Acute and sub-acute effects of enrofloxacin on the earthworm species Eisenia fetida in an artificial soil substrate

• Enrofloxacin is potentially toxic to earthworms in artificial soil.
• The high concentration of enrofloxacin inhibits earthworm growth and reproductive rate.
• Enrofloxacin could inhibit earthworm avoidance responses and respiratory rates.

Enrofloxacin (EF) is widely used in veterinary medicine while the bulk accumulation of EF residues and their metabolites have been raised more and more public concerns nowadays. The aim of this study was to explore the acute and sub-acute toxicity of EF on the earthworms (Eisenia fetida) in an artificial soil substrate. The 50% lethal concentration (LC50) of EF to earthworms at day 14 after exposure to different concentration of EF (0, 2.5, 5, 10, 15 and 25 g EF per kg soil dry weight) was calculated to examine the acute toxicity of EF. Sub-acute toxicity test was conducted through detecting the effects of EF on growth, reproduction, avoidance response and respiration on earthworms. The LC50 of EF at day 14 to earthworms was 11.01 g kg−1, which was far higher than the environmentally relevant concentration of EF residues. The inhibition of EF on the growth and reproduction of earthworms was shown in a dose-dependent manner and the high concentration of EF (above 1 g kg−1 on growth rate; above 0.05 g kg−1 on juvenile amounts) obviously disturbed the growth and reproduction of earthworms. Earthworms exposed to ≥0.25 g kg−1 of EF displayed avoidance response while the soil only spiked with ≥2 g kg−1 of EF showed decreased habitat function. The respiration of earthworms was inhibited when exposed to 2.0 g kg−1 of EF for more than 14 days or 1.0 g kg−1 of EF for more than 28 days. It is concluded that EF could cause acute and sub-acute toxicity to earthworms (E. fetida) at relatively high concentration. The long-term exposure of EF to earthworms and the test conducting on natural soil substrates specific to that region should be further studied.