Dissipation Of Carbendazim And Chloramphenicol Alone And In Combination, And Their Effects On Soil Fungi: Bacteria And Soil Enzyme Activities

Artificial introduction of fungicides and the use of sewage sludge and manure contaminated with antibiotics as fertilizer into to soil result in combined contamination. The effect of combined contamination depends on the composition of the mixture and may vary significantly, there is a need to investigate their combined effect on soil microorganisms. In the present study, carbendazim and chloramphenicol were selected as representatives of fungicides and antibiotics duo to their intensive application, respectively. The dissipation of carbendazim and chloramphenicol alone and in combination, and their effects on soil fungi:bacteria and soil enzyme activities were investigated. The results were summarized as follows:The dissipation of carbendazim and chloramphenicol in field soil were investigated under laboratory condition. Carbendazim dissipation was little affected by chloramphenicol. It was inhibited by chloramphenicol of 10.0 mg kg-1, but not by chloramphenicol of 20.0 mg kg-1. Chloramphenicol dissipation was not affected by carbendazim of 4.0 mg kg-1. However, it was significantly inhibited by high dosage of carbendazim (8.0 mg kg-1).Soil microbial community was evaluated with the ratio of fungal:bacterial activity detected by the selective respiratory inhibition method. With the amendment of carbendazim into soil, the ratios of fungi:bacteria were reduced throughout the experiment compared to those in the control. A significant reduction was observed at day 4 in soil amended with carbendazom at both high (8.0 mg kg-1) and low (4.0 mg kg-1) dosages. The effect of chloramphenicol on fungi:bacteria ratio is governed by its concentration and incubation times. No significant effect of chloramphenicol at concentration of 10.0 mg kg-1 on soil fungi:bacteria was observed. However, soil bacteria seemed to be inhibited slightly by chloramphenicol at high level of 20.0 mg kg-1 within 9 days after treatment, and this effect was disappeared with disappearence of chloramphenicol. Fungi:bacteria ratio in soil treated with their combination were permanently smaller than those in the control and closely related to carbendazim concentration. The activities of soil neutral phosphatase, invertase, urease and catalase were also adopted as indexes for the assessment. Carbendazim had slight effect on soil neutral phosphatase and invertase, whereas it increased soil catalase anf urease activities. Amendment of chloramphenicol into soil caused marked and permanent inhibition in soil neutral phosphatase activity. Combined effect of carbendazim and chloramphenicol were found to be depended upon chloramphenicol on neutral phosphatase, carbendazim on urease, and both on inverase and catalase.