PESTICIDE RESIDUES IN FOOD - 1984 Sponsored jointly by FAO and WHO EVALUATIONS 1984 The monographs Data and recommendations of the joint meeting of the FAO Panel of Experts on Pesticide Residues in Food and the Environment and the WHO Expert Group on Pesticide Residues Rome, 24 September - 3 October 1984 Food and Agriculture Organization of the United Nations Rome 1985 MALEIC HYDRAZIDE Explanation Maleic hydrazide was evaluated in 1976, 1977 and 1980 1/. A temporary ADI was estimated for the sodium and potassium salts in 1980 and previously recorded Guideline Levels were converted to temporary MRLs. An extensive review of the biological and economic features of maleic hydrazide in the USA was available which, together with other information, enabled the meeting to deal with questions raised by the 1976 and 1980 JMPRs. (US Department of Agriculture, 1979). IDENTITY Purity of the Technical Product It was stated in the 1980 evaluation that the temporary ADI estimated at that meeting referred to maleic hydrazide containing up to 15 mg/kg hydrazine. This was a typographical error. This was the upper limit of the concentration of hydrazine present in maleic hydrazide used in animal feeding studies that did not give rise to the development of cancer in laboratory animals. The figure should have been 1.5 mg/kg. The figure was correctly recorded as 1.5 mg/kg in the report of the 1980 meeting. Liu et al. (1974) reported that commercial maleic hydrazide formulations may contain amounts of hydrazine varying from 0.14 to 870 mg/kg. Bakker et al. (1983) reported the results of a survey of maleic hydrazide formulations including several stored at 50°C for 10 weeks. Fourteen commercial formulations with maleic hydrazide concentrations ranging from 180-360 g/l were investigated. The hydrazine content of the maleic hydrazide in these formulations ranged from less than 0.05 to 53 mg/kg. During the storage of two samples at 50°C for 10 weeks, the hydrazine contents increased from 2.2 to 120 and 0.4 to 54 mg/l. Thirteen of the formulations were diethanolamine salts, the other a potassium salt. The hydrazine content of the potassium salt was less than 0.05 mg/kg. In later studies (personal communication) it was found that all samples of the potassium salt contained less than 1 mg/kg of hydrazine and that the potassium salt was stable to storage at 50°C. 1/ See Annex 2 for FAO and WHO documentation The withdrawal by the principal US manufacturer of the diethanolamine salt in 1980 has reduced the concern over the possible presence of hydrazine as an impurity in commercial formulations. The meeting was not convinced that all sources of the diethanolamine salt had yet disappeared from European markets but recommended that the FAO Specification for maleic hydrazide should be adopted and enforced world-wide. This incorporates a limit of 1 mg/kg for hydrazine as an impurity in maleic hydrazide. RESIDUES IN FOOD AND THEIR EVALUATION USE PATTERN Two formulations of maleic hydrazide (MH), the diethanolamine (DEA-MH) and potassium (K-MH) salts, were marketed for many years but the DEA-MH formulation was withdrawn by the principal manufacturer in 1980 when a means was found to increase the efficacy of the K-MH formulation. Since then the K-MH form has mainly been used. The rate of application is 3.3 kg/ha. The systemic action of MH makes it important for the control of tobacco suckers, and of sprouting in stored potatoes and onions. About 80% (1.45 million kg a.i.) of the total MH marketed in the USA is used to control tobacco suckers. Sprout inhibition in potatoes for storage accounts for 16.3% (300,000 kg), and about 1.5% (30,000 kg) is used to inhibit sprouting of stored onions. K-MH formulations are also registered for use on tobacco, potatoes and onions in Austria, Australia, Canada, Czechoslovakia, Italy, Kenya, The Netherlands and Taiwan among others. It is registered for use on tobacco only in Bulgaria, Colombia and Mexico. MH is used on other root crops in Canada. Use on potatoes Stored potatoes will sprout at temperatures above 5°C unless sprouting is inhibited. At temperatures below 7°C however the starch in potatoes is converted to sugar, a change which gives rise to an unacceptable dark brown colour in cooked potato products such as crisps and chips. The use of an inhibitor is therefore virtually essential. The USA produces about 1.37 million tonnes of fall-crop potatoes annually, 1.2 million tonnes of which are stored for 1 month or longer. More than half of the total US production of potatoes is grown in three Pacific Northwest States, Idaho, Washington and Oregon, which are also the major processing States. Thirty-one percent of the total potato production used for food is processed into some type of frozen product, 13% is processed into potato chips, 7% is dehydrated, 2% is canned, and the remaining 47% is marketed fresh. Some kind of sprout inhibitor is used on about 60% of fall-produced potatoes. MH is applied in the field to the green vines of fall crop potatoes destined for storage. The treatment prevents sprouting and maintains the original high quality. The best figures available indicate that 220,000 tonnes of potatoes are treated each year with MH, using 272,000 to 320,000 kg of MH. This is applied to 80,000 to 100,000 hectares of potatoes. Yields are not reduced if the recommended rate of one application at 3.3 kg ai/ha is applied to the vines 2 to 3 weeks after full bloom. Application of MH too early in the growing season, or application of more than double the recommended rate, can cause a cracking of the bud end, and in some cases an internal brown spot flecking on the apical end of the potato tuber. MH is absorbed through the leaves and translocated into the tubers, where it suppresses external and internal sprouting. Because of its internal mode of action, MH is the only chemical that will prevent tubers left in the field at harvest from growing into volunteer plants the next year. If allowed to grow, these volunteer plants serve as a source of leaf roll virus, which reduces yields and causes an internal discolouration in many varieties, called "net necrosis." This often renders the tubers unusable for table stock and many forms of processing. Inhibition of volunteer growth of potatoes reduces the potential source of leaf roll virus inoculum by as much as 98% (Sparks, 1978). Volunteers can also interfere with harvesting machinery and contaminate or compete with other vegetables. There is no alternative sprout inhibitor that will prevent volunteer potatoes, since all other inhibitors are applied after the tubers have been harvested and removed from the field. Other methods of control are only partially effective, and are more expensive. In addition to controlling sprouting of potato tubers, MH has been found by some workers to increase the food value and quality of tubers. Wittwer and Patterson (1951) state that MH-treated tubers held at low temperatures accumulate less sugar and produce lighter-coloured potato chips than the non-treated control. Patterson et al. (1952) indicated that treatment with MH appeared to result in lower contents of reducing sugars (see also the 1976 evaluation). Use on onions Maleic hydrazide is used to prevent sprouting in stored onions. It is applied to onions in the field at a rate of 2.2 kg/ha when the bulbs are mature. Five to seven green leaves are essential for adequate absorption of the compound. The crop is harvested after 2-4 weeks and the tops are removed. The onions are then cured before storage. In addition to its direct effects, an indirect benefit of MH Treatment is the elimination of volunteer onions, which often carry disease, in the following season. FATE OF RESIDUES In plants MH is absorbed into plant leaves and readily translocated. Movement occurs from xylem to phloem and vice versa, and the chemical is distributed throughout plants after application to leaves (Crafts, 1959, 1967; Crafts and Yamaguchi, 1958). In the early work on translocation, the translocated compound(s) containing the 14C from 14C-MH were not identified, but generally assumed to be MH. More recent studies with tobacco show that 14C-labelled MH moves as the intact molecule from one leaf to another (Frear & Swanson, 1978). Burley tobacco was grown and treated with 14C-labelled MH under controlled conditions (Davis and Grunwald, 1974). More 14C-MH was absorbed at 100% than at 75% relative humidity. Light stimulated the uptake of MH in leaf disks, and the increased uptake was not due to an increase in transpiration. 14C-MH was translocated and most of the translocated radioactivity was recovered from the top leaves. In other work by Davis and Atkinson (1976), the concentration in the untreated lower leaves of tobacco reached about 100 mg/kg within 24 hours after treating the upper leaves. Concentrations in the upper leaves declined rapidly from 300 mg/kg initially as MH was transported away from the treated area. In tests conducted in North Carolina, residues in mid-stalk flue-cured tobacco averaged 514 mg/kg immediately after application and decreased to 344 mg/kg over a 10-day harvest period of dry weather. The decrease was not statistically significant, but suggests that residues decline with time. Further, in a companion test at another location where 5.7 cm of rain fell on the third day after treatment, residues had decreased by 66% by the fourth day after treatment. Pendergrass (1969) applied 14C-MH to the green foliage of 22 onion plants near maturity. The 14C-MH had a specific activity of 0.3 MCi/m mole and was combined with 1.000 mg/l of Dupanol WAQ wetting agent. Volumes of 0.1 ml of this solution were injected into the internal cavity of four leaves per onion for a total dosage of 10 uCi per onion. In a separate treatment, the onions were sprayed with unlabelled MH at the normal rate of application for sprout control. Results indicated that distribution was fairly uniform, with 69% of the applied MH translocated to the bulb. At this point in onion growth, about 30 to 35% of the total weight of the plant is in the foliage. Of the total MH, 49% was found in the outer bulb leaves, 16% in the inner shoot leaves, and 4% in the root plate. The concentration in the root plate, however, was six times that found in the outer bulb leaves. In culinary preparation most of the root plate of an onion bulb is discarded as it is discoloured or appears soiled. It is not included in such preparations as, for example, frozen fried onion rings. The results of Crafts (1959) showed that MH diffused readily into potato tuber tissue within 2 days after application to the cut surface. In tests conducted in Canada with MH as a 2500 mg/l spray applied to potato foliage 3 weeks after full bloom, sufficient was absorbed in 24 hours to inhibit sprouting (Franklin, 1959), and residues of 6 mg/kg were found in the tubers. A 48-hour absorption period provided complete inhibition of sprouting. MH residues in tubers increased to a maximum of 36 mg/kg 1 week after application. Although some early work on translocation suggested that MH was not readily held in storage tissues along the translocation path (Crafts, 1959), other research conducted during the same period (Towers et al., 1958) indicated that the ß-D-glucoside of MH is formed in Nicotiana rustica, N. sanderae, and representatives of three other plant species. About 15% of the MH in leaf tissues was present as the glucoside. Recent studies on the fate of MH in tobacco plants confirmed the formation of the ß-D-glucoside in N. tabacum (Frear & Swanson, 1978). Although MH residues decline with time, the growth regulator is only slowly degraded within plant tissues and residues may persist for extended periods. From 17 to 22% of the MH remained unchanged in the tobacco plant four weeks after application to leaves, and was extractable with methanol (Frear & Swanson, 1978). Methanol-soluble metabolites were present in amounts ranging from 14 to 18% of the applied 14C. In fresh tissue after short periods (Davis & Grunwald, 1974), 99% of the 14C-label could be extracted with trichloracetic acide-acetone and perchloric acid. In cured tobacco, however, all the radioactivity was recovered from the RNA, DNA and proteins. Frear and Swanson (1978) also reported that 27 to 33% of the applied 14C was present as a methanol-insoluble fraction four weeks after leaf treatment. A large amount of this fraction was found in the roots, and 30 to 40% of the foliar-applied MH was excreted into the growing medium unchanged. Davis and Grunwald (1974) showed that relative humidity affected the translocation of MH to the stem and to the root. Translocation, excretion and glucoside formation were similar in selected flue-cured and burley varieties of tobacco (Frear & Swanson, 1978). Morphological and physiological responses of plants to MH have been investigated by workers since its growth-regulating properties were first recognized. Summaries of the literature on MH (Zukel, 1957, 1963) include many references and abstracts as well as a synopsis of the major observations in the abstracts cited. MH was discussed briefly in reviews by Crafts (1953), Woodford et al. (1958), and Shaw et al. (1960). Because MH has an exceedingly low vapour pressure (essentially zero at 50°C), it was concluded that losses of MH from soil and plant surfaced by volatilization would be negligible. Observations on loss rates of MH from leaf surfaces support this conclusion (Smith et al ., 1959). In soil Published data on loss rates from soil show that MH disappears rapidly. In a study reported by Levi and Crafts (1952), oats planted 2 months after treating the soil were not injured by 80 mg/kg of MH in any of 11 California soils. When oats were planted immediately after application, however, seedling plants were injured by 5 mg/kg of MH in the soil. In some soils, initial concentrations as high as 490 mg/kg were not toxic to oats planted 2 months after application. In later research with more refined detection methods and under laboratory conditions the level of MH in soil dropped from 100 to 5 mg/kg in 3 weeks (Helweg-Anderson, 1971). Another experiment reported by the same author showed that about 90% of 4.5 and 9 kg/ha applications disappeared in 12 days. Only traces were present after 80 days. In work reported by Hoffman et al. (1962), an application rate of 2.25 kg ai/ha resulted in 1 mg/kg of residue in the surface 15 cm of soil immediately after application. The disappearance of MH was very rapid from sand and muck and somewhat less rapid from clay soils. Following a farmer application of 15 kg ai/ha of MH on burley tobacco, it was not possible to detect any residue in the soil 12 months later. Also, in tobacco grown on soil where the crop had been treated with the recommended rate (170 mg/plant) of MH the previous year, leaf residues of MH were not detected (Davis & Massie, 1977). In later studies, Helweg (1975a, 1975b) showed that the decomposition of MH at concentrations of 20 mg/kg or less followed first-order kinetics, whereas at 120 mg/kg, zero-order kinetics more closely described the loss. The addition of activated carbon to soil retarded decomposition. With time in the soil, the capacity of carbon to retard degradation decreased. The rapidity with which phytotoxic effects of MH disappeared from soil in the studies by Levi and Crafts (1952) strongly suggested that micro-organisms were involved. Lembeck and Colmer (1957) reported the isolation of two soil bacteria (Alcaligenes faecalis and Flavobacterium diffusum) capable of using the diethanolamine salt of MH as an energy source. They also showed that the phytotoxic effects of MH were reduced by the action of the bacteria. The results of Helweg-Anderson (1971), showing that sterilizing the soil by autoclaving or gamma radiation prevented breakdown of MH, confirmed the earlier report of Lembeck and Colmer (1957). Kaufman and Kalayanova (1977) obtained similar results by the use of potassium azide as a soil sterilant. In another publication by Helweg (1975b) on the degradation of MH, 45% of the 14C added to soil in a 26 mg/kg treatment was liberated in 20 days and 56% was liberated in 255 days of incubation. However, micro-organisms capable of utilizing MH as a sole source of carbon were not isolated. It was concluded that the initial decomposition, if microbial, was by co-metabolism. Recent work by Kaufman and Kalayanova (1977) suggested that cleavage of the MH ring occurred by chemical mechanisms with subsequent degradation by soil micro-organisms. The degradation pathway of MH in soil was established in this work, with no evidence for the formation of hydrazine. Limited information is available on the movement of MH into soil. In a leaching experiment, Levi and Crafts (1952), through the use of a bioassay, showed that MH was displaced downward when relatively large quantities of water were added to the surface of soil columns. The fact that it is rapidly degraded generally eliminates movement below a few centimetres into the soil, except when rates of application are excessive and when rain occurs soon after application. At recommended rates, significant movement below the usual 15-cm plough layer would seldom, if ever, occur. RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION Potatoes The MRL for MH residues on potatoes is 50 mg/kg. The average residue is 15 to 25 mg/kg, and most residues would fall in a range of 10 to 40 mg/kg (Sparks, 1978). Routine monitoring of MH on potatoes is not known to be carried out at any agency concerned with residue analysis, but the potatoes themselves serve as a useful bioassay for MH residues at or above the MRL because tuber injury occurs at the 45 to 50 mg/kg level (Sparks, 1978). Potatoes damaged by MH account for an extremely small part of total production and are rejected for normal food use. On the basis of estimated consumption rates for potatoes and potato chips, the average daily exposure for a 60 kg person is about 0.019 mg/kg per day. Onions The MRL for MH in onion bulbs in 15 mg/kg. Experience has shown that the amount required for total sprout inhibition is 5 to 7 mg/kg. At the recommended application rate the amount of MH absorbed is usually within this range. Residues of 2 to 7 mg/kg occurred in New York in 1962 when MH was applied to onions at different stages of maturity (Isenberg, 1977). In the United Kingdom residues of 4.1 to 11.0 mg/kg were found in 1968 and 2.8 to 3.1 mg/kg in 1969 (Whitewell, 1977). The principle manufacturer of MH undertook a survey throughout the USA and Canada (Uniroyal, 1984). 39 samples of potatoes from the major potato-growing areas were analysed for MH residues by the method of Lane et al. (1958) with the results shown in Table 1. Table 1. Residues of maleic hydrazide in onion (survey data) Location Residue, mg/kg New York 2, 6, 10 Ohio 5, 3, 4, 7 Michigan 3, 2, 2 Washington State 2, 2, 3, 3, 12, 5, 15, 7, 12, 5, 3, 3, 6 Canada 9, 10, 11, 8, 8, 10, 10, 6, 10, 9, 4, 10, 7, 10, 5, 6 Mean of 39 results 6.5 mg/kg At recommended application rates of 2.2 kg/ha, residues are generally within the 5 to 7 mg/kg range. Per caput consumption of treated onions in 1976 was roughly 2 kg. On the basis of 2 kg and 6 mg/kg residues, this equals about 0.00055 mg/kg per day for a 60-kg person. METHODS OF RESIDUE ANALYSIS The 1976 meeting required that the GLC method should be further developed to make it suitable for regulatory purposes. The present meeting was advised that considerable time and effort had been given to this task but the outcome was still not satisfactory. The original method of Wood (1953) as modified by Lane et al. (1958) was later developed by the Naugatuck Chemical Division of the United States Rubber Company. This development was subjected to collaborative study (Lane, 1963, 1965), which showed that a wide range of concentrations of maleic hydrazide could be accurately determined in any likely substrate. The method recovers both free and conjugated maleic hydrazide. APPRAISAL The meeting had available an extensive review of the biological, agricultural and economic implications of the use of maleic hydrazide in agriculture, which provided some of the information required by the 1976 JMPR. Further information was received from the principal manufacturer. The diethanolamine salt is no longer available, the potassium salt being the only form now in use. Maleic hydrazide is essential to the production, storage and marketing of both potatoes and onions to prevent sprouting and subsequent deterioration of their acceptability and food value. It is applied to the growing crop and is distributed uniformally throughout the tuber or bulb by systemic transfer. It is therefore possible to obtain a long-lasting effect (9 - 12 months) on the whole crop with minimal rates of application. This avoids the need for grading and rejection of some of the crop prior to marketing. An additional advantage derived from spraying potato crops with maleic hydrazide is that it prevents the growth of volunteer potato plants from tubers left in the field, thus preventing the carry-over of potato virus diseases from one crop to the next. Valuable information on the fate of maleic hydrazide in various components of the environment was available. This confirmed that there was no risk of carry-over into subsequent rotational crops. Approved treatments of potatoes lead to residues in the tubers which, under some conditions, can be in the range 40-50 mg/kg. However, the average is between 15 and 25 mg/kg and most residues fall within the range 10-40 mg/kg. The potatoes themselves serve as a useful bioassay for maleic hydrazide residues at or above the MRL because tuber injury occurs at the 45-50 mg/kg level. Potatoes damaged in this way account for an extremely small proportion of the total production and are rejected for normal food use. The MRL for maleic hydrazide in onion bulbs is 15 mg/kg. Experience has shown that the amount required for total sprout inhibition is 5 to 7 mg/kg. Following the use of maleic hydrazide at the approved rate the amount absorbed is usually within this range. Monitoring studies indicated residues in the range 2-11 mg/kg in both potatoes and onions. The distribution of maleic hydrazide in onion bulbs has been studied with the labelled compound. Following approved treatments approximately 70% of the applied maleic hydrazide is transferred to the bulb, which represents about 65-70% of the total weight of the onion plant. Of the 70% in the bulb, 48% was found in the outer part, 16% in the inner shoot leaves and 4% in the root plate. The root plate is discarded in culinary practice. It had been established that the diethanolamine salt was unstable, giving rise to hydrazine. Information available confirmed that the commercial formulation of the potassium salt contained less than 1 mg/kg of hydrazine. Hydrazine does not occur as a metabolite in plants, animals or soil because strong reducing conditions are needed to convert maleic hydrazide to hydrazine (e.g. sodium hydroxide and zinc dust). Maleic hydrazide residues occur as a mixture of the parent compound and various conjugates. The method of analysis, which involves heating at 160°C in a 600g/l solution of sodium hydroxide, effectively converts these conjugates into free maleic hydrazide. The meeting agreed that the residue should therefore be defined as "sum of free and conjugated maleic hydrazide." Attempts to develop alternative methods of analysis based on GLC procedures have so far been only partially successful. Reliable information indicated that there were no significant uses on crops other than tobacco, potatoes and onions. The use on trees, grass and other ornamentals is small and does not lead to residues in food. There does not appear to be any possibility that maleic hydrazide residues on waste commodities such as potato skins could give rise to residues in foods of animal origin when such wastes are used as animal feeds. RECOMMENDATIONS The meeting was satisfied that all the information and further work listed as required in 1976 had now been supplied and that there were no further questions concerned with residues evaluation to be pursued. It recommended that the maleic hydrazide used in agriculture be confined to the potassium salt which should be 99.9% pure and contain not more than 1 mg/kg of hydrazine. The meeting agreed that the TMRLs previously recommended were appropriate. As an ADI was estimated, the limits were converted to MRLs. REFERENCES Bakker, H., Martyn, A., & Schreuder, R.H. Gas-liquid chromatographic 1983 determination of hydrazine in maleic hydrazide formulations and in samples stored at an elevated temperature. Pestic. Sci. 14:470-474. Crafts, A.S. Herbicides. Annu. Rev. Plant Physiol. 4:253-282. 1953 Crafts, A.S. Further studies on comparative mobility of labelled 1959 herbicides. Plant Physiol. 34:613-620. Crafts, A.S. Bidirectional movement of labelled tracers in soybean 1967 seedlings. Hilgardia 37:625-638. Crafts, A.S., & Yamaguchi, S. Comparative tests on the uptake and 1958 distribution of labelled herbicides by Zerbrina pendula Trandescantia fluminensis. Hilgardia 27:421-454. Davis, D.L., & Atkinson, W.O. Maleic hydrazine levels during 1976 maturation and curing of burley tobacco. Proc. 6th Int. Tob. Sci. Congr. 6:123. Davis, D.L. & Grunwald, C. Maleic hydrazide residues and isoprenoid 1974 leaf constituents in burley tobacco (Nicotiana tabacum L.) genotypes. Final Prog. Rep., USDA Contract No. 12-14-100-11042(34). pp. 1-31. Davis, D.L., & Massie, I. Univ. Kentucky. (Unpublished data). 1977 Franklin, E.W. Absorption of MH by potatoes. Proc. Canadian Committee 1959 on Fruit and Vegetable Preservation. Frear, D.S., & Swanson, H.R. Behaviour and fate of (14C) maleic 1978 hydrazide in tobacco plants. J. Agric. Food Chem. 26:660-666. Helweg, A. Degradation of 14C-labelled maleic hydrazide in soil as 1975a influenced by sterilization, concentration and pre- treatment. Weed Res. 15:53-58. Helweg, A. Degradation of 14C-maleic hydrazide in soil as influenced by 1975b absorption on activated carbon. Weed Res. 15:129-133. Helweg-Anderson, A. Maleinhydrazids nedbrydning of indflydelse pa 1971 respirationen i jord. Tidsskr. Planteavl 75:84-89. Hoffman, I., Parups, E.V. & Carson, R.F. Analysis for maleic 1962 hydrazide. Part 2. Determination and persistence in soils. J. Agric. Food Chem. 10:454-455. Isenberg, F.M.R. Cornell University, Ithaca, NY. (Unpublished data). 1977 Kaufman, D.D., & Kalayanova, N.A. Maleic hydrazide degradation in 1977 soil. USDA, SEA, AR, Beltsville, Md. (Unpublished data). Lane, J.R. Collaborative study of maleic hydrazide residue analysis. 1963 J. AOAC 46(2):261-268. Lane, J.R. Collaborative study of maleic hydrazide residue analysis. 1965 J. AOAC 48(4):744-748. Lane, J.R., Gullstrom, D.K. and Newell, J.E. Extension of the residue 1958 methods for 1,2-dihydro-3,6-pyridazinedione (maleic hydrazide) and N-1-naphthylphthalamic acid ('Alanap'). J. Agr. Food Chem. 6:671-674. Lembeck, W.J., & Colmer, A.R. Aspects of the decomposition and 1957 utilization of maleic hydrazide by bacteria. Weeds 5:34-39. Levi, E., & Crafts, A.S. Toxicity of maleic hydrazide in soils. 1952 Hilgardia 21:431-463. Patterson, D.R., Wittwer, S.H., Wheeler, L.E. & Sell, H.M. The effect 1952 of pre-harvest foliar sprays of maleic hydrazide on sprout inhibition and storage quality of potatoes. Plant Physiol. 27:135. Pendergrass, A.M. Influence of maleic hydrazide on the metabolism of 1969 onion bulbs (Allium cepa L.) during storage. PhD thesis, Cornell Univ., Ithaca, NY. Shaw, W.C., Hilton, J.L., Moreland, D.E., & Jansen, L.L. Fate of 1960 herbicides in plants. In The Nature and Fate of Chemicals Applied to Soils, Plants, and Animals. USDA, ARS 20-9. pp. 119-123. Smith, A.E., Zukel, J.W., Stone, M., & Riddle, J.A. Factors affecting 1959 the performance of maleic hydrazide. J. Agric. Food Chem. 7:341-344. Sparks, C. Comments on maleic hydrazide as a sprout inhibitor for 1971 potatoes. Reprinted by the Ansul Co., Marinette, Wis. 4 DD. Sparks, C. Univ. Idaho Research and Extension Center, Aberdeen, Idaho. 1978 (Unpublished data). Towers, G.H.N., Hutchinson, A. & Andreae, W.A. Formation of a 1958 glucoside of maleic hydrazide in plants. Nature 181:1535- 1536. Uniroyal Chemical Co. Information on maleic hydrazide supplied to FAO 1984 for consideration at the 1984 JMPR. US Department of Agriculture. The biologic and economic assessment of 1979 maleic hydrazide. Technical Bulletin 1634 submitted to US Environmental Protection Agency on 1 October 1979 - US Department of Agriculture, Washington. Whitewell, J.D. Kirton Experimental Horticulture Station, Boston, 1977 Lincs., United Kingdom. (Unpublished data). Wittwer, S.H., & Patterson, D.R. Inhibition of sprouting and reduction 1951 of storage losses in onions, potatoes, sugar beets, and vegetable root crops by spraying plants in the field with maleic hydrazide. Michigan Agric. Exp. Stn. Q. Bull. 34:3-8. Wood, P.R. Anal. Chem. 25:1879. 1953 Woodford, E.K., Hally, K., & McCready, C.C. Herbicides. Annu. Rev. 1958 Plant Physiol. 9:311-358. Zukel, J.W. A literature summary on maleic hydrazide 1949-1957. MHIS 1957 No. 8, Naugatuck Chemical Div., US Rubber Co., Naugatuck, Conn. 170 pp. Zukel, J.W. A literature summary on maleic hydrazide 1957-63. 1963 Naugatuck Chemical Div., US Rubber Co., Naugatuck, Conn. 111 pp.
See Also: Toxicological Abbreviations Maleic hydrazide (Pesticide residues in food: 1976 evaluations) Maleic hydrazide (Pesticide residues in food: 1977 evaluations) Maleic hydrazide (Pesticide residues in food: 1980 evaluations) Maleic hydrazide (Pesticide residues in food: 1984 evaluations) Maleic hydrazide (Pesticide residues in food: 1996 evaluations Part II Toxicological) Maleic Hydrazide (IARC Summary & Evaluation, Volume 4, 1974)