Potentiation pesticide mixtures

Locust (Locusta migratoria) is an important pest in Africa. In order to find a suitable pesticide or pesticide mixture, fenitrothion or deltamethrin was tried alone or in combinations by B. Johannesen, a Food and Agriculture Organizaton (FAO) junior expert working in Mauritius. Dilution series of mixtures with different compositions were made and the LD50 values of these mixtures were determined. These values were plotted as shown in Figure 2.7. We see that the two pesticides potentiate each other. 

Although there is nu doubt (hut humans are exposed to low doses of mixtures of pesticides (Caslorina e( at, 2003 Duggan et ai, 2003 Fenskc et al. 2002 Sanchez-Pena et ai, 2004), the question is whether mixtures are more toxic than the sum of the toxicity for each pesticide alone. In the literature describing the toxicity of mixtures of organophosphorus (OP) or carbamate (CM) pesticides, concern is expressed that exposure to mixtures of pesticides may be much more toxic than the toxicity of the individual pesticides. This concern about potentiated toxicity is all the more worrisome because data are lacking on the toxicity of pesticide mixtures, whether OP or CM, at less than lethal dosages. There is such scarcity of data, and the data arc so disparate, that a science-ba.scd conclusion on the toxicity of OP or CM pesticide mixtures is not possible,... 

Lord and Pawliszyn" developed a related technique called in-tube SPME in which analytes partition into a polymer coated on the inside of a fused-silica capillary. In automated SPME/HPLC the sample is injected directly into the SPME tube and the analyte is selectively eluted with either the mobile phase or a desorption solution of choice. A mixture of six phenylurea pesticides and eight carbamate pesticides was analyzed using this technique. Lee etal. utilized a novel technique of diazomethane gas-phase methylation post-SPE for the determination of acidic herbicides in water, and Nilsson et al. used SPME post-derivatization to extract benzyl ester herbicides. The successful analysis of volatile analytes indicates a potential for the analysis of fumigant pesticides such as formaldehyde, methyl bromide and phosphine. 

Nonylphenol ethoxylates (NPEOs) are extensively used as surfactants in industrial products (see Chap. 1). NPEOs are a mixture of polyethoxylated mono-alkylphenols, predominantly para-substituted, and are used in the manufacturing of paints, detergents, inks, and pesticides [435, 446]. Surfactants are common water pollutants because of their use in aqueous solutions, which are discharged into the environment in the form of wastewater from treatment plants or sludge stored in landfills. Degradation products of alkylphenol polyethoxylates, i. e., nonylphenol (NP), have the potential to be bioaccumulated, thereby becoming toxic to aquatic [447] and soil microorganisms [435,448]. 

Petty et al. (1998, 2000) used a vitellogenin (VGT) assay to assess the endocrine disrupting potential of contaminants in purified SPMD extracts. VGT is an egg yolk phosphoprotein precursor that is synthesized in the liver of female teleosts in response to estrogen from the ovary (Bailey, 1957). A wide variety of environmental contaminants have been shown to have estrogenic activity (Colborn et al., 1993). Equal portions of purified extracts from SPMDs, exposed in the Missouri River after the flood of 1993 and from the IWWTP at the Nogales Wash deployment were individually injected into immature rainbow trout (Oncorhynchus mykiss) as described in Section 6.4. The SPMD extracts contained elevated levels of complex mixtures of contaminants, including PAHs and pesticides. The fish injected with these sample extracts exhibited VGT induction, while no induction was observed in fish injected with any of the blank sample extracts. 

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