4-(1,1,3,3-tetramethylbutyl)phenol

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, well documented and acceptable for assessment

Study type:

direct photolysis

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Aqueous solutions of octylphenol (OP; 0.48 µmol/L) were prepared from their saturated solutions obtained by a generator column technique.

SUNLIGHT PHOTOTRANSFORMATION
- Sunlight phototransformation of OP was performed in 50 mL quartz tubes which were suspended in a shallow flat-bottomed container filled with tap water or in Chriesbach creek at a depth of 20-25 cm.
- The solutions of OP was prepared in filtered (0.45 µm) lake water (Greifensee, DOC=4 mg/L; pH=8.4).
- The spectra of the lake water in which solutions were prepared and waters of Chriesbach creek showed no difference in the UV and visible ranges.
- During the experiment the creek water was clear and the temperature, varied between 14.5-17 °C, depending on the time of day. The temperature in the shallow vessel was adjusted (addition of ice) to be similar to that of the creek (17+3 °C).
- The total sunlight irradiation was determined by integrating the values which were recorded in time intervals of 10 min.
- The average sun irradiation intensities during the experiment was 0.705 kW/m²
- The experiment was performed at the original pH value of lake water (8.4)

GLP compliance:

not specified

Radiolabelling:

no

Analytical method:

high-performance liquid chromatography

Light source:

sunlight

Duration:

6 h

Temp.:

17 °C

Initial conc. measured:

0.48 other: µmol/l

Computational methods:

The photolysis rate constants (kp) were calculated by presuming first-order kinetics (Scully and Hoigné, 1987) as described by the following equation: kp=-ln(C/Co)/t,
where Co and C are the initial concentration of analytes and its concentration at the time t, respectively. Consequently, the photolysis half-life was calculated from: t1/2=0.693/kp

DT50:

6.9 h

Test condition:

Sunlight photolysis in lake water (DOC = 4 mg/l), tubes suspended in water-filled flat-bottom container, kp = 0.10 h^-1

DT50:

13.86 h

Test condition:

Sunlight photolysis in lake water (DOC = 4 mg/l), samples suspended in a creek at a depth of 20-25 cm, kp = 0.05 h^-1

Predicted environmental photolytic half-life:

The half-life of the photochemical degradation was estimated from the irradiation dose needed for 50 % degradation. The estimated t1/2 values range from 15-20 hours and correspond to a continuous sunlight intensity of 0.700 kW/m² which is a typical value for late summer at noon in Diibendorf. In June and July (sunlight intensity of approximately 1000 kW/m²; Haag and Hoigné, 1986) the half-life values are expected to be considerably lower (approximately 10-15 hours). Consequently, it is expected that in clear and shallow waters photochemical degradation could play a role in the elimination of OP.

Transformation products:

not measured

Details on results:

SUNLIGHT PHOTOLYSIS
- The photolysis was much faster (kp=0.1 h^-1) in tubes suspended in a water-filled flat-bottomed container than in the tubes suspended in a creek (kp= 0.05 h^-1).
- This difference could be attributed to light attenuation in the creek, as proved by actinometry with p-nitroanisol (NA). Radiation intensity in the flat-bottomed container (kpNA=0.12 h^-1) was estimated to be about three times higher than that in the creek at a depth of 20-25 cm (kpNA=0.04 h^-1).

Validity criteria fulfilled:

not applicable

Conclusions:

Although sunlight photolysis rates of OP were found to be much slower than previously reported for some other alkylphenols (Faust and Hoigné, 1987), the results suggest that a significant portion (30 %) of these compounds could be photochemically degraded in the surface layer of natural waters within one day.

Executive summary:

The rates of photochemical transformation of octylphenol (OP) in natural waters were assessed by exposing the solutions in filtered lake water (DOC=4 mg/L) to sunlight.

The first-order rate constant of sunlight photolysis (kp) for OP was estimated to be between 0.10 and 0.05 h^-1. This corresponds to a half-life of approximately 7-14 hours under continuous clear sky, noon, summer sunlight in the surface layer of natural waters.

The photolysis rate in the deeper layers is strongly attenuated, being approximately 1.5 times slower at depths of 20-25 cm than at the surface.

Although sunlight photolysis rates of OP were found to be much slower than previously reported for some other alkylphenols (Faust and Hoigné, 1987), the results suggest that a significant portion (30 %) of OP could be photochemically degraded in the surface layer of natural waters within one day.

Description of key information

Ahel et al. /1994) assessed the rates of photochemical transformation of octylphenol (OP) in natural waters by exposing the solutions in filtered lake water (dissolved organic carbon, DOC=4 mg/L) to sunlight. 

Additional information

The first-order rate constant of sunlight photolysis (kp) for OP was estimated to be between 0.10 and 0.05 h^-1. This corresponds to a half-life of approximately 7 -14 hours under continous clear sky, noon, summer sunlight in the surface layer of natural waters.

The photolysis rate in the deeper layers is strongly attenuated, being approximately 1.5 times slower at depths of 20-25 cm than at the surface.

Although sunlight photolysis rates of OP were found to be much slower than previously reported for some other alkylphenols (Faust and Hoigné, 1987, as cited in Ahel et al., 1994), the results suggest that a significant portion (30 %) of OP could be photochemically degraded in the surface layer of natural waters within one day.