Styrene

Endpoint summary

Additional information

In Annex X of the Regulation (EC) No 1907/2006 REACH concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), it is suggested, that "in the absence of toxicity data for soil organisms, the equilibrium partitioning method may be applied to assess the hazard to soil organisms. The choice of the appropriate tests depends on the outcome of the chemical safety assessment.In particular for substances that have a high potential to adsorb to soil or that are very persistent, the registrant shall consider long-term toxicity testing instead of short-term.These studies do not need to be conducted if direct and indirect exposure of the soil compartment is unlikely."

Only an acute test for earthworm is available and a weight of evidence approach for the acute toxicity on plants using structurally related chemicals. No data on soil microorganisms and no data on long term toxicity to soil organisms are available.

 

However in the case of readily biodegradable substances which are not applied to soil it is generally assumed that the substance will not enter the terrestrial environment and as such there is no need for additional testing on soil organisms. Styrene is not a strong adsorptive substance, is highly volatile and rapidly degraded in the air via photo-oxidation, so that an indirect soil exposure via STP sludge and aerial deposition is considered as not relevant.

There is only one result for terrestrial organisms (acute toxicity to earthworm, Springborn 1995). In this test however, exposure concentrations are not well defined since a considerable loss of styrene concentrations was observed during the test. The relevance of the analytical results is therefore questionable. Basing the results on the nominal concentrations the EC50 would lie in the range 500 - 1000 mg/kg soil dw.

Therefore, the equilibrium partitioning method has been used to estimate a PNEC for styrene. This method is considered to be suitable for a substance like styrene with a moderate log Kow value.

Using the equilibrium partitioning method, the PNECsoil for Styrene is calculated according to the TGD (EC 2003, part II, chapter 3, p. 117):

PNECsoil = (Ksoil-water/ RHOsoil) · PNECwater · 1000

With the default parameters of the TGD concerning the fractions and densities in soil as well as the substance parameters Koc = 352 L/kg, H = 232 Pa m3 mol-1 and PNECwater = 0.028 mg/L, the PNECsoil for styrene is derived as follows:

PNECsoil = 0.177 mg/kg wwt = 0.2 mg/kg dwt

(For comparison, using the acute LC50 value for earthworm and an assessment factor of 1000 the PNECsoil would give a similar result of 0.12 mg/kg.)

Secondary poisoning

The environmental fate and the low log Kow of Styrene indicate, that secondary poisoning is an unlikely exposure pathway.