Vol. 10 No. 4 September 1990

Special Edition


Last week, a copy of the 1989 results of the pesticide residue monitoring program from the California Department of Food and Agriculture (CDFA) arrived in our office. The report is titled "Residues in Fresh Produce - 1989" and each Agricultural Commissioner's office received a few copies. If you wish to look at the entire report it is available there. Included in this issue are the figures that we think will be most useful for your public education programs and an explanation of some of the terms, as well as an analysis of what these findings mean. Because of the importance of these findings to all of our food safety programs statewide, we decided to put out this "special edition".

If you have any questions about the report or our interpretations of it, please call us and we will try to help. We cannot provide copies of the report but they might be obtained through your agricultural commissioner.

The following are definitions of the testing programs which will be helpful for interpreting the results.

Marketplace Surveillance is the program in which the samples are taken throughout all channels of trade (wholesale and retail markets, chainstore distribution outlets, points of entry and points of origin). It also includes special surveys conducted by CDFA.

Preharvest Monitoring is the program designed to monitor for improper use of pesticides during the growing season before a crop is marketed. Improper use would include such things as using higher rates of application than permitted by the label, or using a pesticide not registered for use on the particular crop. The samples are taken prior to harvest of the crop and at any time during the growing season.

The Priority Pesticide Program was known before as the Focused Monitoring Program. Samples are taken from crops known to have been treated with particular pesticides of special health interest (those for which illegal residues might also entail a health risk). These samples are especially significant because the crops are known to have been treated, and the time when they were treated is also known.

Produce Destined for Processing is exactly that, harvested produce on its way to a commercial processor.

To properly interpret the CDFA residue findings it is necessary to make the distinction between "illegal" residues and "unsafe" residues. Tolerance levels are set for enforcement purposes and do not represent health-based standards. A finding that a residue level exceeds the established tolerance level indicates that the pesticide was probably not applied properly, but may not be of any health significance since only rarely are illegal residues cause for health concern. Illegal residues also occur when a pesticide is detected on a commodity for which it is not registered, regardless of the level detected. This type of illegal residue may occur through the intentional application of a pesticide to a commodity for which it is not registered as well as through drift from legal pesticide applications on adjacent crops or plant uptake of soil residues of previous pesticide applications. Again, illegal residues encountered in this fashion are rarely of health significance. In the CDFA Marketplace Surveillance Program in 1989, 69 percent of the illegal residues resulted when residues of pesticides not authorized for use on the commodity were detected, while only 31 percent of the illegal residues actually exceeded tolerance levels.

Rick Melnicoe of the CDFA Pesticide Enforcement Branch provided us with some additional information concerning the monitoring program. The total number of samples analyzed in 1989 was 14,987 at a cost of 4.2 million dollars (which calculates out to $280.24 per sample). In 1987, the number of samples tested was just about doubled to 13,445 compared to previous years (6,503 in 1985 and 7,268 in 1986). Rick provided us with statistics on the totals for all categories during the last four years, and these figures are particularly striking. From 1986 through 1989 (four years) 50,202 samples were tested. Of the total, 81.34% contained no detectable residues, and only 0.88% contained illegal residues.

Breaking these figures down by category, there was a total of 31,206 Marketplace Surveillance samples tested, and 79.6% of these contained no detectable residues. There were 300 samples (0.96%) which contained residues for which no tolerance had been established, and 84 samples (0.27%) were over tolerance. This is a total of 1.23% with illegal residues. In the Priority Pesticide Program, 5,157 samples were tested and 86% contained no detectable residues. Only 1 sample (0.02%) contained residues which were over tolerance. For Produce Destined for Processing, 3,840 samples were tested and 87% contained no detectable residues. Only 7 samples (0.18%) contained residues for which no tolerance was established, and only 3 samples (0.08%) contained residues which were over tolerance.

The following table shows the results of all programs combined for the years 1984 through 1989.

YEAR TOTAL # No Detectable Residues Illegal Residues
1984 7,249 6,258 (86.33%) 101 (1.39%)
1985 6,503 5,632 (86.61%) 102 (1.57%)
1986 7,268 6,130 (84.34%) 108 (1.49%)
1987 13,445 11,070 (82.34%) 129 (0.96%)
1988 14,502 11,429 (79.5%) 127 (0.88%)
1989 14,987 12,107 (80.78%) 80 (0.53%)

It is interesting to note that there is a decline in both the percentage of samples with no detectable residues, and also in those containing illegal residues. One possible explanation for the decline in the samples with no detectable residues is the increasing sensitivity of our analytical tests. One possible explanation for the decline in the number of illegal residues is that the expanded testing program is resulting in better pesticide use practices. There are of course, other equally believable explanations for each of these trends. It is particularly interesting that the overall results in terms of the "no detectable residues category " do not vary much (less than 10%) during the last six years, despite expansion of the testing program. The numbers (and percentage) of illegal residues has declined almost 50% during this 6 year period. As stated earlier, illegal residues are not necessarily "harmful" residues. Information on the actual number of "potentially harmful" residues would be illuminating, and we hope to be able to provide that information sometime in the future.

We hope that these data will be useful to you in your public education food safety programs.

Art Craigmill
Extension Toxicologist
U.C. Davis

Carl Winter
Extension Toxicologist
U.C. Riverside

Mike Stimmann
Statewide Pesticide Coordinator
UC Davis