Biomarker Response of the Earthworm (Eisenia fetida) Exposed to Three Phthalic Acid Esters

Biomarkers are useful for evaluating exposure and toxic effects of chemicals on invertebrates. Earthworms (Eisenia fetida) were exposed for 28 days to three phthalic acid esters (PAEs), dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP), in artificial soil to examine the potential of several biomarkers as indicators of environmental pollution. Survival, growth, sperm count, cocoon production and hatchability, and the lysosomal membrane stability, measured by neutral red retention time (NRR-time), were measured in the earthworm after exposure. DMP, DEP, and DBP showed significant toxicity to earthworm growth, and a 10% reduction in biomass occurred at soil concentrations of DMP 3.48 mg/kg, DEP 5.63 mg/kg, and DBP 4.42 mg/kg. LC50 values of DMP and DEP were 1,560.120 and 1,516.186 mg/kg, respectively, after 14 days of exposure. The LC50 value of DBP could not be determined. The most sensitive biological parameters were reproduction (cocoon production and hatchability) and NRR-time. The number of cocoons was reduced at concentrations above DMP 35 mg/kg, DEP 25 mg/kg, and DBP 20 mg/kg, and cocoons had reduced hatching success at concentrations above 1.5 mg/kg. NRR-time was reduced significantly at exposure concentrations above DMP 250 mg/kg, DBP 150 mg/kg, and DEP 200 mg/kg. These results indicated that soils contaminated with phthalic acid esters can harm or eliminate earthworm populations. Cocoon production rate, hatchability, and NRR-time can be used as biomarkers for monitoring levels of PAE contamination in soils.