Acute toxicity tests using earthworms to estimate ecological quality of compost and digestate

Ecological quality of compost and digestate,used as fertilizers for agricultural use, was assessed throughan acute ecotoxicological bioassay testing the earthwormEisenia fetida (Annelida). The test evaluates the earthworm’sattitude to dig within 15 min into a soil mediumconstituted by a mixture of a standardized soil and differentconcentrations of compost/digestate. According to differentclasses of behavior responses, the sample is classified asgood or bad quality (ON/OFF). The validity of this test wasconfirmed comparing the observations with the results froma standard chronic test developed by OECD (Organisationfor Economic Co-operation and Development). Consideringsamples from different plants and at different stages ofdegradations, the replicates, the number of tested concentrationsand the measured endpoints (ability to dig, mortality,growth, reproduction), a total of 996 observationswere analyzed. The chronic test on earthworms uses thesame media as in the acute one and measures the endpointsof mortality and growth within 28 days and reproductionwithin further 28 days. Thus, the test proposed here can beconsidered a not expensive and quick laboratory test and itsimplementation in quality assurance (QA) and quality of product (QC) schemes would enhance the protection of soil fauna. This last purpose is very important considering that,concerning the biological indicators of the quality ofcompost and digestate, the most important studies focusedon the use of plants and microorganisms and scarceattention has been paid to soil invertebrates.