1,2,4-trichlorobenzene

Endpoint summary

Description of key information

For transported isolated intermediates according to REACh, Article 18, this endpoint is not a data requirement. However, data is available for this endpoint and is thus reported under the guidance of "all available data".

 

Adsorption/ desorption

KOC values between 780 - 47479 (soil), 500 - 9200 (sediment) and 530 (muck) have been reported. 1,2,4-TCB has a high adsorption capacity and the mobility in soil is expected to be low. However, because the degradation is slow in soil, 1,2,4-TCB may leach through sandy soils low in organic carbon content and reach groundwater.

Mobility was studied in a soil column study on a sandy soil in a 5 cm diameter and 140 cm high soil column. The soil contained 92% sand, 2.1% clay, 0.067% organic carbon and pH was 6.4. The soil column received 14 cm water per day over 45 days with the measured concentrations 3.4 and 0.57 mg/l 1,2,4-TCB. When 3.4 mg/l was applied, 46% was leached and 54% was degraded or not accounted for. When 0.57 mg/l was applied, 39% was found in eluate and 61% was degraded or not accounted for. The amount of volatiles was not determined (Wilson et al., 1981) although other studies indicated volatility to be essential. The study indicates that 1,2,4-TCB may leach into groundwater in sandy soils with low content of organic carbon. The potential for mobility is confirmed by recoveries in groundwater surveys.
Adsorption

Henry's Law constant

Followin Henry's law constants were reported:

• 1.42 x 10e-3 atm-m³/mol (calculated from water solubility and vapour pressure)


• 277 Pa m³/mol (calculated)


• 0.439 kPa m³/mol


• 108.4 Pa m³/mol


• 0.077 at 20°C (calculated); 0.093 at 25°C (calculated)

Volatility from aqueous solutions:

• calculated: t 1/2 (1 m depth, 25 °C)= 25 x 10 E 3 s (7.0 hours)


• measured: t1/2 (1 m depth, 20 °C)=23 x 10 E 3 s (6.5 hours)


• evaporation from water (10 cm depth): t1/2 = approx. 45 min. (calculated)

The volatilisation of 1,2,4-TCB in clean water may be high but will be reduced in natural surface water according to the depth of the water body, possible stratification or turbulence of the water body and to the content of dissolved organic carbon (DOC) and particulate organic carbon (POC). The volatilisation is slow from soil and sludge because adsorption to organic carbon takes place.
Volatilisation from surface water is estimated by means of 1,2,4-TCBs Henry's Law constant (H). Using a vapour pressure of 36 Pa at 20°C and a water solubility of 36 mg/l, the estimated Henry's Law constant would be 181 Pa*m3/mol which indicates that volatilisation from shallow waters and after accidental spillage to water may take place.
A more reliable value may be obtained by measuring H directly by direct measurement of concentrations in the gas phase and the water phase in a system at equilibrium. Using a gas-purge technique, a water concentration of 10µg/l and GC determination, ten Hulscher et al. (1992) measured the dimensionless Henry's Law constant (Kair-water) to 0.041 equivalent to a H of 101 Pa.m3/mol for 1,2,4-TCB. The measurements were carried out in a buffer solution at pH 6.4 which may have changed the solubility of 1,2,4 -TCB. Other measured values ofH at 20ºC were 122 Pa.m3/mol (Kair-water 0.050) and 185 Pa.m3/mol (Kair-water 0.076) (Oliver, 1985; Ashworth et al., 1988, respectively).
QSAR estimation of Henry's Law constant by the bond contribution method resulted in a H estimated to be 2.19*10-3 atm.m3/mol (290 Pa.m3/mol) (EPIWIN, 1995).
The volatilisation rate in an aqueous solution has been observed to be 6.5 hour/m depth at 20°C (Geyer et al., 1985). The volatility from an aqueous solution was studied using the water sampling method. The initial concentration was 10.7 mg/l and the half-life was estimated to be 22 minutes at 20°C using 14C-labelled substance (Korte and Freitag, 1986). These studies confirm that volatilisation takes place but the results are not in a form that can be used quantitatively in this risk assessment.
The volatilisation from soil is reduced at increasing content of organic matter due to adsorption. In soil incubated with 1,2,4-TCB at the concentration 50 ppm, the amount of volatile substances recovered from the test systems was 4 to 18% of the initial concentration from soil with high organic matter and 20 to 40% at low organic matter (Marinucci and Bartha, 1979). (EU Risk Assessment 2003)

 

Distribution modelling

The result of a Mackay model estimation of the distribution in the environmental compartments may vary according to the age of the model as they develop in time and the input data used.
The distribution in the environment, based on the EQC model (developed by Di Guardo according to Mackay et al., 1996) using the relevant physico-chemical data from this report at 20ºC results in the distribution: 76.9% in air, 2.1% in water, 20.5% in soil, 0.5% in sediment, 0.014% in suspended sediment, and 0.002% in fish. Another Mackay Level I model calculation employing also slightly different relevant physico-chemical data (Mackay, 1991; Bayer, 1996) is included for comparison in the table below.