Ecotoxicological effect assessment and risk characterisation of selected contaminants in sewage sludge

Ž .Linear alkylbenzene sulphonates LAS are a group of anionic surfactants, characterised by having both ahydrophobic and a hydrophilic group. LAS is one of the major ingredients of synthetic detergents and surfactants andis used world-wide for both domestic and industrial applications. LAS is relatively rapidly aerobically degraded, butonly very slowly or not at all degraded under anaerobic conditions. Therefore, LAS can be found in very highconcentrations in most sewage sludge and enter the soil compartment as a result of sludge application. LAS can befound in elevated concentrations in soil immediately after sludge amendment, but a half-life of approximately 1 3weeks will generally prevent accumulation in soil and biota. The concentration in soils that have not received sewagesludge recently, is generally less than 1 mg kg 1 and not more than 5 mg LAS kg 1. This is below the lowestconcentration of LAS where effects have been observed in the laboratory. The laboratory data is in accordance withfield studies using aqueous solutions of the sodium salt of LAS. However, observations of the ecological impact ofsewage sludge applications or application of LAS spiked into sludge indicates a lower toxicity of LAS when applied insludge. On the basis of the information reviewed in this paper, it is concluded that LAS can be found in highconcentrations in sewage sludge, but that the relatively rapid aerobic degradation and the reduced bioavailabilitywhen applied via sludge, most likely will prevent LAS from posing a threat to terrestrial ecosystems on a long termbasis. 1999 Elsevier Science B.V. All rights reserved.