http://gmopundit.blogspot.com/2005/11/copper-fungicide-use-in-farms-can.html
Sunday, November 13, 2005
Copper fungicide use in farms can promote dangerous bacteria – threatening
hospital patients.
(This issue was discussed recently on the <http://www.abc.net.au/landline/content/2005/s1498030.htm>ABC
channel television program Landline , the transcript
of which is a great introduction to this topic)
Survival of bacteria in adverse circumstances is promoted by special
cellular mechanisms to detoxify chemicals. The biology of these remarkable
detoxifying mechanisms has some surprising consequences. One of these is that
toxic chemicals permitted in organic farming are relevant to dangerous
outbreaks of untreatable infections in today’s hospitals.
The genetic trait of bacterial resistance to toxic heavy metal metals (such
as copper or mercury) is similar to the trait of bacterial resistance to
antibiotic drugs. Both these types of survival ability involve mobile forms of
genes that can be widely transmitted between different species of bacteria.
They are transmissible because they are carried in the bacteria on <http://escience.ws/b572/L2/L2.htm>mobile
mini-chromosomes called plasmids that can be naturally injected from one
bacterial cell to another in mating events.
Plasmids that bear resistance traits (eg
copper-resistance in multiple-drug resistant plasmids) are thus themselves
infectious, and can move from one species of bacterium to another. They are
really analogous to dangerous viruses, and plasmids in the soil can become
hospital plasmids quite easily. <http://www.cdc.gov/ncidod/eid/vol6no4/collignon_letter.htm>Plasmids
bearing multiple resistance traits are a major reason why many dangerous
bacteria such as Staphylococcus aureus are resistant
to most modern antibiotics, and why hospitals outbreaks of infections that are
untreatable by any antibiotic currently available are such a terrifying modern
reality. We now live in the post-antibiotic era.
Overuse of antibiotics is the main cause of this problem, and restricting
the use of antibiotics when they are not vital to human welfare is a good place
starting point.
But it is important to bear in mind that antibiotics are not the only
selective pressure that promotes spread of multiple-drug resistant plasmids in
the environment. Copper resistance is in fact a genetic a trait that is carried
by many plasmids. (For example Voloudakis
AE, Reignier TM, and Cooksey DA. (Appl Environ Microbiol. 2005 Feb;71(2):782-9. ) describe details of
a copper resistance genetic trait carried by plasmids in the plant pathogen Xanthomonas axonopodis pv. vesicatoria.
)
Resistance by bacteria to the killing ability to copper can arise, for
instance, because of their ability to actively pump toxic excess copper out of
the cell, and miniature bacterial pumps that eliminate many different compounds
from the bacterial cell (copper included) are common in many organisms. These
pumps are often of the type of pump called MDR pumps. Thus copper resistance
may directly promote resistance of bacteria to other compounds through the
pumping ability of a shared MDR pump.
For many years microbiologists have been investigating the origins of
multiple-drug resistant plasmids and the genetic traits – such as copper
resistance genes – carried on plasmids. (see for
example Ana Alonso, Patricia Sanchez and Jose L. Mart nez
Environmental selection of antibiotic resistance genes Environmental
Microbiology, 2001, 3, 1-9). In fact is quite likely that resistance to toxic
metals, such as copper and mercury, is a primary driver of plasmid evolution,
as metals have been around the natural environment for billions of years.
The fact that copper is extremely broad spectrum in its toxicity, is highly
persistent in the environment, has been around the environment for billions of
years, and that mechanisms of copper risistance are
widely spread among different organisms underlines the importance of taking the
human welfare implications of copper resistance traits of bacteria seriously.
A recent scientific paper
“Copper amendment of agricultural soil selects for bacterial antibiotic
resistance in the field” (J. Berg1,2, A. Tom-Petersen1,2 and O. Nybroe1 Letters
in Applied Microbiology 2005, 40, 146–151 765X.2004. (1Department of Ecology,
Royal Veterinary and Agricultural University,
provides strong evidence on why we should
be concerned about agricultural use of copper based fungicides as definite
activities that promote the spread of multiple-drug resistant bacteria. To
quote the Berg 2005 papers’ main conclusion
“The results of this field experiment show that introduction of Cu [copper]
to agricultural soil selects for Cu resistance, but also indirectly selects for
antibiotic resistance in the Cu-resistant bacteria. Hence, the widespread
accumulation of Cu in agricultural soils worldwide could have a significant
effect on the environmental selection of antibiotic resistance.”
Over use of copper is an issue in Australian farms. The quote another
publication:
“In
(Lukas Van-Zwieten, Graham Merrington and Melissa Van-Zwieten,
2004. SuperSoil 2004: 3rd Australian
Van-Zweiten go on to explain how copper is a
persistent poison that accumulates in the soil:
“Horticultural and viticultural operations with a
long history of copper fungicide application have resulted in accumulations of
copper in surface horizons (Gallagher et al. 2001; Chaignon
et al. 2003). Prolonged use in
<http://www.soilassociation.org/web/sa/saweb.nsf/0/cae68a6d579c7ffc80256df60040a7e0?OpenDocument>Organic
farmers generally ban antibiotic use, <http://www.soilassociation.org/web/sa/saweb.nsf/printable_library/NT00027E1A>but
continue to tolerate use of copper based fungicides. In the GMO Pundit's
opinion, if they are to continue to have credibility in providing the community
with environmentally virtuous practices, they should be consistent, and ban
copper fungicides.
There good synthetic antifungal alternatives to copper but the organic
movement decline to use them for no good reason.
For example Anthony Trewavas in
Trewavas, A. 2004. <http://www.biology.ed.ac.uk/research/institutes/plant/PDF/2004/Trewavas-2004-757.pdf>A critical assessment of organic farming-and-food assertions
with particular respect to the
has provided a critical comparison of mancozeb, a synthetic fungicide, with copper sulphate used by the organics movement.To
quote him:
Table 1 makes some limited comparisons between mancozeb,
a synthetic copper fungicide usually used to treat late blight, and the organic
pesticide equivalent, copper sulphate. The full table
can be found in Leake (1999a). In environmental
qualities, mancozeb is superior in all categories
compared to copper sulphate. In terms of human
health, copper sulphate is corrosive and toxic and
has caused liver disease in European vineyard workers. Although the EC
theoretically banned copper sulphate in 2002, no
alternative has been found for organic farmers and thus it continues to be
used. The consequences of not using copper sulphate
properly have been reported as organic farms acting as repositories of late blight, a serious disease of potato (Eltun,
1996; Zwankhuizein et al., 1998) or seriously damaged
orchards (Van Embden and Peakall,
1996). Any sensible approach would determine use based on toxicity.
Leake, A., 1999a. House
of Lords Select committee on the European communities. Session 1998–1999, 16th report. Organic
farming and the European Union. HMSO,
Labels: <http://gmopundit.blogspot.com/search/label/Environmental%20management>Environmental
management, <http://gmopundit.blogspot.com/search/label/Organic%20farming>Organic
farming, <http://gmopundit.blogspot.com/search/label/Safety%20and%20Regulations>Safety
and Regulations
Thomas R. DeGregori, Ph.D.
Professor of Economics
University of Houston
Department of Economics
204 McElhinney Hall
Houston, Texas 77204-5019
Ph. 001 - 1 - 713 743-3838
Fax 001 - 1 - 713 743-3798
Email trdegreg@uh.edu
Web homepage http://www.uh.edu/~trdegreg