Question

What are some materials and methods I could use to test if pesticides were present in baby food? Explain the methods.

Answer 1

The presence of pesticides in baby food is a matter of concern. The presence of pesticides can be determined by broadly two methods. Single residue methods and multiresidue methods.

The single residue method is to quantitatively determine the presence of a single pesticide that can be converted by metabolism to toxic products. These are detected according to procedures specified in theFood and Drug Administration(FDA)'s Pesticide Analytical Manual (PAM).

The multiresidue methods are capable of detecting and quantifying more than one pesticide in food.It determines how much of which pesticide is present in a particular type of food.

Some of the methods adopted for checking of multiresidue pesticides are

use of cholinesterase enzyme inhibition test for organophosphorous and carbamate pesticides. use of insect bioassays to check for insecticides.

pesticides are often detected by high performance liquid chromatography or gas chromatography. The luke method of extraction was used for all polar and non polar pesticides detected by gas or liquid chromatography. For baby food testing the extraction solvent often used is acetonitrile. The use of this with fast temperature ramps that shorten Gas chromatographic technique is used to detect pesticides faster.Pesticides detected by Gas chromatography were confirmed by dual columns and detectors,while others are confirmed by other processes.

Detection Limits

All analytical methods have a limit below which the chemical could not be detected even if present. This limit of detection (LOD) is the lowest concentration that can be determined to be statistically different from a blank. Elsewhere in this report, the committee refers to the limit of quantification (LOQ), which differs from the LOD in that it refers to the concentration above which quantitative results may be obtained with a specified degree of confidence.

The LOD is influenced by extraneous, background material that is always present in the sample and the sensitivity of the instrumentation used for detection and quantification. Moreover, the LOD may vary according to application. LODs are determined by analyzing background (untreated) samples of the food products of interest and spiked samples, which contain known amounts of the chemicals. LODs for a given method will vary with the type of sample, the chemical, and the extent of sample cleanup provided.

LODs can be as low as twice the background reading. That is, a signal

Page 214

Suggested Citation:"6 PESTICIDE RESIDUES." National Research Council. 1993. Pesticides in the Diets of Infants and Children. Washington, DC: The National Academies Press. doi: 10.17226/2126.

×

Save

Cancel

that is twice the background could be measured and result in a calculated residue value. In practice, however, most laboratories set an LOQ that is several time higher than the theoretical LOD. Keith (1983) provides general guidelines for establishing the LOQ, but in practice, the criteria for setting the LOQ varies among laboratories.

To be of regulatory use, detection limits must be below established tolerance levels. The California Department of Food and Agriculture sets LODs at approximately one-tenth the tolerance level; FDA generally sets them at 0.1 to 0.01 ppm, depending on the chemical; and Florida's Department of Agriculture and Consumer Services sets them at or just below tolerance in order to screen large numbers of samples for clear violations. Unfortunately, LODs are not always specified in residue reports so that samples with no detectable residue levels cannot be assigned an upper limit of finite residue content. Furthermore, the reports do not clearly describe the extent to which residues below tolerance but above LOD are quantitated and confirmed, and they may not include a complete list of the pesticides that were not found but could have been detected had they been present. A report of pesticides not found (i.e., below the LOD) is usually not included in descriptions of the results of the overall programs but is done when there is special regulatory interest in specific pesticide residues (McMahon and Burke, 1987). Reporting only positive findings leads to a bias in the residue results.

Accuracy and Precision

Accuracy refers to agreement between a measured value and the true value. In residue methods, accuracy is often defined as the percentage recovery. Acceptable residue methods will give 80% to 120% recovery, indicating that if 1 ppm of a chemical were present, the analytical method would yield results between 0.8 and 1.2 ppm. Precision refers to reproductibility and the variability existing in a set of replicate measurements. Precision errors caused by variable reproducibility in residue methods tend to run high, with relative standard deviations (expressed as a percent of the mean) of 25% or more. The total error (accuracy plus precision) ideally should not exceed 100%. This must be assessed by the analyst running replicate spiked samples through the method.

Speed and Cost

Regulatory agencies require fast-response methods that can produce results in an 8-hour workday or less so that produce does not spoil when awaiting the results of an analysis. These faster methods are less expensive because they require less of an analyst's time. Needless to say, however,

Page 215

Suggested Citation:"6 PESTICIDE RESIDUES." National Research Council. 1993. Pesticides in the Diets of Infants and Children. Washington, DC: The National Academies Press. doi: 10.17226/2126.

×

Save

Cancel

the quickest, least expensive analytical method may not be the best one in terms of other criteria. As a result, many of the methods used are compromises of speed for quality.