Detecting microplastic’s bioaccumulation in red earthworm Eisenia fetida (Savigny, 1826) via FTIR assay

Abstract

Microplastics (MPs), are smaller than 5 mm in size, and recognized as emerging persistent pollutants in Agro-ecosystems through leaked sewage sludge, plastic mulching, and compost. The effects of MPs on earthworm remain inadequately understood. This study investigates the bioaccumulation of MPs in Eisenia fetida using Fourier Transform Infrared (FTIR) assay of earthworm samples. Twelve 10Kg capacity bins, each containing 2 kg of cow dung slurry and 1kg teak leaves (2:1) were used for the experiment. Four different treatments (T1, T2, T3 and T4) such as without microplastic [control], 5g, 10g and 50g respectively. A total of 100 earthworms were carefully weighted and released into each treatment. The treatments were arranged in Completely Randomized Design (CRD).Weight of earthworms were recorded every 14 days for 45 days. Earthworms’ samples were collected from each treatment and subjected to FTIR analysis to quantify the bioaccumulated MPs. Collected data were subjected to ANOVA and DMRT mean separation using SAS 9.4 version. The initial mean weight across the treatment was 2.15±0.10 mg. After 45 days, control group showed significantly increased biomass of 130 ± 0.06% [2.81 ± 0.08mg], whereas in 5g MPs added treatment showed biomass decrease of 13 ± 0.09% [1.89 ± 0.11mg] at P ≤0.05. In contrast highly significant weight loss occurred in the 10g and 50g treatments, with average biomass loss of 25 ± 1.09 % and 35 ± 0.79%, respectively, in comparison to initial body weight at P ≤0.01. Further, MPs exposure reduced composting efficiency. The FTIR analysis shows the prominent absorbance peaks centered at approximately 720 cm-1 and 1460 cm-1 in the 50g MPs added treatment suggesting a predominance of polyethylene (PE) like polymeric structure within the sample confirming the bioaccumulation of MPs in the earth worm body. This study highlights the ecological risk of microplastics in soil ecosystems and suggests the need for regulating plastic waste disposal and monitoring compost input to ensure sustainable vermicomposting.