The use of integrated soil microcosms to assess the impact of carbendazim on soil ecosystems

Our investigation used carbendazim as a representative pesticide for testing an integrated soil microcosm ( ISM) test protocol. Microcosms, set up in a greenhouse, consisted of cylinders made from high-density polyethylene (HDPE) pipe, 7.5 cm (i. d.) x 15 cm high. A. ne nylon mesh was placed across the bottom of each microcosm for leachate collection. Field soil, (silty clay loam), collected from Florsheim, Germany, was sieved through a 5 mm screen and mixed thoroughly. Earthworms, enchytraeids, and microarthropods were added to each microcosm. Each microcosm contained five wheat seedlings, and was maintained at a 12 h - 12 h light - dark cycle. Artificial rainwater was used to water microcosms as required. Soil microcosms were treated with carbendazim at concentrations 1, 3, 9, 27, and 81 times higher than the predicted environmental concentration (PEC) of 0.76 mg a. i./kg soil dry weight. A water-only control treatment was also used. The key soil processes used as endpoints were microbial activity, nitrogen mineralization, soil enzymatic activity, ammonium and nitrate leaching, organic matter decomposition and biological feeding activity. Key structural parameters measured were microbial biomass, nematode communities, microarthropod populations and diversity, enchytraeid and earthworm populations and plant growth. Pesticide degradation, leaching and uptake into plants and earthworms were also assessed. Carbendazim had significant effects on several key soil processes including soil ammonium-N and nitrate-N concentrations and soil dehydrogenase activity. Wheat growth, nematode and earthworm populations, and invertebrate feeding activity were soil structural parameters affected significantly by carbendazim. Earthworm biomass was the most sensitive parameter measured with an EC50 of 1.9 mg a. i./kg soil dry weight 28 days after treatment. A comparison of these results with results from single-species tests, small microcosms, large terrestrial model ecosystems, and field tests indicated that the ISM protocol may adequately predict environmental effects.