Abstract : Toxicity testing remains largely in the same position as it was 50 years ago, i.e. measuring the ef
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Abstract : Toxicity testing remains largely in the same position as it was 50 years ago, i.e. measuring the effect of increasing doses of toxicants on populations at fixed times of exposure. Certainly, endpoints other than lethality are tried in ecotoxicology, but the underlying approach is always the same – to estimate the median (or other percentile) effect dose or concentration at a given time. However useful this information may be, it ignores the fact that internal doses are time-dependent and therefore the values of the estimated endpoints vary with the exposure time. Besides, what really matters is the survival of populations in time after repeated exposure of several generations to a toxicant. Two recent developments that tackle these issues are presented here: time-to-effect (TTE) bioassays and population growth rates. TTEs address the first deficiency, allowing the estimation of percentile effects for doses at variable exposure times by effectively integrating these two essential parameters in a single test. Data from a TTE take the form of a matrix of measured endpoints vs time, which can be analysed using simple models. Moreover, as the estimated median effective times (ET50) are related to the doses, standard L(D)C50s can be obtained directly from that relationship, and such median values can be used to predict any level of effect for any dose at any time using appropriate modelling. The second issue is crucial for the protection of species and the management of natural resources. Indeed, species reproduce while being unaware of their exposure to toxic pollutants, and the rate of growth of their populations will determine whether they survive or eventually go extinct. Procedures for measuring this rate in laboratory cultures were determined time ago, but so far have not attracted sufficient attention in ecotoxicology. The implementation of both approaches needs to be discussed. - Slides
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