Many contaminated sites contain a variety of toxicants. Risk assessment and the development of water quality criteria therefore require information on the interactive effects among toxicants in such mixtures. Interactions between metals are relatively well studied, but little is known about interactions between metals and hydrocarbons. This study investigated the interaction between phenanthrene and zinc in the sheepshead minnow Cyprinodon variegatus. Interaction studies were performed with 7-day-old minnows in 96-h bioassays with zinc and phenanthrene at a fixed ratio and with varying proportions of zinc and phenanthrene. Mixture toxicity was quantified with the toxic unit, additive index, and excess function methods. All three methods generally indicated an antagonistic interaction between phenanthrene and zinc, though the results also provide some evidence for a synergistic interaction at low toxicant levels or at specific phenanthrene-to-zinc ratios. Short-term uptake experiments were conducted to determine if the strong antagonistic interaction observed when zinc and phenanthrene were present at 50% of their LC50 values was due to effects of zinc and phenanthrene on each other's uptake. Significantly less 65Zn uptake occurred in the presence of phenanthrene than in its absence. In contrast, zinc did not appear to affect the uptake of 14C-phenanthrene.http://link. springer-ny.com/link/service/journals/00244/bibs/37n2p251.++ +html
Resistance heritability (the additive genetic variance out of the total phenotypic variance, signifying a population's potential to genetically adapt to detrimental levels of contamination) was quantified in the sheepshead minnow (Cyprinodon variegatus). Heritability was estimated for tolerance to individual contaminants (phenanthrene, zinc) and to contaminant mixtures (phenanthrene plus zinc, and a complex mixture with three metals and three polycyclic aromatic hydrocarbons). Estimates were obtained from resemblances between relatives, both parent-offspring pairs, and families of sibs and half-sibs. Heritabilities determined from parent-offspring regressions averaged only 0.08 (scale, 0-1), whereas resemblance among full sibs yielded heritabilities averaging 0.85. The half-sib analysis yielded heritabilities of -0.01 (sire component) and 0.77 (dam component). This pattern in the magnitude of heritabilities indicates that heritabilities for the resistance of C. variegatus to these chemicals are low (with the high resemblances among sibs being due to common environmental and dominance genetic variation rather than additive genetic variation). The parent-offspring regressions provide evidence that heritabilities may be lower if more contaminants are involved. Our results mean, then, that C. variegatus in contaminated environments is not likely to become resistant to these contaminants very rapidly, and that resistance may develop even more slowly as more contaminants become involved.
Resistance heritability (the additive genetic variance out of the total phenotypic variance, signifying a population's potential to genetically adapt to detrimental levels of contamination) was quantified in the sheepshead minnow (Cyprinodon variegatus). Heritability was estimated for tolerance to individual contaminants (phenanthrene, zinc) and to contaminant mixtures (phenanthrene plus zinc, and a complex mixture with three metals and three polycyclic aromatic hydrocarbons). Estimates were obtained from resemblances between relatives, both parent-offspring pairs, and families of sibs and half-sibs. Heritabilities determined from parent-offspring regressions averaged only 0.08 (scale, 0-1), whereas resemblance among full sibs yielded heritabilities averaging 0.85. The half-sib analysis yielded heritabilities of -0.01 (sire component) and 0.77 (dam component). This pattern in the magnitude of heritabilities indicates that heritabilities for the resistance of C. variegatus to these chemicals are low (with the high resemblances among sibs being due to common environmental and dominance genetic variation rather than additive genetic variation). The parent-offspring regressions provide evidence that heritabilities may be lower if more contaminants are involved. Our results mean, then, that C. variegatus in contaminated environments is not likely to become resistant to these contaminants very rapidly, and that resistance may develop even more slowly as more contaminants become involved.
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