MIGRANT AND SEASONAL (Pesticides and the Farmworker) TUESDAY, SEPTEMBER 30, 1969 U.S. SENATE, SUBCOMMITTEE ON MIGRATORY LABOR OF THE COMMITTEE ON LABOR AND PUBLIC WELFARE, Washington, D.O. The subcommittee met at 9:45 a.m., pursuant to recess, in room 4232, New Senate Office Building, Senator Walter F. Mondale (chairman of the subcommittee) presiding. Present: Senators Mondale (presiding), Cranston, Murphy, and Schweiker. Committee staff members present: Robert O. Harris, staff director; and Boren Chertkov, counsel to the subcommittee. Senator MONDALE. The subcommittee will come to order. Our first witness this morning is Dr. Paul Porter, assistant director, Shell Development Research Co., from Modesto, Calif. Dr. Porter, will you please come to the witness table? STATEMENT OF PAUL PORTER, PH. D., ASSISTANT DIRECTOR, SHELL DEVELOPMENT RESEARCH CO., MODESTO, CALIF. Senator MONDALE. Do you have a prepared statement, Dr. Porter? Mr. PORTER. Yes, I have. I would like to read it, if I may. Senator MONDALE. You may proceed. Mr. PORTER. My name is Paul Edward Porter and I reside at 506 Bowen Avenue, Modesto, Calif. I received a Ph. D. in physical chemistry from Iowa State University in 1951. I am an associate member of the International Union of Pure and Applied Chemistry on Terminal Residues. This commission was formed by the International Union of Pure and Applied Chemistry at the request of the food and agricultural organization and the World Health Organization of the United Nations to give them advice on the nature of the terminal residues, metabolic products, and breakdown products of pesticide compounds used in agriculture. My function on the committee is to follow new developments on the "cyclodiene" insecticides of which aldrin is an example. Each year I prepare a summary of recent information on terminal residues of the cyclodiene insecticides. I am presently assistant (3687) to the director, physical sciences, at Shell Development Co., Biological Sciences Research Center in Modesto and have been employed by Shell Development Co. since graduation. For the past 15 years I have been concerned with residue analysis and metabolism studies on pesticide compounds. During the period from 1955 to 1968, I was manager of our physical and analytical chemistry laboratories. I participated in the development of analytical methods for determination of aldrin, dieldrin, endrin, and other compounds; and I supervised their use in obtaining residue data for registration. The Woodstock laboratories of Shell in England originated the application of the electron capture detector to pesticide residue analysis, and my laboratories utilized this technique before commercial equipment was available. From the beginning we have kept up with progress in the residue analysis field and have had experience with every type of analysis now in general use. Aldrin is a chlorinated hydrocarbon insecticide in which the active ingredient is 1,2,3,4,10,10-hexachloro-1,4,4a,6,8,8a,-hexahydro-1, 4-endo-exo-5,8-dimethanonaphthalene. It is a light tan solid insoluble in water but readily soluble in most common organic solvents. It is moderately volatile: about 30 times as volatile as its epoxide dieldrin and about 150 times as volatile as DDT. Owing to this volatility its persistence on foliage is short, typically 1.5 to 2 days for disappearance of half the residue. Aldrin is therefore principally used as a soil insecticide or as a seed dressing and I know of no instance where it has been used on grapes within the last 3 years. Senator MONDALE. You say that you know of no instance where aldrin is used on grapes. Yet, Senator Murphy introduced some materials in the Congressional Record on August 12, 1969, that have been introduced for the record hearing. On page S. 9868 you will find the study by the B. C. Laboratory, apparently a laboratory endorsed by growers and Senator Murphy, which says, among other things, that there was found on Bianco grapes 0.008 of aldrin. How did that get there? Mr. PORTER. Whose laboratory was that? Senator MONDALE. B. C. Laboratory. Mr. PORTER. Well, later in my presentation I am going to develop the reasons why these analyses are very uncertain, particularly if they are only gas chromatographic analyses and unsupported by other work. Now, I have no way of knowing whether this Senator MONDALE. You have no knowledge of that particular survey? Mr. PORTER. No, but I can say that at this level of residue you have a particularly difficult time in identifying what the compound is we are looking at. If these analyses were on grapes within the last 3 years, I would say that it is probably a signal from the gas-liquid chromatography which was unsupported. Senator MONDALE. This is the past year. One of the arguments is that no aldrin is being used there. What I cannot understand, if it is not being used, is how do these tests continue to show its existence? Are there other possible explanations? Mr. PORTER. Later in this presentation, I am going to try to say why it is that these things do appear to have aldrin content, but the signal from the method does not necessarily identify aldrin being present. It is very difficult to say positively that aldrin is there and particularly when you get below 0.01 parts per million it takes a great deal of effort and work to establish what the nature is. If I could go into that, I think I can explain. When applied to the foliage of plants, aldrin is rapidly oxidized to its epoxide dieldrin. This reaction has been found to take place on glass plates in sunlight, and it also can take place as a result of metabolic processes in the plant as recently demonstrated by Oloffs and Lichtenstein (Journal of Agriculture Food Chem. 17,-143147 (1969)). Owing to this rapid conversion, I cannot remember any case of an aldrin residue which did not also show some dieldrin, even when samples were taken immediately after spraying. Typical examples are the following:-These were just some that I pulled out of our files. To show a typical result for aldrin on tea at 4 ounces per acre immediately after spraying, zero days after spraying the aldrin gives 6.5 parts per million, the dieldrin 1.2 parts per million. At 7 days aldrin 0.7, dieldrin, 2.6. This is a particular dissipation. Aldrin disappears very rapidly from the foliage, the dieldrin tends to increase. At 8 ounces per acre, 8 eight ounces of aldrin we close at 0.2 parts per million and dieldrin 1.9 parts per million. And the aldrin on grass is a very similar situation with definite amounts of dieldrin present along with the aldrin. Another good example is provided by the work of Harrison et al, Journal of Science and Food Agriculture, Volume 18, pages 10 to 15, 1967. We have carried out field trials designed to show whether residues occur at application rates double those recommended for use against grasshoppers. Determinations were made on samples taken 1 day after spraying in order to determine maximum residues. At a quarter of a pound per acre there was less than one-tenth part per million on grapes at 1 day, at a half pound per acre applied less than a tenth of a part per million at 1 day. Based upon these considerations, I believe that application rates of at least 10 to 15 pounds of aldrin per acre would be needed to produce residues of 18 parts per million on grape berries immediately after spraying. This would be a ridiculous rate of application and is extremely unlikely to be used in any known application of aldrin. Going over to the subject of analysis of crop samples for pesticide residues, tremendous progress has been made in recent years in analytical instrumentation and techniques; however, there is still a lot of room for improvement. In particular, it is still extremely difficult and expensive to ascertain whether or not the apparent pesticide content of a sample resulting from applica tion of an analytical method is truly the pesticide or some other chemical which responds similarly to the technique used for analysis. There is some confusion on this point because equipment and methods are available which can almost unequivocally establish the presence of a given pesticide in the part per million range; however, the equipment is expensive in the range of $30 to $40,000 per unit, and it is slow to use. Accordingly, it is used only on a few critical samples. The equipment I refer to is the mass spectograph preferably directly coupled to a gas-chromatographic column. Reasonable certainty in identification can sometimes be achieved by appropriate combinations of techniques such as chemical transformations together with several chromatographic methods. Again this multiplies costs and requires highly skilled analysts. Routine laboratories cannot afford this type of checking except upon an extra-cost basis on special samples. The presently preferred methods for pesticide residue analysis are gas-liquid, thin layer, paper, and liquid-liquid chromatography; classical colorimetric methods; and electrometric methods. Each of these was originally developed for analysis of ordinary chemical and petroleum products. They are still used for this purpose, and each of the methods yields responses to a wide assortment of compounds with sensitivities depending upon the type of detector or sensing device used. The secret of success in applying these methods to trace analysis lies in finding sensing methods which are very selective, having far higher sensitivity to the compound of interest than to other assorted compounds which fall in the same chromatographic range. Remarkable success has been achieved in finding such selective detectors in all the general areas mentioned above; however, there are limits to the selectivity and in each case many compounds will appear identical insofar as a given method is concerned. Those compounds which cannot be told apart by a method are usually called interfering compounds or artifacts of the method. Due regard must be paid to all of these possibilities in assigning a method response to a given compound. The most common method of analysis applied to the chlorinated insecticides is gas-liquid chromatography. In this technique the various chemicals in a sample solution are separated by passing them in a stream of gas over a column of suitable liquid supported on a solid carrier, and are usually detected as a series of peaks on a recorder chart representing the output responses of the detector. These peaks have a characteristic bell-shaped form; the time or distance to the maximum value from the time of injection is usually called the retention time, and each compound on a given column should produce a peak having a very definite value of this retention time. The width of the peak is a very important characteristic and it is determined by many factors associated with the efficiency of the column being used. In general, longer columns and slower flow rates yield more favorable ratios of peak widths to retention times and should be used whenever possible since the greater efficiency provides more freedom from interferences. On the other hand, highly efficient columns require a great deal of analysis time, and sensitivity is lower than for the shorter less efficient columns. As a result, most laboratories compromise, and use the shortest column that they feel will provide an adequate result. This leads to difficulty in definite assignment of peaks and increases chances of interference. Of the detectors available for gas-liquid chromatography, the most popular for chlorinated insecticides is the electron-capture detector. It responds strongly to any compound which readily absorbs an electron to form a negative ion. Chlorine containing compounds generally give a powerful response while most other chemicals commonly encountered in crop extracts do not. It is thus somewhat selective, but it still responds to a wide range of chemicals, and it is rare that one finds a crop extract that does not have a number of peaks in the electron-capture chromatogram at the levels of sensitivity which are employed in pesticide residue analysis. Thus, when a peak is absent at the characteristic point for a given pesticide, there is certainly none of that compound in the extract. On the other hand, if a peak is present at exactly that point, the pesticide may be present, but the signal may be due to an interference. The analyst as a practical matter often relies in such a case upon the relative probability that the particular chemical would or would not be in his sample to make a decision as to its identity. If, for example, aldrin had just been sprayed, it would be reasonable to assign the signal to aldrin. Even if such knowledge is available, however, this does not prove the identity of the material producing the response. If this probability is not known, confirmatory tests are definitely necessary. That is, the analyst must apply additional different techniques which are thought to differentiate most of the interferences of the first method. If these additional tests agree with the first, both qualitatively and quantitatively, it greatly increases confidence in the assignment of identity. Many laboratories choose thin-layer chromatography as a second technique. This is usually a good choice if the proper system is used, but it is not absolutely conclusive. Compounds which interfere in one type of chromatography often interfere in other types owing to a general similarity in physical properties. Introduction of a selective chemical reaction at this stage is advisable. In the case of chlorinated compounds reaction with silver nitrate provides a degree of specificity, but does not guard against sulphur containing compounds which also react with silver ion. An example of chemical treatment which is particularly effective in the identification of aldrin, is its oxidation to dieldrin as suggested by Noren (Analyst 93, 94-41 (1968)). Quoting the summary of Noren's article: "The determination of aldrin in certain samples of vegetables by gas chromatography has proved to be difficult as peaks from impurities interfere. To eliminate this disadvantage, a method was developed in which aldrin was converted to dieldrin and the amount of dieldrin determined by gas chromatography. |