Impact of horticultural practices on the availability of organochlorine pesticides to organically cultivated vegetables

GONZALEZ, MARIANA; MIGLIORANZA, KARINA SILVIA BEATRIZ; AIZPÚN, JULIA ELENA; MORENO, VICTOR JORGE

Pulawy, Polonia

Workshop; Fate and Impact of Persistent Pollutants in Agroecosystems; 2005

IUNG, Centre of Excellence PROLAND, European Comission

Organochlorine pesticides (OCP) such as DDT, chlordane, dieldrin and heptachlor are included into the group of  Persistent Organic Pollutants (POPs). They are a class of compounds of particular concern in the environment due to their recalcitrance in natural solids, global transport, distribution, and toxicity. The impact of such contaminants on human health and accumulation in food crops is relevant due to increased dietary exposure of consumers. During the last decade organic agriculture has been developed rapidly on the assumption that such food is free of synthetic pesticides. However, it has been demonstrated that topographic position, wind dispersion and drift of pesticides from neighbouring farms are the main factors affecting the levels of contamination in organic products. In addition, horticultural practices itself such as organic amendments are known to be an important source of organic contaminants but the impact of other practices is less know. For these reasons, the goal of this work was to evaluate the effect of different growing conditions on the uptake and mobilisation of OCP in leek plants from organic farming. Plants were grown outdoor, in presence or absence of plastic bedspreads, as well as in greenhouses. The organochlorine compounds analyzed included: a-, b-, g- and d-hexachlorocyclohexanes (HCHs), p,p'-DDT and their degradation products, p,p'-DDE and p,p'-DDD,  heptachlor and its metabolite (heptachlor epoxide), a- and g-chlordane, aldrin, dieldrin, and  a- and b-endosulfan. OCP levels were quantified by GC-ECD in vegetative tissues (roots, stem and aerial) and soils where plants were grown. Three operationally defined soil samples differing in proximity to plant roots, were considered. Bulk soil samples were collected at harvest at a distance of 1 m from vegetation. Near root soil was defined as the soil in closer contact to plant root, but not attached to them. While, the rhizosphere was the soil that did not fall off the roots at harvest. The levels of OCP were decreasing as the fraction of soil  was nearer leek roots, leading to the following distribution pattern: bulk soil > near root > rhizosphere. These differences were greater in plants from greenhouses and outdoor with plastics. The OCP groups distribution pattern in plants from the greenhouse was similar to that from outdoor with plastic showing a pesticides enrichment in stem and leaves. These results is indicating the translocation of OCP from roots towards aerial tissues. Moreover they agree with the diminution of OCPs in the rhizosphere, probably as a result of the movement of pesticides throughout a chemical gradient. That fact was true for pesticides such as DDTs, Chlordanes and HCHs despite their different physicochemical characteristics. The similar behaviour of OC pesticides under greenhouses and outdoor with plastic conditions, would be a consequence of a higher temperature and humidity in both cases, leading to an increase in the microbial activity, degradation and solubilization of OCP. Finally, the mobilisation and availability of OCP were in narrow relation with the growing conditions, determining so that cultivation under greenhouses or the use of plastic bedspreads on soils modify the dynamics of these compounds in the system soil-plants and in ultimate instance the fate of these pollutants in agricultural ecosystems.