Coco peat - An alternative artificial soil ingredient for the earthworm toxicity testing

Abstract

The artificial soil medium recommended for invertebrate toxicity studies by OECD and ISO contains sphagnum peat as an organic component. Sphagnum peat is not widely available in tropical countries especially in the Indian subcontinent. Importing of sphagnum peat is not economically feasible and also time consuming Using of native organic matter source is also much more ecologically relevant for the region. Hence, development of an alternative is needed as a replacement of sphagnum peat. As coco peat is easily available as an organic component in tropical countries, earthworm toxicity studies were conducted with coco peat to assess its suitability to be included as an alternative in the artificial soil medium. Artificial soils were prepared with 70% sand, 20% kaolin clay and 10% coco peat (COPS )  or/ sphagnum peat (SPPS). Acute and reproduction toxicity studies were conducted with the earthworm, Eisenia fetida using 2-chloroacetamide and carbendazim, respectively . Validity criteria specified by the guidelines  were met in tests with either soil media. In the acute test, no significant difference was  observed between the soils in terms of mortality (p > 0.05 ) based on the LC50 values for COPS and SPPS of 35.56 and 32.36 mg 2-chloroacetamide /kg dry soil, respectively. Significant effect in terms of reproduction was observed at 2.06 mg carbendazim/kg dry soil for both COPS and SPPS . The other parameters such as biomass change, mortality  and food consumption of COPS and SPPS were comparable. Key words: Coco peat, shagnum peat, artificial soil, earthworm toxicity, carbendazim, 2-chloroacetamide.