Acrylaldehyde

Biodegradation in water: screening tests

Description of key information

Despite the lack of a well-performed ready biodegradability test, it is expected that acrolein will be completely mineralised within 3 weeks because of rapid primary degradation of acrolein within 7 days and no stable metabolites are formed. In addition, the outcome of two different QSAR calculations (BIODEG and OECD-model 75; Rorije et al., 1997) also point to the ready biodegradability of the substance. Based on the entire data set on biodegradation and the QSAR estimates, acrolein will be considered in the current risk assessment as ready biodegradable with a biodegradation rate constant of 1 h-1 (STP).
Insufficient data are available regarding anaerobic biodegradation to establish the significance of this process as a removal mechanism or to determine the rate at which such a process would proceed.

Additional information

1. European Union Risk Assessment Report of Acrolein (EU, 2001)

Biodegradation

The current information on several technical aspects is incomplete for nearly all biodegradation tests. Nevertheless, the total set of data is regarded sufficient to draw conclusions upon the degradation potential of acrolein.

Ready and inherent biodegradability tests

The BOD5-tests with unadapted inoculum indicate no biodegradation of acrolein. This may be due to the toxicity of the substance to micro-organisms. However, the acrolein concentrations in this test are unknown. For BOD5-test (no. 4) with adapted inoculum, 6.7-30% biodegradation was found. In another test acrolein was degraded aerobically within 7 days. The unadapted inoculum was taken from a domestic sewage treatment plant. This test, carried out according to the procedures of Bunch and Chambers, can be counted among the ready biodegradability tests. However, it should be emphasised that the biodegradation tests carried out by Tabak have a number of limitations. For example, in mosts cases only primary degradation was assessed and because of the use of yeast as an extra carbon source, cometabolism may occur. One inherent biodegradation test was conducted. In this test 100% biodegradation was measured after 2-6 days. In another test the primary degradation of acrolein was measured. After 7 days 100% of the substance was eliminated.

Anaerobic biodegradation tests

Anaerobic biodegradation (42%) was measured in an acclimated system. No biodegradation was observed in the anaerobic test with unacclimated microorganisms. This can be explained by the toxicity of the substance to micro-organisms. Another test is difficult to evaluate because no data is available on the adaptation status of the micro-organisms.

2. Agreement with further international Reports and Studies published after finalisation of the EU Risk Assessment Report 2001

US ATSDR (2007): Low concentrations of acrolein may degrade in natural water by either aerobic biodegradation or reversible hydration to beta-hydroxypropionaldehyde, which subsequently undergoes aerobic biodegradation. Acrolein at a concentration of 5–10 mg/L was completely degraded in 7–10 days in a static culture flask screening procedure. Acrolein applied to surface waters at application rates suggested for herbicidal use can persist up to 6 days. Bowmer and Higgins measured acrolein removal in both laboratory water and in field experiments using irrigation channels. Their studies suggested that the degradation of the hydration product of acrolein, 3-hydroxypropanal, occurs after the concentration of acrolein falls below 2–3 ppm. The degradation of 3-hydroxypropanal was also preceded by a 100-hour lag period, suggesting that biodegradation was occurring through the action of acclimated cultures.

In buffered laboratory water, acrolein reached its equilibrium apparently with beta-hydroxypropionaldehyde in approximately 300 hours (92% beta-hydroxypropionaldehyde, 8% acrolein); in irrigation channels, acrolein removal was complete. Half-lives were reportedly 1–3 days in surface water, but values were for the combined effect of degradation and volatilisation. Kissel et al. measured acrolein removal in buffered laboratory water and natural river water using both chemical analysis methods and bioassays. Based on fish kill bioassays in natural river water at pH 8.1, >93% degradation of acrolein occurred within 6 days. The half-lives of acrolein in aerobic test systems that were treated at an application rate of 15 mg/L were 9.5 hours in water and 7.6 hours in sediment. The half-lives of acrolein in anaerobic test systems treated at the same rate were 10.3 hours in water and approximately 10 days in sediment. Degradation products included 3-hydroxypropanal, acrylic acid, and allyl alcohol, which indicate that both hydrolysis and biodegradation contributed to the degradation of acrolein during this study.

Jacobson and Smith studied the dissipation of acrolein, applied at the highest recommended rate according to the label, to achieve a 15 ppm concentration for a 2-hour duration in an irrigation canal and a lateral of the canal, which was infested with aquatic plants. The dissipation half-lives for acrolein in the irrigation and lateral canals were 275 and 64 minutes, respectively. No acrolein residues were detected (detection limit, 0.01 ppm). No residues of 3-hydroxypropanal were detected (detection limit, 2.0 ppm) in any of the water samples from either canal. These data suggest that acrolein will not persist for moderate or long periods of time in aerobic aquatic environments and that hydration of acrolein may not be an important degradation pathway for acrolein. The decay rate constants for acrolein applied to irrigation canals have been reported to be similar (0.14-0.21) regardless of the difference in time-concentration regimens (100 µg/L for 48 hours to 15,000 µg/L for several hours). The half life of acrolein, applied at a flow rate of 3,964 L/second to achieve 15 ppm for 1 hour, was 10.2 hours in a weedy canal and 7.3 hours in a non-weedy canal. The concentration of acrolein was 25 µg/L in samples from the Columbia River collected 65 km from where it was applied at a concentration of 125 µg/L. Nordone et al. studied the dissipation of acrolein applied to agriculture canals with flow rates of 142, 283, and 453 L/second to achieve target concentrations of 7.5, 11.6, and 10.4 ppm, respectively. These authors concluded that typical application of acrolein as an aquatic herbicide in agricultural canals does not result in the introduction of acrolein into natural receiving waters 2.7 km downstream.

Oxidation of small amounts of acrolein in natural waters would not be environmentally significant; however, highly concentrated acrolein solutions (i.e., spills) may be polymerized by oxidation or hydration processes. Insufficient data are available regarding anaerobic biodegradation to establish the significance of this process as a removal mechanism or to determine the rate at which such a process would proceed.

WHO (2002): Acrolein is removed from surface water primarily by reversible hydration, biodegradation by acclimatized microorganisms, and volatilization. In groundwater, acrolein is removed by anaerobic biodegradation and hydrolysis. The overall reactivity-based half-life of acrolein in surface water is estimated to be between 30 and 100 h. In groundwater, half-lives of 11 days and 336-1344 h (14–56 days) are estimated based on aerobic and anaerobic degradation, respectively. Observed dissipation half-lives of acrolein applied as a herbicide in irrigation canals range from 7.3 to 10.2 h. The relatively short observed half-lives of acrolein in surface waters make long-range aquatic transport unlikely.

3. Substantial disagreements in comparison to further international Reports to European Union Risk Assessment Report 2001

None

4. Additional aspects in further international Reports

None

5. Additional information in newer Studies, not included in the European Union Risk Assessment Report 2001 or further cited international reports

None

6. Conclusions

Despite the lack of a well-performed ready biodegradability test, it is expected that acrolein will be completely mineralised within 3 weeks because of rapid primary degradation of acrolein within 7 days and no stable metabolites are formed. In addition, the outcome of two different QSAR calculations (BIODEG and OECD-model 75; Rorije et al., 1997) also point to the ready biodegradability of the substance. Based on the entire data set on biodegradation and the QSAR estimates, acrolein will be considered in the current risk assessment as ready biodegradable with a biodegradation rate constant of 1 h^-1 (STP).

Insufficient data are available regarding anaerobic biodegradation to establish the significance of this process as a removal mechanism or to determine the rate at which such a process would proceed.