The effect of initial concentration of carbofuran on the development and stability of its enhanced biodegradation in top-soil and sub-soil

Abstract

Carbofuran was incubated in top-soil and sub-soil samples from a pesticide-free site at a range of initial concentrations from 0.1 to 10 mg kg-1. Amounts of the incubated soils were removed at intervals over the subsequent 12 months, and the rate of degradation of a second carbofuran dose at 10 mg kg-1 was assessed. An applied concentration as low as 0.1 mg kg-1 to top-soil resulted in more rapid degradation of the fresh addition of carbofuran for at least 12 months. The degree of enhancement was generally more pronounced with the higher initial concentrations. When the same study was conducted in sub-soil samples from the same site, an initial dose of carbofuran at 0.1 mg kg-1 resulted in only small increases in rates of degradation of a second carbofuran dose. However, degradation rates in the sub-soil samples were, in many instances, considerably greater than in the corresponding top-soil samples, irrespective of pre-treatment concentration or pre-incubated period. Initial doses of 0.5 mg kg-1 and higher applied to sub-soil successfully activated the sub-soil microflora. Application of the VARLEACH model to simulate carbofuran movement through the soil profile indicated that approximately 0.01 mg kg-1 of carbofuran may reach a depth of 70 cm 400 days after a standard field application. The results therefore imply that adaptation of the sub-soil microflora (c 1 m depth) by normal field rate applications of carbofuran is unlikely to occur. In experiments to investigate this in soils exposed to carbofuran in the field, there was no apparent relationship between top-soil exposure and degradation rates in the corresponding sub-soils. The results further confirmed that same sub-soil samples have an inherent capacity for rapid biodegradation of carbofuran. The high levels of variability observed between replicates in some of the sub-soil samples were attributed to the uneven distribution of a low population of carbofuran-degrading micro-organisms in sub-surface soil. There was no apparent relationship between soil microbial biomass and degradation rates within or between top-soil and sub-soil samples.

Rainfall effect on dissipation and movement of diuron and simazine in a vineyard soil

“…However, in irrigated plots DT 50 values from the whole soil profile (0-90 cm) and at 0-15 cm soil layer were the same, indicating that the herbicide degradation was not reduced with soil depth (Di et al, 1998;Sparling et al, 1998;Karpouzas et al, 2001). This is supported by the low K d and high desorption percentage determined in the soil profile (Table 4).…”

Spatial heterogeneity in degradation characteristics and microbial community composition of pesticide biopurification systems

“…However, other authors (Karpouzas et al . ; de Wilde et al . ) have found higher degradation rates in subsoil compared to topsoil, for which the proposed mechanism entails a decrease in sorption and higher bioavailability of the pesticides linked with a decrease in organic matter content with soil depth.…”

“…; Karpouzas et al . ). It would be interesting to assess whether biodegradation activity varies spatially within a BPS in order to be able to better understand and improve the BPS design parameters.…”

Nematicidal efficacy, enhanced degradation and cross adaptation of carbosulfan, cadusafos and triazophos under tropical conditions

“…Dramatically decreased persistence of nematicides by repeated applications even at minimal dosage rate of 0.1-0.5 μg g −1 (Karpouzas et al, 2001) was attributed to build up and adaptation of a streptomycete (Gauger et al, 1986) and bacteria, such as Arthrobacter (Racke & Coats, 1988a), Flavobacterium (Kearny et al, 1986 and Pseudomonas (Racke & Coats, 1988b), which are capable of rapid catabolism of the nematicides or metabolites (Racke & Coats, 1987;Felsot, 1989;Racke et al, 1990). Accelerated biotransformation has also been evinced for aldicarb (Read, 1987;Suett & Jukes, 1988), carbofuran (Harris et al, 1984;Read, 1986;Suett, 1986Suett, , 1987Racke & Coats, 1988b, Morel-Chevillet et al, 1996Karpouzas et al, 2000a), carbosulfan (Sahoo et al, 1990(Sahoo et al, , 1998, cadusafos (Anderson et al, 1998;Karpouzas et al, 2004), ethoprophos and oxamyl (Smelt et al, 1987;Karpouzas et al, 1999Karpouzas et al, , 2000b, fenamiphos (Ou, 1991;Chung & Ou, 1996;Pattison et al, 2000) and terbufos (Felsot, 1998).…”