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

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

IUNG, Pulawy, Polonia

Workshop; Int. Workshop “Fate and Impact of Persistent Pollutants in Agroecosystems”; 2005

Organochlorine pesticides (OCPs) 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 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 neighboring 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 OCPs in leek plants from organic farming. Plants were grown outdoor, in presence or absence of plastic bedspreads, as well 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 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 pattern distribution Bulk soil > near root>rhizosphere.  Being these differences greater in plants from greenhouses and outdoor with plastics. DDTs, Chlordanes and HCHs were the main OCP groups affected despite their different physicochemical characteristics. In presence of the plastic bedspreads, the proportion of pesticides in stem and leaves was increased whereas in roots diminished.  On the other hand the distribution pattern of OC pesticides groups in plants from the greenhouse, was similar to the one outdoor with plastic. Moreover, these results agree with the diminution of OCPs in the rhizosphere, indicating the translocation of OCPs from roots towards aerial tissues The similar  behaviour of OCPs under greenhouses and outdoor with plastic conditions, would be in relation to a greater temperature and humidity in both cases, leading to an increase in the microbial activity , degradation and solubilization of OCPs. Finally, the mobilization 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 modifies the dynamics of these compounds in the system soil-plants and in ultimate instance the fate of these pollutants in agricultural ecosystems.