Reaction mass of ethylbenzene and m-xylene

Toxicity to terrestrial plants

Description of key information

A weight of evidence (WoE) approach was utilised as an alternative to ‘long term testing on plants’ endpoint as it is believed that the proposed study alone is unlikely to produce reliable or repeatable toxicity results due to the rapid volatilisation of xylenes from soil. QSARs supported by relevant, reliable and robust existing data from experimental studies and from literature are used to fill this endpoint.

The TLM-EqP predicted effected values for Avena sativa were 56.759 - 191.263 mg/kg soil dw for short term (14 day LL50) and 10.873 - 36.640 mg/kg soil dw for long-term effects (21 day NOELR) respectively.

The TLM-EqP predicted effected values for Brassica rapa were 36.646 - 123.490 mg/kg soil dw for short term (14 day LL50) and 7.020 - 23.657 mg/kg soil dw for long-term effects (21 day NOELR) respectively.

The Draft Screening Assessment Report (Environment Canada 2014) presents results from ESG International (2002) for the toxicity of ethylbenzene to Northern wheatgrass of 14 day LC25 of 3 mg/kg dw (coarse sandy loam). The Northern Wheatgrass value was taken by Environment Canada as the critical toxicity value for ethylbenzene toxicity to terrestrial species.

Key value for chemical safety assessment

Short-term EC50 or LC50 for terrestrial plants:

36.646 mg/kg soil dw

Long-term EC10, LC10 or NOEC for terrestrial plants:

7.02 mg/kg soil dw

Additional information

A single study to investigate the effects of o-xylene on terrestrial plants was found. This study reported a 14 day EC50 of >1 mg/kg nominal, although analytical measurements indicated that <10% nominal remained at the end of the test. The methods used in study were equivalent to OECD 208 (1984). The main deviations from this guideline were a higher clay content than recommended, and the reporting of results at 14 days post sowing, not 14 days post germination of the controls. Insufficient details are given in the paper to allow us to conclude whether the validity criteria of the test were met as results from the controls are not reported. Despite these restrictions this study does allow us to conclude that major effects on the growth of lettuce are not seen at the highest concentration tested although this is probably due to reduced exposure due to volatilisation or biodegradation. The results from this study will not be used to calculate a PNEC in the risk assessment due to these limitations.

The EU RAR (ECB 2007) discusses a single study on the toxicity of ethylbenzene to terrestrial plants via the atmosphere (Ivens, 1952). The study exposed the leaves of plants to concentrations of ethylbenzene as vapour for 1 hour and found that the NOEC was very close to the concentration which killed leaves completely. The reported EC50 are 27 g/m3 for runner bean (Phaseolus multiflorus) and 48 g/m3 for parsnip (Pastinaca sativa).

The Draft Screening Assessment Report (Environment Canada 2014) presents results from ESG International (2002) for the toxicity of ethylbenzene to Northern wheatgrass of 14 day LC25 of 3 mg/kg dw (coarse sandy loam). The Northern Wheatgrass value was taken by Environment Canada as the critical toxicity value for ethylbenzene toxicity to terrestrial species.

Due to the technical challenges of testing volatile substances, a TLM-EqP modeling framework was used to support terrestrial effect values derived experimentally and are presented as supporting studies. These data were considered reliable and comparable to experimentally derived values; however, were not used in the PNEC derivation in order to comply with ECHA FDL (2014) on using experimental data to derive PNEC. The hazard to soil organisms was assessed by using the experimental data. The TLM-EqP predicted effected values for Avena sativa were 56.759 - 191.263 mg/kg soil dw for short term (14 day LL50) and 10.873 - 36.640 mg/kg soil dw for long-term effects (21 day NOELR) respectively.

The TLM-EqP predicted effected values for Brassica rapa were 36.646 - 123.490 mg/kg soil dw for short term (14 day LL50) and 7.020 - 23.657 mg/kg soil dw for long-term effects (21 day NOELR) respectively.