Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.005 mg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.001 mg/L
Assessment factor:
1
Extrapolation method:
sensitivity distribution

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
0.05 mg/L
Assessment factor:
100
Extrapolation method:
assessment factor

Hazard for air

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
0.007 mg/kg soil dw
Assessment factor:
100
Extrapolation method:
assessment factor

Hazard for predators

Additional information

There is a significant body of data on environmental toxicity effects of cyanides. PNEC values for cyanide are derived from applying a range of AF’s to experimental NOECs, ranging in value from 10 to 100. Murgatroyd et al. (1998) proposed an assessment factor of 10 applied to LC50/EC50 values for higher organisms.  When compared to actual data obtained in experimental studies, this provides a 5-fold margin of safety, deemed appropriate considering the steep slope of the dose-response curve for lethal effects.  From data in the EAT 3 database, ECETOC (2003) examined the extrapolation from acute ecotoxicity data, to levels which are safe after chronic exposure. For more than half of the situations examined, an ‘acute to chronic ratio’ of less than 10 is evident. For the vast majority of situations the value 70, compared to the current value of 100, is more than adequate, providing a generous margin within the total factor (acute to ecosystem) of 1,000 to allow for extrapolations between the results of chronic studies and safe levels for ecosystems.  For the overall aquatic PNEC, species sensitivity distribution (SSD) estimation was utilized. This generates an ‘HC5’ level, which is regarded as a ‘safe’ concentration for 95% of the species (Posthuma et al, 2002), and is used in the current EU chemical risk assessment paradigm that is based on a generic model representing the freshwater and terrestrial environment of Europe (ECB, 2003). No assessment factor is applied to this number.

Conclusion on classification

Hydrogen cyanide is classified as Aquatic Acute 1, Aquatic Chronic 1. Very toxic to aquatic organisms, may cause long term adverse effects in the aquatic environment. This is based on the values of numerous LC50's across many species of aquatic organisms at less than 0.1 mg/L. Hydrogen cyanide is not readily biodegradable, but it is inherently biodegradable upon acclimatisation by organisms in the innoculum.