Agriculture Reference
In-Depth Information
private f flocks in a polluted area, found that the levels of dioxin contamination in eggs from
seven organic farms were slightly (but not significantly) lower than samples from 10 conven-
tional farms, and all within a level normally considered safe (Pussemier
et
al
. 2004). Since
then, one study showed elevated dioxin levels in eggs from two out of four organic farms in an
Irish survey (Food Safety Authority of Ireland 2004). Here it was found that the age of the hens
was also important for this pollutant, which is known to accumulate in the body. The f flocks
with the highest values comprised hens of up to four years of age, but the concentrations were
still lower than eggs from polluted areas, and did not exceed the safety limits. In general, while
additional experiments are required to test the hypotheses presented, if they are confirmed,
two simple safety precautions should be able to control this problem for organic (and other
free-range) egg producers: test for soil pollution before establishing chicken production, and
limit the age of the hens to no more than two laying seasons. Conventional producers and
most organic ones keep layers for only one laying season, but in accordance with organic prin-
ciples, healthy animals should keep producing for longer periods if this does not conf lict with
animal welfare considerations. Dioxins do not accumulate in plants (Harnly
et
al
. 2000), and
cattle and pigs, which occupy more space than chickens, are less likely to be produced near
large cities where polluted areas typically occur. New data indicate that low levels of dioxins
may not be as dangerous as was previously estimated; a review by Calabrese and Blain (2005)
states that 42 papers show beneficial health effects of low doses of dioxins (hormesis).
Similar considerations are relevant for other airborne, persistent, bioaccumulating pollut-
ants, primarily polychlorinated biphenyl (PCB) and dichlorodiphenyltrichloroethane (DDT).
Naturally occurring toxins - mycotoxins
Mycotoxins are fungal metabolites produced in infected plant material following infection
with various fungal species, such as af latoxins from
Aspergillus
species and fumonisins
produced by strains of
Fusarium
. Studies of samples taken from fields have shown either no
difference in mycotoxin content (Hietaniemi
et
al
. 2004) or lower content in the organic
samples compared to the conventional ones (Schollenberger
et
al
. 1999, Schollenberger
et
al
.
2002, Birzele
et
al
. 2002, Doll
et
al
. 2002). Although most studies were surveys, the study by
Bizele
et
al
. (2002) included a controlled cultivation experiment where the infection rate was
consistently highest in wheat grown with conventional mineral fertiliser and without pesti-
cides, intermediate in conventionally grown wheat (mineral fertiliser, with pesticides) and
lowest in organic wheat (organic fertilisation, no pesticides). The mycotoxin content in the
grain was more variable, as the conventional and organic treatments were similar, with both
still lower than the experimental combination of mineral fertiliser without pesticides. This
study showed that under German climatic and soil conditions, the type of fertility manage-
ment is more important for the extent of
Fusarium
infection than the use of pesticides. While
this conclusion may be unexpected for conventionally trained scientists and advisers (e.g.
Trewavas 2004), it is consistent with some other studies showing no or small differences in
infection rates between organic and conventional crops (e.g. van Bruggen 1995). However, of
note to the organic community is that although the relatively low and/or slow nutrient supply
in organic farming helps to trigger the plants' natural defences against infections, it is achieved
at the expense of some of the theoretical yield potential. This problem cannot be solved by
improving the methods for acquisition, retention and release of nutrients - excessive use of
organic fertilisers may lead to the same quality problems that haunt conventional cereal pro-
ducers (e.g. Pedersen and Bertelsen 2002).
In the late 1990s, Danish studies found problems with the concentrations of mycotoxins in
organic cereals. They were as a result of improper management, drying and storage facilities,
related to easily alleviated deficiencies in the advice provided to farmers and not due to the
farming system (Elmholt 2003). Nevertheless, this caused the average contamination in
