Novel egg life-stage test with Folsomia candida - A case study with Cadmium (Cd)

Toxicity of pollutants is known to have a different impact depending on the organisms' life stage. Standard tests are often based on one life stage, i.e. effects could be underestimated. We aimed here to develop and optimize a test system using eggs of Folsomia candida (4-5 days) instead of the juveniles (10-12 days old) required by the OECD standard test guideline No. 232 (2009). Accordingly, the exposure time and thus the test duration was extended. Tests with "standard" juveniles (10-12 days old) and, adults (21 and 28 days old) were also performed. Cadmium (Cd) was used as test substance. The extension to the test guideline starts as follows: 1) synchronization of eggs in a thin soil layer on plaster of Paris, 2) selection of viable eggs, 3) burying these eggs in groups of 5 in soil. Afterwards, the test procedure will follow the standard procedure as described in the OECD standard test. Cadmium caused ca. 50% effects on reproduction at 60 mg Cd/kg soil dry weight (DW) when exposing juveniles or adults. There was no significant impact of Cd on the eggs, the hatching process or the latter life stages until ca. 250 mg Cd/kg DW (Cd is stable during this exposure period). Hence, Cd seems to affect reproduction before egg laying, i.e., during egg formation or during juvenile-adult stages. In order to clarify whether other chemicals do act in a similar way testing with different chemicals is highly recommended. Testing of different life stages does provide insight on the mechanisms and effects of contaminants and offers important insight.