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TERRESTRIAL PLANTS

There is a significant amount of data on the toxicity of ethanol to terrestrial plants, although results are not often expressed in a useful format for risk assessment purposes. A number of studies examined ethanol as growth stimulant or assessed end points of unknown toxicological significance. These are not reported in this summary. Only those studies showing adverse toxicological effects and clear no effect levels re reported here.

In a root growth inhibition test using alliums (allium cepa) proposed for use as a screening test for toxicity assessment of effluents, rivers etc, ethanol was found to have an EC50 value of 11800mg/l and an estimated EC10 of 789mg/l when the sets were placed in aqueous ethanol solutions. The dose response curve was relatively shallow and effectively linear over the concentration range examined. This study is used as the key for deriving a no effect level (EC10).

In a study for which basic details only are available, the toxicity towards lettuce seeds (Lactuca sativa) was reported for a large number of aliphatic alcohols and glycols, including ethanol. Measurement of toxicity was in terms of inhibition of germination. The EC50 (50% inhibition) for ethanol at 30C was found to be 117mM or 5382mg/l. The result from this study is used to derive the critical EC50 value for terrestrial plants.  Lactuca sativa germination was also examined in another study that examined the use of solvents as prospective carriers of other substances, such as herbicides, into seeds.  The study also examined peas (Pisum sativum). Seeds were treated for 24 and 44 hours with pure absolute ethanol or water as a control and the impact of this treatment on subsequent germination was assessed. The study found that ethanol inhibited germination in lettuce to about 30% of the level found in controls but there was no effect in peas. The study cannot be used in quantitative risk assessment but it does confirm that lettuce seeds are a relatively sensitive species but also that the dose response curve is very shallow and that ethanol is actually of very low toxicity to seeds.

In a study that measured the growth and respiratory response of maize seedlings (Zea mays), ethanol was found to have significant inhibitory effects. The seedlings were exposed to ethanol solutions up to 1.5% volume for a period of 9 hours. Growth of coleoptiles and roots and overall respiration was reduced by around 10% in solutions of 1000ppm (789mg/l) compared to controls. The dose response curve was however very shallow; 50% inhibition by any measure was not reached at the maximum tested dose of 15000ppm (11800mg/l).

In a study to examine the effects on growth of oat seedlings (Avena sativa) of exposure to ethanol solution through the roots, seedlings were exposed to ethanol solution at levels of 0.2% and 0.3% under different combinations of light and dark and co-exposure to CO2. A mixed response was seen with growth of both mesocotyls and coleoptiles depressed by ethanol exposure during the first 3 days pretreatment but with mesocotyl promoted by around 60 -70% during further exposure under darkness but a lesser depression of 10 -20% of coleoptiles with exposure to ethanol. With this mixed result, interpretation of the information is unclear.

Overall, ethanol can be considered as of very low toxicity to plants based on this result. This is supported by the fact that ethanol is recommended as a potential vehicle in OECD guideline 227 on assessment of vegetative vigour.

OTHER TERRESTRIAL SPECIES

Based on the use pattern for this substance and the fact that it is both readily biodegradable and photo-reactive in the atmosphere, direct and indirect exposure of soil is unlikely. Based on this low likelihood of exposure and the fact that good data is available for the aquatic compartment, the equilibrium partitioning method is considered adequate to estimate the toxicity to soil macro and micro organisms along with terrestrial arthropods based using the existing aquatic toxicity hazard data as a starting point and this end point is considered complete. There is some test data available but the results from these studies cannot be converted into a useable format for risk assessment purposes.

Based on the use pattern for this substance, and considering its ready biodegradability and photo-reactive nature,, direct and indirect exposure of birds is unlikely. There is also a sufficient mammalian dataset on this substance to allow reliable extrapolation to predict within acceptable levels of reliability the toxicity to avian species if required.