title: Bioavailability models for predicting acute and chronic toxicity of zinc to algae, daphnids, and fish in natural surface waters.
abstract: Bioavailability models predicting acute and/or chronic zinc toxicity to a green alga (Pseudokirchneriella subcapitata), a crustacean (Daphnia magna), and a fish (Oncorhynchus mykiss) were evaluated in a series of experiments with spiked natural surface waters. The eight selected freshwater samples had varying levels of bioavailability modifying parameters: pH (5.7-8.4), dissolved organic carbon (DOC, 2.48-22.9 mg/L), Ca (1.5-80 mg/L), Mg (0.79-18 mg/L), and Na (3.8-120 mg/L). In those waters, chronic zinc toxicity (expressed as 10% effective concentrations [EC10]) varied up to 20-fold for the alga (72-h EC10 from 27.3 to 563 microg Zn/L), and approximately sixfold for the crustacean (21-d EC10 from 59.2 to 387 microg Zn/L), and fivefold for the fish (30-d LC10, lethal concentration for 10% of the organisms, from 185 to 902 microg Zn/L). For P. subcapitata a refined bioavailability model was developed by linking an empirical equation, which predicts toxicity expressed as free Zn2+ activity as a function of pH, to the geochemical speciation model WHAM/Model V. This model and previously developed acute and/or chronic biotic ligand models for D. magna and 0. mykiss generally predicted most effect concentrations by an error of less than a factor of two. In waters with pH > 8, however, chronic toxicity to D. magna was underestimated by a factor 3 to 4. Based on the results of this validation exercise and earlier research, we determined applicability ranges for pH (6-8) and Ca (5-160 mg/L) in which all three developed models are valid. Within these ranges, all three models may be considered useful tools for taking into account bioavailability in regulatory assessments of zinc.
authors.affiliation: Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, Jozef Plateaustraat 22, B-9000 Gent, Belgium. karel.deschamphelaere@ugent.be
authors.forename: Karel A C
authors.initials: KA
authors.lastname: De Schamphelaere
authors.forename: Stephen
authors.initials: S
authors.lastname: Lofts
authors.forename: Colin R
authors.initials: CR
authors.lastname: Janssen
mesh_terms: D000818:Animals; D001682:Biological Availability; D003621:Daphnia / Q000187:drug effects* / Q000378:metabolism; D056890:Eukaryota / Q000187:drug effects* / Q000378:metabolism; D005399:Fishes / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D018570:Risk Assessment; D023382:Toxicity Tests, Acute / Q000379:methods; D036401:Toxicity Tests, Chronic / Q000379:methods; D014867:Water / Q000737:chemistry*; D014873:Water Pollutants / Q000633:toxicity; D015032:Zinc / Q000633:toxicity*
chemical_list: D014873:Water Pollutants; D014867:Water; D015032:Zinc