Assessing the suitability of alternative organic matter materials for peat replacement in standard artificial soil formulations

Artificial soil has been used in regulatory ecotoxicology and in general chemical toxicity testing with soil organisms since 1984. Formulated standard artificial soil (SAS), consisting of 10% finely ground Sphagnum sp. peat, 20% kaolinite clay, 69% quartz sand, and 1% CaCO3, is often used for assessing the toxicity of chemicals to various terrestrial organisms, including earthworms, enchytraeids, collembola, and terrestrial plants. Recently, however, the use of peat in the SAS formulation has become less advisable due to peatland degradation. Therefore, toxicity studies have been conducted with the earthworm Eisenia andrei and the plants Medicago sativa (alfalfa), Echinochloa crus-galli (barnyard grass), and Lolium perenne (perennial ryegrass) to assess the utility of two potential organic matter (OM) alternatives to peat, including rye (Secale cereale) straw and fermented timothy grass (Phleum pratense) hay. These studies included exposing earthworms to boric acid in SAS (containing 5% peat) and in formulated soils with 5% rye straw or fermented timothy hay as OM components. Toxicity benchmarks derived from the present studies indicate that the two chosen OM alternatives have the potential to be suitable replacements for peat in SAS. However, the suitability of the alternative formulations may be species-specific and would require further testing to support regulatory acceptance of the investigated components for use in toxicity testing.