Agriculture Reference
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observed (NOAEL), the lowest level at which adverse effects appear (LOAEL) and the
level at which a compound becomes overtly toxic and/or lethal—often expressed as the
level at which 50 percent of the animals die (LD50). In practice, an important indicator
of study quality is that as dose increases, the level and severity of any observed adverse
effects increases. Using these studies, and taking into account differences between the
test animals and humans as well as biological variation, toxicologists are able to estimate
an acceptable daily intake (ADI), which is the level at which the compound may be safely
consumed for a lifetime without adverse effect. This level is often set at 100- or 1000-fold
higher than the LOAEL, which ensures a large margin of safety; note, however, that set-
ting the level of desired safety is a political risk-management decision. These carefully
designed studies are described in several internationally accepted protocols published
by OECD, WHO, EPA and FDA.
The 90-day rat model study is sometimes used to evaluate potential toxicity of novel
proteins that have been inserted into crop plants (Delaney et  al., 2008). More com-
monly, a very high-level single dose can be used in an acute toxicity study. The under-
lying rationale is that toxic proteins are almost without exception acutely toxic, since
they are either quickly digested or eliminated and are not absorbed as such. Proteins
that have been incorporated into GM crops have been evaluated in an acute toxicity
study and found to produce no harmful effects when fed at levels 1000- to more than
one-million-fold higher than would normally be encountered in the diet. Some have
been evaluated in 90-day chronic toxicity studies and found to be innocuous.
Whole food feeding studies (WFS) are also sometimes performed (Delaney et  al.
2008, van Haver et al. 2008, Snell et al. 2012). These feeding studies are often performed
using rats, and the design resembles the 90-day rat chronic-toxicity study described ear-
lier. In WFS 10-30 percent, and sometimes even higher portions, of the test animal diets
are composed of the transgenic crop being evaluated. Diets with a high percentage of
a single ingredient are sometimes not palatable to animals, and it is often difficult to
provide all necessary nutrients in a diet with exaggerated composition of one ingredi-
ent. Moreover, adverse effects are sometimes seen in animals fed large amounts of single
food ingredients. A 42-day broiler study is also used in the same manner since it is both
sensitive and rapid. These studies are particularly useful for evaluating nutritional value
and feed performance; when similar studies are performed with production farm ani-
mals, they are called feed-performance studies.
Nonexperts generally believe that if a food contains potentially toxic components
they could be detected by such feeding studies. At first glance, this seems to be a reason-
able approach. Toxicologists have, however, determined that WFS lack power, have a
number of other defects, and would be unable to detect novel toxicants present at the
levels at which they would be likely to occur in transgenic crops—if such compounds
occur at all since the generation of novel, and, therefore, not analyzed, toxic compounds
in food and feed crops has never been observed. There are several recent papers, and
another in press, that describe the deficiencies of whole food animal studies (Chassy
et al., 2004; van Haver et al., 2008; Kuntz and Ricroch, 2012; Snell et al., 2012; Herman
and Ekmay, 2013; Bartholomaeus et al., 2013).11 This is not, however, a new conclusion.
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