Environmental Exposure and Fate
Sources of Environmental Exposure
During use of DL-lactone some losses to the environment may occur. Based on a production mass balance at the manufacturing plant of the main producer in UK, a maximum of 30 kg/day DL- lactone is lost to the waste water and approximately 50 kg/day to the distillation residues. The wastewater enters an on-site chemical and biological wastewater treatment plant with a hydraulic flow of approximately 7’000 m3/day. The water treated on-site subsequently enters a municipal sewage works (STP) where the industrial water is mixed up with approximately the seven-fold amount of municipal wastewater (total influent ~ 54’000 m3). The effluent of the plant is discharged to coastal waters.
In wastewater treatment plants, 87.3–91.5% of DL-lactone will be removed through biodegradation while 8.5–12.7% will be released to receiving waters, 0.0–0.4% will partition to sludge and <1E– 4% to air (Simple Treat Model v3.1; STP Model v1.50, both configured for ready biodegradability). The concentration of DL-lactone in the influent of the on-site wastewater treatment plant is approximately 4.3 mg/l, in the effluent ~ 0.43 mg/l. The concentration of DL-lactone in the influent of the municipal wasterwater treatment plant is estimated at about 0.056 mg/l. The predicted concentration in the effluent is 0.006 mg/l.
Dewatered sludge of the industrial plant is sent to landfill. The liquid waste stream is incinerated together with other wastes during the process. It is filled directly into a dedicated bulk tanker, will be treated as special waste and is used as CEMfuel (i.e., hazardous compounds will not reach the environment).
The calculated half-life for the photo-oxidation (reaction with hydroxyl radicals) of DL-lactone in air is 39 hours (EPISuite 3.11, 2003).
Stability in Water
A hydrolysis study at 50 °C, resulted in half-lives for DL-lactone of 144, 3.7 and 1 day(s) at pH 4, 7 and 9, respectively (based on nominal concentrations). After extrapolation from nominal and mea- sured concentrations at 50 °C to values at 25 °C, DL-lactone is expected to have a half-life of 1-3 years at pH 4, of approximately 30 days at pH 7 and of approximately 6-20 days at pH 9 (Brekel- mans, 1999). No degradation products were identified by analytical method, but, assuming hydroly- sis of the cyclic lactone ester, 2,4-dihydroxy-3,3-dimethyl-butanoic acid (pantoic acid) is the pro- bable hydrolysis product of DL-lactone. In conclusion, DL-lactone is expected to be hydrolytically stable at low pH values and to be prone to moderate hydrolysis at higher pH values.
Transport between Environmental Compartments
Level III fugacity modelling shows that after release to surface water approximately 99.9% of DL- lactone ends up in water. Negligible amounts will be distributed towards air (5E-05%), soil (5E- 0.3%) and sediment (0.14%). In the model physico-chemical properties were withdrawn from table 1 (Level III Model v2.7, 2004).