REPORT
FOR
ANALYSTS
After analysis, official residue samples are retained for possible future legal needs
USDA entomologist O. T. Dean dusts experimental plot of sweet potatoes with promising new weevil control insecticide
N e w Laws M a k e Analyst Key M a n in Pesticide Industry Under current f e d e r a l laws, use o f both new a n d o l d pesticides is g o v e r n e d b y a v a i l a b i l i t y of a d e q u a t e toxicity a n d residue d a t a . The toxicologists, entomologists, p l a n t p a t h o l o gists, a n d agronomists have d e v e l o p e d a d e q u a t e methods f o r toxicity determinations. The residue d a t a p r o b l e m , however, being a much more recent d e v e l o p m e n t , is still l a r g e l y unsolved. Such factors as the n e e d f o r methods accurate t o the parts p e r million or less o f materials t o b e d e t e r m i n e d a n d reducing the e x t r e m e l y high costs o f d e v e l o p i n g a n a l y t i c a l methods a r e challenging problems to analysts. Many experts in the field consider the analyst t o b e the k e y man in the future d e v e l o p m e n t o f the highly essential pesticide industry. A b r i e f résumé o f the l e g a l , economic, a n d technical aspects o f the p r o b l e m , a n d the a p p r o a c h e s t o w a r d solving it, a r e the subject o f this month's Report f o r Analysts, HETHER a chemical m a y be used as a Wpesticide is based on knowledge of its toxicity a n d a determination of residues left on crops. I n t h e determination of residues, which are often in t h e parts per million range or less, the analyst is t h e key figure. With insect damage t o crops totaling an estimated $4 billion a year, pest control chemicals are vitally important. A continued supply of adequate chemicals is becoming ever more dependent on t h e analytical chemist. Until recent changes were made in federal laws, t h e major problem with respect t o pesticides was t h a t of toxicity of t h e chemicals. T h e toxicologists, entomologists, plant pathologists, and agronomists developed adequate methods for toxicity determinations. The Miller Pesticide Residue Amendment t o t h e Federal Food, Drug, and Cosmetic Act prohibits t h e interstate shipment of foods subject t o t h e law if they bear residues of pesticide chemicals unless t h e chemical generally is recognized by experts as safe or t h e govern-
ment h a s established a safe tolerance for the residue or h a s exempted it from a tolerance. Where a tolerance h a s been established, t h e residues on t h e food m u s t be within t h e safe tolerance level. T h e Food and Drug Administration (FDA) in establishing a tolerance, considers t h e toxicity of t h e residue a n d the a m o u n t which will result from proper usage of t h e pesticide chemical. Tolerances are set, n o t a t t h e highest figure permissible from a health standpoint alone, b u t also on t h e basis of t h e amount of residue which will normally result from recommended or proposed uses of t h e material. I n short, residue levels are held a t a practical minimum. T h e Federal Insecticide, Fungicide, and Rodenticide Act, administered b y the U . S. D e p a r t m e n t of Agriculture, requires t h a t pesticide chemicals be registered before they m a y be shipped in interstate commerce. Registration is granted only for pesticide formulations which, when used in accordance with label directions, will either leave no pesticide residue or only a legal residue.
These two federal laws, therefore, make determination a n d compilation of d a t a on residues a vital factor n o t only for new pesticides b u t also for older ones. This in t u r n focuses a t t e n tion on t h e need for adequate methods of analysis. Objectives Simple—Attaining Objectives Difficult T h e objective of t h e Miller bill i s simplicity itself. Implications t o t h e pesticide manufacturer and, more specifically, t o t h e analyst, are something less t h a n simple. F D A ' s operating philosophy with regard t o residues is t h a t they be held t o a practical m i n i m u m . F r o m this stems two guiding principles in specifying safe tolerances. First, if t h e q u a n t i t y of pesticide thatm a y be contributed t o t h e diet from all sources exceeds t h e a m o u n t estimated to be safe, t h e tolerance is set a t t h e point of estimated safety. Second, if t h e estimated safe q u a n t i t y is n o t exceeded, then t h e tolerance is based. VOL. 2 9 , N O . 10, OCTOBER 1 9 5 7
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REPORT FOR ANALYSTS
This Month's REPORT FOR
ANALYSTS
. . . is α condensation of several p a p e r s presented a t the Symposium on Methods for Analysis of Pesticide Residues. They w e r e presented jointly b y the Divisions of Analytical Chemistry a n d Agricultural a n d Food Chemistry, a t the spring meeting of the AMERICAN CHEMICAL SOCIETY at
Miami.
The papers included in the condensation are: L· "Development and Status of Modern Analytical Methods for Pesticide Residues in Crops and in Foods," by F. A. Gunther, Uni versity of California Citrus Experiment Station, Riverside, Calif. Courtesy Esso Research & Engineering Co.
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k
"Residue Determinations—A Limiting Factor in Pesticide Usage," by Joseph A. Noone, National Agricultural Chemicals Association, Washington, D. C.
k
"Some Basic Principles Involved in Obtaining Valid, Useful Pesti cide Residue Data," by C. H. Van Middelem, Department of Food Technology and Nutrition, Florida Agricultural Experiment Station, University of Florida, Gainesville, Fla.
k
"Important Considerations in Collecting and Preparing Samples for Residue Analysis, " by Louis Lykken, L. E. Mitchell, and S. M. Woogerd, Shell Chemical Corp., New York Citv, Ν. Υ.
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A multi-purpose unit with quickly adjusted vertical opening, by hand wheel, per mits many different set-ups in minimum time.
22
"Analytical Method and Residue Data Requirements for Federal Registration of Pesticide Formulations," by Thomas H. Harris, Pesticide Regulation Section, Plant Pest Control Branch, Agricul tural Research Service, U. S. Department of Agriculture, Washingtion, D. C.
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ANALYTICAL CHEMISTRY
on the quantity resulting from sufficient pesticide needed to protect the crop. It is necessary, therefore, to provide data showing residue levels resulting from recommended or proposed use of a given pesticide on a given crop. The burden of obtaining required informa tion is placed on the manufacturer. Unless such data are forthcoming, there is no basis upon which to register the material. Without this registration, the company cannot ship the pesticide in interstate commerce. Prerequisites for establishment of tolerance standards are knowledge of the toxicity of the residue and of the amount of residue resulting from recom mended use of the pesticide. A few years ago acceptance or rejection was based only on the first requirement. As a result, well standardized programs of toxicity determination have been developed. Difficulties now experi enced in obtaining registration are not those relating to toxicity. They accrue from the necessity of obtaining quanti tative residue data, not only for any new products that may be under develop ment, but also for those chemicals
whose usage has been long established. Although much of this work has been done, many old line pesticides do not yet have necessary clearance. With out the residue data required by law, these cannot be maintained on the ac ceptable list. Government Requirements are Extensive
The question then arises as to the amount of data that are needed. In general, industry spokesmen feel that it is necessary to make separate deter minations of residues for each com pound being considered, for each crop, and for each method of application. Further, each of these tests must be replicated four or five times to adjust for regional differences in climate, soils, and horticultural practices. The De partment of Agriculture indicates that data should, in general, include ten results each on treated samples, un treated samples, and on untreated samples to which known quantities of the pesticide have been added. In par ticular cases this requirement may be
REPORT FOR ANALYSTS insufficient. Considerable importance is attached to sampling methods. Reverting again t o the prerequisites for establishment of tolerance standards, both toxicity and residue phases should be given equal consideration in t h e over-all development program for new pesticide chemicals. T h a t is, if routine determination of toxicity is considered desirable, then so also must routine determination of residue concentration. In planning a residue determination program, first consideration is given t o the possibility t h a t a specific pesticide use does not result in a persistent residue. Examples are the early season use of nonsystemic pesticides before edible parts of the plant have begun to form, or the use of pesticides which are destroyed in the plant metabolic processes before harvest. Pesticides which leave no residue are not subject t o registration. However, to prove t h a t there are no residues it requires complicated and involved experimental work. Analytical procedures must b e instituted for those compounds which leave residues. I n applying for registration of a compound, the analytical procedures used must be described in detail and submitted with residue data. Evaluation of the analytical procedures as well a s residue d a t a arc necessary in determining whether or not a residue will be present in or on the raw agricultural commodity in question. Also, a detailed description of sampling procedures is required. Because generally pesticides are relatively specific in their use, i t necessarily follows t h a t there is n o general procedure for all analyses. E a c h pesticide must be considered as a specific case.
Analysis Requires Careful Preplanning Analytical programs require consideration of certain special factors in the quest for suitable data. Degree of persistence in various types of soil must be taken into account, and so must the relationship between amount of pesticide applied and possible residue uptake. Some pesticide or degradation product may enter the plant through its root system, in which event i t is necessary to determine whether the compound remains unchanged and whether it is present in edible parts of the plant. The analytical chemist, before planning his program, must become familiar with certain characteristics of the compound. Knowledge of physical a n d chemical properties, with special regard for stability, is imperative. Toxicity to mammals should be known. I n tended use of the pesticide should also
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2 3A
REPORT FOR ANALYSTS
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ANALYTICAL CHEMISTRY
be known, along with economic implications of such use. With all this information at hand, it is then necessary to survey the field for possible methods \vhich may be utilized to acquire complete residue data. The complexity of the problem indicates that both chemical and instrumental micromethods are needed. The modern residue analyst can and should employ every useful tool and device known to biology, chemistry, and physics for assistance in isolating, measuring, and identifying persisting or degrading residues. These are located usually within a plant part contacted by the parent pesticide or intermediate metabolite. Recent literature on residue methods indicates that the problem is being attacked by a variety of methods. Included are biochemistry, chromatography, electrode reactions, radioehemistry, selective organic reactions, spectrometry, and both direct and indirect biological assay. At present there are no broadly applicable residue techniques that will isolate, measure, and identify in one or even several standardized operations. However, combinations of techniques can be adequately standardized for a specific problem if the analyst is sufficiently familiar with the tools and devices available. Considering that an effective pesticide may occur on or in the substrate in quantities less than 1 p.p.m. or 0.5 mg. per pound, it is not reasonable to expect simple chemistry, equipment, and techniques to afford residue data adequate for the necessary appraisal of any hazard that might exist from persisting pesticide residues. Analytical methods are usually typed according to their discriminatory capabilities, although the ultimate means of measurement is always physical. The distinguishing feature is that the significant interaction is between the pesticide molecule and living matter, energy, or another chemical. The selection of a means of measurement is always influenced by the presence or absence of interfering extractives in the analytical samples as received for the ultimate determination after cleanup, as well as by the sensitivity requirements of the problem. Most, if not all, organic pesticide chemicals in residue form behave similarly in that they seem to obey certain fundamental laws of physical chemistry. This situation makes available to the analyst the confirmation of predicted residue behavior and thus permits the ready establishment of a "confidence factor" for the total program from field application to final analytical operation.
Costs of Testing A r e High
Estimates have been made of the cost of carrying out programs of the type under discussion here. These run from a low of about $10,000 up to almost $400,000. Therefore, planning of the analytical program must be made with due regard to costs. Perhaps the specific method being considered is too expensive, or the equipment called for may be too highly specialized and costly. The objective, of course, is to choose the most economical method, commensurate with requirements of the Food and Drug Administration. For most efficient completion of the program, it is imperative that the analyst work closely with the entomologist, pathologist, and other personnel concerned from the earliest stages. In planning test programs, there is often a tendency to make them too comprehensive. It has been found advisable, for example, to concentrate residue studies on materials in the form recommended by the agricultural station, that is, emulsifiable concentrate, wettable powder, or dust, rather than all three. Where the active ingredient is comparable, appreciable differences in residue according to formulation are not generally found. Further, it has been found more advantageous to use a single formulation in widely variant dosage levels. In most cases, two dosage levels are sufficient. One level would be according to station recommendation and the other considerably higher. The number of applications used should be as high as, or probably higher than, that recommended by the station. A procedure such as this will give residues that are comparable to those obtained by most growers and will allow for persons who tend to be overly enthusiastic in their control program. The over-dose treatment will lead effectively to an additional safety factor in the compound's ultimate use. because it will influence recommendations on suggested time interval between final pesticide application and harvest. Convincing results can be obtained only through replication of procedure. Economics on the one hand, and desired degree of precision on the other, will tend to fix the number of practical replications at a unique figure. It has been found that in most instances three field replications are sufficient.
Sampling—a Critical Phase
Benefits of the most carefully spelledout analysis program can be completely nullified by a sampling proce-
REPORT FOR ANALYSTS dure which has not been planned with equal care. Generally, data obtained from samples replicated two or three times at several locations are better than from many replications at one location. One person should be designated coordinator for all phases of sampling. The number of samples taken should be kept as nearly as possible within predetermined and reasonable bounds. Practical considerations will place a limitation on the number and size of samples that can be taken from a given test crop. Sampling techniques are determined by the type of crop, its end use, the size of its commodity unit, and the yield per unit area. Uniquely selected sampling techniques, superimposed on certain fundamental rules for sampling must be carefully followed in taking the gross sample. This same care must be continued in reduction of the gross sample to the final laboratory sample, its transportation, and its storage prior to chemical analysis. Although inherent weaknesses of residue chemistry are generally recognized, many persons overlook the fact that some avoidable discrepancies in results follow from inadequately planned sampling procedures. Sampling methods used are influenced by variation in methods used for processing the crop, and by its manner of end use. With this in mind, it has been suggested that various commodities be classified into general categories. These include large and small fruits, nuts, legumes, and grains for food and forage, leafy vegetables, head crops, perennial crops, solanaceous fruits, and root crops. There are instances where crops must be placed in more than a single category. This indicates the need for separate sampling procedures and contrariwise implies that a single crop may be used in some cases for studies of a given pesticide in relation to more than a single group. According to the type of crop being tested, the gross sample taken may measure from 25 to 100 pounds or more. It is then necessary to subdivide the sample, bringing it down to a size suitable for shipment to the laboratory. Circumstances may be such as to require some storage of the gross sample before subdivision. In this event, the main criterion in considering temporary storage is the ability of the crop to withstand spoilage or shrinkage. Some items—potatoes, for example—can keep for several weeks in ordinary containers, although decomposition characteristics of the residue itself may need consideration. In other cases, storage may be
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25
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REPORT FOR ANALYSTS
Explosion proof
limited to several days under refrigerated conditions. Similar types of reasoning must be made when planning shipping methods. Samples collected in the field must often be delivered long distances to the laboratory for analysis. Some thought must then be given to the mode of transportation (company delivery, air freight, etc.), to manner of packing (for example, refrigeration), and to clear and complete labeling. Complete label information will include at least the following : harvest and application dates, dosage and formulations, number of applications, field replications, and sampling and subsampling details, solvent used, extraction time, storage temperature and duration of storage, and weather data over the period from first application to harvest.
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Requirements for obtaining comprehensive residue data, some of which have been discussed here, are inherently complicated and expensive. I t is extremely difficult to visualize a common thread of analytical procedure running through even a small group of two or three residue programs. Nevertheless, under terms of the Miller Amendment, the role of the residue analytical chemist is preordained. He must work in cooperation with entomologists, pathologists, economists, and other professional classifications. But in the end it is the planning and operations of the analysts that result in acceptance or rejection of a particular pesticide for interstate commerce.
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ANALYTICAL
With the burden of proof under the new laws resting primarily with the manufacturer, the producer is obliged to conduct considerable research. He is not alone, however, in this area. The TJ. S. Department of Agriculture, for example, is spending an estimated $500,000 a year on residue research. The USDA program includes all phases from application and sampling to laboratory analysis. It is estimated that the states are spending an equal amount on such studies. Joint federal-state programs are being carried out on a regional basis, Land-grant colleges also are working in this area. One area where government assistance is felt desirable is with regard to crops which are in limited production. In such cases, industry cannot justify the expenditure of thousands of dollars on a crop residue program, where the gross sale for the crop is less than the cost of the research project.
CHEMISTRY
