Combined Effects of Cadmium and Sulfamethoxazole on Eisenia Fetida: Insights into Accumulation, Subcellular Partitioning, Biomarker and Toxicological Responses

Abstract

Cadmium (Cd) and sulfamethoxazole (SMX) are commonly coexists in farmlands, but their combined toxicity to terrestrial invertebrates has not been studied. Here, earthworms were exposed to artificial soils percolated with Cd (5 mg/kg), SMX (5 mg/kg) or their mixture. Cd and SMX uptake by earthworms and their subcellular partitioning were studied. Multiple biomarker responses (superoxide dismutase (SOD), catalase (CAT), lipid peroxidation (MDA), and weight loss) were also determined to estimate health status and mixture effects. In the presence of SMX, the weight loss of Eisenia fetida was much greater (41.25%) than that in the treatment with Cd alone (26.84%), indicating a cooperative effect. Similarly, compared with each individual treatment, the cotreatment group exhibited significantly greater concentrations of Cd in the total internal body, Fraction C (cytosol) and Fraction E (tissue fragments and cell membranes), as well as SMX in the total internal body and Fraction C in Eisenia fetida. Additionally, Eisenia fetida subjected to the combined treatment presented obviously increased levels of SOD, CAT, and MDA, indicating oxidative stress and lipid peroxidation. The effect addition indices (EAIs) ranged from 1.00 to 2.23, indicating that the Cd-SMX mixture had synergistic effects on all the studied treatments. Moreover, transferring the earthworms into uncontaminated soil did not alleviate the existing injuries. These results indicated that the Cd-SMX complex increased the risk of Cd or SMX in agricultural areas.

Keywords: sulfamethoxazole, Cadmium, Eisenia fetida, Subcellular fraction, Synergistic effect