Browsing by Subject "Toxicity Tests"

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    Evaluating Variation in Terrestrial Plant Toxicity Tests
    (2008-04-25T14:28:35Z) Kurnath, Lindsey
    The Office of Pesticide Programs of the U.S. EPA conducts the national pesticide review process, under authority granted by FIFRA. Ecological risk assessments are performed on many different organisms to identify ecosystem-level impacts. Among these organisms are non-target terrestrial plants, which are specifically used to understand the risk to plants exposed to spray drift or runoff. Guidelines were developed from field-based methods rather than a traditional interlaboratory precision analysis, thus the natural variation in measurement endpoints for terrestrial plant toxicity tests has not been established. Recognizing the inherent sensitivity of the assessments currently conducted helps the U.S. EPA better understand the implications of the pesticide review process. The following report aims to determine the natural variability of the response endpoints (i.e. emergence, plant length, plant weight) for these studies. This project involved the development and design of two databases in MS Access, the selection of control data from existing studies, an analysis of the among and within laboratory variability in response measures, and a trend analysis for environmental conditions. The findings supported the currently accepted coefficient of variation (CV) of 20% used by the U.S. EPA. All seedling emergence studies in all laboratories had average CV values of less than 40% and laboratories who were responsible for conducting a majority of the studies exhibited CV values less than 20%. Similar patterns were observed in the length data from the vegetative vigor studies. The weight data presented variation that was often greater than the expected 20% even for the most frequently tested species. The most data was available for corn and soybean plants and these species were also the least variable. The historical value of a 20% coefficient of valuation seems to be, on average, an acceptable value for the terrestrial plant toxicity tests used for pesticide registration. The data of this report indicates particular species, specifically corn and soybean, tend to have CV values closer to 10%. The addition of more data and a more sophisticated analysis into the underlying causes of variation could reveal a lower CV across all species.
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    Silver toxicity across salinity gradients: the role of dissolved silver chloride species (AgCl x ) in Atlantic killifish (Fundulus heteroclitus) and medaka (Oryzias latipes) early life-stage toxicity.
    (Ecotoxicology, 2016-08) Matson, Cole W; Bone, Audrey J; Auffan, Mélanie; Lindberg, T Ty; Arnold, Mariah C; Hsu-Kim, Heileen; Wiesner, Mark R; Di Giulio, Richard T
    The influence of salinity on Ag toxicity was investigated in Atlantic killifish (Fundulus heteroclitus) early life-stages. Embryo mortality was significantly reduced as salinity increased and Ag(+) was converted to AgCl(solid). However, as salinity continued to rise (>5 ‰), toxicity increased to a level at least as high as observed for Ag(+) in deionized water. Rather than correlating with Ag(+), Fundulus embryo toxicity was better explained (R(2) = 0.96) by total dissolved Ag (Ag(+), AgCl2 (-), AgCl3 (2-), AgCl4 (3-)). Complementary experiments were conducted with medaka (Oryzias latipes) embryos to determine if this pattern was consistent among evolutionarily divergent euryhaline species. Contrary to Fundulus data, medaka toxicity data were best explained by Ag(+) concentrations (R(2) = 0.94), suggesting that differing ionoregulatory physiology may drive observed differences. Fundulus larvae were also tested, and toxicity did increase at higher salinities, but did not track predicted silver speciation. Alternatively, toxicity began to increase only at salinities above the isosmotic point, suggesting that shifts in osmoregulatory strategy at higher salinities might be an important factor. Na(+) dysregulation was confirmed as the mechanism of toxicity in Ag-exposed Fundulus larvae at both low and high salinities. While Ag uptake was highest at low salinities for both Fundulus embryos and larvae, uptake was not predictive of toxicity.