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During the slow transformation of Sb2O3in soil into soluble Sb, the bioavailable Sb concentration (i.e. Sb in soil solution) will gradually increase and there will, as a consequence, not be a constant “toxic pressure” during the exposure period. As long as full equilibrium is not reached, the total Sb toxicity will be underestimated. However, the use of soluble Sb salts for toxicity testing introduces other changes in soil chemistry, besides increasing the concentration of Sb, such as increased concentrations of counter ions (e. g. chloride, sulphate) and protons. These changes in soil chemistry also have the potential to affect the observed toxic response.

At TC NES I ´07 it was concluded that the preferred exposure regime for terrestrial toxicity studies is sufficiently aged soil spiked with Sb2O3. This would ensure i) a constant Sb pore water concentration (i.e. constant toxic pressure) during the entire test period and ii) avoids toxic effects due to increased concentrations of counter ions and/or protons.

TC NES I ´07 decided that both the critical NOECs on plants (Oorts et al., 2005; 5.8 mg Sb/kg dw) and invertebrates (Kuperman et al.,2002; Phillips et al., 2002; both 58 mg Sb/kg dw) would be overruled by the results of new plant and invertebrate tests, if the latter were considered valid. Two new toxicity studies, which are both considered valid and were performed in the same Sb2O3-spiked and sufficiently aged soil, generated the toxicity data for invertebrates, plants and microrganisms that are used to derive the PNECsoil(and thereby overrule the results by Oorts et al. (2005), Kuperman et al. (2002), and Phillips et al. (2002)).

 The first of these two studies was performed by Smolders et al. (2007) and reported on the endpoints of lettuce emergence and growth (ISO 11269-2), barley root elongation (ISO 11269-1), and nitrification rate (ISO 14238). The second study was performed by Moser (2007) and reported on the endpoints of mortality and reproduction of Folsomia candida (ISO 11267).