Influence of soil pH on the toxicity of aluminium for Eisenia andrei (Oligochaeta : Lumbricidae) in an artificial soil substrate

Toxicity of aluminium for the earthworm Eisenia andrei was studied in artif icial soil at different pH levels. In a range-finding test, effects of thre e different aluminium salts on earthworm survival were determined. AlCl3 ap peared to be most toxic, with LC50 values of 316, 359 and > 1000 mg Al/kg d ry soil at PHKCl of 3.5, 4.4 and 6.7, respectively in the control soils. Ef fects of this salt interfered with a strong decrease of soil pH with increa sing aluminium concentration. Al-2(SO4)(3) was less toxic with LC50 values of 457, > 4000 and > 4000 mg Al/kg dry soil at pH 3.24, 4.86 and 7.22, resp ectively. Al2O3 did not affect earthworm survival at concentrations of 5000 mg Al/kg and pH levels between 2.4 and 7.1. In the main test, earthworms were exposed for 6 weeks to soils treated with Al-2(SO4)(3). As in the range-finding test, aluminium sulfate was most tox ic at a pH of 3.4 with an LC50 of 589 mg Al/kg dry soil. At this pH, growth and cocoon production of earthworms were significantly reduced at 320 mg A l/kg dry soil, while at 1000 mg Al/kg dry soil all earthworms died. Surviva l was not affected by 1000 mg Al/kg dry soil at pH 4.3 and 7.3. At pH 4.3, growth was significantly reduced at 1000 mg Al/kg dry soil and cocoon produ ction at 320 and 1000 mg Al/kg dry soil. At pH 7.3, aluminium only affected cocoon production at the two highest exposure levels. At the highest two e xposure levels at pH 7.3, growth was significantly increased, suggesting a trade-off between growth and reproduction. These effects of aluminium at th e highest soil pH could not be explained from the concentration of extracta ble, monomeric (labile) aluminium in soil, which decreased with increasing soil pH.