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Land spreading is a major option internationally for the disposal/use of treated sewage sludge (biosolids), but effects of this practice on soil organisms are largely unknown. This study investigated the effects of biosolids on two soil invertebrate species, earthworms (Eisenia fetida) and Collembola (Folsomia candida), in laboratory tests. Five biosolids from different sewage works were assessed at rates equivalent to 0, 2, 5, 10, and 20 t ha −1 . Biosolids applied at 2 and 5 t ha −1 did not cause mortality of adult earthworms but did at 10 and 20 t ha −1 . At 5, 10 and 20 t ha −1 , all biosolids had significantly fewer juvenile worms relative to controls. Increasing the rates from 2 to 10 t ha −1 did not impact on the number of adult Collembola, but at 20 t ha −1 there were significantly fewer adults. There were significantly fewer juvenile Collembola recorded for biosolids applied at the 2 t ha −1 when compared with controls, and also when biosolids were applied at 5, 10, and 20 t ha −1 relative to 2 t ha −1 . Some significant difference between biosolids were observed, but generally, negative effects were not related to heavy metal concentrations in biosolids. It is recommended that possible detrimental mechanisms (e.g., ammonia production, lack of oxygen) be investigated in future work. It is concluded that biosolids, applied at legal, low rates (about 2 t ha −1 ) are unlikely to be detrimental to earthworms or adult Collembola but can be detrimental to Collembola reproduction.

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 ). 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.