Judy Carman
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Judy Carman
The safety of genetically modified (GM) food is a
central issue driving the genetic engineering controversy today. This chapter
explores the potentially harmful effects of GM foods on human health and - in
doing so - focuses upon the most commonly eaten GM foods in Australia. I look first
at how GM foods are made and then consider some of the potential risks that
inform a safety evaluation of these foods, especially in relation to the safety
testing that has been done.
Essentially, living tissue is made up of cells, each
cell has a nucleus, each nucleus has chromosomes, and chromosomes contain most
of the organism’s DNA. Some of the DNA is in the form of genes that code for
proteins, enzymes and other biochemical substances that organisms need to
function. Traditional plant breeders take a plant with a desired
characteristic, such as high yield, and cross-pollinate it with another plant
with another desired characteristic, such as disease resistance. Progeny with
both characteristics can then be chosen and used. In contrast, genetic
engineers take a section of DNA from an organism that expresses a desired
characteristic, join it with other sections of DNA such as viral promoters, and
insert the resultant gene cassette
into the plant.
It is possible to contest
the claims of genetic engineers that their methods of insertion are precise
(see also Traavik’s points discussed in Chapter 3). The biolistics process, for
example, takes gold or tungsten particles, coats them with the desired DNA and
fires them into the plant. As the cells repair, the new DNA is integrated into
the plant’s genome. As the inserts are placed where they may not normally be
found in nature, some inserts may affect the expression of the plant’s genes.
This may turn genes off or on, affect the function of other genes, produce new
toxins or allergens, or produce a wild
characteristic, such as higher levels of toxins found in a wild ancestor.
Partial copies may also be
inserted. For example, seven years after the release of Roundup Ready soy,
Monsanto has found that is contains two DNA segments about which they were
previously unaware.1 Another concern is that the insert may not be
stable over many generations, resulting in the insert degrading, changing, or
moving. That concern is exacerbated by the use of viral promoter sequences in
inserts, such as the cauliflower mosaic virus, reputed to be prone to high
rates of recombining with DNA. Furthermore, sections of inserted DNA can come
from plants not normally eaten (for example, petunias), bacteria (for example, Bacillus thuringiensis), animals (for
example, fish genes in tomatoes), or viruses, (for example, cauliflower mosaic
virus). Another concern centres on the use of DNA that codes for antibiotic
resistance in GM plants. One GM potato has DNA coding for resistance to five
antibiotics.2 Resistance to antibiotics used in humans is frequently
encoded. There are concerns that if these DNA sequences cross into gut
bacteria, our current problems with antibiotic resistant bacteria may worsen
considerably.
Proponents and critics of GM
food have very different views about GM plants. Proponents argue that the GM
plant has changed insignificantly and that the rest of the plant will behave as
before. Therefore the plant is substantially
equivalent to the parent plant and does not need safety testing. Critics
argue that these are untested hypotheses, and with the technology in its
infancy, unknown and unintended consequences may result. In keeping with the
precautionary principle (see Chapter 3), thorough safety testing should be
undertaken before feeding GM food to millions of people.3
GM versions of soya bean, canola, corn, potato, sugarbeet and cotton have been approved for sale in Australia by Food Standards Australia New Zealand (FSANZ), formerly the Australia New Zealand Food Authority (ANZFA). The foods are widely present in breads, pastries, snack foods, baked products, oils, fried foods, confectionary, soft drinks, and sausage skins. Labelling laws were introduced in December 2001, but do not cover foods that are made from animals fed with GM feed (for example, meat, milk, eggs, honey), that are highly refined (for example, cooking oils, sugars, starches), or that are prepared at bakeries, restaurants and takeaways. These laws also exclude foods ‘unintentionally’ contaminated by up to one per cent per ingredient, that have been processed before 7 December 2002, that are made with processing aids or food additives using GM microbes, or that contain GM flavours present at less than one per cent.
Most GM foods
eaten in Australia are from plants genetically engineered to express either a
protein that degrades a specific herbicide so that spraying a field of crop and
weeds with the herbicide saves the crop and kills the weeds, or a protein that
when eaten by a grub, ruptures the grub’s gut, killing it. Some GM plants do
both.
What could go wrong?
One concern is that novel
DNA from GM food could be taken up by microbes in the gut or tissues of the
body. GM advocates and FSANZ have stated this as unlikely, as any DNA would be
quickly degraded.4 Others argue that transgenic DNA is specifically
designed to cross species barriers and to jump into other genomes.5
In fact, human simulations indicate that transgenes in GM food may survive in
the human stomach and small bowel for up to four hours.6
Furthermore, an oral bacterium was found to take-up and express free exogenous
DNA within a minute.7 In addition, foreign DNA ingested by mice can
reach peripheral leukocytes (a type of white blood cell), spleen and liver via
the intestinal wall mucosa and can be found in B and T cells of the immune
system and covalently linked to mouse DNA.8 Other work has indicated
that short DNA fragments from plant chloroplasts can be found in the
lymphocytes of cows, and possibly in their milk, while muscle, liver, spleen,
and kidney tissues from chickens were found not only to contain, but to
amplify, certain gene fragments.9
In addition, in
the only GM food study that could be found on humans, seven people - who had
previously had their lower intestine removed and consequently used colostomy
bags -were fed a single meal of a burger and milkshake, both containing GM soy.
It was found that ‘a relatively large proportion of genetically modified DNA
survived the passage through the small bowel’.10 There was also
evidence of genes being transferred from the GM soy to intestinal microbes.11
Yet, because no GM transgenes were detected in bacteria from faeces in people
with entire gastrointestinal tracts, the authors sweepingly suggested that
these bacteria did not survive passage through the human colon.12
Another interpretation is that the transgeneic DNA may have entered intestinal
cells and/or passed into the bloodstream.13 This went unassessed,
even though several bacteria can invade intestinal cells and transfer genes
into mammalian cells.14 Critics also pointed out that the
experimental design allowed for only a tiny fraction of the GM DNA transfers to
be detected.15 This may explain why GM DNA was not found in those
faeces but, in a different experiment, was found in rat faeces for up to seventy-nine
hours after feeding the rats ingested GM DNA.16
A further
concern involves proteins that the GM plant has been engineered to produce that
are not normally found in the human diet, or not in the human diet in such high
concentrations. Particular concerns have been expressed about the grub-killing
(insect protected) GM plants containing Bt toxin. This toxin is produced by a
soil bacterium called Bacillus
thuringiensis (Bt). In organic agriculture, an emergency insecticidal spray
containing the whole bacterium is used, and this can be washed off by the
consumer. A plant that has been genetically engineered with a Bt toxin gene,
however, constantly makes the toxin internally and the toxins cannot be washed
off. FSANZ regards Bt GM foods as safe because Bt has previously been used in agriculture
without known harmful effects, the grub gut is alkaline whereas the human
stomach is acidic, and there are no receptors on the surface of mammalian
intestinal cells for the proteins expressed.17 However, Bt proteins
have never occurred before in such high concentrations in food, and protein
degradation is known to be incomplete in the stomach, after which the meal
passes into the much more alkaline duodenum - the first part of the small
intestine. In addition, adverse effects have been found in animals eating these
proteins. For example, researchers fed mice potatoes containing a Bt toxin
approved for human consumption in some countries. To another group of mice,
they fed potatoes treated with the d-endotoxin believed to have
the insecticidal properties of that GM potato. Both types of potato caused
damage to the microscopic structure of the ileum (part of the small intestine).18
Mice fed the d-endotoxin had hyperplasia
and other changes often considered precursors to cancer.
Yet another concern is about the potential for GM plants to unexpectedly produce substances that are novel for that plant. Specifically, there are concerns that such unexpected substances may be dangerous, especially novel proteins. Advocates of GM technology and FSANZ have argued that any novel proteins would be quickly degraded so that they wouldn’t enter bodily tissues.19 Yet, it is well known that proteins can cross the gut wall into bodily tissues to create toxicological and other health problems. Food allergies - for example, to peanuts - can kill susceptible people,20 and eating meat from cattle with bovine spongiform encephalopathy (BSE, or mad cow disease) can kill people by causing variant Creutzfeldt-Jakob disease.
Of particular concern is the case of the Showa Denko KK company, which produced tryptophan, an amino acid used as a dietary supplement, from a GM strain of the bacterium Bacillus amyloliquefaciens. It resulted in an epidemic of eosinophilia-myalgia syndrome in the United States and Europe.21 Although the product was 99.6 per cent pure,22 thirty-seven people died within months and 1500 were permanently disabled before governments stopped counting.23 Proponents of GM food have argued that cost-cutting procedures and reduced purification were at fault, rather than the GM organism. Investigations, however, concluded that these two factors could not be separated because both events happened at a similar time.24 Thus, a new GM strain of the bacterium produced contaminating substances, which were then not sufficiently removed due to less stringent purification. Further investigation of the manufacturing process proved impossible, as the company quickly destroyed all batches of the GM bacteria.25
There are three important points about the tryptophan example. First, a GM organism produced one or more dangerous substances. Second, the sold product, at 99.6 per cent pure, was much more substantially equivalent in its chemical composition to pure tryptophan than products of GM crops are to their non-GM counterparts (see ‘Further problems: compositional analyses’, below). This shows how dangerous the ‘substantially equivalent means its safe’ argument is, yet it was used by various government regulators to decide that GM food was safe, and some groups still use it. Third, even if insufficient purification had a role to play, the product had still been greatly purified. Most GM products are not even slightly purified before entering our food, making them potentially more dangerous than this company’s tryptophan.
The safety testing that has
been done
In science, results of new work are published in
peer-reviewed scientific and medical journals, so that others can repeat and
extend the experiments and hence build-up a picture-in-progress of the area.
Yet, rather incredibly, a recent literature search of the safety assessments of
GM foods currently available in Australia yielded safety assessments of only
one food: Monsanto’s Roundup Ready soy. Furthermore, it was written by
Monsanto-paid scientists. So how can we be satisfied that GM foods are safe
when independent scientists cannot easily verify the accuracy and veracity of
the results of existing safety assessments? The only effective way to assess
data is to review documents written by FSANZ when it is asked by an applicant company
to approve a GM food for consumption. Yet, this government watchdog agency does
none of its own safety testing, instead relying on the company data. It has,
however, produced a document describing its guidelines for assessing safety of
GM foods,26 which are best described as safe until proven harmful, the opposite of
a precautionary approach. Perhaps the agency is constricted by its mandate,
which is to both protect public health and safety and to promote fair trade,
trade and commerce, and consistency between domestic and international
regulations.
Whenever FSANZ
reviews the safety of a GM food, it reviews the information presented to it and
generates a report of about seventy pages per application. A review of twelve
reports covering twenty-eight GM crops - four soy, three corn, ten potatoes,
eight canola, one sugarbeet and two cotton - revealed no feeding trials on
people. In addition, one of the GM corn varieties had gone untested on animals.
Some seventeen foods involved testing with only a single oral gavage (a type of
forced-feeding), with observation for seven to fourteen days, and only of the
substance that had been genetically engineered to appear, not the whole food.
Such testing assumes that the only new substance that will appear in the food
is the one genetically engineered to appear, that the GM plant-produced
substance will act in the same manner as the tested substance that was obtained
from another source, and that the substance will create disease within a few
days. All are untested hypotheses and make a mockery of GM proponents’ claims
that the risk assessment of GM foods is based on sound science.
Furthermore,
where the whole food was given to animals to eat, sample sizes were often very
low - for example, five to six cows per group for Roundup Ready soy27
- and they were fed for only four weeks. Moreover, some of these experiments
used some very unusual animal models for human health, such as chickens, cows
and trout. Some of the measurements taken from these animals are also unusual
measures of human health, such as abdominal fat pad weight, total de-boned
breast meat yield, and milk production. So it would appear that many of these
tests have not been designed to measure human health at all, but rather to
reassure primary producers that GM feed will permit farm animals to grow
sufficiently to get a reasonable price at market. In its safety assessments,
FSANZ uses these kinds of experiments as evidence that these foods are safe for
human consumption. Even worse is that often the only results given from these
experiments were the death of experimental animals. If other information was
given, it was usually only body weights, with possibly some organ weights. If
gross pathology was examined, there was no description of what was involved.
Certainly, biochemistry, immunology, tissue pathology, and gut, liver and
kidney function and microscopy results were not given, and were therefore
probably not done when they should have been done and the results disseminated.
In addition, animals were not fed for long enough for cancer studies, or
studies into the effect of offspring, to be done. Consequently, those
experiments could be regarded as initial experiments in what should have been a
long series, starting with several thorough animal experiments and finishing
with several detailed human experiments, yet they remain the only ones done.
Even more
disturbing is that, even with these existing experiments, which are limited in
their ability to pick up health problems, some adverse effects were found. For
example, rats fed canola meal from GM canola GT73 had liver weights increased
by twelve to sixteen per cent.28 However, rather than being investigated
further, these results were attributed to a higher level of glucosinolates (a
known toxin in canola) in the GM canola compared to controls. Yet the level of
glucosinolates was only about a third of the official level of concern as
measured by the Codex Alimentarius Commission,29 a global United Nations
agency for setting food standards. This indicates that this substance may be
innocent of these adverse effects. Consequently, a different substance may have
caused the adverse effects, and, if it is oil-soluble, it may be in the oil
fraction that people eat. However, there appear to be no feeding studies on
canola oil to check this potential.
In another
example, in addition to their normal diet, one group of rats was fed control
potatoes while another was fed a Bt GM potato line. After a month, a ‘number’
of abnormal findings were noted, such as enlarged lymph nodes, hydronephrosis,
and enlarged adrenal glands.30 It was reasoned that, because at
least some of these results were also found in the control rats, no statistical
difference was found between the two groups, and so FSANZ decided that the GM
potatoes were safe for eating. Control rats are supposed to remain healthy; that
they did not indicates either that rats are an inappropriate animal model for
safety testing of potatoes, or that something unusual was happening with all
the rats. A virus, for example, may have infected the rats, masking any effect
of the GM food, or the controls may have been inadvertently fed the GM food.
Put simply, the experiment should have been repeated and expanded to determine
what was occurring and why, followed by extensive human experiments, before the
food was considered safe.
Further problems:
Compositional analyses
Another notable problem with
the FSANZ reports is that often only the concentrations of amino acids - the
building-blocks of proteins - are given in the reports, rarely the fatty acids
(the components of fat) or anti-nutrients. Moreover, the type of statistical
detail required by a scientific journal is not given for any analyses,31 thereby preventing others from properly reviewing
the data and doing sample size calculations.32 The sample sizes are
very small indeed, usually about five to seven, and as low as two.33
This allows the applicant company to too-easily find no statistical difference
between the composition of the GM food under assessment and its control. This
is profoundly inadequate to assess what may occur in the real world.34
Even so, some significant differences were found with some GM foods. For example, eight of the eighteen amino
acids (forty-four per cent) measured in corn line MON 810 were significantly
different to the control corn.35 Yet, those differences were
ascribed to natural variation and were not investigated further, even though
such significant amino acid differences could also signal the production of
potentially harmful novel proteins. Adding weight to that possibility is that
the amino acid differences could not be explained by the production of the
proteins that were genetically engineered to appear, for any of those foods.
Such results
have led the Royal Society of Canada to describe the notion of substantial
equivalence as ‘scientifically unjustifiable and inconsistent with
precautionary regulation of the technology’,36 and the American
National Academy of Sciences to describe human health safety testing procedures
to be ‘woefully inadequate’. The Royal Society in London has also weighed into
the argument, describing the current system of safety screening, developed in
the United States, as flawed, subjective and inadequate and that manufacturers’
tests on such foods should be tightened and opened to independent scrutiny.37
Best
practice human health safety testing
Safety testing for GM foods is far below the best practice of human safety testing involved in the clinical trial of, for example, of a new pharmaceutical drug. Before a clinical trial is even begun, thorough animal testing is undertaken to determine adverse and therapeutic effects of the treatment in those animals. If the tests are passed, the four phases of the clinical trial begin. Phase I tests for adverse effects in a small number of healthy volunteers, Phase II tests for the therapeutic effect in a small number of volunteers, and Phase III is the randomised controlled trial (RCT). This is where a large number of people are randomly assigned to one of two groups. One group is the control. It takes a placebo (for example, a sugar pill) or the existing therapy, while the experimental group takes the new treatment. Neither the participants nor those involved with the participants know who is taking which. After a suitable period the results are analysed. If the new treatment passes, it is then monitored in the community (Phase IV). As a result of the push towards evidence-based medicine a further step is often undertaken - the meta-analysis. This process statistically sums the results of a number of randomised controlled trials to get a better picture. It is championed by an international collaboration of scientists known as the Cochrane Collaboration.
For this
procedure to apply to GM foods, animals should be fed each GM food - one food
per experiment - under investigation, and the results compared with results in animals
fed the equivalent non-GM food. Animals should be fed for long enough to
determine any cancer risk. Foods should also be fed to pregnant animals to
determine any effect in new-born animals. At a minimum, biochemistry,
immunology, tissue pathology, microscopy, and gut, liver and kidney function
should be measured. If the food passes these tests, then the four phases of a
clinical trial should be undertaken. This is where volunteers would be fed the
foods for at least several months. However, even these studies cannot determine
the long-term health effects of GM foods on humans. To do this, long-term
cohort studies are required, where people’s current self-selected exposure to
various GM foods are measured over future years and any diseases noted as they
arise. In addition, specific surveillance systems would be required to pick-up
any ill-health effects in the general population.
But, where are all the sick
people?
People are worried that GM food could make them ill.
However, the proponents of GM food and FSANZ argue that, because no-one has
found any documented cases of people who have become ill from eating GM food,
GM food must be safe. To see whether this statement makes sense, let’s assume
for a moment that GM food is making people ill and see how easy it would be to
find the proof that GM food is causing the illness.
The first problem is to
recognise that there is a new health problem in the community. Without full
animal testing, we don’t even know which diseases to look for in people. If the
resultant disease is an existing disease, for example, cancer, that has a
registry or effective surveillance system established for it, we will be alerted
to an increase in that disease if people are paid to look for it. If the
disease has no effective surveillance system, either because it is a new
disease and therefore cannot be under surveillance, or because it is an
existing disease without a surveillance system, the problem may go completely
unnoticed. Most diseases have no surveillance system, including diseases that kill
many Australians each year, such as asthma.
Consequently, we are likely
to be unaware of any problem until a critical mass of clinicians begins to
individually recognise that they have been seeing a lot of syndrome X, start
asking their colleagues if they have seen the same, and push for an
investigation. If this does not happen, we may never know there is a problem. The
HIV/AIDS epidemic went unnoticed for decades, even though it created memorable
secondary infections, such as those obtained from cats, and had a focus in
young gay men who tended to cluster geographically and see the same doctors. It
was largely picked-up by chance, because record-keeping of one pharmaceutical
drug, pentamidine, indicated an unusually high number of patients with a rare
pneumonia,38 even though there were by then thousands of HIV/AIDS
cases worldwide. We still do not know how many people are infected, even in
Australia, which has one of the best surveillance systems in the world. It is
also important to note that, by the time some surveillance data are collected
and made available for analysis,
several years can elapse. This can lead to a lag of several years between the
cases occurring and appearing in a surveillance system.
Finding cases of illness is however only the first step. Then we would need to prove that GM food was the cause by mounting an investigation, because surveillance only indicates there is a disease. It does not inform us of the cause. Anything that looks like an infectious disease usually results in an investigation by a state or local health authority. Anything else, for example, an increase in cancer, relies on someone, usually an academic, having an interest in the disease and applying in a competitive medical research grant system, for funding to do the investigation. Applicants to one of the main sources of medical research funding, the National Health and Medical Research Council, can expect on average an eighty per cent failure rate overall - often higher for public health-related work such as this - resulting in a possible delay of many years before an investigation could begin.
If funding is secured,
various causes of the disease would be suggested and tested by different
investigating teams. For an existing disease, existing hypotheses would be
considered and tested before GM foods. For example, for immune function
problems, infectious diseases would first be considered. For diseases where
food is traditionally suspected, for example, gut cancers, food consumption
would likely concentrate on existing hypotheses such as fat or fibre content
rather than GM, leading to another potential lag time of several years.
Moreover, investigations involving food eaten over several years are fraught
with difficulty. Most people cannot even remember everything they ate the day
before. Try it. Now, try to quantify, for example, the amount of chocolate you
have consumed in the last five years, in all its food combinations. Consumption
of GM food components are even harder to quantify, as many manufacturers still
do not know whether they are using ingredients derived from GM sources, or they
do not label the food as containing these. So how can the consumer or
investigator determine the amount or types of GM foods eaten in a group of ill
people? It therefore becomes almost impossible to prove that a GM food has
caused a disease, even if there are thousands of cases.
Let’s continue this exercise by asking: what would happen if a link were found between a GM food and human ill-health? It would be reasonable to expect that the public would want this food removed from the food supply. However, experience with the tobacco industry indicates that affected industries tend to argue and lobby against evidence for lucrative plant products. This would be compounded by the political considerations and lobbying of many thousands of disaffected farmers whose livelihoods depended on growing the crops. Action becomes even harder the weaker the link is between exposure and the disease. One of the strongest relationships between an exposure and a chronic disease ever found, and repeatedly found, is the relationship between smoking and lung cancer. The chance of smokers getting lung cancer is about twelve times that of non-smokers. Even so, public health action to reduce smoking such as banning advertising and smoking in some buildings, has taken decades. Risks for other exposures, particularly food, and their cancers tend to be much lower. Therefore, obtaining sufficient proof and getting action tends to be much harder for these. So, even if a GM food is found to cause harm, it may take many years of effort to remove it from the food supply.
Even if immediate action were instigated and the GM food were
banned, our previous experience of the release of live organisms into the
environment, such as cane toads, indicates that we would not be able to
effectively recall it, but that it could continue to spread its genes through
the non-GM equivalent plant population (as Chapter 4 also recognises).
Furthermore, even if a recall were effective, any ‘incubation period’ - that
is, the delay between exposure and disease - could see cases appearing long
after the recall. Any incubation period could also result in a lag time of many
years before cases even begin to appear in the population.
In short, with the level of
current safety testing, if GM foods do cause human health problems, it will be
very difficult to determine this, even though there may be many many cases, and
finding the cause and doing something about it may take decades.
CONCLUSION: RISK AND THE FUTURE
Scientists tend to measure
risk as a combination of the probability of something happening and the
consequences if it does. A useful analogy is a footpath, where the narrower the
footpath, the greater the probability of falling off, and the higher the
footpath, the greater the consequence of falling off. It is unlikely that many
people would take a challenge of walking along even a wide footpath strung
between two tall buildings, because even if the probability of falling off is
low, the consequence could be awful. Similarly, even if the probability of GM
foods causing adverse health effects is low, the consequences of exposing a
billion people to it, including the whole of the Australian population, could
be dire. If only one person in a thousand became seriously ill, then with about
a billion people currently exposed worldwide, the result would be a million
people seriously ill worldwide, and about 19 000 in Australia.
In conclusion,
there is an urgent need for the full labelling of GM foods, comprehensive
safety testing by independent researchers of all GM foods currently in the
marketplace and of all subsequent GM foods before they enter the marketplace.
Until these measures are adopted, a statement needs to be placed on GM foods
that human safety testing has not been done. Finally, a dedicated long-term
national surveillance system for the potential health effects of GM foods is
long overdue.
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2
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22 Belongia, An investigation; Mayeno & Gleich, Eosinophilia-myalgia syndrome,
23 Anderson,
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24 Belongia, An Investigation; Mayeno & Gleich, Eosinophilia-myalgia syndrome
25 Anderson,
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26 FSANZ, GM foods and the consumer.
27 Food
Standards Australia New Zealand. 2000. Draft Risk Analysis Report. Application
A338. Food derived from glyphosate-tolerant soybeans. FSANZ, Canberra.
28 Food
Standards Australia New Zealand. 2000. Draft Risk Analysis Report. Application
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29 FSANZ,
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30 FSANZ, Application A382.
31
The Public Health Association of Australia. 2000.
Comments to ANZFA about applications A346, A362 and A363 from the Food
Legislation and Regulation Advisory Group (FLRAG) of the Public Health
Association of Australia (PHAA) on behalf of the PHAA, The Public Health
Association of Australia, Canberra.
32
In the case on one food, sufficient information to
calculate these has been requested of FSANZ by the Public Health Association of
Australia (PHAA) repeatedly since late October 2000, but the data have still
not been received by the PHAA, more than two years later.
33 FSANZ, 2000. Application A363.
34 Public Health
Association of Australia, Comments.
35 Food Standards Australia New Zealand. 2000. Draft Risk Analysis Report. Application A346. Food produced from insect-protected corn line MON 810, FSANZ, Canberra.
36 Health Canada 2001. Elements of Precaution: Recommendations for the Regulation of Food Biotechnology in Canada. An expert panel report on the future of food biotechnology prepared by the Royal Society of Canada at the Request of Health Canada, Canadian Food Inspection Agency and Environment Canada, January.
37 Anonymous. 2002. Good Enough To Eat? New Scientist, 9 February, p 7.
38 Shilts, R. 1987. And the Band Played On: Politics, People and the AIDS Epidemic. Penguin, London.