Soil Biodegradation of Carbofuran and Furathiocarb Following Soil Pretreatment With These Pesticides

Abstract

A field application level (9 pg .g-') of carbofuran was completely hydrolyzed within 1 to 3 days in a loamy sand soil pretreated with the same level of carbofuran, while <5% of the carbofuran was hydrolyzed in control soil not pretreated. The number of microbial carbofuranhydrolyzers was substantially greater in loamy sand soil treated twice with a field application level (9 pg.g-') of carbofuran than in untreated soil. Also, carbofuran-adapted soil showed no significant change in the number of carbofuran-hydrolyzers during the period of rapid degradation. Inorganic nitrogen, at a typical fertilization level, appeared to slightly stimulate the enhanced degradation of carbofuran in the pretreated soil. Soil pretreated with an application level hydrolyzed 65% of a residue level (8 ng.g-') within two days, but virtually none of the remaining carbofuran was hydrolyzed thereafter. A microbial biomass carbon experiment with a sandy loam soil indicated that only 0.2% of the applied carbonyl-C could be attributed to biomass. Soil pretreated with a residue level did not show rapid degradation of the same level or a field application level, although the field application level was degraded slightly faster in this soil than in soil not pretreated. Soil pretreated with a field application level of carbofuran or furathiocarb also rapidly hydrolyzed the same level of furathiocarb, but furathiocarb is probably converted into carbofuran before hydrolysis.

Populations and activity of carbofuran-degrading microorganisms in soil

“…Furthermore, they observed that this increase in the number of microorganisms following carbofuran amendment correlated with the changes in rates of degradation following additions of carbofuran. The differences between the present findings and those of Hendry and Richardson (1988) in regard to the marked effect on biodegradation of pretreatment with this insecticide thus probably reflect the initially far larger populations in Kendaia clay loam than in the loamy sand used by Hendry and Richardson (1988) and the subsequent increase in cell number in the loamy sand. If the population capable of acting on a specific compound is large before that chemical is added to soil, the chemical would not cause a detectable increase in cell numbers, as observed here for carbonyl-labelled carbofuran.…”

“…The reasonably rapid conversion in soil of 14C-ring-labelled carbofuran to 14CO2 and the few organisms able to carry out the analogous reaction in MPN media indicate that the conversion in soil requires more than one species, none of which uses the compound as the sole C source for growth. Hendry and Richardson (1988) found that two additions to loamy sand of carbofuran (9mg kg 1) resulted in an increase in the number of cells converting the carbonyl C to CO 2 from 1.6 x 103 in untreated soil to 3.1 × 105 per g following treatment. The higher value is close to the expected population size in this soil if it is assumed that methylamine derived from carbofuran is the sole C source and that 1 pg of C is oxidized to form one cell.…”

“…Much of the research on this phenomenon, which is known as accelerated or enhanced biodegradation, has been concerned with carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-ylmethylcarbamate) (Hendry and Richardson, 1988;Read, 1983;Suett, 1986). Microorganisms have been isolated from soil that degrade this insecticide (Chaudhry and Ali, 1988;Ramanand et al, 1988;Venkateswarlu and Sethunathan, 1984), and it has been suggested that an increase in the number of microorganisms degrading pesticides is responsible for the enhanced degradation in soil (Fournier et al, 1981;Hendry and Richardson, 1988), but enhanced degradation may result from an increase in the activity rather than the abundance of pesticide-degrading microorganisms (Moorman, 1988;Racke and Coats, 1988).…”

Aquatic fate and effect of Carbofuran

“…26 " 29 Enhanced carbofuran biodégradation was associated with the increased growth of individual strains of microbes within the general microbial population which had the ability to degrade carbofuran. 27 Although these investigations focused on the terrestrial environment, the same biodegradation and enhancement processes should also apply to the aquatic environment. Carbofuran-degrading strains of the genus Pseudomonas isolated from soil also degraded carbofiiran in fortified (100 mg/1) oligotrophic lake water, groundwater, and trickling filter sewage effluent.…”

Effects of conditioning, cross-conditioning, and microbial growth on development of enhanced biodegradation of insecticides in soil

“…Our tests did not include parallel observations for trimethacarb and bendiocarb. Others have measured proliferation of specific insecticidedegrading microorganisms after treatment of soils with carbofuran (Hendry and Richardson 1988) or isofenphos (Racke and Coats 1987). …”