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. 1. Introduction The application of exogenous organic matter to agricultural land is considered to be one of the most serious anthropogenic pressures on soils in the European Union [1]. European law and Irish law [2–4] aim to promote the recycling of municipal sludge in agriculture and to set standards to protect the environment and food safety. Treated sludge of an appropriate standard is termed “biosolids”. By 2015, towns of more than 2000 people in Ireland will be obliged to have sludge treatment plants complying with adopted standards. Over the next decade it is estimated that 150.000 tonnes of dry solids will be produced annually [5] which is more than a doubling of current production, mirroring international trends. The only means currently of disposing of this material is to apply it to agricultural land. In Ireland, land spreading of exogenous organic matter is increasing rapidly because alternative disposal options have recently been eliminated (sea dumping) or are soon to be precluded (landfill); a third option, incineration, is not available, at least in the medium term. Because
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