Carbaryl degradation

In pond water, carbaryl degraded very rapidly to 1-naphthol. The latter degraded, presumably by Flavobacterium sp., into hydroxycinnamic acid, salicylic acid, and an unidentified compound (HSDB, 1989). Four d after carbaryl (30 mg/L and 300 ng/L) was added to Fall Creek water, >60% was mineralized to carbon dioxide. At pH 3, however, <10% was converted to carbon dioxide (Boethling and Alexander, 1979). Under these conditions, hydrolysis of carbaryl to 1-naphthol was rapid. The authors could not determine how much carbon dioxide was attributed to biodegradation of carbaryl and how much was due to the biodegradation of 1-naphthol (Boethling and Alexander, 1979). Hydrolysis half-lives of carbaryl in filtered and sterilized Hickory Hills (pH 6.7) and U.S. Department of Agriculture Number 1 pond water (pH 7.2) were 30 and 12 d, respectively (Wolfe et al., 1978). 

In water, carbaryl reacted with OH radicals at a rate constant of 3.4 x 10 /M-sec (Mabury and Crosby, 1996a). Carbaryl degradation followed first-order kinetics and it was more reactive than another closely related carbamate, carbofuran. 

Figure 8. Carbaryl degradation with time in the presence of five other formulated pesticides. , amount in soil and water o, amount in water.

In a small watershed, carbaryl was applied to com seed farrows at a rate of 5.03 kg/ha active ingredient. Carbaryl was stable up to 166 days, but after 135 days, 95% had disappeared. The long lag time suggests that carbaryl degradation was primarily due to microbial degradation (Caro et al., 1974). 

There are more and more facts that show that, after they have been exposed to pesticides such as granosan, carbaryl, and captan, living organisms are more sensitive to the subsequent effects of these and other pesticides. This is one reason for the rapid degradation of high-yield crops - a dangerous phenomenon that spreads together with pesticide use. 

Although previous applications of this technique in our laboratory had been concerned with aquatic animal metabolism of pesticides such as DDT, parathion, carbaryl, and trifluralin (14, 15), we also became interested in comparing metabolic routesljy means of a "metabolic probe". Such a compound ideally should be stable to nonbiological degradation, of low toxicity to maximize the dose, and subject to as many major routes of metabolism as possible without undue analytical complexity. 

Sud et al. (1972) discovered that a strain of Achromobacter sp. utilized carbaryl as the sole source of carbon in a salt medium. The organism grew on the degradation products 1-naphthol, hydroquinone, and catechol. 1-Naphthol, a metabolite of carbaryl in soil, was recalcitrant to degradation by a bacterium tentatively identified as an Arthrobacter sp. under anaerobic conditions (Ramanand et al., 1988a). Carbaryl or its metabolite 1-naphthol at normal and ten times the field application rate had no effect on the growth of Rhizobium sp. or Azotobacter chroococcum (Kale et al., 1989). The half-lives of carbaryl under flooded and nonflooded conditions were 13-14 and 23-28 d, respectively (Venkateswarlu et al., 1980). 

Liu and Bollag (1971) reported that the fungus Gliocladium roseum degraded carbaryl to 1-naphthyl TV-hydroxymethylcarbamate, 4-hydroxy-1-naphthylmethylcarbamate, and 1-naphthyl-hydroxymethylcarbamate. 

Gonzalez, J. and Ukrainczyk, L. Transport of nicosulfuron in soil columns. J. Environ. Qua ., 28(1) 101-107, 1999. Gonzalez, V., Ayala, J.H., and Afonso, A.M. Degradation of carbaryl in natural waters enhanced hydrolysis rate in micellar solution. Bull. Environ. Contam. Toxicol, 42(2) 171-178, 1992. 

Peris-Cardells, E., Terol, J., Mauri, A.R., de la Guardia, M., and Pramauro, E. Continuous flow photocatal3Uic degradation of carbaryl in aqueous media, J. Environ. Sci. Health, B28(4) 431-445, 1993. 

Pramauro, E., Prevot, A.B., Vincenti, M., and Brizzolesi. G. Photocatal3Uic degradation of carbaryl in aqueous solutions containing Ti02 suspensions. Environ. Sci. Technol., 31(11) 3126-3131, 1997. 

Studies were initiated at Iowa State University in 1977 to determine if pesticides would be contained and degraded when deposited in water/soil systems. Although the addition of known amounts of the selected pesticides was controlled, the physical environment was not temperature, humidity, wind speed, etc. were normal for the climate of Central Iowa. Four herbicides and two insecticides were chosen on the basis of three factors. Firstly, they represented six different families of pesticides. The four herbicides, alachlor, atrazine, trifluralin, and 2,4-D ester, represent the acetanilides, triazines, dinitroanilines, and phenoxy acid herbicides, respectively. The two insecticides, carbaryl and para-thion, represent the carbamate and organophosphorus insecticides, respectively. Secondly, the pesticides were chosen on the basis of current and projected use in Iowa Q) and the Midwest. Thirdly, the chosen pesticides were ones for which analytical methodology was available. 

Figure 15. Degradation of alachlor (ALA), trifiuraiin (TRI), parathion (PAR), 2,4-D ester (2,4-D), carbaryl (CAR), 2,4-D acid (ACID) and 1-naphthol (NAP) at low concentration and ambient conditions. , amount in soil and water o, amount in water.

Those degradation products which have been identified in our investigations are 1-naphthol from carbaryl, 2,4-D acid and 2,4-dichlorophenol from 2,4-D ester, 2-chloro-2, 6 -diethylacetanilide from alachlor, o,o,oe-trifluro-2-nitro-6-amino-N,N-dipropyl-p-tolu-idine and o,o,o-trifluro-2,6-diamino-N,N-dipropyl-p-toluidine from trifluralin, and a variety of phenols and acids from the degradation of the aromatic solvents used in the formulation of the liquid pesticides as emulsifiable concentrates (41,42). 

For the study of the degradation of carbaryl, 25 leaves were picked from each of the 3 apple trees in each plot as follows starting near the crown of the tree, 8 leaves were picked randomly down to the drip line and this procedure was repeated at 2 other positions approximately 1/3 of the way around the tree. At the 3rd position, 9 leaves were picked. The leaves from each tree were then composited into one sample, so there were 3 replicate samples from each plot, and taken to the laboratory where they were immediately prepared for the extraction. Leaf samples were taken at intervals of 0, 1, 3, 7, 17, 24, 31, 38, and 52 days after the trees were sprayed with a carbaryl. 

Figure 1. Degradation of carbaryl residues on apple leaves plotted on semi-log graph. Key O, 0.5 lb/100 gal application rate and , 1.0 lb/100 gal application...

The amounts volatilized in 10 days were extremely low in most cases. Dicamba was the only herbicide exhibiting significant volatilization and that only in the presence of high water evaporation. Apparently the insecticide carbaryl, has the potential to volatilize significantly from the soil with or without water evaporation, particularly when it is present near the soil surface. The reference insecticide, lindane, will appreciably volatilize when it is present near the soil surface, but its volatility decreases markedly when present within the entire 0 - 10 cm depth. Volatilization of the other insecticides will be essentially insignificant due either to their rapid degradation rate or low Kh-... 

Their volatilization from litter on the forest floor will also be appreciable. With the possible exception of carbaryl, their volatilization after being washed into the soil will be relatively low or insignificant because of their low volatility, low Henry s constants, Kh> and/or their high rates of degradation in the soil environment. The rapid disappearance of the phenoxy herbicides (2, 31) and the insecticide, fenitrothion (28) from vegetation and the forest floor is supporting evidence that volatilization is an important pathway for loss of applied pesticides from the forest canopy and litter on the forest floor. 

Figure 6. Sunlight degradation products of carbaryl and dieldrin on surfaces or as vapor.

---