ECOSYSTEM-LEVEL MICROCOSM-WET ASSESSMENT OF ADSORPTION AND REMOVAL By CALCIA-IMPROVED SOILS For Ulva spp. ELUATE

Abstract

An ecosystem-level evaluation was conducted to assess the adsorption and removal characteristics of Calcia-improved soil for eluate derived from decaying green tide algae (Ulva spp.) using a microcosm-based whole effluent toxicity (WET) test. Calcia-improved soil, produced from steelmaking slag, is recognized as a useful recycled material; however, due to its chemical characteristics, evaluation of its potential environmental impact is required prior to practical application. The microcosm (N-system) is a flask-scale model ecosystem composed of three phytoplankton species as producers, four zooplankton species as consumers, and four dominant bacterial species as decomposers, and is known for its high reproducibility and stability. In the microcosm-WET test, dissolved oxygen (DO) as a functional parameter was continuously monitored, and changes in microbial abundance as structural parameters were observed microscopically following the addition of treated or untreated eluate obtained from unsolidified Calcia-improved soil. Statistical evaluation was performed using a branched-type analysis of variance (ANOVA). For both parameters, the highest concentration showing no statistically significant effect was defined as the microcosm no-observed-effect concentration (m-NOEC), and the toxicity unit (TU) was calculated based on the dilution factor. The m-NOEC for the treated eluate was determined to be 2.5%, corresponding to a TU value of 40, indicating a lower impact compared with the untreated eluate. Considering the reported safety factor of 200 for extrapolating microcosm results to real environments, Calcia-improved soil was not expected to have a significant environmental impact.