Modern Agrochemicals Influence Bioaccumulation of Incurred DDT Soil Residues in Pumpkins – Residue Risk or a Chance for Phytoremediation?

Abstract

Due to the high persistence of DDT and its metabolites DDE (1-chlor-4-(2, 2-dichlorphenyl-1(4chlorphenyl) ethenyl) benzene) and DDD (1-chlor-4-(2,2-dichlor-1-(4-chlorphenyl) ethyl) benzol) (-DDX‖) against microbial and chemical degradation, still distinct quantities of DDX are found in many soils all over the world [2-5]. The main hot spots are found in Asia [2,3], America [4,5] and southern Africa, while levels in Western Europe [6,7] are comparably low. In combination with the highly lipophilic character (log K ow DDT = 6,91 [8]), DDX remain adsorbed mainly to soil organic matter and therefore, relatively static in upper soil layers. It is however known that lipophilic contaminants adsorbed to the dissolved organic carbon (DOC) fraction of the soil show an increased water solubility and therefore, mobility. This mobility may be significantly influenced by the application of surfactants, which was demonstrated in a number of studies [9-15], where surfactant/ water mixtures were directly applied to soil samples or used to extract soils. Such mixtures are commercially used for the removal of non-aqueous phase liquids (NAPLs) [16] from highlycontaminated soils, e.g. resulting from oil leakages. This process is commonly performed by the Abstract: Although banned more than 50 years ago, residues of first generation organochlorine pesticide residues, such as DDT are still found in agricultural soils all over the world. Phytoremediation is a potential remediation strategy, using plants to remove these residues from the soils. One limiting factor is the low mobility and bioavailability of lipophilic compounds for plants. Soil mobility can be significantly increased by the application of surfactants to the soils. Agrochemicals, in particular crop protection formulations commonly contain major amounts of surfactants as adjuvants, a fact which so far has not been considered an influencing factor for the mobilization of organochlorine contaminants such as DDT. This study evaluated the influence of commonly applied agrochemical products on the bioavailability of DDT and its metabolites in pumpkins in an open-field trial. To compare different typically used products, organic farming pesticides were compared against conventional formulations.