Increased Mycotoxins in Organic Produce?

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23 Nov 2004 14:56:03 -0000

 

Increased Mycotoxins in Organic Produce?

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ISIS Press Release 23/11/04

 

Increased Mycotoxins in Organic Produce?

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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 http://www.i-sis.org.uk/full/IMIOFFull.php.

Details here http://www.i-sis.org.uk/membership.php.

 

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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