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The cladoceran Daphniamagna has been used as an aquatic test species in aquatic toxicology. To evaluate the aquatic toxicity of leachate from concrete, the immobilization of D. magna was observed after treatment of various concentrations of leachate specimens. Reliabilities of the culture condition and the experimental protocol for acute toxicity test were successfully achieved from the standard toxicity test. The leachates were prepared from the mixture of Ordinary Portland Cement (OPC) and pozzolanic admixtures, Pulverised fuel ash (PFA), Ground granulated blast furnace slag (GGBS) and GGBS containing loess. Acute toxicity test showed 100% immobilization of D. magna for OPC or PFA. The leachates from OPC or PFA had high pH 10 to 12. However, GGBS and GGBS containing loess showed less toxicity according to the concentrations. Especially, immobilization was not observed at the concentrations below 12.5% of GGBS containing loess. Also the range of pH for these specimens was 8 to 9. This suggested that the use of loess as the admixture in concrete may be useful to reduce eco-toxicity of leachates from concrete. This our study provided the harmfulness of the alkali leaching from concrete in aquatic environment and the usefulness of D. magna to evaluate the toxicity of leachates from concrete.

The use of steelmaking slag as a recycled material is being progressed in coastal waters for marine environment improvement, by exploiting the characteristics of steelmaking slag. However, regarding its use in coastal waters, there are as yet no criteria for determining which bioassay should be used for assessing its effect on marine organisms. As a method of voluntary quality control of steelmaking slag, we selected a suitable battery of bioassays. The acute toxicity of steelmaking slag leachate on a copepod (Tigriopus japonicus) and a luminescent bacterium (Vibrio fischeri) was evaluated. As a result of the bioassay tests on some types of steelmaking slag, the leachate from the steelmaking slag with the pH preadjustment carbonation process showed smaller pH increases and no inhibitory effect on the marine organisms evaluated. On the other hand, the leachate from the steelmaking slag without carbonation showed an inhibitory effect on both organisms, as shown by an increase in its pH up to 12. This inhibitory effect was observed only in T. japonicus even when the pH was reduced to 8. The inhibitory factors of such leachate on T. japonicus and luminescent V. fischeri were examined. No hazardous substances were detected in the leachate. However, the calcium and magnesium concentrations of the leachate markedly changed compared with those of seawater. When the calcium concentration of the leachate was adjusted to that of seawater, the inhibitory effect on T. japonicus almost disappeared. Therefore, calcium concentration changes brought about by pH changes were considered to be the main inhibitory factors in the leachate. When bioassays with marine organisms are used to evaluate a recycled material such as steelmaking slag, the calcium and magnesium concentrations of the leachate should be carefully considered.