Forty-eight hours after fertilization, fathead minnow (Pimephales promelas) eggs were exposed to the synthetic estrogen 17alpha-ethinylestradiol (EE2) at nominal concentrations of 0.32 and 0.96 ng/L and measured concentrations of 3.5, 9.6, and 23 ng/L. The fish were observed through the larval, juvenile, and adult stages. Growth, secondary sex characteristics, the liver somatic index, the gonadosomatic index, and fecundity were examined after several lengths of exposure. No significant changes were seen in fry or juvenile growth from 8 to 30 days posthatch (dph). An increase in the ovipositor index (a female secondary sex characteristic) was the most sensitive early response at 60 dph and was seen in fish exposed to EE2 concentrations > or = 3.5 ng/L. Continuation of the EE2 exposure until 150 dph, through maturation and reproduction, allowed measurement of two sensitive end points: decreased egg fertilization and sex ratio (skewed toward females), both of which were significantly affected at the lowest EE2 concentration tested, 0.32 ng/L. The next most sensitive end point was demasculinization (decreased male secondary sex characteristic index) of males exposed to an EE2 concentration of 0.96 ng/L. The effects of low concentrations of EE2 (0.32 and 0.96 ng/L) were manifested in male fish (decreased male sex characteristics and reduced egg fertilization success), whereas female fish showed no changes in the gonadosomatic index. Exposure to higher EE2 concentrations negatively affected females, as shown by a reduced gonadosomatic index at 150 dph in fish exposed to > or =3.5 ng/L EE2. Although there were some end points that showed changes at 60 dph, the reproductive end points and external sex characteristics measured in mature fish at 150 dph were more sensitive, with response thresholds of EE2 ranging from 0.32 to 0.96 ng/L. The concentrations of EE2 that negatively affected fathead minnows were similar to or lower than those detected in many municipal wastewater effluents. In conclusion, life-cycle exposure of fathead minnows proved to be a very sensitive bioassay, and responses were seen at concentrations of less than 1 ng/L, which are environmentally relevant concentrations of EE2.
The activity of erythrocyte δ-amino levulinic acid dehydratase (ALA-D) of fish is easily measured under a variety of experimental conditions. Exposure of rainbow trout (Salmo gairdneri), brook trout (Salvelinus fontinalis), goldfish (Carassius auratus), and pumpkinseeds (Lepomis gibbosus) to lead consistently inhibited ALA-D within 2 wks at concentrations as low as 10, 90, 470, and 90 μg/ℓ, respectively. In rainbow and brook trout these concentrations were closely related to the published minimum effective concentrations causing sublethal harm. There was a significant linear relationship between ALA-D activity and log of blood lead concentration, between ALA-D activity and log of lead in water, and between blood lead and lead in water. Near lethal exposures to cadmium, copper, zinc, and mercury did not significantly inhibit ALA-D activity. Recovery of ALA-D activity of rainbow trout after transfer from 120 μg/ℓ lead to clean water occurred in 8 wk. This enzyme provides fast, consistent, specific, and sensitive estimates of lead concentrations causing sublethal harm to fish and may help to relate sources of lead to degree of exposure of fish populations in the field. Key words: lead, sublethal toxicity, fish, indicator enzyme, δ-amino levulinic acid dehydratase
Contaminant concentrations in aquatic ecosystems vary spatially and temporally, SOthat surveillance data exhibit a log-normal distribution; i.e., the majority of measurements are low but a few are quite high. These data are best characterized by geometric means. Contaminants that are taken up quickly but excreted slowly should accumlate in fish at concentrations that reflect the highest exposure rather than the geometric mean exposure. To confirm this prediction, blood lead concentrations of rainbow trout were measured after 20-d exposures to concentrations of waterborne lead that fluctuated about a fixed geometric mean. Four levels of exposure variability were used. A lead exposure characterized by wide fluctuations was expected to cause greater lead uptake by trout than the equivalent exposure with less variability. Lead accumulation was best described by the following equation: loglo blood lead concentration (pglL) = 0.814 + 0.999 loglo waterborne lead (pglL) + 1.335 x standard deviation of loglo waterborne lead. Increasing lead concentrations and increasing variability of waterborne concentrations increased lead accumulation by trout. These results were accurately predicted by a simple one-compartment model of contaminant kinetics in fish. Applying this model to other contaminants and to hypothetical exposure regimes demonstrated that high depuration rate constants increase the importance of exposures over the previous 24 h. This anaylsis also demonstrated that arithmetic mean exposures were a better way of describing contaminant accumulation by fish than were geometric mean exposures. Therefore, brief (24 h) violations of water quality criteria may cause a greater toxicity to fish than would be expected from simple estimates of the geometric mean concentrations in water. Water quality surveillance programs must be designed to accurately describe both contaminant variance and the arithmetic mean concentration.
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