Priority Substances List Assessment Report for Acrylonitrile

2.0 Summary of Information Critical to Assessment of "Toxic" Under CEPA 1999

2.1 Identity and physical/chemical properties

Acrylonitrile (ACN) is also known as acrylic acid nitrile, acrylon, carbacryl, cyanoethylene, fumigrain, propenenitrile, 2-propenenitrile, propenoic acid nitrile, propylene nitrile, VCN, ventox and vinyl cyanide. Its Chemical Abstracts Service (CAS) number is 107-13-1, its molecular formula is CH₂=CH-C≡N and its molecular weight is 53.06 g. Acrylonitrile's molecular structure is shown in Figure 1.

Figure 1 Chemical structure of acrylonitrile

The physical and chemical properties of in Table 1. At room is a volatile, flammable, colourless liquid with a weakly pungent odour (WHO, 1983). Acrylonitrile has two chemically active sites, at the carbon-carbon double bond and at the nitrile group, where it undergoes a wide variety of reactions. It is a polar molecule because of the presence of the cyano (C≡N) group. It is soluble in water (75.1 g/L at 25°C) and miscible with most organic solvents. The vapours are explosive, with cyanide gas being produced.

Acrylonitrile may polymerize spontaneously and violently in the presence of concentrated caustic acid, on exposure to visible light or in the presence of concentrated alkali (WHO, 1983), and it is stored accordingly, often as an acrylonitrile-water formulation that acts as a polymerization inhibitor (Kirk et al., 1983).

2.2 Entry characterization

2.2.1 Production, importation and uses

Acrylonitrile has not been produced in Canada since 1972, although it is imported and used. The amount of acrylonitrile imported into Canada has generally declined over the last two decades, falling from 21 000 tonnes in 1976 to 7600 tonnes - all from the United States - in 1994. Camford Information Services (1995) forecast the demand for acrylonitrile in 1997 to be 8300 tonnes (Table 2). The large majority of acrylonitrile is used as a feedstock or chemical aid in the production of nitrile-butadiene rubber (68% of 1994 imports) and in acrylonitrile-butadiene-styrene (ABS) and styrene-acrylonitrile (SAN) polymers (30% of 1994 imports).

2.2.2 Sources and releases

2.2.2.1 Natural sources

Acrylonitrile is not known to occur naturally, and there are no known reactions that could lead to in situ formation of this substance in the atmosphere (Grosjean, 1990a).

2.2.2.2 Anthropogenic sources

The total release of acrylonitrile in 1996 was 19.1 tonnes (97.3% to air and 2.7% to water) (Environment Canada, 1997b). The major source of releases was the organic chemicals industry (97.4%) (namely, the chemicals and chemical products industries and the plastic products industries), while municipal wastewater treatment facilities accounted for 2.6% of releases. All releases occurred in Ontario and Quebec.

Table 1 Physical and chemical properties of acrylonitrile¹

Property	Mean (range)	Reference
Density at 20°C	806 g/L	American Cyanamid Co., 1959
Melting point	-83.55°C	Riddick et al., 1986; Budavari, 1989
Boiling point	77.3°C	Langvardt, 1985; Howard, 1989
Water solubility at 25°C	75.1 g/L	Martin, 1961; Spencer, 1981; Langvardt, 1985; Howard, 1989; DMER and AEL, 1996
Solubility	Miscible with most organicsolvents	American Cyanamid Co., 1959
Vapour pressure at 25°C	11 (11-15.6) kPa	Groet et al., 1974; Riddick et al., 1986; Banerjee et al.,1990; BG-Chemie, 1990; Mackay et al., 1995
Henry's law constant2 at25°C	11 (8.92-11.14) Pa·m3/mol	Mabey et al., 1982; Howard, 1989; Mackay et al., 1995
Log organic carbon/waterpartition coefficient (log Koc)	1.06 (-0.09-1.1)	Koch and Nagel, 1988; Walton et al., 1992
Log octanol/waterpartition coefficient (log Kow)	0.25 (-0.92-1.2)	Collander, 1951; Pratesi et al., 1979; Veith et al., 1980;Tonogai et al., 1982; Tanii and Hashimoto, 1984;Sangster, 1989; DMER and AEL, 1996
Log bioconcentrationfactor (BCF) in fish	0.48-1.68	Barrows et al., 1980; Lech et al., 1995
Half-life (t½)
air	55 or 96 (4-189) hours	Callahan et al., 1979; Cupitt, 1980; Atkinson, 1985; DMER and AEL, 1996
	96 (13-198) hours	Atkinson et al., 1992
water	170 (30-552) hours	Going et al., 1979; Howard et al., 1991
soil	170 (30-552) hours	Howard et al., 1991
sediment	550 hours	DMER and AEL, 19963

¹Conversion factors between concentration by weight and concentration by volume: 1 mg/m³ = 0.4535 ppmv (20°C, 101.3 kPa); 1 ppm in air = 2.205 mg/m³.
² Vapour pressure (at given temperature) × molar mass/water solubility (at same temperature).
³No specific sediment value was found in the literature; this is based on the assumption of slower reactivity compared with soils (DMER and AEL, 1996).

Table 2 Demand for acrylonitrile in Canada, 1990-1997¹

Use	Acrylonitrile demand (tonnes)
	1990	1991	1992	1993	1994	19972
Nitrile-butadiene rubber	3 800	3 300	3 600	4 400	5 200	5 700
ABS terpolymers, SAN	10 000	9 200	5 200	2 500	2 300	2 500
Miscellaneous	100	100	100	100	100	100
Total	13 900	12 600	8 900	7 000	7 600	8 300

¹Camford Information Services (1995).
²Forecast.

2.2.2.2.1 Organic chemicals industry

Data from the National Pollutant Release Inventory are in close agreement with Environment Canada (1997b), although the inventory does not capture releases from municipal facilities. Total on-site releases from industrial sources have decreased recently, with releases of 19.6, 16.8 and 10.7 tonnes in 1994, 1995 and 1996, respectively (Environment Canada, 1994, 1995, 1996). In 1996, the plastics products industry transferred 17 tonnes of acrylonitrile off-site in waste. This was a one-time cleaning procedure required to close a polymerization facility (Environment Canada, 1996, 1997b).

A small amount (0.21 tonnes) of acrylonitrile was released by industry to municipal wastewater treatment facilities in 1996, but it is expected that this is effectively biodegraded by the acclimated microbes present in wastewater treatment facilities (see Section 2.3.1.2).

Since acrylonitrile is explosive, flammable and able to spontaneously and violently polymerize, wherever possible it must be transported and stored in closed containers in cool, dry, well-ventilated areas away from sources of heat and ignition; alternatively, polymerization inhibitors can be added to the system (Kirk et al., 1983; CCOHS, 1995).

Spills of acrylonitrile during transport are rare in Canada. One litre of acrylonitrile leaked from rail transport in 1992 (Charlebois, 1996). In 1991, a rail accident during transport of 76 tonnes of acrylonitrile did not result in any release of the substance (Charlebois, 1996).

2.2.2.2.2 Vehicles

The release of acrylonitrile from vehicle exhaust is not considered significant. Mizuno et al. (1980) reported acrylonitrile in vehicle exhaust; however, improved catalysts in motor vehicles contain a large amount of cerium oxide, which acts as an "oxygen reservoir." This, coupled with the engine control system, ensures more complete combustion to carbon dioxide, resulting in exhaust gas with low concentrations of hydrocarbons (Graham, 1997). The large majority of the vehicle fleet on the road today in Canada has stoichiometric control of engine operation coupled with cerium catalysts, which means that acrylonitrile is unlikely to be released in significant quantities, if at all.

2.2.2.2.3 Municipal wastewater treatment

Three (Toronto Main, Toronto Highland Creek and Québec) of seven Canadian municipalities that used sewage sludge incineration in 1997 have facilities that can potentially produce acrylonitrile, although relevant monitoring data are not available (Campbell, 1997). If it is assumed that these facilities operate in a manner similar to U.S. facilities that emit acrylonitrile, an estimated 64.8 kg per year may be emitted from each of the three Canadian facilities, for a total of 194 kg (0.19 tonnes) per year. This represents approximately 1% of the releases of acrylonitrile to air from chemical industries. Given the small number of wastewater sludge incineration facilities, the small amount of acrylonitrile produced and the reactivity of acrylonitrile in air (see Section 2.3.1.1), possible releases of acrylonitrile to air in the Canadian environment during incineration of wastewater sludge are not considered significant.

Only one community (Montréal) using acrylonitrile polymers as conditioners for wastewater treatment was identified based on a Canada-wide survey of municipalities conducted in late 1997. Based on manufacturers' specifications for the polymer and the amount of polymer used annually at the site, 0.29 tonne of acrylonitrile is estimated to be released per year.

If sludge containing acrylonitrile were spread on soil for agricultural use, it is possible that the substance might react in soil and volatilize to air. However, no data on potential losses from this exposure pathway were identified.

2.2.2.2.4 Transboundary sources

Acrylonitrile is produced in Texas, Louisiana and Ohio. Going et al. (1979) reported levels of acrylonitrile in air in the vicinity of acrylonitrile production or processing facilities in 11 industrial areas of the United States ranging from <0.1 to 325 µg/m³ (detection limit 0.3 µg/m³). It should be noted, however, that since this study, increasingly stringent controls on emissions have reduced reported atmospheric levels in the vicinity of such facilities. Wiersema et al. (1989) did not detect acrylonitrile over a six-month monitoring period of urbanized and industrialized air in the Gulf Coast of Texas (detection limit 0.122 µg/m³). The U.S. EPA (1986) reported levels of acrylonitrile in urban air in the United States; mean levels of 0.35-0.46 µg/m³ were found in three cities in New Jersey in July-August 1981, and a mean level of 0.46 µg/m³ was reported for Texas cities sampled between October 1985 and February 1986.

Based on its half-life in air of between 55 and 96 hours (Section 2.3.1.1), acrylonitrile could travel as far as 2000 km from its source (Hoff, 1998). However, concentrations of acrylonitrile were not detected (detection limit 0.5 µg/m³) in a 1991 study of transboundary air quality in Windsor, Ontario (Karellas, 1996) or elsewhere (Section 2.3.2.1). Therefore, under current conditions, it is believed that long-range transport is not a significant source of acrylonitrile input to the Canadian environment.

2.2.2.2.5 Pesticide use

Acrylonitrile was used in Canada in the past as a pesticide fumigant for stored grain. However, it is no longer present in registered pesticides and was last registered in Canada as a grain fumigant in 1976 (Ballantine, 1997). Therefore, releases of acrylonitrile from pesticidal uses are considered to be zero.

2.3 Exposure characterization

2.3.1 Environmental fate

2.3.1.1 Air

Acrylonitrile emitted to air reacts primarily with photochemically generated hydroxyl radicals (·OH) in the troposphere (Atkinson et al., 1982; Edney et al., 1982; Munshi et al., 1989; U.S. DHHS, 1990; Bunce, 1996). The atmospheric half-life, based on hydroxyl radical reaction rate constants, is calculated to be between four and 189 hours (Callahan et al., 1979; Cupitt, 1980; Edney et al., 1982; Howard, 1989; Grosjean, 1990b; Kelly et al., 1994). DMER and AEL (1996) and Bunce (1996) selected mean half-lives of acrylonitrile in air of 55 and 96 hours, respectively, in order to calculate environmental partitioning (Section 2.3.1.5) and abiotic atmospheric effects (Section 2.4.2).

The reaction of acrylonitrile with ozone and nitrate is slow, because of the absence of chlorine and bromine atoms in the molecule, and is not likely to constitute a major route of degradation (Bunce, 1996).

The reaction of hydroxyl radicals with acrylonitrile yields formaldehyde and, to a lesser extent, formic acid, formyl cyanide, carbon monoxide and hydrogen cyanide (Edney et al., 1982; Spicer et al., 1985; Munshi et al., 1989; Grosjean, 1990a).

2.3.1.2 Water

The significant fate processes of acrylonitrile in water are biodegradation by acclimatized microorganisms and volatilization (Going et al., 1979). In water, half-lives of 30-552 hours are estimated based on aqueous aerobic biodegradation (Ludzack et al., 1961; Going et al., 1979; Howard et al., 1991). DMER and AEL (1996) selected a mean half-life of 170 hours (seven days) for use in environmental partitioning (Section 2.3.1.5). The half-life based on volatilization is 1-6 days (Howard et al., 1991). The hydrolysis of acrylonitrile is slow, with half-lives under acidic and basic conditions of 13 and 188 years, respectively (Ellington et al., 1987).

Acrylonitrile has an initial inhibitory effect on activated sludge systems and other microbial populations and does not meet the Organisation for Economic Co-operation and Development (OECD) Test Method 301C for ready biodegradability (Chemicals Inspection and Testing Institute of Japan, 1992; AN Group, 1996; BASF AG, 1996). However, acrylonitrile will be extensively degraded (95-100%) following a short acclimation period if emitted to wastewater treatment plants (Tabak et al., 1980; Kincannon et al., 1983; Stover and Kincannon, 1983; Freeman and Schroy, 1984; Watson, 1993).

2.3.1.3 Soil and sediment

Acrylonitrile is biodegraded in a variety of surface soils (Donberg et al., 1992) and by isolated strains of soil bacteria and fungi (Wenzhong et al., 1991). Concentrations of acrylonitrile up to 100 mg/kg were degraded in under two days (Donberg, 1992). Similar breakdown by microbial populations present in sediment is likely (DMER and AEL, 1996; EC, 1998). Experimental adsorption studies (Zhang et al., 1990), together with calculation of soil sorption coefficients using either quantitative structure-activity relationships (Koch and Nagel, 1988; Walton et al., 1992) or water solubility (Kenaga, 1980), indicate that acrylonitrile shows little potential for adsorption to soil or sediments.

Half-lives of acrylonitrile in soil of 1-30 days have been calculated based on ready biodegradability data (EC, 1998) and the work performed by Donberg et al. (1992) and reported by Howard et al. (1991). DMER and AEL (1996) selected a mean half-life in soil of 170 hours (seven days). The half-life in the oxic zone of sediment can be assumed to be similar.

2.3.1.4 Biota

Bioaccumulation of acrylonitrile is not anticipated, given experimentally derived values of log K_owranging from -0.92 to 1.2 (mean 0.25) (Collander, 1951; Pratesi et al., 1979; Veith et al., 1980; Tonogai et al., 1982; Tanii and Hashimoto, 1984; Sangster, 1989) and a log bioconcentration factor (log BCF) of 0 calculated from the water solubility of acrylonitrile (EC, 1998).

Log BCF values of 0.48-1.68 have been derived from experiments with bluegill (Lepomis macrochirus) (Barrows et al., 1980) and rainbow trout (Oncorhynchus mykiss) (Lech et al., 1995). The experimentally derived log BCF of 1.68 reported by Barrows et al. (1980) in whole-body tissue of bluegill may overestimate the BCF, since the ¹⁴C uptake method may include degradation products in the BCF value (EC, 1998).

2.3.1.5 Environmental partitioning

Fugacity modelling was conducted to characterize key reaction, intercompartment and advection (movement out of a compartment) pathways for acrylonitrile and its overall distribution in the environment. A steady-state, non-equilibrium model (Level III fugacity model) was run using the methods developed by Mackay (1991) and DMER and Paterson (1991). Assumptions, input parameters and results are presented in Mackay and AEL (1996) and summarized here. Values for input parameters were as follows: molecular weight, 53.06 g/mol; water solubility, 75.5 g/L; vapour pressure, 11.0 kPa; log K_ow, 0.25; Henry's law constant, 11 Pa·m³/mol; half-life in air, 55 hours; half-life in water, 170 hours; half-life in soil, 170 hours; half-life in sediments, 550 hours. Modelling was based on an assumed default emission rate of 1000 kg/hour into a region of 100 000 km², which includes a surface water area (20 m deep) of 10 000 km². The height of the atmosphere was set at 1000 m. Sediments and soils were assumed to have an organic carbon content of 4% and 2% and a depth of 1 cm and 10 cm, respectively. The estimated percent distribution predicted by this model is not affected by the assumed emission rate.

As a result of acrylonitrile's physical and chemical properties, modelling indicates that when acrylonitrile is continuously discharged into a specific medium, most of it (84-97%) can be expected to be found in that medium (DMER and AEL, 1996). More specifically, Level III fugacity modelling by DMER and AEL (1996) predicts that:

• when acrylonitrile is released into air, the distribution of mass is 92.8% in air, 6.4% in water, 0.8% in soil and 0.0% in sediment;
• when acrylonitrile is released into water, the distribution of mass is 2.5% in air, 97.3% in water, 0.0% in soil and 0.1% in sediment;
• when acrylonitrile is released into soil, the distribution of mass is 4.4% in air, 11.9% in water, 83.7% in soil and 0.0% in sediment.

The major removal mechanisms in air, water and soil are reaction within the medium and, to a lesser degree, advection and volatilization. Abiotic and biotic degradation in the various compartments result in low persistence overall and little, if any, bioaccumulation.

Fugacity modelling with the ChemCAN3 model (version 4) was also conducted with the conservative assumption that all known 1996 releases (Environment Canada, 1997b) in Canada occurred in southern Ontario. Since the half-life of acrylonitrile in air is the major determinant of its fate in the environment, the model was run using the minimum, median and maximum half-life values (four, 55 and 189 hours) under summer, winter and year-round conditions. The results of the ChemCAN3 model indicate that long-term continuous release of acrylonitrile may result in very low levels in air, water, soil and sediment across the southern Ontario region (Table 3). Modelling predictions do not purport to reflect actual expected measurements in the environment, but rather indicate the broad characteristics of the fate of the substance in the environment over a large region and its general distribution between the media. The model does not address the likely impact of point source releases on a local level. Information on measured concentrations in air and water and dispersion modelling carried out at the local level are presented in Section 2.3.2.

Table 3 Predicted concentrations of acrylonitrile in southern Ontario from ChemCAN3 modelling with various half-lives in air given (reported releases under Section 16 of CEPA for 1996)

Enlarge image

2.3.2 Environmental concentrations

Since the use of acrylonitrile and resulting emissions are highly localized, concentrations of acrylonitrile are not measured on a routine basis in Canadian air monitoring programs. There are, however, some data on both measured concentrations and those predicted from dispersion modelling for ambient air and air close to industrial sites.

2.3.2.1 Ambient air

Maximum predicted rates of emission of acrylonitrile during any half-hour period were 0.003, 0.018 and 0.028 g/s for stacks 14, 17 and 11 m high, respectively, near the site of the largest user in Canada (a Sarnia, Ontario, plant), based on dispersion modelling conducted in 1998 as part of the requirements for the Ontario Ministry of the Environment emissions inventory (Michelin, 1999). The two most common atmospheric stability classes in dispersion modelling are class C (where inversion occurs just above stack height, and the plume is therefore forced to the ground) and class D (close to stable or neutral conditions). Predicted concentrations at 11, 25, 41 and 1432 m from the stacks under atmospheric stability class C were 6.6, 2.2, 0.4 and 0.1 µg/m³. Predicted concentrations at 11, 35, 41 and 3508 m under atmospheric stability class D were 9.3, 2.9, 0.6 and 0.1 µg/m³ (Table 4). This recent determination of 9.3 µg/m³ at 11 m from the stack of the largest user of acrylonitrile is considered to be the highest reliable (predicted or measured) concentration in ambient air in Canada. It is noted that, in reality, discharges from each of the stacks are not continuous over time. For example, the reactor opening occurred six times in 1998 and gave a combined loss of 0.3 g of acrylonitrile. The latex stripping column was opened five times in 1998, and the combined loss of acrylonitrile was estimated at 31 g. The maximum predicted concentration of 9.3 µg/m³ was only for five 30-minute periods during the year (Wright, 1999). In addition, testing by the Ontario ministry of the Environment on the accuracy of the model indicated that the model overpredicts the actual value by about two orders of magnitude.

Table 4 Maximum predicted ground-level concentrations of acrylonitrile at an Ontario industrial site ¹

Stack2	Atmospheric stability class3	Emission rate (g/s)	Wind speed (m/s)	Distance from stack (m)	Maximum predicted concentration4 (µg/m3)
N2	C	0.003	5	41	0.4
N2	D	0.003	5	41	0.6
N4	C	0.018	5	11	6.6
N4	D	0.018	5	11	9.3
N5	C	0.028	5	25	2.2
N5	D	0.028	5	35	2.9
H5	C	0.05	2.2	1432	0.1
H5	D	0.05	2.7	3508	0.1

¹ Source: Michelin (1999).
² Stacks:
N2: NBR Reactor Opening and Vent Gas Unit (stack height="14" m)
N4: Latex Stripping Column (stack height="17" m)
N5: NBR Finishing Building (stack height="11" m)
H5: East Flare (stack height="66" m)
³ Atmospheric stability classes:
C: Inversion occurs just above stack height; plume is therefore forced to the ground.
D: Close to stable or neutral conditions.
⁴ For all stacks tested, the maximum off-property ground-level concentration was found to be 3.6 µg/m 3 within 10 m of the property fence line (atmospheric stability class: D, wind speed 5.0 m/s).

The most recent sampling of air for acrylonitrile at an industrial site was at the site of nitrile-butadiene rubber production in Sarnia, Ontario. Sampling took place on January 8, 1997 (four samples) and on January 13, 1997 (two samples), 5 m outside the company fence line, 2 m above ground and directly downwind of the stacks. Acrylonitrile was not detected in any of the six samples. The concentration in the ambiant air downwind of the plant was therefore less than the detection limit of 52.9 µg/m³ (Sparks, 1997; Wright, 1998).

Acrylonitrile levels ranged from 0.12 to 0.28 µg/m³ in ambient air sampled for six days near a chemical manufacturing plant in Cobourg, Ontario, that uses acrylonitrile. Measurements from stacks of the facility in 1993 ranged from <251 to 100 763 µg/m³ (Ortech Corporation, 1994). These measurements were used in dispersion modelling to estimate the point of impingement concentration (the concentration of acrylonitrile in air at the point where the plume contacts the ground). The estimated point of impingement value was 1.62 µg/m³, or 0.5% of the Ontario Ministry of the Environment half- hour allowable point of impingement concentration of 300 µg/m³.

At six urban stations in Ontario in 1990, concentrations of acrylonitrile in 10 of 11 samples were below the detection limit of 0.0003 µg/m³. In this study, the maximum and only detectable concentration of acrylonitrile was 1.9 µg/m³ in one sample (OMOE, 1992a).

Levels of acrylonitrile were <0.64 µg/m³ in all seven samples of ambient air taken in the industrialized area of Windsor, Ontario, in August 1991 (Ng and Karellas, 1994).

Ambient air samples were collected from downtown (n = 16) and residential (n = 7) areas of Metropolitan Toronto, Ontario, during a personal exposure pilot survey. The air samples were obtained at 1.5 m above ground for 12 consecutive hours. Acrylonitrile was not detected (detection limit 0.9 µg/m³) in any sample analysed (Bell et al., 1991).

Air samples were collected within the inhalation zone by a personal unit for 1-2 hours while commuting to and from work (n = 19) and while spending the noon-hour period (n = 8) in downtown Toronto, Ontario, from June to August 1990. Acrylonitrile was not detected (detection limit 0.9 µg/m³) in any sample analysed. Acrylonitrile was also not detected (detection limit 0.9 µg/m³) in four special composite samples collected during the same study; the first two samples were collected while the participants were attending meetings, the third was collected at a barbecue, and the fourth was an overall composite sample of the afternoon and morning commutes and the overnight residential indoor air quality (Bell et al., 1991).

2.3.2.2 Indoor air

Acrylonitrile was not detected in samples collected overnight (duration up to 16 hours) from June to August 1990 in four different residences near Toronto, Ontario (detection limit 0.9 µg/m³) (Bell et al., 1991).

Environmental tobacco smoke appears to be a source of acrylonitrile in indoor air (CARB, 1994). Data on acrylonitrile levels in indoor air in a survey conducted in the United States indicate that there may also be unidentified non-smoking sources (CARB, 1996).

2.3.2.3 Surface water and groundwater

Acrylonitrile has been detected only in water associated with industrial effluent; it has not been detected in ambient surface water in Canada (detection limit 4.2 µg/L).

The most comprehensive sampling of acrylonitrile in effluents in Canada was that conducted in 1989-90 under Ontario's Municipal/Industrial Strategy for Abatement (MISA) Program. Acrylonitrile occurred at six of the 26 industrial sites sampled, but only five of these companies had waste streams that were discharged to the environment. Of the effluents sampled from these five companies, acrylonitrile was detected in 12 of 256 samples (OMOE, 1993). Daily concentrations ranged from 0.7 to 3941 µg/L; annual site averages ranged from 2.7 to 320 µg/L.

In the intervening decade since the widespread MISA sampling took place, there have been important changes in the organic chemical manufacturing industry. Three of the five companies did not report commercial activity involving acrylonitrile in 1997, and the two remaining companies have both added biological treatment reactors (e.g., Biox reactors) to process their waste streams before discharge to the environment. Currently, levels from both sites are below the recommended method detection limit of 4.2 µg/L (Hamdy, 1998).

In 1989-90, acrylonitrile was detected in 12 of 382 effluent samples from five of the 26 organic chemical manufacturing plants in Ontario mentioned above (OMOE, 1992b). The maximum daily concentrations ranged from 0.7 to 120 µg/L. The means at different sites ranged from 0.4 to 20 µg/L. The maximum concentration occurred in one sample of clarifier effluent discharged to Lake Ontario at Cobourg. At this site, acrylonitrile was detected in two of 50 samples (mean 4 µg/L). In the same study, intake water (i.e., ambient water) at the 26 Ontario organic chemical manufacturing plants did not contain detectable amounts of acrylonitrile in 207 samples (detection limit 4.2 µg/L) sampled over 12 months in 1989-90 under the MISA Program (OMOE, 1992b).

In a large study of Canadian municipal water supplies in 1982-83, acrylonitrile was not detected in any of the 42 raw (and 42 treated) water samples from nine municipalities on the Great Lakes (detection limit 5 µg/L) (Otson, 1987). Acrylonitrile was not detected (detection limit 2.1 µg/L) in groundwater samples downgradient of a wastewater treatment pond at an Ontario chemical industry site (Environment Canada, 1997b).

2.3.2.4 Drinking water

Acrylonitrile was monitored in municipal water supplies at 150 locations in Newfoundland, Nova Scotia, New Brunswick and Prince Edward Island over the period 1985-1988. It was detected at a trace concentration (0.7 µg/L) in only one sample of treated water in Nova Scotia in June 1988 (detection limit 0.5-1.0 µg/L) (Environment Canada, 1989a,b,c,d).

Acrylonitrile was not identified in treated (or raw) water at facilities near the Great Lakes in 1982-83 (n = 42; detection limit 5 µg/L during the initial sampling and <1 µg/L during later sampling after the technique was modified) over three sampling periods (Otson, 1987). Analyses were by gas chromatography/mass spectrometry.

No other Canadian data were identified.

2.3.2.5 Soil and sediment

Significant concentrations of acrylonitrile are not expected in Canadian soil or sediment based on the release patterns and the environmental partitioning, behaviour and fate of the substance (see Section 2.3.1).

Significant levels of acrylonitrile have not been detected in Canadian soils. Levels in 18 soil samples at an Alberta chemical blending plant were below the detection limit of 0.4 ng/g (Dinwoodie, 1993). Significant quantities of acrylonitrile in soil at a LaSalle, Quebec, chemical industrial site have not been identified since regular monitoring began at the site in 1992 (Environment Canada, 1997b).

Data on levels of acrylonitrile in Canadian sediment have not been identified.

2.3.2.6 Biota

Information on the levels of acrylonitrile in biota in Canada was not identified.

2.3.2.7 Food

Acrylonitrile-based polymers are not used in Canada to any great extent in direct food contact application. If used, they would be primarily applied as the outside layer of laminated structures (Salminen, 1993, 1996). Past analysis of food products indicates that residual acrylonitrile from acrylonitrile-based polymers, if used in this manner, could conceivably migrate into foods, although at low concentrations (Page and Charbonneau, 1983; Page, 1995).

Regulations of the Food and Drugs Act prohibit the sale of food containing acrylonitrile as determined by official method FO-41 (Determination of Acrylonitrile in Food). The detection limit of that method is approximately 15 ng/g (Salminen, 1999).

Page and Charbonneau (1983) measured concentrations of acrylonitrile in five types of food packaged in acrylonitrile-based plastic containers, purchased from several stores in Ottawa, Ontario. Average concentrations of acrylonitrile (measured in three duplicate samples of each food type by gas chromatography with a nitrogen-phosphorus selective detector) ranged from 8.4 to 38.1 ng/g (see footnote 12 in Table 9, Section 3.3.1).

A survey of food packed in acrylonitrile-based plastics, containing up to 2.6 mg acrylonitrile/kg, was conducted in Ottawa, Ontario. The samples represented five food companies and a variety of luncheon meats, including mock chicken, ham, salami, pizza loaf and several types of bologna. Acrylonitrile was not identified (detection limit 2 ng/g). Analyses were by gas chromatography, with nitrogen-phosphorus selective detection (Page and Charbonneau, 1985).

No other Canadian data were identified, and limited data from other countries are inadequate to serve as the basis for characterization of exposure through foodstuffs.

2.3.2.8 Multimedia study

In a multimedia study carried out for Health Canada (Conor Pacific Environmental and Maxxam Ltd., 1998), exposure to several volatile organic chemicals, including acrylonitrile, was measured for 50 participants across Canada. Thirty-five participants were randomly selected from the Greater Toronto Area in Ontario, six participants from Liverpool, Nova Scotia, and nine from Edmonton, Alberta. For each participant, samples of drinking water, beverages and indoor, outdoor and personal air were collected over a 24-hour period. Acrylonitrile was not detected in air (detection limit 1.36 µg/m³), water (detection limit 0.7 ng/mL), beverages (detection limit 1.8 ng/mL) or food (detection limit 0.5 ng/g).

2.4 Effects characterization

2.4.1 Ecotoxicology

The toxicity of acrylonitrile to aquatic organisms has been studied in a wide range of organisms, while a smaller data set exists on the toxicity of acrylonitrile to terrestrial organisms. A brief summary of effects is presented below, with an emphasis on the most sensitive endpoints for aquatic and terrestrial organisms. More extensive descriptions of environmental effects are provided in several reviews (U.S. EPA, 1980, 1985; WHO, 1983; EC, 1998) and in the environmental supporting documentation (Environment Canada, 1998).

2.4.1.1 Terrestrial organisms

While no data on the toxicity of acrylonitrile to terrestrial vertebrate wildlife were found in the literature, data are available from mammalian toxicology studies (Section 2.4.3). No data were found on avian toxicity. The focus of this section is on studies of insect species exposed to acrylonitrile in air.

In nine studies conducted on 13 insect species - including pulse beetle, rice weevil, lesser grain borer, granary weevil, saw-toothed grain beetle, red flour beetle, confused flour beetle, Mediterranean fruit fly, Oriental fruit fly and honey bee - acute and chronic exposure via fumigation with acrylonitrile affected survival, reproduction and enzyme activity. These studies are presented in the environmental supporting documentation (Environment Canada, 1998). LC₅₀s in insects ranged from 0.107 to 36.7 mg/L air (1.07× 10⁵-3.6 7× 10⁷ µg/m³). In 14 of 17 studies on 11 species, the 24-hour LC₅₀ was ≤5 mg/L air (≤5× 10⁶ µg/m³).

The most sensitive effect on growth, survival or reproduction in insects exposed to acrylonitrile via the atmosphere was the effect of fumigation on the one-day-old eggs of the pulse beetle (Callosobruchus chinensis) (Adu and Muthu, 1985). The LC₅₀ for eggs exposed to a constant concentration of the fumigant for 24 hours and examined for survival up to 30 days post-fumigation was 0.107 mg/L air (1.0 7× 10⁵µg/m³) (95% confidence limits 0.094-0.122 mg/L air) (Adu and Muthu, 1985).

Rajendran and Muthu (1981a) reported that for adults and pupae of rice weevil (Sitophilus oryzae L.) exposed to the LC₅₀ of 0.40 mg/L air (4.0× 10⁵µg/m³) for eight hours, there was a 50% decrease in the number of progeny.

Of the knockdown times reported for insects, the most sensitive organisms were Sitophilus oryzae L. adults, for which exposure to 1-1.5 mg/L air (1-1.5× 10⁶ µg/m³) for four hours resulted in 100% mortality (Rajendran and Muthu, 1977).

Of phosphorylase, trehalase and acetylcholinesterase enzymes involved in carbohydrate and energy metabolism, phosphorylase was the most susceptible and diminished to below detectable activity (100% decrease) at a concentration of 1.05 mg/L air (1.05× 10⁶ µg/m³) in adult red flour beetle (Tribolium castaneum), which survived exposure to the LC₅₀ of 0.79 mg/L (7.9× 10⁵µg/m³) (Rajendran and Muthu, 1981b).

2.4.1.2 Aquatic organisms

The data set for acrylonitrile includes a wide range of information on short- and long-term toxicity in 34 species of fish, amphibians, aquatic invertebrates and algae, although none complies totally with the requirements of OECD or similar test guideline protocols.

The majority of studies did not take into account the volatility of acrylonitrile. Those tests in which concentrations were not measured or could not be adequately adjusted, as explained below, are not considered valid for risk assessment purposes. Below, a brief summary is presented of the key studies carried out in general compliance with current OECD testing protocols and appropriate for risk assessment purposes.

Due to potential loss from water via volatilization and biodegradation, concentrations of acrylonitrile should be measured in static or static-renewal tests. Alternatively, for flow-through tests with nominal concentrations, there should be roughly five turnovers per day (Henderson et al., 1961; Bailey et al., 1985; Nabholz, 1998). Tests with measured concentrations or flow-through tests with this rate of turnover are considered primary evidence for the assessment.

Sabourin (1987) determined the ratio of flow-through to static concentrations at the 96-hour period to be 0.23. Therefore, studies with 96-hour endpoints can be adjusted by multiplying the reported concentration by 0.23, although the data provided by these studies are considered secondary evidence. Tests done under static conditions or those with nominal concentrations only at a time period different from 96 hours are considered as supporting evidence only.

Of the freshwater studies, there are five studies on five fish species and one study with an amphibian that are considered to provide primary data (Henderson et al., 1961; Sloof, 1979; ABCL, 1980a; Bailey et al., 1985; Zhang et al., 1996). In addition to these, there is secondary evidence (adjusted concentrations) from studies with six fish, seven invertebrate and one plant species. In these studies, a variety of endpoints was examined, including survival, growth, respiration and mobility at exposure durations ranging from 24 to 840 hours (1-35 days). The remainder of the studies were considered as providing supporting evidence.

Based on the primary and secondary studies, acrylonitrile is moderately toxic to fish and amphibians, with the 96-hour LC₅₀s for freshwater fish generally lying in the range of 10-20 mg/L (nominal) (Henderson et al., 1961; ABCL, 1980b; Zhang et al., 1996). Toxicity to acrylonitrile increases with increasing exposure duration. Reported 48-hour LC₅₀ values lie between 14.3 and 33.5 mg/L. At 840 hours, the LC₅₀for fathead minnow (Pimephales promelas) was 0.89 mg/L (ABCL, 1980a).

Based on the primary evidence, the most sensitive aquatic endpoint was that following chronic exposure of the frog, Bufo bufo gargarizans, in its early life stage (Zhang et al., 1996). Three-day-old tadpoles were exposed for 28 days in a flow-through system with four turnovers per day. The most sensitive endpoint was foreleg growth, where the lower and upper chronic limits around the 28-day EC₅₀ were 0.4 mg/L and 0.8 mg/L, respectively. The 96-hour and 48-hour EC₅₀ for immobility were 11.59 mg/L and 14.22 mg/L, respectively.

The effect of acrylonitrile on the growth (length and wet weight) and mortality of the early life stage (<18-hour-old eggs) of the fathead minnow (ABCL, 1980a) in a flow-through system with more than 5.5 turnovers per day has been examined. Mean measured concentrations were 98% of nominal. The most sensitive endpoint in the study was the 840-hour (35-day) Lowest-Observed-Effect Concentration (LOEC) for weight (20% reduction in wet weight) at 0.44 mg/L; the corresponding No-Observed-Effect Concentration (NOEC) was 0.34 mg/L. For mortality, the 840-hour NOEC (LC₁₅) was 0.44 mg/L and the LOEC (LC₄₆) was 0.86 mg/L.

Henderson et al. (1961) reported mortality of fathead minnow exposed to acrylonitrile in a flow-through system in which solutions were renewed every 100 minutes. Test durations were 24, 48, 72 and 96 hours and five, 10, 15, 20, 25 and 30 days (720 hours). Effects ranged from the 24-hour LC₅₀of 33.5 mg/L through decreasing concentrations to the most sensitive endpoint in the study, the 720-hour LC₅₀ at 2.6 mg/L.

Sloof (1979) reported the impact of acrylonitrile as increased respiration in rainbow trout within 24 hours of exposure to 5 mg/L in a flow-through system with continuous injection.

Bailey et al. (1985) examined the effect of acrylonitrile on the mortality of bluegill in a flow-through system with measured concentrations. The most sensitive endpoint in the study was the 96-hour LC₅₀at 9.3 mg/L.

In addition to primary studies with adequate flow-through or measured concentrations, 96-hour LC₅₀s in six species of fish in studies conducted with static/static-renewal nominal concentrations can be adjusted by the factor 0.23 (Sabourin, 1987; Nabholz, 1998). Using this method, the adjusted 96-hour LC₅₀s ranged from 1.18 to 5.4 mg/L. The lowest 96-hour LC₅₀ of 1.18 mg/L was that for grass carp (Ctenopharyngodon idella) (Zhang et al., 1996).

It is noted that for vertebrate species, the most sensitive endpoints were observed in primary studies. That is, overall, the most sensitive endpoint for aquatic vertebrates was the lower chronic limit around the EC₅₀ of 0.4 mg/L in the frog, Bufo bufo gargarizans, determined by Zhang et al. (1996) in a flow-through system with measured concentrations.

Of the studies on 14 invertebrate and one freshwater plant species, 96-hour tests in seven invertebrate and one plant species can be adjusted and considered to provide secondary evidence. Based on the secondary information, which must be interpreted with caution, it appears that, overall, invertebrates are more sensitive to acrylonitrile than vertebrates, although this was not discussed further by the authors. Effects in invertebrates range from the most sensitive, the 96-hour LC₈₀ at 0.16 mg/L (adjusted concentration 0.04 mg/L) in the pond snail (Lymnaea stagnalis) (Erben and Beader, 1983), to the 96-hour immobility EC₅₀ at 17.94 mg/L (adjusted concentration 4.1 mg/L) in the common stream snail, Lymnaea plicatula (Zhang et al., 1996).

More sensitive endpoints have been reported for invertebrates but are considered supporting information only, not primary or secondary data, since the tests were based on nominal concentrations under static conditions for exposure durations other than 96 hours. The remainder are considered to provide supporting information only, since there was no replication of doses or there were other confounding factors (e.g., lack of aeration).

In the one study on freshwater aquatic plants, the effect of a 96-hour exposure to acrylonitrile on plant growth was examined in duckweed (Lemna minor) (Zhang et al., 1996). Solutions were renewed every 24 hours, with five test concentrations, 10 fronds per concentration and four replicates. The 96-hour growth inhibition EC₅₀ was 6.25 mg/L (adjusted EC₅₀ is 1.44 mg/L).

2.4.1.3 Mode of action

The toxicity of acrylonitrile to environmental organisms is believed to result largely from direct effects of the acrylonitrile itself or other organic metabolites, such as hydrogen peroxide or an epoxide (Heald, 1980). The blocking of important enzymes containing sulphydryl groups by cyanoethylation has been suggested as a possible mechanism for acrylonitrile toxicity (Kayser et al., 1982). The liberation of free cyanide was originally thought to be responsible for the toxicity of acrylonitrile, since cyanide easily diffuses to all body tissues and rapidly inhibits specific enzymes responsible for respiration on the cellular level, stopping the utilization of molecular oxygen by cells. The signs of acrylonitrile poisoning are typical of hydrogen cyanide poisoning, but with a slight delay of the onset of symptoms (Patterson et al., 1976).

2.4.1.4 Microbial populations

There is considerable evidence of the effectiveness of acclimated soil or sludge microorganisms in degrading acrylonitrile in industrial wastewater treatment systems (e.g., Biox reactors). Wyatt and Knowles (1995a,b) demonstrated that complex mixtures of microorganisms in combination with different dilution rates and a combination of batch and continuous culture can be used to mineralize (degrade) acrylonitrile, acrylamide, acetic acid, cyanopyridine and succinonitrile, as well as more recalcitrant compounds (e.g., maleimide, fumaronitrile and acrolein), to carbon dioxide, ammonia and biomass.

Generally, concentrations of acrylonitrile up to 5000 mg/L do not appear to be toxic to bacteria, since they are readily degraded by Corynebacterium boffmanii and Arthrobacter flavescens (Wenzhong et al., 1991), Arthrobacter sp. (Narayanasamy et al., 1990), Acinobacter sp. (Finnegan et al., 1991) and an assemblage of acclimated anaerobic microorganisms (Mills and Stack, 1955). Nocardia rhodochrous can degrade acrylonitrile in a more limited manner, based on its use as a nitrogen rather than carbon source (DiGeronimo and Antoine, 1976).

Kincannon et al. (1983) reported almost complete biodegradation with 99.9% and 99.1% removal of acrylonitrile after eight hours in batch reactors and two days in complete mixture activated sludge, respectively. Initial concentrations of acrylonitrile were 110 and 152 mg/L, respectively; effluent concentrations post-treatment were 1.0 mg/L after eight hours and <0.05 mg/L after two days, respectively. In the batch reactor, biodegradation accounted for 75% and stripping accounted for 25% of acrylonitrile removal. In the activated sludge system, biodegradation was responsible for 100% of the removal.

Tabak et al. (1980) reported 100% biodegradation within seven days in a static screening flask test method when microbial inoculum from a sewage treatment plant was mixed with 5 and 10 mg acrylonitrile/L.