title: Baseline toxic mixtures of non-toxic chemicals: "solubility addition" increases exposure for solid hydrophobic chemicals.
abstract: This study addresses the question whether hydrophobic organic chemicals exerting no toxicity at their solubility limit (saturation) can form a toxic mixture. Spiking methods generally do not allow testing exactly at saturation without introducing microcrystals. Passive dosing was thus applied to test the acute toxicity of several high melting point PAHs and their mixtures at the respective saturation levels to aquatic and terrestrial invertebrates. With the aquatic Daphnia magna, anthracene, chrysene, and benzo(a)pyrene resulted in no or limited acute toxicity (0-20%), whereas binary and tertiary mixtures of these resulted in significant acute toxicity (70-88%). Toxicity of PAHs and their mixtures could be fitted with one (sum) chemical activity-response curve in accordance with a similar mode of toxic action (i.e., concentration addition). The effective chemical activity (Ea-50) of 0.029 and the effective concentration on a lipid basis (EC(lipid, eq.)-50) of 95.7 mM were well within the range for baseline toxicity. Similar mixtures showed less toxicity to the terrestrial Folsomia candida due to steady-state body-burdens being below equilibrium partitioning levels. The results of the present study raise questions about the focus of risk assessment schemes and toxicity testing guidelines on individual substances, since apparently non-toxic chemicals might become toxic in a mixture.
authors: Department of Environmental Science, Aarhus University, Frederiksborgvej 399, PO Box 358, 4000 Roskilde, Denmark.
authors: Kilian E C
authors: KE
authors: Smith
authors: Stine N
authors: SN
authors: Schmidt
authors: Nathalie
authors: N
authors: Dom
authors: Ronny
authors: R
authors: Blust
authors: Martin
authors: M
authors: Holmstrup
authors: Philipp
authors: P
authors: Mayer
mesh_terms: D000818:Animals; D003621:Daphnia; D004347:Drug Interactions; D008055:Lipids / Q000737:chemistry; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis / Q000737:chemistry / Q000633:toxicity*; D011786:Quality Control; D012995:Solubility; D023382:Toxicity Tests, Acute
chemical_list: D008055:Lipids; D011084:Polycyclic Aromatic Hydrocarbons