Bioassay of Components Eluted from Electric Arc Furnace Steel Slag Using Microalgae Chlorella

Some electric arc furnace (EAF) steel slag ultimately ends up in final landfill sites. After developing a method to estimate the impacts of the eluate from the slag, particularly on phytoplankton, this study assessed novel slag applications to aquatic environments. First, metal components were eluted from EAF slags of normal steel or stainless steel with a leaching condition based on JIS K 0058-1. The slag metal components were analyzed using emission spectrochemical analyses. After incubation of Chlorella as phytoplankton with culture media including eluates from the respective slags, the effects of each eluate were investigated using microscopy and flow cytometry. Results demonstrated that concentrations of metal effluents from slags, even for EAF steel slag, which included more hazardous materials than normal slag, were almost all lower than environmental quality standards for effluent and drinking water. Analyses of algal cells treated with each eluate revealed that eluate induced neither lethality nor growth inhibition. Instead of cytotoxicity, the addition of each eluate enhanced algal growth. Infrared spectroscopy and potentiometry using a diaphragm-type electrode to measure aquatic CO2 revealed that metal components from both slags in media produced greater amounts of aquatic CO2 available for photosynthesis, thereby enhancing algal proliferation. Taken together, results show that using EAF slag in aquatic environments might be beneficial, not toxic, for photosynthetic organisms. Furthermore, bioassay using flow cytometry can estimate vigorous and aberrant algal growth simultaneously.