Subtilisin

Endpoint summary

Description of key information

No toxicity to earthworms was observed up to 1121 mg enzyme concentrate dry matter/kg soil for an exposure of 14 days. Therefore, the LC50 is greater than 1121 mg enzyme concentrate dry matter/kg dry weight of artificial soil.
The overall no observed effect concentration (NOEC) was considered to be 1121 mg enzyme concentrate dry matter/kg soil dry weight of artificial soil corresponding to 576 mg active enzyme protein/kg soil dw.

Data waiving of the remaining terrestrial toxicity studies is based on following argumentation: Subtilisin has a very low Henry’s law constant (<10^-4) and a low octanol-water partition coefficient (logPow<-1.3). Therefore, exposure to agricultural soil via sludge application as well as via aerial deposition is very low. Exposure to soil may occur if waste water is discharged of via septic tank. According to the EUSES calculations, less than 0.01% of enzymes entering a sewage treatment plant (STP) will bind to sludge. As enzymes are degradable at both aerobic and anaerobic conditions, a high rate of inactivation and degradation of subtilisin in soil is expected. Assuming a degradation rate in soil at the same level as degradation rate in surface water, i.e. a half life of 5 hours, calculations show that the risk characterisation ratio (RCR) for soil is 25% below the RCR for the surface water. Thus subtilisin applied to agricultural soils via sludge application do not present a risk to the soil compartment due to sludge application. Subtisin may potentially leach into the soil, if waste water is discharged to a septic tank, or if it is used in connection with septic maintenance. The chemical safety assessment based on the equilibrium partitioning method showed that subtilisin does not exhibit a risk to soil living organisms in these situations.