Crop protection chemicals, detection

The persistence (half-life) of atrazine in the subsurface is governed by chemically and biologically mediated transformations. Because the solubility of atrazine is relatively high ( 30mg/L) compared to its toxicity level in water (5 Lig/L), atrazine has become a hazard to groundwater quality. Atrazine has been detected in groundwater more than any other crop protection chemical two examples of atrazine persistence-transformation in aquifer environments are discussed next. 

Detection and Quantification of Crop Protection Chemicals. Immunoassay procedures provide additional analytical tools for determining the presence and quantity of specific crop protection chemicals in various matrices. The specificity of an immunoassay is provided by the antibody reagent rather than by the analytical apparatus. The specificity, as noted above, allows the analysis of relatively crude preparations rapidly if the appropriate reagents (ie. antibodies) are readily available. Since a specific reagent must be prepared for each analyte, the greatest utility for these... 

Measurements of behavioral endpoints in honey bees should provide an effective assessment of hazards caused by crop protection chemicals especially when applied to melliferous plants. Under laboratory conditions, the conditioned proboscis extension (CPE) assay provides detectable sub-lethal effects due to pesticides, and also to gene products potentially used in plant genetic engineering (see other chapters of this book). Impairment in olfactory learning abilities have been shown for chemical concentrations at which no additional mortality occurred. Thus, the use of the CPE assay as a method to evaluate the potential effect on the honey bees foraging behavior can help to assess the toxicity of chemicals in a more comprehensive way than by considering the mortality endpoint alone. The CPE procedure can be used to compare responses to different chemicals (Table... 

Figure 6.12. Separation of a mixture of polar crop-protecting agents on silica gel by automated multiple development. Shown are the gradient profile used for the separation, the use of multiple wavelength scanning for detection and an in situ UV spectra for one peak (=s 50 ng). Solvent compositions for the gradient 1 = aqueous ammonia 2 = acetonitrile 3 = dichloromethane 4 = formic acid and 5 = hexane. (Adapted from ref. [21] American Chemical Society).

Monitoring plants for the presence of antidotes would seem to be particularly necessary when disease control involves the use of systemic fungicides (rather than those which act principally as protectants on the surface of the plant), since compounds of this type, which are now widely employed in agriculture, pass into the tissues of the plant where they are more likely to encounter any antidotes that may be present in the cells. If antidotes are detected in crop varieties, and if their presence appears to interfere with the efficiency of certain fungicides, the knowledge may allow different chemical treatments to be selected at an early stage. Alternatively, plant breeders may be able to develop varieties which lack, or contain only low levels of, the antidote compound(s) as, for instance, has already been done for different commercial reasons with crops such as lupin (low-alkaloid content), and sweetclover (low-coumarin content). 

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