ISIS Report 23/11/04
Increased Mycotoxins in Organic Produce?
Prof. Joe Cummins exposes the
propaganda campaign against organic food that has little or no scientific
basis; and genetic modification is not the answer to reducing aflatoxin
contamination
A fully referenced version
of this paper is posted on ISIS members’ website.
Details here.
Corporate propaganda against organic produce
Mycotoxins are toxic metabolites produced by fungi. Mycotoxin poisoning
has been known since the beginning of agriculture and has taken a large toll on
humans and farm animals consuming contaminated crops. Mycotoxins cause
immunological effects, specific organ damage, cancer, and in some cases, death.
Agricultural workers may also suffer from skin and respiratory exposure during
crop harvest and storage. Mycotoxin poisoning is a worldwide problem associated
with maize, rice, tree nuts and peanuts along with fresh fruits and vegetables.
Many countries regulate specific mycotoxins and most countries try to
limit exposure to the toxins [1]. Poor rural populations suffer greater impacts
from mycotoxin exposure than urban dwellers because the urban food supplies
have begun to be more strictly regulated [2].
Recently, pro-GM scientists in academia and biotech corporations have
been claiming that organic food and feed is more heavily contaminated with
mycotoxins than conventional and genetically modified foods, on grounds that
organic production does not use chemical fungicides, and are hence more likely
to be infected. But the United Nations Food and Agriculture Organization (FAO)
states [3] that, "studies have not shown that consuming organic products leads
to a greater risk of mycotoxin contamination."
In fact, numerous publications support the comment of FAO; furthermore,
there is no evidence that organic foods are more contaminated than conventional
foods.
The fungal species of Fusarium, Penicillium,
Aspergillus and Stachybotrys are the main producers of
mycotoxins. The genes for the biosynthetic pathways for mycotoxin production
are extensive and tend to cluster on a few chromosomes, which are passed on
through vertical or horizontal gene transfer; in fungi, horizontal gene
transfer is most effective [4]. The structure, synthesis and biosynthesis of
mycotoxins such as fumonisin have been extensively analyzed [5].
Scientific studies refute corporate smear
The exaggerated claims about greatly elevated levels of mycotoxin in
organic foods on the internet or in news media have not been borne out by the
peer-reviewed scientific literature.
Ochratoxin, a toxin produced in Penicillium and
Aspergillus, is mainly found in grain, nuts and dried fruits and usually
associated with storage of such foods. The toxin damages the kidney, causes
cancer and immune suppression. Conventional and organic cereals on the Italian
market were compared and no differences were found between the two agricultural
practices [6]. Ochratoxin was evaluated in cereal baby foods on the Italian
market derived from integrated pest management, organic and conventional farms.
Cereals from integrated pest management had no detectable toxin, those from
conventional practices had elevated toxin levels in multigrain and
seminola-based cereal while only organic rice-based cereal contained the toxin.
The study concludes, however, that there is no significant risk to children who
occasionally consume toxin contaminated at the observed levels [7].
Ochratoxin has also been found in the milk of cows consuming
contaminated grain. Norwegian milk and baby formula from organic and
conventional production was therefore compared. No toxin was found in any of
the infant formulae. But the toxin was detected in 6 out of 40 conventional
milk samples and 5 out of 47 organic milk samples, the highest level detected
in conventional milk was twice the highest level detected in organic milk
[8].
Conventional and organic Italian foodstuffs made up of maize, wheat,
rice or mixed products were compared for the Fusarium toxins fumonisin
and deoxynivalenol. Fumonisin causes cancers of liver or kidney along with
blood disorders and pulmonary edema in farm and experimental animals.
Deoxynivalenol (vomitosin) causes anorexia at low levels and vomiting at higher
levels, and also damages the immune system. Both organic and conventional foods
contained the toxins, but more of the conventional foods were contaminated than
organic foods. The highest deoxynivalenol levels were found in conventional
rice-based foodstuffs while the highest level of fumonisin was found in
conventional maize-based foodstuffs. Organic foodstuffs contained consistently
lower contamination than conventional foodstuffs [9].
A broad study including heavy metals, nitrates and mycotoxins in a range
organic and conventional foods in France found no significant differences
between organic and conventional foods in a number of mycotoxins. One high
level of patulin was observed in a sample of organic apples but no values for
patulin content in conventional apples were reported in the study [10].
Patulin is produced by Penicillium and Aspergillus, and
is known to damage genes, cause birth defects, immune and neurological
dysfunction. No significant difference in patulin levels was found between
organic and conventional apple products [11]. Nevertheless, a report from
Science in Africa indicated that patulin was present in commercial apple
products and claimed that a study on organically produced apple cider has found
"levels up to 40,000 micrograms per liter". It used that finding to make
general claims about the unsafe practices in organic agriculture [12]. Despite
extensive and repeated literature searches, I have been unable to locate a
single peer-reviewed report documenting such a huge level of toxin
contamination. But that value has been promulgated through a number of news
media and web reports.
Genetic modification (GM) has been promoted as a means of preventing
mycotoxin contamination, particularly in maize. Several strategies have been
proposed but the only one deployed is to incorporate Bacillus
thuringiensis (Bt) toxin to prevent corn borer tunneling which encourages
fungal growth in maize [13]. Bt and conventional isogenic maize was studied in
France and Spain. Moderate to low levels of mycotoxins were found on both GM
and conventional maize but significant differences were found in some areas
[14]. The presence of mycotoxins in Bt and conventional maize tested in central
Europe concluded that under European conditions the use of Bt maize will only
slightly reduce contamination of maize with mycotoxins produced by
Fusarium fungi [15].
Aflatoxin is a mycotoxin of global significance
Aflatoxin is a naturally occurring mycotoxin that has attracted
worldwide attention because it is a powerful toxin that damages genes. Two
types pf mould - Aspergillus flavus and Aspergillus parasiticucus
- can produce the toxin. Aspergillus flavus is widespread in soil, and
mouldy grains and nuts are commonly contaminated with the fungus. Aflatoxin
production is favoured by moisture and high temperature. At least 13 different
types of aflatoxin are produced and the most potent of these is aflatoxin B1.
Grain testing for aflatoxin is provided by the Grain Inspection Packers and
stockyard administration of USDA at a cost of $25 per test [16].
Liver cancer is the fifth most prevalent cancer in the world; and 80%
of the cases are in the developing world. The primary causes of liver cancer in
the developing world are the hepatitis B virus and aflatoxin, and most
ferociously, the two combined. Limiting the contamination of foodstuffs by
aflatoxin is a particularly important target for public health [17]. However,
aflatoxin contamination of food is also a major problem in the developed
world.
The biological strategies explored to reduce or eliminate aflatoxin in
food and feed include inoculating seeds with Aspergillus strains unable
to produce aflatoxin, to replace toxin-producing strains in the soil. Crops
resistant to Aspergillus are selected using traditional genetic methods
with molecular marker-assisted selection or by direct genetic modification.
A workshop on aflatoxin elimination and fungal genomics provided an
overview on ecological and genetic approaches to controlling aflatoxin [18].
Cotton seed is an important crop for oil and feed. Strains of Aspergillus
flavus without toxins were made to colonize sterile seed, a treatment that
reduced the proportion of toxin-contaminated seed by over 50% the first year,
and more in later years, providing an economic benefit to the producer [19].
Non-toxin strains of Aspergillus flavus and Aspergillus
parasiticus alone or in combination significantly reduced aflatoxin content
of peanuts, a mixture of the two types of fungus being the most effective [20].
Intra-specific competition is the basis of the biological control of aflatoxin.
Sexually compatible strains fuse to form mycelia that produce aflatoxin, while
vegetative incompatibility reactions result in the death of the fused mycelia
resulting in reduced aflatoxin production [21]. The strain of Aspergillus
flavus used to reduced aflatoxin in cotton has been found to be defective
in aflatoxin synthesis [22]. Growth and mycotoxin production of Aspergillus
flavus and Aspergillus parasiticus were inhibited by extracts of
Agave cactus (the cactus used in tequila). Scaling up production of such
natural inhibitors may be worthwhile [23].
Conventional plant breeding and conventional breeding using molecular
markers are being used to select for genes conferring resistance to
Aspergillus infection. Genetic resistance to Aspergillus and to
aflatoxin production have been identified in maize but more work is needed to
produce commercial varieties [24]. It is becoming clear that traits for low
aflatoxin production are quantitative trait loci (QTL) involving the additive
effects of many genes, rather than a qualitative effect of one or a few genes.
Such quantitative loci are the most important kind of genes in plant breeding,
governing plant size, yield of grain, disease resistance, etc. QTL for low
aflatoxin have been identified in maize [25]. QTL have been pyramided
(pyramiding is combining genes from many strains into a single strain by
crossing) in maize combining resistance to Aspergillus with resistance
to ear feeding insects, which wound the maize and allow fungal infection to
take place [26]. QTL provide the most promising long term protection against
aflatoxin crop pollution.
Genetic engineering has focused on Bacillus thuringiensis (Bt)
toxin to reduce wounding of the crop to allow fungal infestation or on more
direct methods to limit fungal infestation. Maize was inoculated with
Aspergillus flavus and infested with corn borers, Bt strains produced
grain with less aflatoxin than isogenic lines lacking Bt [27]. The experiment
was interesting but employed artificial conditions, with neither natural fungal
infection nor borer infestation. Peanuts modified with a Bt cry 1Ac gene were
found to contain reduced levels of aflatoxin. Peanuts were also modified with a
bacterial choroperoxidase gene that resisted Aspergillus infection and
showed promise in producing peanuts with reduced aflatoxin [28]. The bacterial
chloroperoxidase gene and several other candidate genes have been used to
transform cotton but data on their effectiveness in reducing aflatoxin has not
yet been obtained [29]. A gene for a ribosomal inhibiting protein (RIP) was
isolated from maize and used to transform peanut, RIP blocked fungal ribosomes
without inhibiting the ribosomes of maize, the effectiveness of the modified
peanut has not yet been tested [30]. In general the GM crops are not yet fully
tested for their ability to reduce aflatoxin pollution of maize, peanut and
cottonseed.
Conclusion
In conclusion, peer-reviewed publications indicate that organic foods
are not more hazardous sources of mycotoxins than conventional foods. On
the contrary, organic foods tend to be less contaminated, and may provide
protection from the toxins. The use of GM maize has not provided major
protection from mycotoxins in comparison to conventional maize.
There is a growing sense that the world of public relations has
unleashed a propaganda campaign against organic food that has little or no
scientific basis.
As far as aflatoxin is concerned, biological control using fungi unable
to make the toxin to control those that produce it has proved effective in
cotton, and conventional breeding using QTL to produce strains resistant to
fungal infestation has proved useful in maize. Genetic modification has had
preliminary success using Bt genes to prevent insect wounding followed by
fungal infestation, though the toxicity of Bt genes and proteins is still
untested and unknown [31]. Thus, the biological control and conventional
breeding methods are the most immediately useful in reducing aflatoxin
contamination of food and feed.
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