Behaviour of the soil microbial community in the presence of the herbicide cinosulfuron
1999
Ferrari, F. | Allievi, L. (University of Milan (Italy). Dipt. di Scienze e Tecnologie Alimentari e Microbiologiche) | Gigliotti, C.
Cinosulfuron is one of about thirty sulfonylureas, a new class of herbicides introduced in agriculture in the 1980's and characterized by very low use rates. Typical field dissipation half-lives are 1-8 weeks. We have been unable to find any study on the microbial toxicity of cinosulfuron. The aim of the work was to study the toxicity of the xenobiotic toward soil microflora and to make some contribution toward the verification of possible environmental risks. Therefore, we studied both the microbial ecotoxicity of cinosulfuron by a laboratory soil incubation test, and the toxicity in vitro on microbial strains isolated from the same soil. We incubated a sandy loam soil (pH 6.8; organic C 2.8/) at 25øC in the dark and in the presence of 0, 0.04 (field rate) and 4 ppm of cinosulfuron. Moisture content was maintained at 60/ of the water-holding capacity. After 1 and 4 weeks we determined the microbial counts of nitrifiers and aerobic and anaerobic bacteria; we also evaluated the behaviour of two microbial activities, respiration (CO2 output) and nitrification. A statistical analysis of the results showed a significant difference between treated and untreated soils only for nitrification at 1 week. To better understand the detailed behaviour of the soil microorganisms, pure cultures of 19 aerobic bacteria, 17 fungi and 2 Azotobacter (aerobic N2 fixers) strains were grown in agar media in the presence or not of 100 ppm of cinosulfuron (preliminary tests with 1 and 10 ppm had shown no effect). The presence of cinosulfuron inhibited the growth of 5 generic aerobic bacteria, 2 fungi and 1 Azotobacter strain, partially or totally, temporarily or permanently. Our data therefore reveal that few of the microorganisms of the studied soil were influenced by the presence of cinosulfuron and generally only at very high concentration of the herbicide.
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