The concept of chronic toxicity has caused confusion in fish toxicology because it has developed four connotations: long duration, inclusion of all life stages, low severity, and high sensitivity. To compare alternate chronic tests and expressions of test results, we extracted concentration‐response data from published life‐cycle, partial‐life‐cycle, and early life‐stage tests and derived concentration‐response relationships by nonlinear regression. The effects examined were reductions in parental survival, fecundity, hatching success, larval survival, weight of early juveniles, and weight of early juveniles per egg. On the average, the most sensitive effect was reduction in fecundity, not effects on early life stages. We also found that maximum acceptable toxicant concentrations (MATCs) corresponded to fairly high levels of effect; mean reductions at the MATC were parental survival, 20%; fecundity, 42%; hatching, 12%; larval survival, 19%; weight, 20%; and weight/egg, 35%. These results indicate that, on average, MATCs are concentrations that cause substantial effects and that MATCs estimated from early life‐stage tests are not good substitutes for life‐cycle tests. We suggest that the acute‐chronic dichotomy be abandoned in favor of tests and benchmarks based on concentration‐duration‐response dynamics.

We investigated three aspects of the use of toxicity test data for population-level risk assessment: (a) the influence of life history characteristics on vulnerability to contaminant-induced stress, (b) the importance of test data availability and (c) the influence of exploitation intensity. We quantified population-level effects of chronic contaminant exposure by coupling standard toxicity test data to matrix-type population models derived from long-term field studies of the Gulf of Mexico menhaden (Brevoortiu patronus) and Chesapeake Bay striped bass (Morone suxutilis) populations. We used statistical regressions to quantify the uncertainty inherent in using test data ranging from life cycle tests to quantitative structure-activity relationships (QSARs) to estimate effects of contaminants on the survival and reproduction parameters of the population models.We found that because of differences in life history, menhaden and striped bass differ in terms of their capacity to sustain the same level of contaminant-induced mortality. Changes in exploitation intensity affect the responses of both populations to the same level of additional contaminantinduced mortality. However, the quantitative effects of both factors are negligible compared to the : uncertainty introduced by estimating long-term effects from short-term tests or QSARs. Our results suggest that consideration of life history may be important primarily for site-specific assessments. For screening-level assessments, the substantial differences in uncertainty associated with different types of test data are of much greater concern.

The concept of chronic toxicity has caused confusion in fish toxicology because it has developed four connotations: long duration, inclusion of all life stages, low severity, and high sensitivity. To compare alternate chronic tests and expressions of test results, we extracted concentration‐response data from published life‐cycle, partial‐life‐cycle, and early life‐stage tests and derived concentration‐response relationships by nonlinear regression. The effects examined were reductions in parental survival, fecundity, hatching success, larval survival, weight of early juveniles, and weight of early juveniles per egg. On the average, the most sensitive effect was reduction in fecundity, not effects on early life stages. We also found that maximum acceptable toxicant concentrations (MATCs) corresponded to fairly high levels of effect; mean reductions at the MATC were parental survival, 20%; fecundity, 42%; hatching, 12%; larval survival, 19%; weight, 20%; and weight/egg, 35%. These results indicate that, on average, MATCs are concentrations that cause substantial effects and that MATCs estimated from early life‐stage tests are not good substitutes for life‐cycle tests. We suggest that the acute‐chronic dichotomy be abandoned in favor of tests and benchmarks based on concentration‐duration‐response dynamics.

In assessments of risks of toxic contaminants to fish populations, the endpoints of ultimate interest are the persistence, abundance, and production of populations. In this article we demonstrate a method for expressing toxicity test data obtained from full‐life‐cycle tests in terms of the same indices used to assess effects of harvesting and power‐plant cooling systems on fish populations. Our approach involves fitting the logistic concentration‐response function to chronic test data and coupling the functions obtained to a fish life‐cycle model. Confidence bands derived from the data quantify uncertainties inherent in predicting population‐level effects from (1) full‐life‐cycle test data for the species of interest, (2) extrapolation of a concentration‐response function from an acute LC50 for the species of interest, and (3) extrapolation from an acute LC50 for another species. Using rainbow trout and largemouth bass as representative species, we evaluate the relative importances of three sources of uncertainty contributing to prediction intervals for populationlevel effects. We also compare population‐level concentration‐response functions to predicted and experimentally derived maximum acceptable toxicant concentrations for five toxic chemicals.

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