Fathead minnows (Pimephales promelas) were exposed to 17 μg Cu∙L−1 or 6 μg Cd∙L−1 in synthetic soft water in the presence of competing ligands. Measured gill metal concentrations correlated with free metal ion concentrations, not with total metal. Langmuir isotherms were used to calculate conditional metal–gill equilibrium constants and the number of binding sites for each metal. Log KCu-gill was estimated to be 7.4 and the number of Cu binding sites on a set of gills (70 mg, wet weight) was ~2 × 10−10 mol (~30 nmol∙g wet weight−1). Log KCd-gill was ~8.6, and the number of Cd binding sites on minnow gills was ~2 × 10−10 mol (~2 nmol∙g wet weight−1). Stability constants for H+ and Ca interactions at metal–gill binding sites and for metal interactions with dissolved organic carbon (DOC) were estimated using these metal–gill constants. All stability constants were entered into the MSNEQL+ aquatic chemistry program, to predict metal accumulation on fish gills using metal, DOC, and Ca concentrations, and water pH. Calculated metal accumulation on gills correlated well with measured gill metal concentrations and with LC50 values. Our approach of inserting biological data into an aquatic chemistry program is useful for modelling and predicting metal accumulation on gills and therefore toxicity to fish.

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Kluyvera ascorbata SUD165 and a siderophore-overproducing mutant of this bacterium, K. ascorbata SUD165/26, were used to inoculate tomato, canola, and Indian mustard seeds which were then grown in soil for 25-42 days in the presence of either nickel, lead, or zinc. The parameters that were monitored included plant wet and dry weight, protein and chlorophyll content in the plant leaves, and concentration of heavy metal in the plant roots and shoots. As indicated by a decrease in the measured values of these parameters, in all instances, plant growth was inhibited by the presence of the added metal. Both bacterial strains were effective, although not always to a statistically significant extent, at relieving a portion of the growth inhibition caused by the metals. In most cases, the siderophore overproducing mutant K. ascorbata 165/26 exerted a more pronounced effect on plant growth than did the wild-type bacterium K. ascorbata SUD165. The data suggest that the ability of these bacteria to protect plants against the inhibitory effects of high concentrations of nickel, lead, and zinc is related to the bacteria providing the plants with sufficient iron.

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Adult fathead minnows (Pimephales promelas) were exposed to 17 g Cu∙L−1 or 6 g Cd∙L−1 for 2 to 3 h in synthetic softwater solutions at pH 6.2 containing either naturally-occurring, freeze-dried dissolved organic carbon (DOC) or synthetic ligands such as EDTA. After exposures, gills were assayed for bound Cu or Cd. As a first approximation, lake of origin or molecular size fraction of DOC did not influence Cu binding to gills, while DOC concentration did. DOC concentrations ≥4.8 mg∙L−1 prevented Cu from accumulating on fathead gills. At the relatively low concentrations used, neither Cu nor Cd interfered with binding of the other metal on gills, suggesting different gill binding sites. Cadmium accumulation on gills was more sensitive to increased concentrations of Ca and H+ than was Cu. Surprisingly, Cd bound to gills to the same or greater extent than did Cu: for synthetic ligands, Cd binds less well than Cu. This result corroborates previously published observations that Cd, unlike Cu, is taken up at gills through high affinity Ca channels. Accumulation of Cd on fish gills was never associated with 14C-labelled EDTA or 14C-citrate, indicating that free metal interacts with the gill while metal–ligand complexes usually do not.

Abstract-Phenanthrene (PHE) undergoes a significant increase in toxicity after exposure to simulated or natural sunlight in aqueous media, coincident with the appearance of PHE photoproducts. To investigate whether the primary photoproduct of PHE, 9,10-phenanthrenequinone (PHEQ), contributes to the increased hazards of solutions containing photomodified PHE, toxicity assays were conducted using the marine bacteria Photobacterium phosphoreum and the aquatic plant Lemna gibba (duckweed). Photobacterium phosphoreum was exposed to PHE, PHEQ, a photomodified PHE mixture containing known amounts of PHE and PHEQ (pmPHE), and a mixture mimicking the amounts of PHE and PHEQ in the pmPHE mixture. The bacteria were found to be equally sensitive to PHE in simulated solar radiation (SSR, a light source with a visible light : UVA : UVB ratio similar to that of sunlight) or darkness, with an EC50 of 0.53 mg/L. In both darkness or SSR, solutions containing PHEQ (with or without PHE) all exhibited an EC50 of 0.06 to 0.10 mg/L based on PHEQ concentrations, indicating that PHEQ was the primary active component of the pmPHE mixture. Lemna gibba was tested in SSR and visible light with PHE, PHEQ, and the pmPHE mixture. The calculated EC50 for PHE was 3.5 mg/L in SSR and 10.8 mg/L in visible light, showing that the presence of UV radiation in the SSR source increased the phytotoxicity of PHE. Strikingly, PHEQ was much more toxic to L. gibba than PHE in a light-independent manner (an EC50 of 0.53 and 0.57 mg/L PHEQ in dark and SSR, respectively). Thus, for both P. phosphoreum and L. gibba the major photooxidation product of PHE in SSR, PHEQ, is the more toxic of the two chemicals.