Leachate Preparation for Toxicity Screening Test

Only material that passed a 1/4-inch meshed screen was used for preparing leachates. The short-term batch leaching procedure was followed, in which deionized water and C R material were mixed end-over-end, in the dark, for 24 h at 24 2 °C. At the end of the 24 h the mixtures were placed into 500 mL tubes and centrifuged to separate the solid materials. The supernatant fluid was filtered through a 0.45 pm filter. A C R material leachate that was processed as described above is referred to as 100% leachate in this study [227,228, 238,239]. 

It is obvious that the laboratory leachate preparation, which involves grinding and extensively shaking the test samples for 24 h, does not represent leaching of materials found in actual highway sites. The laboratory-prepared leachates have extremely high concentrations of water-born substances/toxicants compared to those expected under actual field conditions. However, the rationale behind this sample preparation was to check toxicity under the worst-case scenario. If a material does not show measurable toxicity under such extreme conditions, no more testing should be required. Materials that show measurable toxicity need to be examined under more representative field conditions for final evaluation of possible toxicity. 

---