1,2,4-trichlorobenzene

Endpoint summary

Description of key information

Biodegradation in water

MITI (1992)

The ready biodegradability was studied with a method corresponding to the OECD TG 301C, Modified MITI (I) test. The test concentration was 100 mg/l and activated sludge concentration 30 mg/l. In the aerobic study, the degradation measured as Biochemical Oxygen Demand (BOD) was 0% after 14 days. However, the high concentration of 1,2,4-TCB employed in the test may have resulted in toxicity to the microorganisms (EU RAR, 2003). Anyhow the result of this study is valid due to an high EC50 value of 500 mg/l in the only performed OECD-guideline study on toxicity to activated sludge (Yoshioka et al., 1986).

Conclusion: Based on the MITI study, the substance may be regarded as not readily biodegradable.

 

Biodegradation in water and sediment: simulation tests

The concentration of 1,2,4-TCB in influents to an advanced wastewater treatment plant was measured at the average value of 0.46 µg/l. The effluent concentration in the same period was 0.01 µg/l in percolating filter effluent treated by lime clarification, ammonia stripping, activated charcoal, chlorination and reverse osmosis. (McCarty and Reinhard, 1980). This removal of 97.8% of 1,2,4-TCB is a special case which is not to be considered a worst case. The "water factory" was designed to improve the quality of biologically treated municipal wastewater before injection into the aquifer system.

The influent to a water factory was the effluent from a municipal STP (Orange county,). In 1976, the STP trickling effluent contained 1,2,4-TCB in the range <0.02 - 4.1 µg/l (geometric mean 0.46 µg/l) and in 1978 after switching from trickling-filter to activated sludge treatment, the measured range in STP effluent was <0.02 - 0.5 µg/l and the geometric mean 0.18 µg/l (McCarty and Reinhard, 1980).

Removal in surface water

The removal in seawater was studied in mesocosmos studies including the volatilisation (Wakeham et al., 1983). The tanks were 5.5 m high and 1.8 m in diameter and contained 13 m³ seawater. In the study, a mixture of volatile organic compounds was added. The dissipation was studied at conditions equal to spring (8-16 °C), summer (20-22 °C) and winter (3-7 °C). The initial concentration 0.5 µg/l was equivalent to the concentration measured in a moderately polluted bay. The concentrations were measured during 1-2 months.

The dissipation was relatively temperature independent with half-life of 2-3 weeks regardless of the season. Retardation of the biological activity by adding HgCl2 (2 mg/l) did not increase the summer dissipation time. Therefore, the dissipation was assumed to be primarily dissipation by volatilisation and not biodegradation. Thus, volatilisation dominates the dissipation of 1,2,4-TCB whereas biodegradation is of less importance according to the authors (Wakeham et al., 1983).

The half-lives in rivers in thewere estimated to be 2.1, 1.5 and 28 days based on monitoring data taken along the River Rhine (Zoeteman et al., 1980). These half-lives differ considerably and are likely to be very inaccurate since only a limited number of samples were taken.

Removal in sediment

Trichlorobenzenes are chemically stable in both aerobic and anaerobic environments. In studies on the degradation in anaerobic sediments, trichlorobenzenes were reductively dechlorinated to monochlorobenzenes via dichlorobenzenes.1,2,4-TCB was transformed via 1,4-dichlorobenzene (Bosma et al., 1988) and via 1,2- and 1,3- dichlorobenzenes (Peijnenburg et al., 1992). The study by Bosma et al. (1988) was performed as a column study using 25 cm high and 5.5 cm internal diameter wet packed with sediment from the River Rhine near Wageningen. The columns were percolated continuously at a flow rate of 1 cm/h in an upflow mode. It was concluded that the observed removal was a biological process because of the long lag-phase preceding the disappearance and that there was no elimination in anaerobic batch with autoclaved sediment. The study by Peijnenburg et al. (1992) was performed in a methanogenic sediment-water system maintained at 22 ºC in a nitrogen atmosphere. The sediments were taken from a slow flowing river and a eutrophic pond. The anaerobic degradation rates were log k = -5.64 min-1 and log k = -5.62 min-1 (corresponding to the half-lives 212 days and 202 days), respectively. 1,2-, 1,3- and 1,4-dichlorobenzenes were formed in ratios of approximately 1.5:1:1.5 as confirmed by GC. Almost immediately after incubation began, monochlorobenzene could be detected.

 

Biodegradation in soil

1,2,4-TCB can be degraded in soil, although very slowly (Marinucci and Bartha, 1979; Wilson et al., 1981). The aerobic mineralisation was studied using 14C-labelled 1,2,4-TCB and a mineralisation rate measured as CO2 development/day (Marinucci and Bartha, 1979).
In a study using a sandy loam (pH 6.5) added 1,2,4-TCB at a concentration of 50 µg/g soil, the degradation in soil was observed to be slow. The incubation was performed at 20°C for 3 to 12 weeks. 1,2,4-TCB was subject to mineralisation as soil poisoned with 1% HgCl2 or NaN3 reduced the CO2 evolution consistently. Anaerobic conditions either continuously or alternated weekly with aerobic incubation periods markedly depressed the mineralisation. The mineralisation rate was 0.181 µg/day/20 g soil equivalent to 9 µg/d/kg. The turnover rate (% 1,2,4-TCB converted to CO2/day = 0.075%) was maximal at 10 µg/g soil and sharply declined at higher concentrations (Marinucci and Bartha, 1979). Haider et al. (1974) used 10 µg/g (in 100 g soil) and observed a mineralisation rate about twice as high.
In a degradation study in soil 1,2,4-trichlorobenzene was converted to 2,4,5- and 2,4,6-chlorophenol (Ballschmiter et al., 1977). Other studies support these findings. Marinucci and Bartha (1979) showed a degradation of 9 µg/kg/day. Adapted microorganisms are able to degrade 1,2,4-trichlorobenzene with high efficiency (Haberer and Normann, 1987). 

1,2,4-Trichlorobenzene will be expected to adsorb to the organic matter in soil. It will not hydrolyze but it may biodegrade, slowly in the soil.

The Half-lives in soil is:
high: 4320 h (6 m)
low : 672 h ( 4 w)

Scientific judgement based upon unacclimated aerobic soil grab data (low t1/2: Haider, K. et al. (1981), high t1/2: Marinucci, A.C. and Bartha, R. (1979)

The suggested half-life in soil is:
mean half-life (hours): 5500 ( ca. 8 months)
range (hours): 3000 – 10000