Acrylonitrile

Endpoint summary

Description of key information

Toxicity to fish

A Japan Ministry of Environment (2011) study with Oryzias latipes was reliably performed, with appropriate measures to ensure that exposure was satisfactorily maintained, and is considered to provide the key acute toxicity endpoint for freshwater fish. The 96-hour LC50 was 5.1 mg/L (mean measured).

The long-term toxicity of acrylonitrile to fish was determined in a fish early life stage test with P. promelas (fathead minnow), using flow-through conditions. No NOEC could be established for this study as the growth rate was significantly reduced at the lowest concentration tested (0.34 mg/L, measured). The report concluded that this concentration represented the MATC. The EU RAR concluded that this concentration represents the LOEC (for risk assessment purposes). The EU RAR calculated a NOEC by applying a safety factor of 2 to the LOEC, giving a NOEC of 0.17 mg/L.

Toxicity to aquatic invertebrates

A Japan MoE (2011) study with Daphnia magna was reliably performed, with appropriate measures to ensure that exposure to acrylonitrile was satisfactorily maintained, and is considered to provide the key acute toxicity endpoint for freshwater invertebrates. The 48-hour EC50 was 2.5 mg/L (mean measured).

Tong et al. (1996) carried out a 14-day and a 21-day chronic toxicity study in D. magna using the OECD 1987 Testing Guidelines with daily renewal of test solutions, but without measurement of acrylonitrile. They reported that the results of the two studies were identical, with a NOEC for survival of 2 mg/L nominal (LOEC > 4 mg/L) and a NOEC for reproduction of 0.5 mg/L nominal. This study is reported by the EU RAR (2004) to be the critical study.

Toxicity to algae

The effects of acrylonitrile on the growth of the freshwater unicellular green alga Pseudokirchneriella subcapitata were reliably determined following exposure for 72 hours under static conditions in sealed vessels (Japan MoE, 2011). The 72-hour ErC50 (growth rate) was 10 mg/L (mean measured) and the corresponding NOErC was 0.95 mg/L. Since the NOErC relates to algal growth (cell multiplication), it is considered to be a long-term endpoint for the primary producer trophic group and is taken into account in setting the assessment factor for the derivation of the aquatic PNEC.

Toxicity to microorganisms

The results of biodegradation testing shows that acrylonitrile has an initial inhibitory effect on non-acclimated microorganisms, but following acclimation EC50s for microorganisms are generally in excess of 100 mg/l.

Sediment toxicity

No data are available and no testing is proposed. A waiver is appropriate for this endpoint on the basis of very low exposure of sediment. Acrylonitrile will be biodegraded in WWTP; any low levels of acrylonitrile present in aquatic emissions will not be expected to accumulate in sediment based on the physicochemical properties of the substance (Koc and water solubility). sediment dwelling organisms will therefore be exposed to acrylonitrile in the aqueous phase.

Studies in other aquatic organisms

The acute toxicity of acrylonitrile to 2 -3 day old Bufo bufo gargarizans toad tadpoles was evaluated in a flow through test, with exposure periods of 48 and 96 hours. The 48-h LC50 was 14.22 mg/L. The 96-h LC50 was 11.59 mg/L (Tong et al., 1996). The same authors also performed a 28-day early life stage toxicity test in the same organism. The 3 day old tadpoles were exposed to acrylonitrile in a freshwater flow through test system for 28 days, according to US EPA guidelines. The NOEC (foreleg development) was 0.4 mg/L, and the LOEC (foreleg development) was 0.8 mg/L, giving a ChV of 0.56 mg/L. The NOEC for survival was 3.2 mg/L.

Terrestrial toxicity

No data are available. Waivers are proposed for terrestrial toxicity endpoints based on exposure considerations.

Acrylonitrile can potentially be redistributed to soil from the atmospheric or aqueous compartments, by the spreading of acrylonitrile-contaminated sewage sludge or as a result of accidental spills. Acrylonitrile is anticipated to be relatively mobile in soil, and this was supported by the results of an adsorption:desorption study of acrylonitrile, which provides no evidence of adsorption, the adsorption:desorption processes being in equilibrium. This is supported by calculation of the Koc (soil adsorption coefficient) using QSAR and from the water solubility of acrylonitrile when values of 11.5 and 9.0 L, respectively were derived, showing little potential for adsorption to soil. Industrial sludge from acrylonitrile production and processing facilities is not spread on land in Europe; contaminated sludge is incinerated. The main source of release of acrylonitrile to soil will therefore be deposition from the atmospheric compartment. Acrylonitrile entering the terrestrial compartment in small quantities will be rapdily degraded by photolysis. Any run-off from the soil will be released to groundwater, where acrylonitrile will also undergo biodegradation. The above considerations would therefore indicate that levels of acrylonitrile in soil are likely to be extremely low.

Additional information

Toxicity to fish

Knight & McHenery (AN Group, 1997) report a 96-hour LC50 of 8.6 mg/L for acrylonitrile in sheepshead minnow (Cyprinodon variegatus), a marine species and this provides the acute toxicity endpoint for salt water fish. The 96-hour LC50 endpoints for O. latipes and C. variegatus are similar and there is no evidence to suggest a substantial difference in sensitivity to acrylonitrile between fresh- and sea-water fish. Numerous other acute toxicity endpoints are available and are summarised in the EU RAR, however the Knight & McHenery study with C. variegatus was considered to be the most reliable result in fish at the time the EU RAR was compiled, and this provides the acute toxicity endpoint for salt water fish. A public domain study (Neuparth et al., 2013) of sub-lethal effects in seabass is also available and provides additional information. The LOEC from a range of sub-lethal effects was found to be 0.15 mg/L. This study has not been considered for derivation of PNECs as it was not performed according to a recognised guideline, and is of unknown reliability.

Toxicity to aquatic invertebrates

The 48-hour EC50 endpoints reported in four supporting acute toxicity studies with D. magna range between 7.6 and 22 mg/L. Neuparth et al. (2011) noted the results of a number of public domain studies where testing had been conducted on aquatic invertebrates. The 48-hour LC50 for Artemia salina was reported to be 14.34 mg/L. The 24 -hour LC50 for Crangon franciscorum was reported to be 10-33 mg/L.

Toxicity to algae

An AN Group study (1997) examined the effect of acrylonitrile on the growth of Skeletonema costatum, a unicellular chain-forming marine diatom over a 72-hour period in accordance with the 1990 PARCOM guidelines for testing of offshore chemicals and drilling muds. In this study the 72-hour ErC50 was 14.1 mg/L (initial measured concentration, with 96% loss in concentration over 72 hours) and the NOErC was 3.0 mg/L. Other data were reviewed in the EU RAR (2004), however the AN Group (1997) study was considered to be the most robust algal study at the time that the EU RAR was compiled.