Ecological effects of PDMS-augmented sludge amended to agricultural microcosms

The potential ecological effects of polydimethylsiloxane (PDMS)-augmented sewage sludge resulting from use of the sludge as an agricultural amendment were evaluated in a preliminary pot test and a definitive test in intact, agricultural soil-core microcosms. Seed germination and early seedling survival were evaluated in the pot study. The parameters investigated in microcosms included soil microorganism populations, crop productivity, and nutrient loss in soil leachate. Intact, soil-core microcosms from two soil types (silty clay or sandy loam) were amended with PDMS-augmented sludge by single or multiple (4) applications. Micrososms were sequentially cropped with spring wheat (Triticum aestivum) followed by soybeans (Glycine max). Ecological effects comparisons were made between microcosms containing one of three PDMS treatment levels in the sludge ( ∼ 290, 1000, or 3500 p.p.m.) and control microcosms containing sludge without PDMS. The three treatments of PDMS in sludge tested had no effect on seed germination and seedling survival when incorporated into soil (< 13 p.p.m. PDMS) in pots. Furthermore, PDMS in sludge amended to microcosm topsoil (< 10 p.p.m. PDMS) appears to have no effect on: (1) cumulative loss of nitrate-nitrogen in leachate; (2) oven-dry biomass of spring wheat or soybeans; (3) Rhizobium bacteria, as indicated by the number of nodules on soybean roots in sandy loam soil; and (4) numbers of soil microorganisms, including bacteria, actinomycetes, and fungi. However, the quantity and timing of sludge amendment may affect (1) loss of nitrate-nitrogen in leachate and (2) soybean yields.