Diversifying crop rotations with temporary grasslands - Université de ...

Herbicides are relatively expensive; farmers in industrialized countries spend more money for
herbicides than for any other pesticides. In 2006-2007, herbicides represented 64.4% of the
US agrochemical market ($3914 out of $6077 million, AGROW, 2008) and 42.7% of the
French marked (€787 out of €1841 million, UIPP, 2009). The high economic costs are the
main reason why herbicides are much less used in poor countries.
Environmental pollution
Herbicides and their metabolites are frequently found in groundwater samples. Herbicides are
the most widely used pesticides before fungicides and insecticides in terms of economic value
(see above) and volume. In Germany, farmers bought more than 16,000 tonnes of herbicides
in 2007, which corresponds to 51% of the total weight of pesticides bought (IVA, 2009), a
proportion that may well be representative for other industrialized countries. Depending on
soil characteristics and climatic conditions, some herbicide active ingredients may be rather
quickly degraded by micro-organisms in the soil. Other herbicide types (including preemergence
herbicides such as the triazines) are designed to stay active for longer times and are
thus more frequently detected in groundwater samples (Arias-Estevez et al., 2008). Moreover,
herbicides are often applied before or shortly after crop sowing, when the soil is not covered
by vegetation, and during wet periods when the risks of run-off and leaching are high.
In France, herbicides have been detected in 91% of 1690 observation points of surface water
courses and in 55% of 846 groundwater observation points spread all over the metropolitan
territory in 2005 (IFEN, 2007). Atrazine, which was officially banned in 2003 in France,
showed only slightly decreasing concentrations from 1999 to 2007 in a catchment near Paris,
and deethylatrazine, a metabolite of atrazine, showed no decreases at all during this time
(Gutierrez and Baran, 2009).
Several active ingredients of herbicides or their metabolites may have negative environmental
side effects (sometimes called ‘externalized ecological costs’). Herbicides may e.g. kill nontarget
plants and may indirectly affect many animals and micro-organisms by suppressing the
plant species they depend on (see review by Freemark and Boutin, 1995; Hawes et al., 2003;
Gibbons et al., 2006). Some herbicide active ingredients and adjuvant compounds may also
have direct toxic effects to micro-organisms and animals but animal toxicity is mostly lower
than for insecticides and fungicides, at least for the herbicides still authorized in the European
Union. Even though evidence of direct toxicity of herbicides and adjuvant compounds to
humans is limited (but see Benachour and Seéralini, 2008), herbicides are considered
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