Rapid field method residue levels

This paper establishes toxicologically-safe levels for total residues of parathion, azinphosmethyl, methidathion and their oxons on tree foliage and reports these levels in terms of absorbance units as determined by the rapid field method. Safe levels for a new insecticide, chlorthiophos, are also proposed based on preliminary residue data. Chemical structures of the four insecticides mentioned above are shown in figures 1, 2, 3 and 6. 

Testing Foliage for Safe Insecticide Residue Levels Using the Rapid Field Method... 

The rapid field method is a kit for making analyses in the field. A leaf punch sampler is used to collect samples of known surface area. The surface residues are removed using 20% NaCl solution and then residues are partitioned into hexane. The hexane is boiled off and the insecticide residues are reacted with 4-(p-nitrobenzyl) pyridine for 3 minutes at 150°C. Addition of base solution produces a purple color whose intensity is measured using a portable mini-spectrophotometer. The absorbance value of the colored solution is used to estimate the residue level present in the collected sample. 

Immunoassays offer much potential for rapid screening and quantitative analysis of pesticides in food and environmental samples. However, despite this potential, the field is still dominated by conventional analytical approaches based upon chromatographic and spectrometric methods. We examine some technical barriers to more widespread adoption and utilization of immunoassays, including method development time, amount of information delivered and inexplicable sources of error. Examples are provided for paraquat in relation to exposure assessment in farmworkers and food residue analyses molinate in relation to low-level detection in surface waters and bentazon in relation to specificity and sensitivity requirements built in to the immunizing antigen. A comparison of enzyme-linked immunosorbent assay (ELISA) results with those obtained from conventional methods will illustrate technical implementation barriers and suggest ways to overcome them. 

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