Kurzbeschreibung
(Englisch)
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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.
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IE, IL, IT, LT, LU, NL, NO, PL, PT, RO, SE, SI, SK, TR, UK
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Abstract
(Englisch)
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The use of organochlorine pesticides (OCP) in the late 1960s in horti- and agriculture was widespread. OCP belong to the persistent, bioaccumulative, and toxic pollutants (PB&T) and cause adverse effects in non target species by entering into the food chain. Two surveys carried out in 2002 and 2005 to assess the loads of OCP in 41 Swiss horticultural fields under organic and conventional production and correspondig Cucurbitaceae fruits revealed that 65.9% of 41 fields and 12.2% of the fruits were contaminated. Contamination of OCP in the fields ranged from <0.01 to 1.3 mg/kg (dry weight) and in the fruits from <0.01 to 0.04 mg/kg (fresh weight). The most detected OCP in the soils were pentachloroaniline, p,p'-DDT, p,p'-DDE, and dieldrin (sum over all soils 2.1, 0.5, 0.4, and 0.4 mg/kg, respectively). A removal of these contaminants from soils is not possible and strategies are needed e.g. to prevent the uptake of bound OCP residues in soils by plants. Activated carbon (AC) amendments are an emerging technique to immobilize the organic contaminants in the soils. In 2006 and 2007 we tested powdered AC amendments of 0, 200, 400, and 800 mg/kg concentrations on their binding effect by planting cucumbers (Cucumis sativus) in pots filled with a soil that had been contaminated in past field applications. The soil contained dieldrin (0.07 mg/kg), pentachloroaniline, and p,p'-DDE (each compound <0.01 mg/kg). Additionally, we wanted to observe the availability of the macro nutrients N, P, K, Ca and Mg and of the micro nutrients Cu, Zn, Mn, Mo and B under AC influence. To quantify the binding effect of the AC added into the soil, we used the promising tool of Tenax beads. It is an infinite sink for the dissolved OCP in the soil pore water. The porous polymer is intended to assess the mobilising effect that cucumber roots exudates may have on the bound OCP residues in soil and therefore serves as a root surrogate. In the 2007 experiment dieldrin uptake was generally much lower than in 2006, and no reduction in dieldrin uptake by cucumbers was observed in AC amended soil in 2007. Over the two years, the uptake of dieldrin in the 800 mg/kg AC amended soil did not exceed 4 ng/g cucumbers (fresh weight). AC soil treatments did neither affect the availability of N, P, K, Ca, Mg, Cu, Zn, Mn, Mo, and B for cucumber plants nor the yield of cucumber fruits. Thus, an important prerequisite for the application of AC amendments in order to immobilise organic pollutants in agricultural soils can be considered fulfilled. The Tenax-extractable dieldrin was reduced by the AC amendment in both years. Comparing the total mass of dieldrin extracted by Tenax per pot and the total withdrawal of dieldrin by the cucumber fruit, there was no (2007) or no significant correlation (2006). This means that Tenax extractability reflected a dieldrin fraction reacting with AC but did not adequately indicate the phyto-availability of dieldrin. It appears that cucumbers can take up a rather immobile dieldrin fraction that does not readily react with AC and is not available to sorption by Tenax. We suggest that this is a bound residue fraction of dieldrin that is released by reaction with specific cucumber root exudates and taken up by the roots immediately after being released. What we have learned so far from this project is (i) contamination with OCP is a widespread problem, (ii) AC amendments into soil is an efficient sorbent for many OCP but at least for dieldrin as proofed by Tenax extractions, (iii) AC amendments seem to be successful in the reduction of exposure to cucumber plants although varying factors like temperature occuring in the open field certainly influence growth conditions and adsorption of the pollutants to AC, (iv) AC does not influence nutrient availability to cucumber plants, and (v) further Tenax experiments are necessary to adequately assess the phytoavailable fraction of OCP in soils.
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