The validation of modified tropical artificial soil by ecotoxicological studies on Eisenia foetida

The standard soil invertebrate toxicity tests developed by OECD (Organization of Economical Cooperation and Development) and ISO (International Organization of Standardization) use an artificial soil as the test substrate, which contains sphagnum peat as a component. This type of peat is not widely available in tropical country like India. Investigation of possible alternative substrates using locally available materials therefore is vital for performing such ecotoxicity tests, particularly in the tropics. In the present study, the suitability of commonly available coir pith as a replacement for sphagnum peat was undertaken. Thus a modified Tropical Artificial soil (TAS) was prepared by mixing 70% sand and 20% kaolin clay with 10% coir pith (fermented). The validity of modified TAS was determined by investigating the acute and chronic toxicity of urea (Nitrogen fertilizer) on Eisenia foetida using the original OECD artificial soil as control. Though both substrates were valid, TAS was considered more valid, as the biomass loss percentage (Acute toxicity) was <20% (recommended by ISO) in control while it was >20% in OECD soil. In the same way, the number of juveniles (Chronic toxicity) in each replicate must be higher than 30 to valid the soil for toxicity tests. This criterion was conquered in TAS whereas it was lower than 30 in OECD soils (1500mg and 2000mg spiked). Thus it was concluded that coir pith might be a suitable replacement for sphagnum peat in artificial soil for ecotoxicological studies in tropical countries.