during the period of the measurement are minimized.
However, in
application to radioactive materials, our interest is primarily in the
long-term average. Thus, predictive calculations should be done using a
wind rose which gives the joint probability of direction, stability, and
wind speed. The wind speed is of particular importance in wind resuspension
since there now appears to be clear evidence that the pick-up rate (or
source term) varies as a multiple power of the wind speed, apparently
on the order of the third power in relatively undisturbed areas such as
the GMX area in Nevada or Rocky Flats, and as powers up to the ninth, and
perhaps higher, in agricultural fields after plowing. I have made a few
calculations using the wind rose in Meteorology and Atomic Energy (Slade,
1968) for the concentration down-wind from various sizes of square areas
of uniform contamination. These results show that with the contaminated
area varying by a factor of 10% to 10°, the concentration close to the
edge of the area varies by only a little more than one order of magnitude.
At distances great enough that the source may be considered a point source
integration over areas up to 2000 meters on a side indicated that the
mechanical disturbance can be of greater importance than wind resuspension
in areas where sizeable disturbances occur, even assuming that the disturbance is carried out only for 40 hours per year.
Local resuspension applies to the concentrations in the breathing zones
of individuals producing resuspension by mechanical disturbance. Either
the resuspension factor approach or the mass-loading approach appears to
be useful and appropriate in this case.
The localized air concentration
from the smal] area of the disturbance can be used meaningfully without
the uncertainties from upwind areas.
However, it is necessary to
categorize the types of actions and their durations to match the categories
of actions leading to the given resuspension factor.
The mass-loading
approach can be used along with estimated or measured dust concentrations
in the air.
Again using the time of 40 hours per year as appropriate to
the variation in concentration is about in the same ratio as the source
size.
a disturbance with a resuspension factor of 5 x 10°’ m~), the local resuspension may be of greater importance than wind resuspension.
In addition to wind-driven pickup, general resuspension can occur from
Transfer resuspension could, in theory, be estimated from data on the
mechanical disturbance of the area.
For this process it appears reasonable
to assume that the rate of resuspension is a function of only the type
and severity of the disturbance with the dispersion downwind a function
of the meteorology. Here, again, the time of averaging is important. However, the time of averaging can also define the shape and size of the
source as well as the effective resuspension rate and dispersion. For
example, a contaminated dirt road can serve as a source as traffic passes
over it. Averaging in time gives this as a line source. If the average
traffic is 10 cars per day then the daily resuspension rate is ten times
that of one car. A farmer plowing a field will at each instant of time
represent a point source. As he passes the length of the field, these
point sources will represent a line source averaged over the time of
passage.
Each line integrated with all others will eventually describe
an area source with the resuspension rate equa] to the point source rate
divided by the time taken to plow the field.
In averaging over a one
year period, the average resuspension rate will be further decreased
by the ratio of the time to plow the field to one year.
Values for the resuspension rate or experiments well enough documented
Sehmel (1976) has studied the reto permit derivations are scarce.
suspension rate from traffic on asphalt roads and on areas covered with
cheat grass. On the asphalt road the values ranged from 107° to 18 x
10-2 sec-'! with the rate proportional to the speed of the vehicle. He
noted that the depletion of the contaminant with any significant traffic
would be rapid. On the cheat grass, no consistent pattern developed since
the rate for the first and slowest truck was higher than subsequent ones
presumably due to the rapid resuspension of the material deposited on the
cheat grass. Several studies of agricultural operations at Savannah
River {mithane, et al. 1976) and Lawrence Livermore Laboratory (Myers
et al. 1975) permitted rough estimates of resuspension rates. Thirteen
of the values were on the order of 10-* to 10°’ sec™' while about five —
were higher with a maximum of 1 x 10-® sec"'. Calculated estimates, using
amount of contamination transferred to clothing or other objects and
the subsequent transfer of this contamination to the body.
However, the
quantity and quality of such data are not adequate to address this
problem in any quantitative fashion, particularly when the large number
of actions possible are considered.
We have attempted to get some feeling for this by looking at the data on
lead in the environment and people, particularly children.
Lead is a
widespread element used in many ways by man and occurs as a waste in
many smelting operations. Lead poisoning is a common ailment. There is
a considerable body of information on exposures from dust or soils in
the vicinity of smelters or in metropolitan areas where the lead has been
released from gasoline fumes.
Unfortunately, it is impossible to obtain a direct correlation between
environmental concentrations and intake because lead is absorbed from
the GI tract, particularly in children, and one cannot distinguish
between inhalation and ingestion. Further, there is no well-established
correlation between lead in the blood, the common method of measurement,
and intake. There have been several studies in cities which indicated
that the ingestion of paint chips could not account for the observed
high blood levels. (Lepow et_al. 1975; Sayre et_al. 1974; Vostal et al.
1974). From measurements of the dirt and lead on children's hands, there
was a clear relationship between these values and the household levels.
Further, the blood levels did not increase until the child reached the
crawling age. It was concluded that the lead in the dust of the home or
area was transferred to the child. Several observations indicated that
the lead in household dust was in concentrations about ten times those in
the soil outside the house. However, this may not be generally true since
it will depend upon the source of the lead.
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