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Ecological Risk Assessment
Published in Lorris G. Cockerham, Barbara S. Shane, Basic Environmental Toxicology, 2019
Donald J. Rodier, Maurice G. Zeeman
Effects other than mortality can be expressed as an EC50. This is basically an effective concentration for which some effect was calculated to affect 50% of the test organisms. Commonly encountered EC50s are an EC50 for growth and an EC50 for immobilization (i.e., the organisms appear paralyzed). For all practical purposes, immobilization can be considered identical to mortality since immobilized zooplankton are likely to be readily preyed upon by predators. For sublethal effects, the results are often expressed as a maximum acceptable toxicant concentration (MATC). The number is ascertained by statistically determining the highest no observable effect concentration (NOEC) and the lowest observable effect concentration (LOEC). The MATC is usually calculated as the (geometric) mean of the NOEC and the LOEC.
Reproduction
Published in Alan G. Heath, Water Pollution and Fish Physiology, 2018
Originally, most of the studies on pollutant effects on reproduction were for the purpose of estimating a maximum acceptable toxicant concentration (MATC), which could then be used in establishing water quality criteria. The concept of the MATC is based on the idea that certain stages in the life cycle will be more sensitive than others. Thus, breeding members of a population of fish in the laboratory were exposed to a graded series of concentrations of the toxicant and this was maintained through two generations. The MATC is defined as the threshold between the concentration where a measured effect is observed and the next lower one where no significant effect is observed.
Environmental Impact Metrics
Published in John Andraos, Synthesis Green Metrics, 2018
Chronic toxicity looks at cumulative adverse effects following continuous exposure to a chemical substance over an extended period of time, often measured in months or years. Quantitative measures of chronic toxicity are: (a) no observed effects concentration (NOEC); (b) lowest observed effects concentration (LOEC); (c) maximum acceptable toxicant concentration (MATC); (d) predicted no effects concentration (PNEC); and (e) acute to chronic ratio (AR), which is determined as AR=LC50(inhal)/MATC. See LC50(inhal); LD50(dermal) (Chapter 11); LD50(oral).
Assessment of risks to listed species from the use of atrazine in the USA: a perspective
Published in Journal of Toxicology and Environmental Health, Part B, 2021
Philip N Smith, Kevin L Armbrust, Richard A. Brain, Wenlin Chen, Nika Galic, Lula Ghebremichael, Jeffrey M Giddings, Mark L Hanson, Jonathan Maul, Glen Van Der Kraak, Keith R Solomon
In discussing endpoints for assessing potential effects on listed species, USEPA guidance (USEPA 2020e) suggested that, where robust data sets of toxicity for animals or plants are available, the 5th centile of a Species Sensitivity Distribution (SSD) could be used as a point of departure for extrapolation of data on LD50s or LC50s to very small levels of mortality or inhibition of growth. The use of a 5th centile species from a SSD is a reasonable worst case for a sensitive species but there are no data indicating that listed species are inherently more sensitive to a chemical than other species; in fact the opposite has been shown to be true for plants (Christl et al. 2018). Other approaches to ERA have used the surrogate 5th centile species and generated concentration- or dose-response curves based on an average slope for the curve to extrapolate to untested species (Aldenberg, Jaworska, and Traas 2002; Clemow et al. 2018; Luttik and Aldenberg 1997; Moore et al. 2014). When there are not enough data for an SSD, USEPA (USEPA 2020e) has recommended that the toxicity value for the most sensitive species be used as a criterion for assessment. If only a few species have been tested, this might introduce uncertainty and result in an ERA that is not protective enough. While it is tempting to apply a large uncertainty factor or extrapolate the dose-response or concentration-response relationship into a realm of statistical uncertainty, this ignores common knowledge that all chemicals have thresholds below which they have no effect. This also ignores the fact that, at small doses or exposures, many substances have stimulatory or “wholly beneficial” effects (as described in USEPA 2020e) through the phenomenon of hormesis (Calabrese 2010). For these reasons, extrapolation beyond the no-observed-adverse-effect concentration (NOAEC) or dose-level, NOAEL) or the Maximum Acceptable Toxicant Concentration (MATC; where this has been estimated from the geometric mean of the NOAEC and LOAEC) is inappropriate.