Michigan Food Monitoring Program
1996
Michigan Department of Agriculture

The goal of the Michigan Food Monitoring Program is to characterize and assess potential pesticide exposure through the food chain in Michigan and to make appropriate recommendations to state and federal agencies for proactive risk management. Now in its fifth year, this program continues to analyze raw agricultural commodities for the presence of pesticides.  It is assumed for purposes of risk evaluation that these commodities will be channeled to the fresh, rather than processed, market.  Eight commodities were examined in this manner during 1996 including potatoes, summer squash, winter squash, blueberries, peaches, apples, grapes and cucumbers.  This document describes the sample collection, analytical methodology, analytical results and program conclusions.

Sample Collection

MDA regional inspectors collected random samples from various post harvest locations including the producer, distributor and, when necessary, the retailer.  However, every attempt was made to collect the sample as close to the "farm gate": as possible.  Regardless of where the sample was collected, the producer of that commodity was always identified.  Twenty 5 to 10-lb samples of each commodity, representing 20 different producers, were collected and then submitted to the MDA laboratory for analysis.  A total of 160 samples were collected (Table 1).

Analytical Methodology

Two multi-residue analyses were employed.  One method referred to as the "Luke" procedure (AOAC Section 29A05) was used to determine a wide range of pesticides that contain the elements of phosphorous, chlorine or nitrogen.   Pesticides detected by this method would include organophosphate compounds such as parathion and malathion.  The second method selected was capable of detecting N-methylated carbamates such as carbaryl and methomyl.  Both methods were used in the screening mode.  A screening analysis refers to the extraction and analysis of a commodity to determine the presence of any compound known to be recovered by the method.   To assure method performance throughout the analytical process, a matrix spike containing representative compounds of the class of recoverable compounds was included. To prevent false positives, every compound detected by screening was confirmed by additional testing including structural analysis by mass spectroscopy.

Analytical Results

Table 2 summarizes the analytical results.  The commodity tested is listed in the first column followed by the sample size, pesticides detected, the frequency at which the pesticide was detected, the range of concentrations, the FDA tolerance for the pesticide and the number of samples found to exceed the tolerance.  The tolerance is the maximum concentration of a chemical permitted in food for human consumption.  For example,  the first line of Table 2 shows that phosmet was found at detectable levels in six of the 20 apple samples. Concentrations of phosmet ranged from trace amounts to 0.44 parts-per-million (ppm).   The tolerance for phosmet in apples is 10 ppm, therefore, none of the samples exceeded tolerance.  Table 3 shows the number of samples of a commodity for which any pesticides were detected.  For example, 12 of the 20 (60 percent) of cucumber samples had one or more pesticides detected.

The data from Tables 2 and 3 are summarized as follows. Fourteen (14) of 20 (70 percent) of apple samples contained one or more of the following pesticides:   phosmet, azinphos-methyl, oxamyl, endosulfan I and II, endosulfan sulfate, chlorpyrifos, dimethoate, methomyl, diphenylamine, propargite, captan and carbaryl.   All residue levels were below tolerance.  All 20 blueberry samples were found to have one or more pesticides including captan, carbaryl, chlorothalonil, malathion, phosmet, methomyl and azinphos-methyl.  All pesticide concentrations were found to be below tolerance.  Cucumbers showed 12 out of 20 (60 percent) samples to have detectable levels of metalaxyl, endosulfan, endosulfan sulfate, dieldrin, acephate, methomyl, and/or chlorothalonil.  Currently there is no tolerance for acephate in cucumbers, therefore, one sample containing 0.1 ppm exceeded tolerance (when no tolerance exists, any detectable level is considered to be over tolerance).  Nineteen (19) out of 20 (95 percent) of grape samples contained one or more of the following: carbaryl, myclobutanil, azinphos-methyl, methyl parathion, phosmet, methomyl, DDE, chlorpyrifos, and 1-napthol (a breakdown product of carbaryl).  No tolerance exists for DDE which is a breakdown product of DDT.  One sample contained 0.011 ppm of DDE.  Analysis of peaches showed the presence of one or more pesticides in 18 samples (90 percent) including chlorpyrifos, pipernyl butoxide, diphenylamine, captan, dimethoate, azinphos-methyl, iprodione, phosmet, permethrin, malathion, endosulfan sulfate, endosulfan I and II, methyl parathion, carbaryl, fenvalerate, and vinclozolin.  Neither diphenylamine nor dimethoate have tolerances.  One sample had diphenylamine at 0.01 ppm, two samples contained dimethoate at 0.02 and 0.05 ppm, and one sample had both dimethoate and diphenylamine at 0.03 and 0.01, respectively.  Eleven (11) of 20 (55 percent) had potato samples containing one or more of the following:  DDE, chlorpropham, and thiabendazole.  All residue concentrations were below tolerance.  Analysis of summer squash showed 14 of 20 (70 percent) of samples containing thiabendazole, metalaxyl, dieldrin, methomyl, and/or endosulfan sulfate.  An FDA administrative guideline of 0.05 ppm for dieldrin in squash had been revoked, therefore, no current tolerance exists.   Three samples had dieldrin concentrations of 0.01 to 0.03 ppm.  The analysis of winter squash found no detectable levels of  any pesticides.

Conclusions

A total of 160 samples were analyzed for pesticides of which 108 (67.5 percent) had detectable residues.  Nine of these samples, or 5.6 percent, were found to exceed tolerance.  In all of these cases, no tolerance existed.  Therefore, any detectable concentration would be considered to exceed tolerance.  Fortunately, the concentrations found for these pesticides were extremely small and of no toxicological significance.  Four of the nine samples (grapes and summer squash) contained the environmental contaminants DDE and dieldrin.  These chemicals are no longer used agriculturally but due to their widespread use at one time and persistance in the environment, they are still easily found in many environmental matrices such as plants, soil and fish.  Follow-up inspections were conducted at the remaining five grower locations where acephate in cucumbers and diphenylamine and dimethoate in peaches were found above tolerance.  In these cases, the pesticides appeared to be present as the result of drift from the treatment of adjacent crops.

Table 1

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