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Toxicity to terrestrial plants

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Description of key information

Based on the concentration that produced a 10% effect (EC10), for lettuce the shoot dry weight was the most sensitive endpoint with an EC10 value of 0.13 mg Ag/kg. For ryegrass, shoot length was the most sensitive with an EC10 value of 0.61 mg Ag/kg.

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Additional information

The plant emergence, survival and growth toxicity testing (AECOM 2011b and 2011c) was conducted to comply with the OECD Guidelines for the Testing of Chemicals Method 208: Terrestrial Plant Test – Seedling Emergence and Seedling Growth Test. This test was conducted with two test species, lettuce and ryegrass and used a test media of acid washed coarse silica sand.

As stated in ECHA R7c guidance "The updated OECD guideline is designed to assess the potential effects of substances on seedling emergence and growth. Therefore, it is specific to a part of the plants life-cycle and does not cover chronic effects or effects on reproduction, however it is assumed to cover a sensitive stage in the life-cycle of a plant and therefore data obtained from this study have been used as estimates of chronic toxicity."

The concentrations of Ag in the test treatments were all measured and ranged from <0.02 to 26.3 mg Ag/kg. The endpoints measured were emergence, survival, shoot length, shoot wet weight and shoot dry weight. For both test species, the measures of emergence and survival were considerably less sensitive than the other measures. Based on the concentration that produced a 10% effect (EC10), for lettuce the shoot dry weight was the most sensitive endpoint with an EC10 value of 0.13 mg Ag/kg. For ryegrass, shoot length was the most sensitive with an EC10 value of 0.61 mg Ag/kg.

The methodology for the seedling emergence, growth and survival outlined in these reports is consistent with the OECD Guidelines for the Testing of Chemicals Method 208. It should be noted however that the use of coarse silica sand as a test media, although compliant with the OECD method, results in a dataset that should be considered as a “worst-case scenario”. This is due to the low degree of Ag partitioning that will be observed in this media and the large influence of various artifacts that are results of spiking with soluble metal salts. An additional concern relating to the results presented for these test species is summarised below:

• The concentration of Ag was measured in the test media at the completion of the study. This was done by combining the sand from each of the replicates into one sample. One subsample was then removed from the bulk sample to determine the Ag concentration. The measured concentrations of Ag in the test treatments were found to be between 47% and 88% of the expected nominal concentration. This large variation between the measured and expected Ag concentrations raises concerns relating to the homogeneity of the Ag in the samples. Due to this, the analysis of replicate samples from each treatment would have been preferable. In addition, no recovery information is provided to validate the digestion and analysis of the soil samples.

Two other studies are included in the dossier as supporting studies (Fjallborg et al 2006 and Hirsch 1998) however, they are considered less reliable than AECOM 2011b and 2011c as Fjallborg et al 2006 is conducted without the presence of soil, and Hirsch 1998 used a non-standard method and non-standard substrate.

A testing proposal was submitted to ECHA for the chronic testing of two plant species in eight soils, after leaching and aging of the spiked soil. There were no objections to the testing proposal by ECHA or the Member State’s Competent Authorities and data will be added to this dossier once results are available.