Silver docosanoate

Toxicity to terrestrial plants

Description of key information

The most sensitive effects data is an EC10 of 0.13 mg/kg Ag for shoot weight in Lactuca sativa (Lettuce) from a 17 day exposure in acid washed silica sand. The physico-chemical conditions of the soil were pH 6.57, Organic Carbon <0.1% and clay <0.02% (Pillard 2011b).

Additional information

Long-term toxicity data for plants are available for seven species (Hordeum vulgare, Lactuca sativa, Lollium perenne, Lycopersicum esculentum, Phaseolus radiates, Sorghum bicolour and Triticum aestivum). Toxicity tests were undertaken in soils with a range of physico-chemical conditions.

Langdon et al. 2013 conducted toxicity tests with terrestrial plants following two procedures: ISO guideline 11269-1 using barley (Hordeum vulgare) and OECD guideline 208 using tomatoes (Lycopersicum esculentum) as the test species.The tests were conducted in eight different soils representing a wide range of soil properties (pH 3.6 – 8.0, organic carbon 0.9 – 12% and clay 1.4 – 60%). Results from leached and unleached soil treatments are reported.

The toxicity of Ag to barley (Hordeum vulgare), assessed using the inhibition of root growth test, was the least sensitive of all toxicity tests reported by Langdon et al. (2013). Overall the EC10 values for root length were found to range from 13 (Houthalen) to 176 (Millicent) mg Ag/kg in the unleached treatment and organic carbon was found to be the soil property responsible for influencing the toxicity of Ag to barley. The EC10 based on shoot length were between 2.3 mg Ag/kg (Kingaroy) and 301 mg Ag/kg (Millicent) in the unleached treatments.

Tomatoes (Lycopersicum esculentum) were more sensitive to silver than barley. EC10 values for plant height in unleached soil ranged from 4.1 (Inman Valley) to 54 (Charleston) mg Ag/kg. The toxicity of Ag to tomato appeared to be controlled by soil pH and organic carbon. EC10 values based on tomato weight were found to range from 0.7 (Inman Valley) to 58 (Port Kenny) mg Ag/kg in unleached soil.

Langdon et al. (2013) also undertook Lycopersicum esculentum studies using soils spiked with silver that were subsequently allowed to age for either one or 12 months. In all cases, the EC10 and EC50 values were significantly lower or there was no significant difference compared to those generated in soils that had been aged for one month. EC10 values for plant height in soil aged for one month ranged between 2.3 (Houthalen) and 62 mg Ag/kg (Millicent), whilst EC10 vales in soils aged for 12 months were between 7.6 mg Ag/kg (Houthalen) and 180 mg Ag/kg (Bakalava) .For biomass, the EC10 values ranged from 0.47 (Houthalen) to 108 mg Ag/kg (Port Kenny) and from 1 mg Ag/kg (Houthalen) to 253 mg Ag/kg (Port Kenny) in one and 12 months aged soils, respectively. The Aging Factors (AFs) determined in the study were found to range from 1.7 to 22 for the EC10 values and 1.3 to 2.8 for the EC50 values with an overall average AF of 2.4 (the Bordeaux EC10 AF of 22 was removed from the calculation of average value as it was considerably higher than the other values). The results indicate that after a 12-month ageing period the toxicity of Ag decreased by a factor of approximately two.

The toxicity of silver (silver nitrate) to lettuce (Lactuca sativa) was determined in acid washed silica sand (pH 6.57, organic carbon <0.1%, clay 1%) in an OECD 208 study (Pillard 2011b). The observed endpoints were emergence, survival, discoloration, malformation, shoot length, shoot wet weight and shoot dry weight. Emergence was the least sensitive endpoint measured. Growth endpoints (length, wet weight, and dry weight) were substantially more sensitive than the emergence and survival endpoints. The growth endpoints all had the same NOEC of 0.16 mg Ag/kg. Based on EC10, EC20, and EC25 values, shoot length and dry weight were the most sensitive endpoints with EC10 values of 0.14, 0.41 and 0.13 mg Ag/kg for shoot length, shoot wet weight and shoot dry weight, respectively.

Pillard (2011c) tested the toxicity of silver (as silver nitrate) to rye grass (Lolium perenne)in a test according to OECD guideline 208. Rye grass was exposed to silver nitrate in acid washed silica sand (pH 6.57, organic carbon <0.1%, clay 1%) for 18 days and the endpoints reported were emergence, survival, discoloration, malformation, shoot length, shoot wet weight and shoot dry weight. Based on the NOEC, the most sensitive endpoint was shoot length, which had a NOEC of 2.40 mg Ag /kg. Based on EC values, wet weight was the most sensitive endpoint, with an EC10, EC20, EC25 and EC50 of 0.62, 1.05, 1.36, and 5.01 (mg/kg Ag, dry weight basis), respectively.

Lee et al. (2012b) report the effects of exposure of silver (as silver nitrate) to two commercially important plant species in soil: mungbean (Phaseolus radiates) and sorghum (Sorghum bicolour). Exposures, based on nominal concentrations, were conducted in synthetic OECD soil over five days with effects on shoot and root length measured. NOECs for effects on root length were reported as 200 mg/kg dry weight and 300 mg/kg dry weight for P. radiates and S. bicolor, respectively. No effects were observed on shoot length in either P. radiatus or S. bicolor at the highest concentration of silver tested (500 mg/kg).

The impact of silver exposure (as silver nitrate) on wheat (Triricum aestivum) seedlings was determined in a three day test performed in sandy loam soil (Shtangeeva et al. 2011). A NOEC of 8.5 mg/kg dry weight was calculated from the results reported in the study.

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