F. A. Gunther

The citrus reentry problem: research on its causes and effects, and approaches to its minimization.

The “reentry problems” arises from agricultural workers becoming ill as a result of entering and working in a field some time after a pesticide application has been made to a crop plant. Although sulfur, with its capacity to cause eye irritations, may be claimed to have caused the first reentry problem in agriculture, the problem as currently evaluated is limited to the use of cholinesterase (ChE)-inhibiting organophosphorus (OP) pesticides. The definition of the problem in the future will likely extend to other compounds and other biological effects, such as conjuntivitis and dermatitis. Table I lists the reported cases of post-treatment illnesses to farm workers in California, where most of the incidents in the United States have occurred. A few isolated incidents have been reported from some of the cotton-and tobacco-growing states in this country; there are no documented reports yet from any other country. It is evident from this table that the problem is not a new one and that it appeared hand-in-hand with the introduction of OP pesticides to agriculture. The use of OP pesticides has increased greatly and will probably continue to increase as the use of organochlorine pesticides becomes more restricted. Production and usage of OP pesticides in the United States are expected to continue at a high level for the forseeable future, even though other approaches to pest controls such as biological control techniques, pheromones, and new classes of pesticides will be added to pest-control methods. More intensive farming methods, including OP pesticides, are being introduced to many other countries, and the same problems experienced in the United States will probably be experienced by these other users. Although foods, fibers, and feedstuffs were grown successfully in the United States prior to the introduction of synthetic pesticides in the late 1940s, expectations have changed regarding both quality and quantity of agricultural production as a result of the effectiveness of chemical pest control. Increasing world population requires greater productivity and it is, therefore, unrealistic to halt the use of OP compounds as a solution to the reentry problem (task group 1974).

Insecticide residues in California citrus fruits and products

Prior to about 1945 it was not realized that spray and dust deposits of most organic insecticidal1 chemicals penetrated, in the field, into subsurface regions of sprayed citrus fruits, even though they were generally nonsystemic in action, as with some of the DN compounds and rotenone. Also, emphasis on “residues” (deposits) prior to this same time was on correlations with pest-control efficacy rather than on safe consumption of the treated commodity, so that initial deposits and aged deposits were most often obtained as weight of insecticide per unit areas of leaf (foliage) tissue2 rather than on and in mature fruits, as with sulfur, lime-sulfur, and lead arsenate, because insect populations were usually evaluated on leaves or twigs rather than on fruits. In connection with the field performance of DDT and other new insecticides against insects and mites in citriculture, however, it was realized shortly after 1940 that the slow disappearance or attenuation from leaves of these (DDT) surface deposits and effective residues from organic pesticides signified at least partial penetration into subsurface tissues (Gunther 1946 and Gunther et al. 1946).

DDD as a decomposition product of DDT

During the past two decades DDT1 has been used in large scale on a world-wide basis, during which time an enormous amount of research has been conducted also throughout the world on numerous ramifications connected with the use of this pesticide, including investigations of its fate as it undergoes decomposition in metabolic and other systems. Despite all the systems and all the decomposition products studied, it is only within the last few years that evidence has been presented that DDD (TDE) is, or can be, a decomposition product of DDT.

OCCURRENCE, ISOLATION, AND IDENTIFICATION OF POLYNUCLEAR HYDROCARBONS AS RESIDUES.

Chemical carcinogens as a world-wide health problem are receiving increasing attention. On the one hand, the contamination of air and water by a variety of industrial and other chemicals of this type is occurring while, on the other hand, more and more direct food-additive and plant-protection chemicals are in increasingly regulated use. Publicity accorded the fact that certain chemical carcinogens occur in tobacco smoke is a well-known example of the interest in this area.

Worker environment research. IV. The effect of dust derived from several soil types on the dissipation of parathion and paraoxon dislodgable residues on citrus foliage

SummaryParathion sorbed to dust can persist as dislodgable residues on citrus leaves. Semi-logarithmic plots of parathion dislodgable residue data were initially linear for the 6 soils studied and then a distinct change to lower rates occurred with 5 of the soils. As initial rates and the residue level at the rate change are dependent on the soil, foliar dust is implicated as a causative factor in the non-uniformity of residue dissipation rates.Soils can influence the conversion of parathion to paraoxon. Paraoxon levels differed greatly with the type of soil and were highest with Pikes Peak clay. Thus, its use in a parathion formulation could produce relatively high levels of paraoxon dislodgable residues. It is significant that, second to Pikes Peak clay, the highest total dislodgable residue level was found with Visalia silt loam which was collected from a grove where a worker poisoning episode had occurred in 1974.

Pesticide stability in cold-stored plant parts, soils, and dairy products, and in cold-stored extractives solutions

The field of pesticide1 residue analyses has seen tremendous advances in recent years. The application of new as well as elsewhere-established analytical techniques and instrumentation to this field of research has been the main contributing factor to these advances. For example, the adaptation in 1961 of gas-liquid chromatography (glc) to the analysis of pesticide residues and their alteration products has given the trained residue chemist a superlative tool for his work, when properly used and interpreted. Other more definitive residue-analytical and confirmatory techniques have exploited infrared, ultraviolet, and fluorescence spectrometry, mass spectroscopy, micropolarography, atomic absorption spectroscopy, carbon skeletonization glc, etc. The importance of colorimetry, thin-layer chromatography (TLC), cholinesterase (ChE) assay, and other separating and determinative techniques should not be overlooked as valuable components of definitive apid credible pesticide residue programs.

Automated pesticide residue analysis and screening

In the United States, with probably the most intense and diversified agriculture in the world, there are registered for permitted use more than 900 chemical compounds1 in more than 60,000 pesticidal formulations (Freeman 1965). In this country uses of these materials on more than 2,500 crop items (Kirk 1964) and other foodstuffs are regulated by joint considerations of the U. S. Food and Drug Administration (F.D.A.) and the U.S. Department of Agriculture (U.S.D.A.) (Harris and Cummings 1964), with assignments of tolerances or permitted residue values for amounts of particular chemicals to be legally acceptable on and in particular raw agricultural commodities at time of sale or consumption. These values may range from an actual zero to more than 100 parts per million (p.p.m.), depending in large measure upon the pharmacology and toxicology of the candidate chemical. Until recently and in broadest terms “zero” as interpreted by regulatory agencies could mean either numerical tolerance denied, because of probable hazard to be associated with the projected use, or a number less than unity predicated upon residue analytical capabilities and credulity at the moment. For certain pesticide chemicals which were of widespread application on certain major crops or products, and which were also of pharmacological concern, as residue analytical methodology improved in minimum detectability, and in reliability, some “zero” and other tolerance values have been lowered with certain commodities (e.g., milk) to accommodate a new analytical capability; present tolerances often reflect residues that could remain at harvest. This completely unsatisfactory dynamic tolerance situation has existed particularly with several of those pesticides which contain organically bound halogens, such as dieldrin, endrin, and heptachlor. It has also been involved both legally and morally with numerous chemicals previously registered by the U.S.D.A., and with F.D.A. concurrence, on a “no-residue” basis (Harris and Cummings 1964): at the time the “no-residue” registration was granted finite residues were not demonstrable yet subsequendly analytical detection of persisting residues was made possible by improvements in methodology, usually through exploitation of modern analytical instrumentation, and the original specific registration was revoked.

Residue behavior of polynuclear hydrocarbons on and in oranges.

In a previous review (GUNTHER and BUZZETTI 1965) it was pointed out that there is abundant evidence for the widespread occurrence of polynuclear hydrocarbons1 in air, soil, and water. That various polynuclears have been found in many members of both animal and plant kingdoms, as well, was also demonstrated with selected references to the rapidly increasing literature on environmental pollution. Most of the explorations in this area have dealt with tobacco, smoked foods, barbecued meat, processed rice, roasted coffee, baked goods, and some marine organisms; very few of these reports of polynuclears in our food supply have involved fresh foods. The present report is intended to illustrate the polynuclear tracecontamination of our environment via the so-called non-processed foods2 or raw agricultural commodities, with Valencia oranges as an example.

Interpreting pesticide residue data at the analytical level.

The natures, locations, and quantities of pesticide residues in foodstuffs are important in the realm of the public health; these residues in animal feeds are important, also, in animal husbandry, for they conceivably could affect the health and well-being of the animal as well as of the ultimate consuming public through possibly pesticide-contaminated edible animal products. Properly used under the now legalized aegis in many countries of “good agricultural practice,” with all the constraints attached thereto, there should be no nutritional or other health-related adverse effects from pesticide or pesticide-derived residues persisting in the agricultural environment. It is the occasional misuse or illegal use of pesticide chemicals,1 however, which could result in possibly deleterious residues persisting from attempted pest-control applications into human foodstuffs or animal feeds. It is not the intent here to dwell on the many complications that can result from over-contamination with pesticide chemicals of the nonedible agricultural environment such as soil, runoff and other initially agricultural waters, nontarget plants, wild animal and aquatic life, and air.

Minimizing occupational exposure to pesticides: Reliability of analytical methodology

In the gross field of occupational human exposure to pesticide chemicals we are concerned with unintentional exposures of man during manufacturing, packaging, formulating, formulation packaging, spray mixing, application, and the postapplication field operations of cultivation, irrigation, pruning, thinning, and harvesting. The epidemiological history of authenticated episodes of pesticide poisonings indict manufacturing, packaging, formulating, formulation packaging, application, and harvesting operations, with “application” including the filling (“mixing”) of the application equipment as well as the application operation itself. In the United States the field operations of cultivation, irrigation, pruning, and thinning seem to be almost devoid of authenticated poisoning episodes, although the opportunities for considerable exposures to pesticide chemicals certainly exist for hand weeding, pruning, and thinning operations [see Gunther et al. (1977), pp. 4 and 5, for examples of such documented cases in California].