Influence of water hardness on the bioavailability and toxicity of linear alkylbenzene sulphonate (LAS)

In the present work, the influence of Ca2+ concentration on the toxicity of single cut linear alkylbenzene sulfonate (LAS) homologues was studied. Pre cipitation boundary diagrams for each homologue were obtained, indicating t urbid and clear zones depending on the LAS and Ca2+ concentrations. The sep aration between transparent and turbid zones is given by the so-called prec ipitation line. LAS toxicity to Daphnia magna was determined at concentrati ons close to this precipitation line. It was observed that when Ca(LAS)(2) precipitation progresses, LAS bioavailability decreases for test animals, a nd the toxicity diminishes even at high nominal LAS concentrations. Accordi ng to the "free ion activity model" (FIAM), the toxicity of a given chemica l compound ii mainly due to the ionic species (Ca2+-LAS-) and not due to th e precipitated molecule, Ca(LAS)(2). The significance of the present study is in connection with the assessment of LAS sorption/precipitation studies in soils and sediments, where in situ toxicity is strongly influenced by Ca 2+/Mg2+ ions, according to the results presented in this work. (C) 2001 Els evier Science Ltd. All rights reserved.