treadmill” has caused a continuous increase in the use of pesticides in the region. The phenomenon is well-established in the scientific literature and is responsible for crop losses due to pests and diseases, which have increased notably despite the ever greater use of pesticides (Pimentel et al., 1978).
     Particularly worrisome at present is the increase in weeds resistant to herbicides, mainly glyphosate, due to the establishment of herbicide-resistant or -tolerant varieties, such as Roundup-Ready soybean from Monsanto (Box 1-7). From 2000 to 2005, the number of biotypes of herbicide-resistant weeds climbed from 235 to 296 and to 178 species. All these factors combine with the vast expanses of single-crop agriculture characteristic of the conventional/productivist production system to create conditions that are unsustainable in the long run (Matson et al., 1997).
1.7.2.3 Agroecological system
The agroecological systems have emerged in response to the lack of sustainability and the environmental and health impacts of the conventional/productivist system. One of the pillars of the agroecological systems is the elimination or reduction in the use of pesticides and synthetic fertilizers; the other pillar is biodiversity. A recent study of 286 agroecological projects with small-scale producers in 57 countries of Africa, Asia and Latin America and the Caribbean found that while the average yield increased 79%, there were also increases in the efficiency of water use and the potential for carbon sequestration. Also contributing to the increase in the sustainability of the systems, the study found that 77% of the producers reported a 71% reduction in the use of pesticides. This study is significant because it covers an area of 37 million ha, which
represents 3% of the area planted in the non-industrialized countries (Pretty et al., 2006). One of the strategies for managing agroecological systems is to increase biodiversity, both planned and associated (Vandermeer, 1995). The increase in biodiversity is accompanied by the restoration of ecological processes such as pollination and the predation of herbivores by natural enemies (Nicholls and Altieri, 1997). Alongside these benefits, agroecological practices may also increase the system’s resistance to catastrophes, thereby bolstering its sustainability. Recently a participatory study by the Movimiento Campesino a Campesino showed that farms managed with agroecological practices were more resistant to the impacts of Hurricane Mitch in Nicaragua (Holt-Giménez, 2001) (Box 1-5).
1.7.3 Quality and food safety
Food quality and safety is understood as the guarantee that a food will not cause harm to the consumer, or in other words that it won’t cause disease. The modern concept incorporates factors such as agricultural practices, genetic manipulation, the inclusion of hormones or other drugs in animals’ diets (Campos, 2000) and post-harvest handling such as storage conditions and the use of unauthorized additives. The Codex Alimentarius Commission, established by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO), prepares risk-based food safety standards that are used as a reference in international trade and give the countries a model for national laws (FAO, 2007).

     The concept of food quality has to do with nutritional value, organoleptic properties such as appearance, color, texture and flavor and functional properties. Quality is related to characteristics that determine value or acceptability by consumers and compliance with standards that ensure that a product is safe for consumers, not contaminated, adulterated, or bearing a fraudulent presentation. Safety therefore has to do with risks associated with production and subsequent handling, processing and packaging, such as contamination with agrochemicals (pesticides and fertilizers), veterinary drugs, or unauthorized food additives; microbiological risks posed by bacteria, protozoa, parasites, viruses and fungi or their toxins (mycotoxins, aflatoxins); natural toxins present in the environment (zinc, arsenic, cyanide) or in foods themselves (solanine and histamine); and toxic industrial chemicals or radioactive waste (arsenic, cadmium, copper, lead, mercury and polychlorinated biphenyls) (FAO, 2000). Exposure to pesticide waste or other contaminants in the diet has adverse effects on the production and reproduction of animals and in human populations (Singh et al., 2007).
     Although until a few years ago authorities and researchers from several countries affirmed that foods produced organically did not differ significantly in terms of food safety and nutrition from conventionally grown foods, there is more and more evidence and official recognition that organic foods contain lower amounts of residue of additives and colors, pesticides, veterinary drugs and in many cases more nitrates and other vitamins, minerals, essential fatty acids and beneficial antioxidants; and they appear to have the potential to lower the incidence of cancer, coronary heart disease, allergies and hyperactivity in children (FAO, 2000; Cleeton, 2004; Soil Association, 2005, 2007). Baker et al. (2002) performed a statistical analysis of data on pesticide residues in 94,000 food samples to describe and quantify differences between fresh fruits and vegetables from three different modes of production: conventional, integrated pest management and organic. A comparison was done of data from three programs: the Pesticide Data Program of the US Department of Agriculture; the Marketplace Surveillance Program of the California Department of Pesticide Regulation; and tests performed by Consumers Union, an independent organization. It was found that concentrations of pesticide residues in organic samples were consistently lower than in the other two categories and the greatest concentrations were found in the conventional samples, which also contain multiple pesticide residues in greater proportions.

      According to Barg and Queirós (2007), in 2004 a study was carried out in Uruguay on the quality of fruits and vegetables and levels of contamination by agrochemicals, with 200 samples. Residues were detected in 72% of them; in 7% of the cases the maximum residue limits (MRLs)— established by Codex Alimentarius for individual products— were exceeded, but in many samples residues of several different pesticides were detected. Combinations of low levels of insecticides, herbicides and nitrates have proven to be toxic at levels at which the chemicals individually considered are not (Cleeton, 2004). Barg and Queirós (2007) added that the MRLs allowed are set based on the technolofromCK