الفهرس 
TitleOnly 14 pages are availabe for public view
 |  | from | 96 |  |  |
| | | from | 96 | | |
Abstract
Our bodies are naturally radioactive, because we eat, drink, and breathe radioactive
substances that are naturally present in the environment. These substances are absorbed by
our bodies, into our tissues, organs, and bones, and are constantly replenished by ingestion
and inhalation.
Ionizing radiation enters our lives in a variety of ways. It arises from natural
processes, such as cosmic rays and the decay of uranium in the earth, and from artificial
procedures, as with the use of X-rays in medicine.
So we can classify radiation according to its origin into. Natural sources that include
cosmic rays, gamma rays from the earth, radon decay products in the air, and various
radionuclides in food and drink, and artificial sources which include medical X-rays,
fallout from the testing of nuclear weapons in the atmosphere, discharges of radioactive
waste from the nuclear industry, Industrial gamma rays, and miscellaneous items such as
consumer products.
Each source of radiation has two important characteristics, the dose that it delivers to
human beings and the ease with which we can intervene to affect such doses. We cannot
change our exposure to natural sources: this basic background of cosmic rays, gamma rays,
and natural radioactivity within the body gives rise to an annual dose around 2.6msv.
The biological effect of radiation depends on the energy in the cell and energy
transferred to tissue volume or critical target and consequent Ionization. It is therefore a
function of LET (linear energy transfer) which is the amount of energy radiation deposits
per unit of path length and biological effect may occur due to direct and/or indirect action
of radiation.
Biological effects of radiation are typically classified into two categories. The first
category consists of exposure to high doses of radiation over short periods of time
producing acute or short term effects (Deterministic) while the second category represents
exposure to low doses of radiation over an extended period of time producing chronic or
long term effects (Stochastic). The high doses tend to kill cells, while low doses tend to
damage or change them.
Water resources in Egypt are limited to the Nile River, rainfall and deep groundwater
in the deserts and Sinai Each resource has its usage limitation, whether these limitations
are related to quantity, quality, space, time, or exploitation cost. Egypt receives about 98%
of its fresh water resources from outside its national borders. This is considered to be the
main challenge for water Policy and decision makers in the country as the Nile River
provides the country with more than 95% of its various water requirements.
It is important to understand water consumption patterns. The daily water volume
ingested will also determine the consumption of any minerals that it contains. An
individual’s daily aqueous fluid ingestion requirement can be said to roughly equate to the
obligatory water losses plus sweat/perspiration losses resulting from increased physical
exertion and climate.
Summary
66
Estimate of committed effective dose for each radionuclide should be made and the
sum of these doses determined.
The current study aims to evaluate the types and concentrations of isotopes present in
drinking water in different parts of lower Egypt and The dose possibly delivered to the
population from consumption of water and of edible fresh - water organisms.
The study area in Lower Egypt extended along the Northern part of Egypt from Sinai
governorate in the East to Marsa Matrouh in the West. 60 samples were collected from
selected cities and towns in the area under investigation and they were divided into four
categories according to their source. 45 water samples (15 tap water, 15 ground water and
15 untreated water samples) and 15 fish tissue samples.
All water samples were acidified. Then concentrated (40 L to 500 ml), 100 ml were
sealed in special canisters. Of each fish sample, 50 gm of the edible part were
homogenized and completed to 100 ml volume in a special canister. All samples were
stored for 4 weeks then analyzed by -ray spectrometry using HPGe detector to measure
the activity corresponding to 232Th, 226Ra and 40K. Then the annual dose corresponding to
ingestion of the radioactivity in water was estimated for various age groups. And for
different body organs.
Results from the current work showed that concentration of 226Ra and 232Th in all
samples under investigation are below the detection limit of the HPGe detector. However,
several studies have attempted to measure 226Ra and 232Th concentrations in water sources
of other parts along the river Nile, and the levels they presented were low.
No significant difference was found between study groups; tap, ground and untreated
water sources; regarding 40K concentration (p=0.52).
40K existed in many samples. Its concentration in untreated water showed an
apparent elevation than in tap and ground water (3.16 Bq/L vs. 1.06 and 1.01 Bq/L;
respectively, but there was no significant difference between groups (0.528). All levels in
all samples were significantly lower than the intervention limit for 40K in water, (1000
Bq/L).
The dose to different organs resulting from consumption of water containing 40K was
calculated using Acute dose calculate. Effective dose per year was calculated by
multiplying the annual effective dose equivalent from consumption of drinking water (Sv
y-1), the activity concentration of radionuclide in the ingested water (Bq l-1), and the rate of
consumption of water (L). The assumed consumption rate being 1.5 Ld-1 for ages 5 and 10
years and 2 Ld-1 for 15 years and adults.
The doses were calculated for four age groups; 5 years, 10 years, 15 years and adults.
The highest annual effective dose equivalents from 40K ingestion were those
delivered to Upper Large Intestine Wall (ULI wall), Lower Large Intestine wall (LLI wall)
and Stomach wall (ST wall), while the dose to the 27 remaining organs was lower but
uniformly distributed and almost homogenous and equal in all of them. The total dose to
the body is presented as the sum of all doses to all 30 organs constituting the body.
Summary
67
All dose estimates whether to individual organs or to the whole body were below the
limit set by the ICRP for public exposure from internal radiation of 0.1 mSv/y (100 μSv/y).
For all water sources, the lower the age, the higher the dose delivered from 40K in water.
For tap-water, the highest annual dose delivered to 5 y age group of 6.16 μSv with an
average of 1.32 μSv, and the lowest annual dose was that delivered to adults with a
maximum of 1.79 μSv and a mean of 0.33 μSv. For ground-water, the highest annual dose
delivered to 5 y age group of 6.12 μSv with an average of 1.35 μSv, and the lowest annual
dose was that delivered to adults with a maximum of 1.71 μSv and a mean of 0.34 μSv. It
is noted that exposure levels for different age groups from tap water and from ground
water are very much similar, with no significant difference between them.
Annual effective doses from ingestion of untreated water was much higher than
ingestion of either tap water or ground water, but no significant difference existed between
them. The highest annual dose delivered to 5 y age group of 37.45 μSv with an average of
3.73 μSv, and the lowest annual dose was that delivered to adults with a maximum of
10.82 μSv and a mean of 1.03 μSv.
The levels of 40K in fish tissues were obtained from places corresponding to group 3
collection places of untreated water, contaminants present in the water is expected to exist
also in the fish that lives in it. However, that assumption was not found correct in the
current study, as no significant correlation was found between 40K concentration in
untreated water and in fish tissues. where for Fish Tissue (0.63±0.54). Median, for fish
tissue was 0.61. Presented in the current work are among the highest reported levels.
Accordingly, the annual effective doses from fish ingestion is also high, however, it
remains less than the 0.1 mSv/y limit set by the ICRP.