Fungicides Thiabendazole

The two examples of sample preparation of solids containing low concentrations of the substances of interest will be the analysis of aflatoxins in corn meal (7) and the determination of the fungicide thiabendazole in citrus fruits. It should be pointed out that the applications chosen in this section attempt to reflect a range of analyses that the analyst is likely to meet in both research and industrial laboratories. 

Further insight on the frequency of multiple residues is evident in Table 14.4, which shows the number of residues found per sample for selected foods tested in 2004 by the PDP. Conventional apples were found to contain, on average, 3.6 residues, while the one positive organic sample had a very minute level of the post-harvest fungicide thiabendazole. The level of residue found in the one positive organic apple sample was 0.0002 parts per million, while the mean thiabendazole residue found in 641 positive conventional samples was 0.43 ppm, over 2100 times higher than the level found in the organic sample. 

Pressurized hot water can be used to extract two fungicides, thiabendazole (TBZ), and carbendazim (MBC), from agricultural commodities including banana pulp, whole lemons, orange pulp, mushrooms, and rice at extraction temperatures below 100°C and an extraction pressure of 50 atm. The extraction parameters that were studied include temperature, equilibration time, flow rate, pH, and collection volume. Liquid-... 

This approach has been extended in several other works. TV-Arylamidine hydrochloride 105 with one equivalent of sodium hypochlorite and a base can be converted into benzimidazoles 107a-c, including the famous fungicide thiabendazole 107b, in excellent yield (65JOC259). The TV-chloroamidine 106 might be isolated, if desired, prior to addition of base (Scheme 32). 

Benomyl and the other benzimidazole fungicides are toxic to earthworms (Stringer and Wright, 1973) and may seriously disturb the earthworm population, for instance, in orchards, so that the leaf litter is not removed. Some benzimidazole fungicides (thiabendazole and mebendazole) may be used as anthelmintica. 

Hexachlorobenzene has been reported to be carcinogenic in hamsters (116). In mice, this compound enhances the carcinogenic response of polychlorinated terphenyls (117). Another fungicide, thiabendazole is also reported to enhance the bladder carcinogenic effect of sodium o-phenylphenate (118). 

Microtubulin Polymerization Inhibitors. The ben2imida2oles were first reported to have systemic fungicidal activity in 1964 (29). Prominent examples include thiabendazole [148-79-8] (42) fuberida2ole [3878-19-1] (43) carbendazim [10605-21-7] (44) benomyl [17804-35-2] (45) and thiophanate methyl [23564-05-8] (46). Benomyl (45), the most widely used member of this group is almost certainly inactive as a fungicide until it is converted in plants and soil to carbendazim (44). Likewise, thiophanate and thiophanate methyl (46) are nonfungitoxic until converted to carbendazin (44). 

A method has been reported for the quantification of five fungicides (shown in Figure 5.39) used to control post-harvest decay in citrus fruits to ensure that unacceptable levels of these are not present in fruit entering the food chain [26]. A survey of the literature showed that previously [27] APCl and electrospray ionization (ESI) had been compared for the analysis of ten pesticides, including two of the five of interest, i.e. carbendazim and thiabendazole, and since it was found that APCl was more sensitive for some of these and had direct flow rate compatibility with the HPLC system being used, APCl was chosen as the basis for method development. 

PMK Friar, SL Reynolds. The effect of home processing on postharvest fungicide residue in citrus fruit residues of imazalil, 2-phenylphenol and thiabendazole in home-made marmalade, prepared from late Valencia oranges. Food Addit Contam 11 57-70, 1994. 

The authors prepared a monolithic MIP CEC column in 100 pm i.d. fused-silica capillary, imprinted with thiabendazole (TBZ). This compound is a commonly used post-harvest fungicide to control diseases during storage and distribution of fruits... 

Application techniques can influence the efficacy of postharvest fungicides and, thus, alter the keeping quality of treated fruit. Application of sodium ortho-phenylphenate (SOPP) in a foam washer with an exposure time of only 15 to 20 sec is not as an effective method as a soak or drench treatment requiring 2-4 min (167). However, if proper pH control is not maintained, fruit may be burned with the soak or drench treatment (169, 170, 171). Applications of SOPP in wax were less phytotoxic (172). Within the last 14 years, development of the benzimidazoles, thiabendazole Q -(4 -thiazolyl) benzimidazole and. benoniyl Tmethyl 1-(butyl carbamoyl)-2-benzimidazole-carba-mat J, has led to the availability of fungicides with high... 

The much wider disease control spectrum of the benzimidazole fungicides (eg. benomyl, BCM, thiabendazole) - permitted far wider usage. In the beginning, these were suitable for control of numerous plant diseases, but a new phenomenon soon emerged - resistance Due to the specific mode of action of these fungicides, resistance could appear quite rapidly. The conventional fungicides previously used had a broad biocidal activity and resistance had never been experienced. 

All benzimidazole fungicides (benomyl, carbendazim, fuberidazole, thiabendazole) and thiophanate fungicides are cross-resistant. However, the reeently diseovered fungicide, zoxamide, which also inhibits the B-tubulin assembly, is not cross-resistant in oomycetes... 

Thiabendazole is widely used as an agricultural fungicide, but most experience with its toxicology in humans has come from medicinal use against intestinal parasites. Oral doses administered for this purpose are far greater... 

Most formulations of benomyl are classified as Toxicity Category IV and are considered relatively nontoxic. Arbotect, a trade name of a prodnct containing thiabendazol, is classified as Toxicity Categrory 111 and is considered a slight eye and skin irritant. Fuberidazol is classified as a Toxicity Category n fungicide. 

Benzimidazoles have been applied rather more as herbicides, and in veterinary problems. There are, for example, many benzimidazole fungicides and herbicides, and the antihelimin-thics thiabendazole (197 R = H) and cambendazole (197 R = NHC02Pr ) are of proven efficiency both for human and veterinary use. There are also some fungicides known among the 2-aminoimidazolines. 

As regards foods, water has been used for the dynamic extraction of fungicides such as thiabendazole and carbendazim from fruits and vegetables, with recoveries of 80.9-100.5% at fortification levels of 0.14-100 ppm [40]. 

Thiophanate methyl (74) is, like thiabendazole (54), a member of the benzimidazole group of fungicides since it is metabolised in vivo to carbendazim (83), which is the active entity. Thiophanate methyl is synthesised by condensation of o-phenylenediamine (82) with potassium thiocyanate and methyl chloroformate (Scheme 17). The benzimidazoles owe their fungicidal action to the inhibition of cell division in the fungus due to interference with the microtubular assembly. 

The continuous use of o-phenylphenol, biphenyl, thiabendazole, benomyl, and sec-butyl amine for 20 years to control postharvest decay of citrus fruits has resulted 1n a serious problem of fungicide-resistance in Peniclllium digitatum and P. italicum. Fungicide-resistant Perilc1111 um Isolates are cross-resistant to structurally-related compounds and, 1n addition, may be resistant to two or more unrelated compounds. Biotypes of P. digitatum resistant to imazalil have been found recently in 19 packinghouses throughout California. 

Benzimidazoles. Thiabendazole, and a few years later, benomyl, were introduced as postharvest fungicides 1n the late 1960s. These outstanding compounds (benzimidazole fungicides) provided excellent control of both fruit decay and Penicmium sporulation (1,2). 

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