Styrene

Toxicity to terrestrial plants

Description of key information

No data on chronic terrestrial toxicity are available. However, the substance is not persistent in the soil compartment. The equilibrium partitioning method has been used for assessing the hazard to soil organisms.

Additional information

No information relating to the effects of styrene on plants via exposure through the air has been located. As the air receives the majority of styrene releases to the environment, further investigation of the effects of close analogues of the substance has been undertaken to establish whether styrene might be expected to have an effect on plants via this route. Aromatic compounds considered as analogues of styrene were benzene, toluene and ethylbenzene. No information was found for the last of these. Both benzene and toluene are being assessed under the Existing Substances Regulation. From the draft risk assessment for benzene, concentrations in the air of the order of 30-160 g/m3 are required to produce an effect on plants. The effects seen are usually reversible after the exposure has ended. The draft assessment concludes that benzene is not of concern for plants except at very high concentrations. In the toluene risk assessment a number of studies are presented which show that toluene can have an effect on plants at high concentrations in air. A screening study involving the exposure of a number of plant species to toluene over 14 days found no effects at concentrations of 60 mg/m3 or below. This value is used in the toluene risk assessment as an indicative level for effects (not a formal PNEC). The assessment concludes that when compared to the estimated air concentrations (up to ~1 mg/m3), this level indicates that toluene does not present a risk to plants. Substances containing an alkenyl group could also be considered as analogues. Ethylene itself is known to be a plant hormone and to have effects on growth. Vershueren (1983) includes a number of values for effects on various plant species, covering a wide range of concentrations. The lowest quoted value is 0.002 ppm, which is 2.3 μg/m3. No indication of the level of effect is included. The addition of substituents to ethylene appears to reduce the toxicity to plants significantly. The IUCLID for propylene indicates effects at 1000 ppm after three days exposure and effects after two days at 50 ppm. The effects seen were declination in pea seedlings and epinasty (growth promotion) in the petiole of tomato plants respectively; the level of effect is not indicated. The concentrations correspond to 1.7 g/m3 and 86 mg/m3 respectively. For butylene, epinasty in the petiole of tomato plants was also reported, at a concentration of 50,000 ppm (125 g/m3) over two days. From the limited amount of information available on the effects of styrene analogues on plants, it is clear that with the exception of ethylene effects are only seen at high concentrations. Ethylene is a special case, and the addition of substituent groups reduces the toxicity markedly. It is also possible that the effects seem in other alkenic substances such as propylene may be due to the presence of ethylene as an impurity. It is therefore concluded that styrene is unlikely to have significant effects on plants except at high concentrations (European Union Risk Assessment Report. STYRENE. Part I - Environment. Final Report, 2002)