A hidden artefact: how surfactants can distort the results of springtail reproduction tests

Soils are exposed to multiple substance groups, including surfactants, which directly enter soils when they are used as additives in firefighting liquids or pesticide mixtures due to their surface tension-lowering properties. The impact of chemicals on soil health is often tested with the springtail reproduction test. We tested the effects of the trisiloxane Break-Thru® S 301 on the reproduction of Folsomia candida in three soils according to Organisation for Economic Co-operaton and Development (OECD) guideline 232. Juveniles were extracted either by heat or flotation. In the latter method, recommended by OECD 232, test soil is flooded with water and stirred so that springtails float and swim on the water surface. Additionally, we tested the impact of Break-Thru S 301 on other life-history endpoints linked with reproduction, namely, reproduction investment and hatching success. We found a significant decline of recovered springtails at soil concentrations of Break-Thru S 301 down to 2 mg/kg in sandy soils when using flotation. However, using heat extraction, no effects were found at the same concentrations. Also, reproduction investment and hatching success did not indicate any toxicity of Break-Thru S 301 to springtails at all. In conclusion, Break-Thru S 301 reduced the water surface tension in the flotation process so that springtail juveniles just sank and disappeared from the water surface. This artefact potentially can occur for all surfactants tested this way. We propose testing surfactant impact on springtail flotation by adding a few drops of surfactant and observing springtail sinking behavior before testing toxicity. Alternatively, heat extraction or surfactant controls can be applied. Most importantly, these options should be mentioned in the respective guidelines, which are highly relevant for chemical risk assessment.