Herbicide nitrosation

In 1976, Ross al. first reported that the powerful carcinogens, N-nitrosodimethylamine (NOMA) and N-nitrosodi-n-propyl-amine (NDPA) were found at parts per million (ppm) concentrations in certain commercial herbicide formulations (1., ). Since then, scientists have learned that carcinogenic N-nitroso compounds can be formed in a wide variety of media of interest to those who manufacture, use, or study pesticide products. Some of these nitrosation-supporting media are listed in Table I. 

The herbicide glyphosate was nitrosated in aqueous solution by third order kinetics to N-nitrosoglyphosate. 

Whether the N-nitrosation of glyphosate in soil to form N-nitrosoglyphosate will occur under natural conditions is still a matter of conjecture. However, based on our studies (12), the formation of detectable amounts of N-nitrosoglyphosate in soil under normal field conditions is not expected. It was observed that high concentrations of the herbicide glyphosate and nitrite were essential to get measureable amounts of N-nitrosoglyphosate in soil. Thus, to produce 5 ppm N-nitrosoglyphosate in the soil used in our study, one requires about 185 ppm of the herbicide... 

Dinitroaniline herbicides have an unusual property of serving both as an amine contributor and nitrosating agent. The phenomenon (Grove, 1979) was observed when solid or liquid dinitroanilines are subjected to heat. For exan le, when trifluralin is heated to 70 0, N-nitrosodipropylamine (NDPA) is formed. Figure 1 shows the accumulation of NDPA with time. Increased nitrosamine formation is a function of temperature and time. 

There are several routes for nitrosamine contamination in pesticides use of contaminated chemicals during synthesis, side reactions, use of nitrite as a preservative and corrosion inhibitor of metal containers and by reactions with environmental nitrosating agents. Over 300 formulations were shown to be contaminated with nitrosamines however, the main contamination was confined to 2,6-dinitroaniline herbicides, dimethylamino salts of phenoxyalkanoic acid herbicide, diethanolamine and triethanolamine salts of acid... 

In the past seven years N-nitrosamines have attracted wide attention due to their carcinogenic properties. In 1977, Ross et al. (67) reported the presence of N-nitrosodipropylamine in the formulation of dinitroaniline herbicide, trifluralin, at the 154 ppm level. Subsequent studies by other laboratories showed that nitrosamine impurities are common to all dinitroaniline-based herbicides. Nitrosamines contamination resulted from the nitration of dipropylamine by the excess nitrosating agent. 

An overview of the transformation pathways of various substrates in the presence of nitrate and nitrite under irradiation is reported in Tables 1 and 2, respectively. Quite interestingly, nitrosation intermediates have been detected only in the presence of phenolic compounds, dimethylamine and the herbicide monolinuron [144],... 

Pesticides N-nitrosated under 1m vitro and vivo conditions in the laboratory have included the fungicide ziram (zinc dimethyldithiocarbamate), the insecticides carbaryl (1-naphthyl methyl carbamate) and propoxur (o-isopropoxy phenyl methyl carbamate) and the herbicides benzthiazuron [N-(2-benzothiazolyl)-N -methylurea], simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine). 

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