Assessment of biosolids in earthworm choice tests with different species and soils

Earthworm avoidance response is a new tool for rapid and efficient screening of potentially toxic
substances added to soil environments. This technique was used to determine if five common,
ecologically different earthworm species (Allolobophora chlorotica, Aporrectodea longa,
Aporrectodea caliginosa, Eisenia fetida and Lumbricus terrestris) avoid soils amended with six
biosolids (treated sewage sludge) applied at rates equivalent to realistic field rates of 0, 2, 5, 10 and
20 t ha-1. The results showed that A. chlorotica, E. fetida and L. terrestris were attracted by low
concentrations of biosolids (2 t ha-1), whereas they avoided the highest concentration (20 t ha-1). The
other species did not show any preferences. An additional treatment comparing the behaviour of E.
fetida in natural and artificial soil suggested that the type of soil can alter the preference of
earthworms. Comparisons of behavioural and actual toxicity data for the same six biosolids suggest
that avoidance responses by earthworms are sensitive enough to reflect different toxicities of
biosolids. It is concluded that earthworm avoidance behaviour offers an ecologically relevant tool for
screening the deleterious rate-effect of biosolid amended soils.