In the present study, a 7-day mixture toxicity experiment with the terrestrial springtail Folsomia candida was conducted, and the effects linked to three different mixture exposure parameters. Passive dosing from silicone was applied to tightly control exposure levels and compositions of 12 mixture treatments, containing the polycyclic aromatic hydrocarbons (PAHs) naphthalene, phenanthrene, and pyrene. Springtail lethality was then linked to sum chemical activities (∑a), sum equilibrium lipid concentrations (∑Clipid eq.), and sum toxic units (∑TU). In each case, the effects of all 12 mixture treatments could be fitted to one sigmoidal exposure-response relationship. The effective lethal chemical activity (La50) of 0.027 was well within the expected range for baseline toxicity of 0.01-0.1. Linking the effects to the lipid-based exposure parameter yielded an effective lethal concentration (LClipid eq. 50) of 133 mmol kg-1 lipid in good correspondence with the lethal membrane burden for baseline toxicity (40-160 mmol kg-1 lipid). Finally, the effective lethal toxic unit (LTU50) of 1.20 was rather close to the expected value of 1. Altogether, passive dosing provided tightly controlled mixture exposure in terms of both level and composition, while ∑a, ∑Clipid eq., and ∑TU allowed baseline toxicity to be linked to mixture exposure.
Environmental Science and Technology (washington), 2013, Vol 47, p. 7020-7027