Influence of plant-earthworm interactions on SOM chemistry and p,p'-DDE bioaccumulation

Laboratory experiments assessed how bioaccumulation of weathered p,p′-DDE from soil and humic acid (HA) chemistry are affected by interactions between the plants Cucurbita pepo ssp. pepo and ssp. ovifera and the earthworms Eisenia fetida, Lumbricus terrestris, and Apporectodea caliginosa. Total organochlorine phytoextraction by ssp. pepo increased at least 25% in the presence of any of the earthworm species (relative to plants grown in isolation). Uptake of the compound by ssp. ovifera was unaffected by earthworms. Plants influenced earthworm bioaccumulation as well. When combined with pepo, p,p′-DDE levels in E. fetida decreased by 50%, whereas, in the presence of ovifera, bioconcentration by L. terrestris increased by more than 2-fold. Spectral analysis indicated a decrease in hydrophobicity of HA in each of the soils in which both pepo and earthworms were present. However, HA chemistry from ovifera treatments was largely unaffected by earthworms. Risk assessments of contaminated soils should account for species interactions, and SOM chemistry may be a useful indictor of pollutant bioaccumulation.