Assessment of Risk

Risk to Aquatic Organisms

The conservative exposure scenario considered release of MBMBP to the aquatic medium following industrial processing of the imported substance entirely at one site and the subsequent treatment and release from an STP. The EEV for the aquatic medium is 0.00746 mg/L.

The CTV for this assessment is the lowest acceptable chronic value (21-day LOEC) of 0.89 mg/L for immobility in Daphnia magna. An application factor of 10 is applied to account for uncertainty in extrapolating from laboratory to field conditions and for intraspecies and interspecies variations in sensitivity, giving an estimated no-effect value (ENEV) of 0.089 mg/L.

Therefore, the quotient for risk to aquatic species is calculated as follows:

Risk quotient = EEV_aq / ENEV_aq = 0.00746 mg/L / 0.089 mg/L = 0.0838

As this calculated risk quotient is much less than 1, it is predicted that MBMBP is unlikely to cause harmful effects to pelagic organisms.

Risk to Soil-dwelling Organisms

The soil CTV for MBMBP is 2670 mg/kg dry weight, which is the LOEC calculated using an equilibrium partitioning approach. The ENEV is determined by dividing the CTV by an application factor of 10 to account for extrapolation from laboratory to field conditions and intraspecies and interspecies variations in sensitivity. Therefore, the ENEV for soil-dwelling organisms is 267 mg/kg dry weight.

A risk quotient can thus be calculated as follows:

Risk quotient = EEV_soil / ENEV_soil = 1.64 mg/kg dry weight soil / 267 mg/kg dry weight soil = 0.00614

Since this quotient is significantly less than 1, it is predicted that MBMBP is unlikely to cause harmful effects to soil-dwelling invertebrate organisms exposed to sewage sludge-amended agricultural land.