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The effects of metal-contaminated sediment extracts and a reference toxicant (zinc sulfate) were determined by examining the developmental morphology, growth and mortality of exposed fathead minnow (Pimephules promelus) and frog (Xenopus luevis) embryos. Sediments from two contaminated stream sites were extracted with reconstituted culture water at various pH values for 24 h. Developmental toxicity tests were performed using the frog embryo teratogenesis assay-Xenopus (FETAX) protocol. The results suggest that Zn was the major developmental toxicant in the sediment extracts. The measured Zn concentration in the sediment extracts that caused malformation in 50% of the fish embryos (EC50) was 0.5 t o 1.4 mg/L (normalized to 100 mg/L hardness). EC5O values for the reference toxicant tests were 0.6 and 0.8 mg/L Zn. The frog embryo EC50 for the extracts ranged from 2.2 to 3.6 mg/L Zn and was 3.6 mg/L Zn in the reference toxicant test. In 67% of the tests, malformation was a more sensitive endpoint than growth inhibition. Mortality was the least sensitive endpoint, that is, the LC50s in the reference toxicant tests were 3.6 mg/L Zn for the fathead minnow and 34.5 mg/L for the frog. The extraction procedure may be useful for determining potential toxicity in the event metals are leached from aquatic sediments by dredging or acidification.

: We present an ecological risk assessment methodology at the watershed level for freshwater ecosystems. The major component is a pollutant transport and fate model (a modified EUTROMOD) with an integrated uncertainty analysis utilizing a two‐phase Monte Carlo procedure. The uncertainty analysis methodology distinguishes between knowledge uncertainty and stochastic variability. The model assesses the ecological risk of lentic (lake) ecosystems in response to the stress of excess phosphorus resulting in eutrophication. The methodology and model were tested on the Wister Lake watershed in Oklahoma with the lake and its trophic state as the endpoint for ecological risk assessment. A geographic information system was used to store, manage, and manipulate spatially referenced data for model input.

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A new bioassay method for determining the effects of environmental contaminants on populations of benthic macroinvertebrates is described. Colonized Hester-Dendy samplers were transported from a natural stream to artificial streams and exposed to industrial wastewater. Species diversity, number of taxa, and density of the aquatic organisms were measured before and after selected time intervals of exposure. A 30 and a 32-day continuous-flow exposure test with the benthic macroinvertebrates showed that activated sludge treated petroleum refinery wastewater caused a greater decrease in species diversity than the sequential activated sludge-dual media-activated carbon treated effluent. The effect upon number of taxa and mean density of individuals was even greater. This procedure permitted exposure of several species of aquatic invertebrates to the test solution and thus measured the effect upon pollution-sensitive and tolerant organisms.

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No abstract

The effects of metal‐contaminated sediment extracts and a reference toxicant (zinc sulfate) were determined by examining the developmental morphology, growth and mortality of exposed fathead minnow (Pimephales promelas) and frog (Xenopus laevis) embryos. Sediments from two contaminated stream sites were extracted with reconstituted culture water at various pH values for 24 h. Developmental toxicity tests were performed using the frog embryo teratogenesis assay‐Xenopus (FETAX) protocol. The results suggest that Zn was the major developmental toxicant in the sediment extracts. The measured Zn concentration in the sediment extracts that caused malformation in 50% of the fish embryos (EC50) was 0.5 to 1.4 mg/L (normalized to 100 mg/L hardness). EC50 values for the reference toxicant tests were 0.6 and 0.8 mg/L Zn. The frog embryo EC50 for the extracts ranged from 2.2 to 3.6 mg/L Zn and was 3.6 mg/L Zn in the reference toxicant test. In 67% of the tests, malformation was a more sensitive endpoint than growth inhibition. Mortality was the least sensitive endpoint, that is, the LC50s in the reference toxicant tests were 3.6 mg/L Zn for the fathead minnow and 34.5 mg/L for the frog. The extraction procedure may be useful for determining potential toxicity in the event metals are leached from aquatic sediments by dredging or acidification.