MadSci Network: General Biology

Re: What are the effects of Nuclear Wasteon the human body?

Date: Thu May 5 22:49:54 2005
Posted By: Dr. Nagesh N Bhat, Scientific Officer
Area of science: General Biology
ID: 1115142518.Gb

Nuclear wastes are safely disposed with maximum precautions. It is a very 
specialized subject to discuss on the disposal methods. The radioactive 
waste materials are sealed in multiple layer containers so that neither 
radiation nor radioactive material can escape out of the container beyond 
permissible levels. Further, most of the radio-nuclides produced in 
nuclear fission are short lived. Hence, the waste is stored at the site of 
the reactors for some time before disposing so that it is easier to handle 
the waste with lesser activity.

Before disposing off the nuclear waste, most of the important radioactive 
materials are recovered, which are useful in many peaceful applications of 
radiation in medicine, industries, agriculture and research.

High dose exposures to human being is possible only in fatal nuclear 
accidents and warfare. Most of the human data available now are from such 
unfortunate incidents. Epidemiological survey of exposed people in such 
accidents reveals many effects. Depending on the nature, the effects are 
classified as deterministic and stochastic effects. 

Deterministic effects are those, which have direct causal relationship 
with the radiation exposure. They can be usually observed only at high 
doses such as 1 Sv and more. It includes induction of cataract, radiation 
sickness, skin erythema (reddening of skin and skin burns), haematopoietic 
syndromes (blood related), gastro-intestinal syndromes and central nervous 
system syndromes. All deterministic effects exhibit threshold doses below 
which there is no clinical manifestation of the effects. The thresholds 
are different for the above-mentioned effects. None of the deterministic 
effects are observed below 1 Gy. The severity of the effects increases 
with exposure.

Stochastic effects are only probabilistic in nature and there is no way to 
distinguish them from normal incidence. All cancers (solid cancers as well 
as leukaemia) and hereditary effects are stochastic effects. It is found 
that radiation exposure increases cancer risk. Increased level of all 
types of cancer is observed in exposed human populations. However, it is 
interesting to note that no increase in hereditary effects is observed in 
exposed population. The risk estimation is based purely on animal 
experiments and it seems to be over estimated. It is also interesting to 
note that no increase in induction is cancer is evident in occupationally 
exposed people to low levels of radiation and also in people living in 
high natural backgroud radiation around the world. The probabilities of 
cancer induction is very less and inconclusive in such doses. The risk 
estimates are based on high dose data from nuclear accidents and atomic 
bomb survivors of Hiroshima and Nagasaki.

No doubt, radiation is harmful to all life. Nevertheless, it is possible 
to suppress the harm by regulatory procedures. ICRP-60 has estimated the 
risk of radiation as 5% per Sv (sievert) for general public and 4% per Sv 
for the occupational workers in the age group of 18 - 65 years. Sv is the 
unit used for estimating radiation quantity. It is a biological equivalent 
of physical dose unit Gy (gray = 1 joul/kg). For sparsely ionising 
radiations such as X-rays, gamma rays, beta rays, both Sv and Gy are 
equivalent. Certain densely ionising radiations such as alpha rays, 
especially when the activity is ingested or inhaled may cause more damage. 
For such radiations, more waitage is given and the weighting factor is 
multiplied to the physical dose to estimate the equivalent dose i.e., Sv.

All risk estimates are purely based on stochastic effects. The limits are 
set such that deterministic effects are completely avoided for both 
general public and occupational workers. Further, the limits are evaluated 
by cancer and genetic effects risk estimates so that the nuclear industry 
can be declared as "safe". 20 mSv per year, averaged over 5 years and not 
exceeding 50 mSv in any given year is the occupational limit as suggested 
by ICRP-60.  The limits for general public are about 1/20th compared to 
the nuclear industry workers.

Further information:
Radiobiology. Eric J. Hall

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