Microbial degradation of two carbamate insecticides and their main metabolites in soil

Abstract

Degradation studies in soil of the insecticides aldicarb and carbofuran and their metabolites (aldicarb sulfoxide, aldicarb sulfone; 3-ketocarbofuran and 3-hydroxycarbofuran) were carried out using laboratory systems under controlled conditions (temperature, water content, light). The insecticides were added to soil samples and subsamples of the soil were analyzed at different times to assess both the bacterial abundance and the concentration of the different chemicals. The epifluorescence direct count method was applied to the subsamples to estimate microorganism numbers (N=g soil). Untreated samples of soil were used as controls for evaluating the effects of the application of the insecticides on microbial abundance. Subsamples treated with the pesticides were analyzed using HPLC and the DT 50 s of the different compounds studied were calculated.The DT 50 values show that neither the parent compounds nor the transformation products have a high persistence in soil and there is a general increase in the concentration of microorganisms as the pesticides diminish.

Simazine biodegradation in soil: analysis of bacterial community structure by in situ hybridization

“…A greater detection of bacterial cells is presumably due to their activation and a consequent increase in their ribosome content 31. The recovery at 7 days of the control microbial community may be a result of favourable experimental conditions (in particular, the addition of water and higher temperature), as found previously 12, 27…”

“…Microbial abundance (bacterial number g −1 soil) was measured by the epifluorescence direct count method, reported in detail previously,12, 13 using DAPI (4′,6′‐diamidino‐2‐phenylindole) as the fluorescent agent.…”

Effect of urea on degradation of terbuthylazine in soil

“…CBET degradation . The herbicide degradation experiment was conducted according to SETAC procedures [13,22–25]. The herbicide and fertilizer were applied to soil samples (200 g) at agricultural doses (2.25 kg/ha of CBET and 330 kg/ha of urea), with the following treatments: Samples of soil were amended with CBET, dissolved in sterile water, to obtain a herbicide concentration of 1.5 mg/kg; samples of soil were first sterilized (autoclaved 120 ± 2°C, 20 min, on two consecutive days) and then amended with CBET (STERILE); samples of soils were amended with both CBET (1.5 mg/kg) and urea (500 mg/kg; CBET‐UREA); samples of soils were amended with only urea (UREA); and samples of soils received only an equivalent volume of pure sterile water (control treatment).…”