

Pb deposition in the body, relative to radon

concentration for three different ventilation conditions characterised by air lifetimes

of 30 minutes, 2 hours and 20 hours.

Surface deposition q of daughters in a room can be defined as a fractional rate, h-1

, so

that q=vgSV-1

, where vg is the average deposition velocity, m h-1

, and S and V are the

room surface area m2 and volume m

3. Two deposition fractional rates need to be

considered, those for attached qa and unattached (free) daughters q

f. Deposition is

much faster for unattached daughters than attached: five recently published

measurements of qa and q

f in dwellings give mean values of 0.17 h

-1 and 33 h

-1

respectively (36)

. Radon daughters rapidly attach to particles, reducing the significance

of unattached deposition for all daughters except the short-lived 218

Po. The attachment

rate X for radon daughters has been measured at 20-50 h-1

in rooms with relatively


Pb uptake

17

clean air, but X can increase to 1000 h-1

in rooms where additional aerosols are

produced by smoking or cooking (39)

. A value for X of 50 h-1

will be adopted here.

To estimate fractions of radon daughters removed by surface deposition, free and

attached, the half lives of the three important daughters must be considered, which are

for 218

Po 3.05 minutes, for 214

Pb 26.8 minutes and for 214

Bi 19.7 minutes.

Porstendorfer showed that the unattached fractions of these three daughters, for an

attachment rate X = 50 h-1

, are 0.21, 0.025 and 0.001 respectively. Knowing these

fractions we can calculate the removal of each daughter by free and attached surface

deposition, and also the removal of 210

Pb formed from 222

Rn.

In general the remaining fraction of a radon daughter (i) is given by:

i e ventilation deposition i

(1)

where is the radioactive lifetime.

The standard radon equilibrium factor F is defined :

F 0105 0516 0 3791 2 3. . . (2)

where 1, 2, and 3 are remaining fractions of 218

Po, 214

Pb and 214

Bi respectively. F

values calculated from eqtns. 1 and 2 for ventilation times of 30 minutes, 2 hours and

20 hours are 0.18, 0.47 and 0.66 respectively. For the general estimates in this study a

ventilation time of two hours and the F value 0.47 will be assumed for dwellings.

(This is conservative for the UK where ventilation rates in housing are higher than in

other temperate countries.) Due to its long radioactive lifetime, 210

Pb formed from


Pb uptake

18

indoor radon is completely removed by surface deposition and ventilation. Thus

airborne 210

Pb in houses originates from outdoor air, where the low surface deposition

allows the build up of 210

Pb activity from 222

Rn decay.

In addition to radon daughters taken up by inhalation and particle deposition in the

lung, there is a second component of 210

Pb uptake from indoor radon, resulting from

decay of the 222

Rn gas dissolved in the body (40)

. Assuming an adult body volume of

70 l and a radon distribution coefficient in the body of 0.9 (41, 42)

, the body will contain

the amount of radon present in 63 l of air. Unlike daughter uptake from particle

inhalation, uptake from dissolved radon is not affected by the daughter equilibrium

ratio in the air. In the body equilibrium is assumed for dissolved 222

Rn through to

214Bi, since Pb, Bi and Po all have retention half lives of a few weeks in soft tissue

(26).

In table 8 the systemic uptake of 210

Pb is given for dissolved radon and particle

inhalation, in relation to ventilation rate. In 30-minute air the two components are

similar in magnitude; as ventilation decreases particle inhalation becomes more

significant as a source of 210

Pb. Table 13 gives an assessment of the significance of

210Pb from radon compared to total

210Pb uptake.

[Table 8]

Foodstuffs

In most foodstuffs 210

Pb concentration is much less than 1 Bq kg-1

. Certain foods

contain significantly elevated 210

Pb concentrations; this is generally related to 210

Pb

root absorption into and deposition onto plant foliage or 210

Pb accumulation by

aquatic organisms. Regions with elevated natural radioactivity can give rise to

foodstuffs with high 210

Pb concentrations, such as areas of North Canada containing


Pb uptake

19

rich uranium ore deposits. Recorded examples of foodstuffs with elevated 210

Pb

include Green Tea leaves: 31 Bq kg-1

(18)

, spinach: 3.3 Bq kg-1

(2)

, marine molluscs:

0.5-16 Bq kg-1

(9)

, sardines: 4.8 Bq kg-1

(18)

and the liver and kidneys of grazing

animals such as cattle: 3.7-13 Bq kg-1

(2)

and Arctic caribou: 57-158 Bq kg-1

(43)

, 300-

1500 Bq kg-1

(44)

. Diets in which any of these foodstuffs are predominant could result

in unusually high 210

Pb intake. Where seafood consumption is high, dietary intake of

210Pb (and to a greater extent

210Po) is significantly elevated. Inuit hunters of Northern

Canada who eat caribou meat including liver and kidneys in significant quantities, and

also reindeer herding people in Lapland and Siberia, are exposed to a highly elevated

intake of both 210

Po and 210

Pb (43, 45, 46)

. The largest intakes of 210

Po and 210

Pb are from

caribou liver and kidney consumption; caribou muscle contains the lowest 210

Po and

210Pb concentrations of all the body tissues, although more muscle is consumed than

offal. Radation doses from caribou consumption are discussed below in the section on

dosimetry.

Alcoholic beverages

Concentrations of 210

Pb (and 210

Po) in beverages such as wine and beer are such that

average beverage consumption is a significant source of 210

Pb. Carvalho (9)

measured

130 mBq kg-1

(wet) of 210

Pb in wine and beer, which with a mean daily consumption

of 0.35 l gave daily ingestion intake of 45 mBq, a contribution of 9% to total daily

systemic uptake of 210

Pb in Portugal. The content of 210

Pb in beverages in UK was

measured previously as 28 mBq kg-1

(47)

. Table 13 in section 2.5 gives an assessment

of the significance of 210

Pb in beverage consumption compared to total 210

Pb uptake.


Pb uptake

20

Smoking

Smoking can be a significant source of 210

Pb intake, owing to appreciable activity of

210Pb in tobacco plants from root absorption and atmospheric deposition of

210Pb onto

the leaves. Inhalation intake of 210

Pb from smoking one cigarette has been quoted by

UNSCEAR (20)

as 1.7 mBq, so that smoking 20 a day gives a daily inhalation intake of

33 mBq of 210

Pb. A later review by Watson (6)

gave an average daily 210

Pb inhalation

from smoking of 34 mBq, in close agreement with the UNSCEAR estimate, although

measured values ranged from 4-77 mBq. Table 13 in section 2.5 gives an assessment

of the significance of smoking compared to total 210

Pb uptake.

Drinking water

Treated tap water is generally a negligible source of 210

Pb uptake; in the review by

Jaworowski (2)

systemic uptake from drinking water was 1% of uptake from food.

This value was derived from a mean measured 210

Pb concentration in tap water of 1.1

mBq l-1

. However, samples of untreated mineral water in France and Poland have

been found to contain 33-260 mBq l-1

of 210

Pb (2)

, and in Spain up to 1130 mBq l-1

(48)

,

so that someone drinking water predominantly from these sources would receive 210

Pb

uptake from water comparable to uptake from food.

Radium-226

Radium-226 is present in the skeleton at an average whole skeleton content of 0.85

Bq, less than a tenth that of 210

Pb (21)

. During the long retention of 226

Ra in bone some

210Pb will ingrow from it. We can calculate the approximate source of

210Pb this

represents to the body. During decay from 226

Ra to 210

Pb, 222

Rn is formed of which

about 70% leaves bone (21)

. The retention time of 226

Ra in bone is controlled by


Pb uptake

21

remodelling, which occurs at rates of 3% and 26% per year for cortical and trabecular

bone, which respectively make up 80% and 20% of the skeleton (26)

. This results in

ingrowth ratios for 210

Pb/226

Ra of 0.38 and 0.06 respectively in cortical and trabecular

bone. Bone remodelling causes a flux of nuclides such as 226

Ra and 210

Pb from bone

to blood. From the above values, the daily input of 210

Pb to blood originating from

226Ra in bone is about 8 × 10

-6 Bq, or 0.02% of daily uptake to blood of

210Pb.

Radium-226 is thus an insignificant source of 210

Pb in the body. About 1% of skeletal

210Pb is derived from

226Ra.

For the purposes of the present study, exceptional sources of high 210

Pb intake will be

considered separately, and the values for systemic uptake of 210

Pb given will be those

considered representative of the general population taken from published

measurements in the literature. However these exceptional sources of 210

Pb intake,

particularly smoking and beverages, are important to large numbers of people.

Revised estimates of systemic uptake of Pb-210 in various countries.

Measurements of 210

Pb in both air and diet are available for eight countries or

locations – Illinois (USA), all USA, Japan, UK, Germany, Poland, Russia and

Portugal. For six of these measurements of 210

Pb in human bone are also available.

210Pb in air

Atmospheric 210

Pb concentration will vary as weather systems bring air masses of

different origin over a given location. Continental air masses have higher 210

Pb

concentration than maritime air masses (9)

. Hötzl and Winkler (29)

measured 210

Pb in

air at Neuherberg in Germany at two week intervals during 1983 through 1985 (72


Pb uptake

22

measurements) and obtained a measurement geometric SD of 1.5, indicating the scale

of the variation. Preiss et al. (49)

comprehensively surveyed 210

Pb measurements in air

from over 800 sites around the world. These authors showed that a small number of

factors could broadly account for the geographic pattern of airborne 210

Pb

concentration. Principally land surfaces release a significant flux of 210

Pb into the

atmosphere while from the sea or ice this flux is negligible. In the northern

hemisphere there is generally a prevailing westerly (west to east) wind especially at

temperate latitudes, and this causes asymmetry in the distribution of 210

Pb

concentration over the North American and Eurasian continents, with concentration

lowest at the eastern continental margin and increasing toward the western margin.

The highest ground flux of 210

Pb to the atmosphere was found in Japan: this was

attributed to rainfall in Japan washing down 210

Pb from eastward-moving air which

had become highly enriched in 210

Pb due to long residence over Eurasia (50)

. Although

Japan is an island its status in regard to airborne 210

Pb is similar to East Asia and the

eastern USA at the eastern continental margins, where the ground flux of 210

Pb is also

high.

[Table 9]

In general Preiss et al. (49)

found that airborne 210

Pb concentration varied with latitude

in proportion to the fraction of a latitude band occupied by land. A cycling of 210

Pb

was described in which ground flux of 210

Pb was increased in areas where rainfall

washed down higher amounts of 210

Pb from air to ground. The relation between

ground flux and airborne concentration of 210

Pb at different latitudes is shown in table

9.


Pb uptake

23

210Pb in diet

It is difficult to obtain a very satisfactory mean value for 210

Pb in diet for any country

or location, due to variation in diet between individuals, although this variation is

somewhat reduced by the increasing prevalence of large supermarket chains as

peoples’ source of food. The systemic uptakes of 210

Pb from air and diet have been

calculated for eight locations from the published values of 210

Pb concentration in air

and diet, and are shown in table 10. It should be emphasised that 210

Pb uptake through

both routes varies substantially under the influence of a number of factors, and thus

the precision of the stated values is low. Possibly the largest source of uncertainty is

in the GIT fractional uptake factor f1; in table 10 three values are given for f1 which

approximately represent 5%, 50% and 95% levels of a log-normal distribution. Figure

1 shows the percent contribution of 210

Pb inhalation (from atmospheric air, excluding

smoking or domestic radon) to total uptake in the eight countries: this is shown to

vary quite widely, with an international mean of 16 ± 6%. The proportion of 210

Pb

uptake by inhalation is highest in the USA among the studied countries, due to high

continental levels of atmospheric 210

Pb, and a diet relatively low in 210

Pb. The

proportion of 210

Pb uptake from diet and air is discussed further below in relation to

table 12.

[Table 10]

210Pb in bone

Lead-210 is a bone-seeking element with an effective half-life in bone of about 15-18

years (51, 52)

. Several authors have demonstrated that bone Pb is a good indicator of

cumulative Pb uptake (16, 17, 25, 51, 52, 53)

. The concentration of 210

Pb in bone can


Pb uptake

24

therefore be used as an integrated measure of systemic 210

Pb uptake. In table 11 the

central estimates of total 210

Pb uptake (f1 = 0.15) are compared to measurements of

210Pb concentration in bone in six of the eight locations. This allows a mean value to

be specified to characterise the concentration of 210

Pb in bone in relation to daily

systemic uptake of 210

Pb, assuming lifetime intake with constant concentration of

210Pb in food and air. The measurements in table 11 suggest that on average the


Pb in bone in adults (Bq kg-1

wet) is related to the daily 210

Pb

systemic uptake (Bq d-1

) by the value 62 d kg-1

. This compares with values for

accumulation in bone measured for radium and uranium (54)

by Wrenn et al. (1985):

for 226

Ra, 30 d kg-1

, for 228

Ra, 12 d kg-1

and for 238

U, 143 d kg-1

.

[Table 11]

Relative uptake of 210

Pb from diet and air

Despite the uncertainties of the uptake estimates, table 12 attempts to find a rationale

behind the widely differing values for relative magnitude of 210

Pb uptake from

inhalation and diet for in the eight countries. Firstly, the two countries with the lowest

air 210

Pb concentration, UK and Portugal, are located on the eastern sea-board of the

Atlantic Ocean and receive a prevailing westerly wind from the Ocean, bringing

maritime air with low 210

Pb concentration. Germany, Poland, Russia and USA have

higher 210

Pb concentration in air consistent with continental land masses. Japan is an

island but has air 210

Pb similar to Germany and Russia, due to the prevailing westerly

wind bringing Eurasian continental air to Japan (49, 50)

. As regards diet, Portugal and

Japan receive the highest 210

Pb dietary intake, reflecting the high content of seafood

consumption in both countries. Of the remaining countries, Germany, Poland and

Russia representing central and eastern Europe would appear to have higher dietary


Pb uptake

25

210Pb than the USA and UK. It is difficult to identify the cause of this difference in

dietary intake but it may be related to differences in consumption of cereal based

products, and possibly also seafood consumption.

[Table 12]

Table 13 shows the additional uptake of 210

Pb that occurs from high domestic radon

levels, smoking and alcoholic beverages. The significance of each of these additional

sources is expressed as an additional percent uptake compared to total 210

Pb uptake

excluding these three sources. Smoking and beverage consumption are estimated to be

potentially highly significant additional 210

Pb sources, but national mean levels of

domestic radon contribute a smaller 210

Pb uptake. In several countries a moderate to

heavy smoker (20 or more cigarettes per day) could approximately double his/her

210Pb uptake from smoking. Similarly, heavy beverage consumption in these countries

could double 210

Pb uptake. Although mean radon levels in dwellings are a small

additional source, radon concentrations in dwellings are sometimes many times higher

than the average concentrations; in south-west Britain for example radon

concentration is above 1000 Bq m-3

in many homes, 50 times the national average (55)

.

In such cases radon would become a significant source of 210

Pb uptake (although

radon itself would cause a vastly more significant radiation exposure in its own right).

[Table 13]

Radiation doses resulting from uptake of environmental 210Pb.

Radiation doses from 210

Pb uptake were calculated using IDS™ (Internal Dosimetry

System: Dr V. Berkovsky, Radiation Protection Institute, 53 Melnikova, Kiev 253050,


Pb uptake

26

Ukraine, [email protected].), a fully integrated programme for internal dosimetry

incorporating the latest ICRP biokinetic and dosimetric information. Table 14 lists the

total radiation doses to adults associated with the estimated levels of 210

Pb uptake in

the eight countries, giving values for ten organs and total effective dose. Doses are

expressed as committed dose equivalent and whole body effective dose to age 75 from

one year 210

Pb uptake at age 25. The largest dose is to bone surfaces, lying in the

range 100-800 µSv. Dose to bone surface has been revised downward with respect to

the current ICRP dosimetry, by a factor of 0.31, due to the recent finding of very low

210Po/

210Pb equilibrium ratio at bone surfaces

(14); this also somewhat reduces the dose

to red bone marrow. Doses to tissues with intermediate 210

Pb and 210

Po

concentrations, namely kidneys, spleen, red marrow and liver, were in the range 40-

500 µSv, and in other tissues, including radiosensitive organs such as thyroid, brain,

breast and gonad, doses are much lower, in the range 1-10 µSv. Total committed

effective dose for the eight countries was between 14-78 µSv, with a mean of 37 µSv.

Although the mean dose given for lung is quite low, a much larger dose - up to 1 mSv

or more - will be received by the lymph nodes from 210

Pb and 210

Po contained in dust

particles residing in the lymph nodes (56, 57)

.

The average doses given above can be substantially exceeded where exceptional

intake of 210

Pb occurs. An example is consumption of caribou or reindeer in Northern

environments. Litvier et al. (46)

measured 210

Po and 210

Pb concentrations in tissues of

reindeer in Northern Russia, and calculated mean annual dose equivalents to bone

endosteum of reindeer herders of 24 mSv, with individual dose equivalents reaching

54 mSv. On the basis of the 210

Pb dosimetry employed in this study these values

correspond to mean and maximum whole body effective dose equivalents of 0.74 and

1.67 mSv. These are consistent with doses calculated by Thomas (45)

in relation to


Pb uptake

27

caribou consumption in Northern Canada: consumption of 250 g day-1

of caribou meat

resulted in annual dose equivalent of 0.13 and 0.28 mSv from 210

Pb and 210

Po

respectively. Yearly consumption of one caribou liver and ten kidneys gave additional

annual dose equivalents of 0.39 and 0.11 mSv from 210

Pb and 210

Po. Northern peoples

such as Inuit can consume significantly more liver and kidney than this in one year.

[Table 14]

Conclusions

Recent reviews of the literature concerning systemic uptake of Pb have been used to

obtain revised estimates of systemic uptake of 210

Pb from inhalation and diet, and

radiation doses to body organs from 210

Pb uptake. This study has indicated the

difficulty involved in obtaining precise values for fractional uptake of 210

Pb from

inhalation and diet, and the limitations of using published values of 210

Pb

concentration in air, diet and human bone. Therefore it is not possible to assess very

precisely the relative systemic uptake of 210

Pb from air and diet. However, it is not

possible to conclude that inhalation uptake is in general insignificant, or that dietary

uptake is always predominant. In some locations inhalation may be the largest source

of 210

Pb uptake. The importance of inhalation uptake of 210

Pb would be clarified by

studies employing personal air samplers, of the type carried out by Azar et al. (58)

for

airborne stable Pb. In figure 2 the relative magnitudes of 210

Pb uptakes from air

inhalation and diet, and from the additional sources of domestic radon, smoking and

beverages, are shown as averages from the eight countries. As an international

average, the contributions to 210

Pb uptake from atmospheric 210

Pb, domestic radon and

diet are 12%, 2% and 86% respectively. Smoking and beverages together add an extra

75% to the total uptake.


Pb uptake

28

Dietary consumption of 210

Pb is mostly from cereal based foods, meat and vegetables.

By contrast 210

Po uptake is often dominated by consumption of fish and other aquatic

meats. High seafood consumption, particularly shellfish, can significantly increase

210Pb intake also. Some dietary items contain exceptional levels of

210Pb (and

210Po);

the example of caribou or reindeer consumption in Nothern environments was

discussed.

Fractional inhalation uptake of 210

Pb is sensitive to the size of aerosol particles to

which 210

Pb is adsorbed, and fractional uptake from particles of different size can

differ by a factor of more than two. Most airborne 210

Pb is particle-associated, and the

distribution of 210

Pb by activity between particle size fraction correlates with particle

surface area. Bright sunlight may decrease fractional inhalation uptake of 210

Pb.

Atmospheric concentration of 210

Pb is reduced where air is of maritime origin.

Smoking and alcoholic beverages are both shown to be highly significant sources of

additional 210

Pb uptake, which in some countries may more than double total 210

Pb

uptake, and may represent a larger proportion of natural internal radiation exposure

than has hitherto been recognised.

Acknowledgements

I would like to thank Dr Roger Clarke and Dr John Harrison of the National

Radiological Protection Board, UK, for first initiating the debate about significance of

inhalation versus diet for 210

Pb uptake.


Pb uptake

29

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55. Green, B. M. R., Cliff, K. D., Miles, J. C. H. and Lomas, P. R. Radon studies in

UK homes, Radiat. Prot. Dosim. 45 (No.1-4 SS), 519-522, (1992).

56. Henshaw D. L., Fews A. P., Maharaj R., Shepherd L., Autopsy studies of the

microdistribution of alpha-active nuclides in lung-tissue. Nuclear Tracks and

Radiation Measurements-International J. Radiation Applications and

Instrumentation Part D 12 (1-6) 821-824, (1986).

57. Henshaw D. L., Fews A. P. The microdistribution of alpha-active nuclides in the

human-lung Nuclear Tracks and Radiation Measurements-International J.

Radiation Applications and Instrumentation Part D 8 (1-4), 447-452, (1984).

58. Azar, A., Snee, R. D. and Habibi, K. An epidemiologic approach to community air

lead exposure using personal air samplers. In: Lead, eds. Griffin T B and Knelson

J H. Academic Press New York, London. 254-290. ISBN 0-12-227062-2, (1975).

59. Kownacka, L., Jaworowski, Z. and Suplinska, M. Vertical distribution and flows

of lead and natural radionuclides in the atmosphere. Sci. Total Environ. 91, 199-

221, (1990).

60. Bradley, E. J. The distribution of 210

Po in human bone. Science of the Total

Environment 130-131, 85-93, (1993).


Pb uptake

37

Tables

Table 1. Intake and output balances for 210

Po and 210

Pb measured by Spencer et al. (5)

in twelve adult males.

210

Pb, mBq / day 210

Po, mBq / day

INTAKE

Ingestion:

Diet

Water

46.3 4.1

60.3 3.7

Inhalation:

Air

Cigarette smoke

3.0 5.6

0.48 13.3

Formed from 222

Rn and 226

Ra 0.89 -

Total 59.9 77.8

OUTPUT

Faeces 51.4 64.4

Urine 9.3 9.3

Total 60.7 73.7

BALANCE -0.8 +4.1


Pb uptake

38

Table 2. Dietary intakes of 210

Pb for several countries summarised from the review by

Bennett and Sandalls (8)

.

Regions / categories Daily 210

Pb dietary intake, mBq

USA 44-58

West Europe (UK, France) 50-82

Central-Eastern Europe (Germany, Italy,

Russia) 110-230

Exceptional intake countries (Finland,

Japan, Alaska) 220-370


Pb uptake

39

Table 3. Content of 210

Pb and 210

Po by percentage in daily diet of adult residents at

Nowe Miasto, Poland (11)

. These values approximately represent the European diet.

Food category 210

Pb 210

Po

% of dietary intake

Milk 13.3 8.1

Meat 19.2 12.7

Fish 1.2 33.8

Flour 30.1 17.6

Potatoes 14.4 10.2

Vegetables 15.7 12.5

Fruit 3.4 4.5

Water 2.6 0.6


Pb uptake

40

Table 4. A comparison of published estimates of relative magnitude of sources of

210Pb uptake from the environment to systemic circulation.

Percent of 210

Pb systemic uptake from each source

Author Location of

study

Food Water Air Smoking Alcoholic

beverages

Radon, 226

Ra

Holtzman

1963 (1)

Illinois,

USA 43 – 47 – – 10

Jaworowski

1969 (2)

World 79 1 20 – – –

Morse and

Welford

1970 (3)

New York,

USA 50 – 50 – – –

Spencer et

al. 1977 (5)

Illinois,

USA 44 – 18 33 – 5

Carvalho

1995 (9)

Lisbon,

Portugal 83 – 2 9 6 –


Pb uptake

41

Table 5. Uptake of Pb from aerosol particles to lung and to blood, according to ICRP

66 (27)

. Pb is classed as having fast uptake to lung.

Aerosol mean

aerodynamic

diameter µm

Total

fractional

deposition

Total

fractional

deposition

excluding

ET1

Transfer

from lung

to blood

Transfer

from lung to

GI tract

Total uptake of

Pb air-blood

0.001 0.98 0.57 0.63 0.37 0.4

0.01 0.85 0.79 0.93 0.08 0.75

0.1 0.35 0.32 0.96 0.04 0.31

1 0.42 0.32 0.79 0.21 0.27

5 0.76 0.48 0.64 0.36 0.34


Pb uptake

42

Table 6. Average daily patterns of activity and breathing level, from the ICRP lung

model, publication 66 (27)

.

Age Sleep Resting, Sitting Light Exercise Heavy Exercise Total

m3/hr hr/d m3/hr hr/d m

3/hr hr/d m

3/hr hr/d m

3/d

3 mo 0.09 17 - - 0.19 7 - - 2.86

1 y 0.15 14 0.22 3.33 0.35 6.67 - - 5.17

5 y 0.24 12 0.32 4 0.57 8 - - 8.72

10 y 0.31 10 0.38 4.67 1.12 8.33 2.03 1 14.2

15 y 0.42 10 0.48 5.5 1.38 7 2.92 1 20.1

Adult 0.45 8 0.54 6 1.5 9.75 3 0.25 22.2


Pb uptake

43

Table 7. The distribution by mass of atmospheric Pb into aerosol size fractions,

measured at a suburban and a city location in Vienna (31)

, and the distribution of

physical parameters of particles - volume, surface area and number, between aerosol

diameter fractions (32)

. Comparison of both sets of data suggests that the mass of

particle-attached Pb is proportional mostly to particle surface area, but also partly to

volume.

Aerosol

diameter

Percentage of atmospheric Pb

by mass in Vienna per particle

size fraction (Horvath et al.

1996)

Percentage distribution of particle

dimensions in urban atmospheric

aerosols, per diameter fraction

(Hinds 1982)

Suburb site City site Volume Surface

Area

Number

>1 µm 33 23 50 17 0

1µm - 60 nm 57 67 47 61 18

< 60 nm 10 10 3 22 82


Pb uptake

44

Table 8. Daily systemic uptakes of 210

Pb from radon inhalation in relation to

ventilation rate, normalised to a 222

Rn concentration of 1 Bq m-3

, showing the

components from dissolved radon and particle inhalation. This table assumes that a

person spends 60% of the day in their dwelling. Other assumptions concerning

inhalation such as particle size distribution are discussed in the text.

Daily uptake to blood of 210

Pb from 1 Bq/m3 222

Rn in indoor air

Lifetime of

indoor air

From dissolved Rn in

tissue (as %)

From inhaled short-lived

daughters on particles

(as %)

Total uptake of 210

Pb /day

30 min 3.22 E-06 (52%) 2.96 E-06 (48%) 6.18 E-06

2 hr 3.22 E-06 (27%) 8.58 E-06 (73%) 1.18 E-05

20 hr 3.22 E-06 (21%) 1.24 E-05 (79%) 1.56 E-05


Pb uptake

45

Table 9. Mean ground flux of 210

Pb (measured over continents only) compared with

airborne concentration of 210

Pb at ground level in relation to latitude band, from Preiss

et al. (49)

Latitude band,

degrees

Mean 210

Pb ground flux

from land, Bq m-2

y-1

Mean ground level airborne


Pb, mBq m-3

60-80 N 25 0.31

30-60 N 117 0.53

10-30 N 161 0.56

10-30 S 66 0.28

30-60 S 53 0.13

60-90 S 3.5 0.024


Pb uptake

46

Table 11. Total 210

Pb intake in the seven locations in relation to measured 210

Pb

concentration in human bone.

Location Total daily 210

Pb

systemic uptake, Bq

(f1=0.15).

Measured


Pb in human bone,

Bq kg-1

wet.

Conc. 210

Pb in bone

per Bq daily 210

Pb

uptake, kg-1

Illinois, USA 0.014 1.5 107

All USA 0.018 1.2 67

Japan 0.068 1.3 19

UK 0.013 0.78 60

Germany 0.029 1.4 48

Poland 0.02 N/A N/A

Russia 0.038 2.7 71

Portugal 0.072 N/A N/A

International

mean ± SE 0.034 ± 0.008 1.5 ± 0.3 62 ± 12


Pb uptake

47

Table 12. Percentage of total 210

Pb uptake in the population from inhalation as against

ingestion, for eight locations. The locations are divided into three categories with

respect to the concentration of 210

Pb in diet and two in regard to airborne 210

Pb.

Percentage of 210

Pb intake from inhalation; (the remainder

is from diet).

D i e t ca t ego r y

1. West European -

USA

2. Central-Eastern

European

3. High seafood

content

A ir ca t ego r y

1. Oceanic UK-4 Portugal-2

2. Continental Illinois-50,

USA-36

Germany-13,

Poland-10,

Russia-10

Japan-6*

*While Japan is an island, prevailing westerly wind brings predominantly Eurasian

continental air to Japan (49, 50)

.


Pb uptake

48

Figures

0

20

40

60

80

100

120

Illin

ois

, U

SA

All

US

A

Ja

pa

n

UK

Ge

rma

ny

Po

land

Ru

ssia

Po

rtu

ga

l

Inte

rnatio

na

lm

ean

Pe

rce

nt P

b-2

10

upta

ke

fro

m in

ha

lation

Figure 1. The percentage of environmental uptake of Pb-210 from inhalation; the remainder is from diet. This excludes additional

uptake from radon, alcoholic beverages and smoking.


Pb uptake

49

(a)

(b)

Figure 2. Breakdown of sources of environmental uptake of Pb-210, (a) excluding

and (b) including smoking and alcoholic beverages.

Inhalation 12%

Diet 86%

Radon 2%

Inhalation 7%

Diet 49%

Radon 1%

Smoking 27%

Beverages 16%

relative importance of inhalation and ingestion as sources of uptake of 210pb from the environment

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