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Ecotoxicological information

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Three studies of acute toxicity to earthworms are available: each includes testing exposure by contact with wetted filter paper and exposure via soil. The lowest EC50 value arising from these studies is that reported by Lee, Yoon and An (2015) for Perionyx excavatus in artificial soil (made with 10% peat moss having a 95% organic matter content): 72h EC50 = 826 mg MTBE/kg dry soil.

 

Three studies of short-term toxicity to higher plants are available: unfortunately two monitored seed germination and post-emergence growth over only 5 days, much shorter than the relevant OECD test guideline requires and neither study is considered reliable for use in assessment. (Although Dodd and Addison, 2010 reported 5-day EC50s for parameters of lettuce seedling germination and growth of 81-127 mg MTBE/kg dry soil, this was not supported by a study of An and Lee, 2008 where for 7 different food crop species, including 3 dicotyledonous species listed alongside lettuce in Annex 2 of the OECD 208 guideline, the lowest 5-day LC50 was considerably higher at 680 mg/kg dry soil). The third study examined effects of MTBE exposure on the growth of white corn, Zea mays L (Ismail et al., 2012), but its report gives insufficient information to transcribe the dose information into a dose per unit of soil.

 

One reliable study of long-term toxicity to terrestrial organisms is available: Dodd and Addison, 2010 studied survival and reproduction in Collembola species (springtails). For the most sensitive of 3 species tested, Onychiurus folsomi, a 35-day NOEC for reproduction of 156 mg/kg dry soil was determined in sandy loam soil with a low organic matter content (1.14%): all other NOECs (across the 3 springtail species in OECD 207 artificial soil, plus O. folsomi tested also in sandy loam and silt loam) were within the range 305-620 mg MTBE/kg dry soil.