Organic EprintsBewirtschaftung von organochlorbelasteten BödenState of the Art: Residues of organochlorine pesticides (OCP) in soils, such as Dieldrin and DDT contaminate crops, even though their use was banned by the European Union 30 years ago. The aim of this project is to develop methods reducing the concentration of OCP in the edible parts of crops grown on contaminated soils. This will be achieved by a two step procedure: First we will add different organic carbon sources to the soil, which can lead to binding and immobilising of OCP, resulting in reduced bioavailability of OCP. Second we will select root stocks of grafted plants (i.e. cucumbers) with a high capacity to exclude OCP from plant uptake. Combinations of these two methods will be evaluated. Definition of the problem: Background: Organochlorine pesticides (OCP) such as Dieldrin and DDT were applied world wide against pests in horticulture, fruit and arable crops. Although OCP are forbidden since more than twenty years in the European Union (EU), the highly persistent compounds are still detectable in soil. Several crops are known to accumulate OCP in edible parts up to critical levels. For instance Dieldrin is detected in high economic value crops such as cucumbers (Cucurbitaceae) and tomatoes (Solanaceae). Besides plant type and climatic conditions, soil properties, e.g. pH and soil organic carbon content influence the plant’s OCP uptake. In particular in premium food and feed stuff production, such as organic farming according to EU Regulation (EEC) No. 2092/91, consumer expectations in safe, high quality food are extremely high. Since organic farming is prospering – more than 10% of vegetable production is certified organic in Switzerland – the OCP residues in organic food stuff have become a major issue for food control authorities. Enquiries showed that some of the imported food from EU countries such as pumpkin seed and oil was highly contaminated with OCP. Hence, the OCP problem in food stuff is expected to occur EU wide or even world wide. Preliminary study: Facing this problem we performed a case study and analysed the OCP content of 15 fields and their grown fruits from the most important Swiss organic cucumber growers. Two out of these 15 field soils revealed Dieldrin leading to surpassing of the tolerance level. It also occurred that the whole crop yield from an OCP contaminated field was rejected by food retailers and the crop had to be ploughed down. The Swiss organic label organisation has the option in their standard now to exclude polluted soils for production of highly OCP accumulating vegetables, but this may severely affect the grower’s economy. Project aims including target group: Objectives: In this project we aim at developing sustainable safe food production on OCP contaminated soils, which is economically and ecologically sound. First we will perform an in-depth field survey on 50 sites to assess the extent of OCP contamination on Swiss farms. Soils and Cucurbitacea crops will be analysed for OCP. Cucurbitacea are chosen because crops of this family accumulate strongly OCP and thus are suitable as indicator plant. Second, we will develop strategies in bioassays in the glasshouse to lower OCP uptake from the contaminated field soils through immobilisation of OCP by organic carbon addition to the soil and by selection of OCP excluder plant varieties. These experiments are organised as follows: i) Test system optimization: We will optimize a previously used test system for the immobilisation and exclusion experiments (see below). We will grow cucumbers in OCP contaminated field soils (little, medium, high) and measure OCP in the growing cucumbers in a time course. As an alternative we will use cress as a test plant to shorten the duration of the experiment. 14C-labelled Dieldrin will be used to calculate fluxes in the soil-plant system. Based on the results of these experiments we will decide which soil and crop we will use in the following tests and when the test plant will be harvested for OCP analyses. ii) Immobilisation of OCP by organic carbon: The aim of these experiments is to immobilise OCP in the soil by the addition of organic carbon to the soil. The hypothesis is that the OCP will be bound by the organic carbon and consequently the bioavailability is expected to be decreased. Organic carbon will be added to the soil in form of compost or as brown coal product (charcoal) at three levels each. The bioavailability of OCP will be assessed by measuring these molecules in the plant shoot. iii) Exclusion of OCP by crops: The aim of these experiments is to identify plant varieties with a low OCP uptake. Since cucumbers are normally cultivated by grafted plants nowadays, where a robust and vital root stock is inoculated by a desired variety, we will select for OCP excluder root stocks. For cucumbers, root stocks from the groups of Cucurbita moschata x C. maxima, Sicyos angulatus and Cucurbit ficifolia are currently in use, but we will test further ones from the same family. The root stocks and the grafted plants will also be cultivated in contaminated field soils and OCP will be measured in the plant’s tissue. The most promising treatments from the immobilisation and the exclusion experiments will be applied in combination. Finally we synthesize the results from the field survey and the glasshouse experiments and, including literature findings, we suggest field evaluations of the elaborated strategies for safe food production on OCP contaminated soils. We already expect after three project years a high degree of applicability of the strategies, since this project bridges basic and applied research and combines different strategies to prevent plant uptake of the harmful OCP. Methodology: Field survey of OCP, OCP analyses by GC-MS (to be adapted), Bio-assay, plant grafting BodenProjektbeschreibung mit Link zur Projekthomepage

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