Sublethal effect of synthetic fertilizers (urea and diammonium phosphate) on biomass accumulation and its histological perspicuity on the gut region of the earthworm, <i>Eisenia fetida</i>

Urea and Diammonium phosphate are commonly used fertilizers in almost every managed agro-ecosystem. The present study assessed the sublethal effect of synthetic fertilizers on biomass accumulation and its histological perspicuity on the gut region of the earthworm, Eisenia fetida. Earthworms, E. fetida (adult), were reared as per the recommendations of the Organization for Economic Co-operation and Development (OECD) guidelines (1984) number 207 for testing the sublethal effect of chemicals in the laboratory. The lethal concentration at which 50% of the worms were dead, i.e., (LC50) was estimated for synthetic fertilizers, urea, and diammonium phosphate by log-probit analysis. The urea LC50 was 862.126 mg/kg, while that of diammonium phosphate was 2098.69 mg/kg in artificial soil. To explore the sublethal effect of synthetic fertilizers on biomass culture (n=10), 1/2 of the LC50 of urea and diammonium phosphate was used. Significant variation in biomass culture was observed in response to the amalgamation of synthetic fertilizers. With in 15 days, in the urea amalgamated culture, the weight of earthworms (n=10), unlike the control group, decreased from 2.86±0.142 g to 2.42±0.120 g, but the weight of the earthworms decreased to 2.72±0.135g after applying DAP. To investigate histological alterations in the gut of earthworms subsequent to exposure, specimens (n=5) were aseptically excised, embedded in paraffin, and subjected to section cutting (thickness- 5µm) after staining with hematoxylin and eosin stain and then examined. Notably, Histological damage was also registered in the chloragogen cells of the gut region of Eisenia fetida (earthworm) on days 15 and 60. Thus, synthetic fertilisers affect earthworms' ability to absorb and digest nutrients and soil health too.