Fukushima: damage limitation | 319 comments (319 topical, editorial, 0 hidden)

UC Berkeley Nuclear Engineering Air Monitoring Station | The Nuclear Engineering Department At UC Berkeley

Response to some misleading claims about our measurements
Some claims have been made recently that our data shows that Bay Area water exceeds EPA regulations by a factor of 181 -- sometimes this has been reported as 18,100% higher, or erroneously as a factor of 18,100 higher. This claim is misleading. Specifically, the reports refer to the I-131 activity of 20.1 Bq/L measured in rainwater on 3/23. The EPA limit for I-131 is 3 pCi/L, or 0.111 Bq/L. There are a number of things wrong with this claim.
First, the measurement we made was of rainwater, not drinking water, so the drinking water limit does not apply. We instead should be discussing tap water, in which we detected a small amount of I-131 (0.024 Bq/L). This is a factor of almost 1,000 below the rainwater measurement and a factor of 4.6 below the EPA limit.
It should also be noted that the EPA limit assumes the water is ingested over the course of an entire year. That is, someone drinking 3 pCi/L water for an entire year would reach the EPA dose limit of 4 millirem, which is a very small dose. The tap water measurement of 0.024 Bq/L on 3/29 is our only detection of I-131; on subsequent days it could not be detected, probably due to the radioactive decay of I-131. So this tap water could have been ingested for at most 1 day, giving the public a dose 365 times smaller than if one assumes an entire year of ingestion. That means the tap water is effectively a factor of 1,700 below the EPA limit.

Economics is politics by other means

by Carrie (migeru at eurotrib dot com) on Wed Apr 6th, 2011 at 06:24:52 AM EST
[ Parent ]

Re: [Crackpot alert] (none / 0)

Amount of radiation in Vancouver rainwater decreasing - scientist

VANCOUVER - Radiation in B.C. rain water is decreasing, a trend that could mean either the end of radiation emissions in Japan or just a change in the weather pattern, a nuclear scientist told The Vancouver Sun.
"We see a consistent decreasing trend. I looked into the sample for yesterday and I see very little iodine-131," Krzystof Starosta, a nuclear chemist and physicist and associate professor at Simon Fraser University, said in an email. "I am not sure if this is the end of the releases or a change in the weather pattern; the time will show."
A chart provided by Starosta shows that iodine-131 in Vancouver's rainwater peaked on March 20 at 12 becquerels (Bq) per litre. Levels were at zero up to March 18, 2011, and as of March 29 had fallen to just above three Bq per litre. (A becquerel is an international measurement of radioactivity related to radioactive decay per second.)
Meanwhile, seaweed samples were still showing increasing iodine-131 as of March 28, according to data provided by Starosta. In samples of dehydrated seaweed taken on March 15 near the North Vancouver SeaBus terminal, the count was zero; on March 22 it was 310 Bq per kilogram; and by March 28 it was 380 Bq/kg.

Any idiot can face a crisis - it's day to day living that wears you out.

by ceebs (ceebs (at) eurotrib (dot) com) on Wed Apr 6th, 2011 at 07:11:13 AM EST
[ Parent ]

Re: [Crackpot alert] (4.00 / 2)

Migeru:

The EPA limit for I-131 is 3 pCi/L, or 0.111 Bq/L

Note the following: the EPA's acceptable level of Iodine in drinking water equals the Minimum Detectable Activity. That is, statistical noise is of the same order as the EPA acceptable limit.

How we calculate Minimum Detectable Activity (MDA) | The Nuclear Engineering Department At UC Berkeley

The Minimum Detectable Activity, or MDA, represents the smallest quantity of a radioisotope which can be detected with 99.7% confidence in one of our systems (rainwater, or the various air sampling systems). It is fundamentally based on the statistical variation of detector counts in the region where a peak from the isotope would appear. If the statistical variation is greater than the counts from an actual amount of radioactivity of that isotope, it is not statistically significant and it is not detected.
...
As of 3/24/2011, the MDAs for our five measured isotopes in rainwater are:
Te-132 0.074 Bq/L
I-131 0.115 Bq/L
I-132 0.115 Bq/L
Cs-134 0.106 Bq/L
Cs-137 0.084 Bq/L