Evidence of contamination
5. MYTH - Positive results were due to "false positives".
FACT - The possibility of "false"
positives was considered and dismissed in the final analysis of
all the results in Dr Hannah's advice to the Government. The most
statistically sound tests registered positives, and separate laboratories
registered positives. No further tests were conducted to justify
a theory that the positives were "false".
Evidence
Dr Hannah looked at the positive test results and determined
that lab error resulting in 'false positives' was unlikely because
the labs ran identical tests on 'controls' (seeds known to be
GE free). The controls registered negative while the Lot NC9114
seeds registered positive. He also concluded that the contaminant
was likely to be a GE variety Bt11 .
The GeneScan lab results are likely to be the most reliable.
Their samples were 100 times the size of the samples sent to Crop
and Food. An important limit on the technical ability of reliably
detecting GE contamination is sample size. The larger the sample
the more statistically reliable it is. Three of the known results
from GeneScan were positive. These were the largest size and therefore
most reliable.
Positive test results were recorded from at least two separate
laboratories from the range of results currently available to
the public: Crop and Food (from the Cedenco sample on the 5th
November 2000) and GeneScan (final round of tests, 24 November
2000). It is unlikely that positive results from two separate
laboratories could all be "false positives".
If there was any uncertainty surrounding the test results (eg.
that the positives were "false"), then further tests
would have been required to be able to categorically dismiss the
positives registered as "false". No such tests were
conducted and so Dr Hannah's conclusion based on all the tests
that were conducted, still stands: the corn was contaminated with
GE material.
Further evidence that the corn was contaminated
Two types of chemicals indicate the presence of GE in a sample:
the "on" switch for an engineered gene (promoter), and
the "off" switch (terminator). The presence of either
indicates GE.
Four samples tested positive for the terminator found in the
GE corn Bt11. The promoter or "on" switch called 35S
was expected to be found in the samples if the GE corn was Bt11.
However the presence of 35S can be difficult and can yield unstable
results. This has been widely discussed in scientific literature.
Therefore the absence of 35S does not rule out GE contamination,
if the terminator (nos) has been found.
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