Reaction mass of carbon tetrachloride and chloroform and 1,2-dichloroethane

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Well documented study applying generally accepted scientific standards and available guidelines if available so far. The characteristics of the test item doesn’t match with recent requirements (e.g. too low recovery after extraction from test soils probably because of volatility).

Qualifier:

equivalent or similar to guideline

Guideline:

EPA OTS 796.2750 (Sediment and Soil Adsorption Isotherm)

Deviations:

yes

Remarks:

- special apparatus for volatile substances: Zero headspace Extractor ( ZHE) used

Principles of method if other than guideline:

A mixture of 16 volatile and semi-volatile compounds including CTC was incubated together in 2 soils at 5 concentrations in order to assess on
mixture effects on adsorption

GLP compliance:

no

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

The test temperature is not stated in the publication of Walton et al (1992) but it is assumed that ambient temperature conditions applied and
therefore 20±5 °C is stated in the sections below.

Analytical monitoring:

yes

Details on sampling:

After 18 h of rotation, movement of the piston was used to effect filtration of the suspension through a glass-fibre filter (0.7-mm pore space) contained within the Zero Headspace Extractor (ZHE). Two 2-mL samples of the aqueous filtrate were withdrawn directly into a glass syringe and transferred to 2-mL septum-scaled glass vials, which were then capped without a headspace, for chemical analysis. The resultant soil cake was then extracted with three 50-mL aliquots of methanol by rotating the ZHB for 15 min during each extraction. Aliquots of the methanol filtrate were taken in a manner identical to the aqueous nitrate samples. The recovery of each chemical as determined from analysis of both the aqueous and methanol extracts.
Samples were stored at 4 °C until analysis, which occurred within 14 d as specified in the USEPA Method 624 (USEPA. 1984). Care was taken to limit exposure of the samples to the atmosphere during all phases of the experiment.

Details on matrix:

Two soils, a Captina silt loam from Roane County, TN, U.S.A and a Laurin sandy loam from Stone County, MS, U.S.A. were used.
Both soils were acidic and low in organic carbon content:
- Captina silt loam, pHcalcium chloride = 4.97±0.08 and organic carbon content = 1.49±0.06%
- McLaurin sandy loam, pHcalcium chloride = 4.43±0.03 and organic carbon content = 0.66±0.04%
The soils were air dried and sieved to 2.0 mm before experimental use.
Selected properties of these soils are given by Walton et al (1989) and Anderson et al (1991).

Details on test conditions:

7 experiments with CTC (2 replicates) were conducted.
Each of the 19 substances were added to the reaction vessel, in individual concentrations of 100, 500, 550, 600 and 650 µg/g (=mg/kg) of soil
Zero Headspace Extractor (ZHE) type reaction vessel was used.

Sample No.:

#1

Duration:

18 h

Initial conc. measured:

100 mg/kg soil d.w.

Sample No.:

#2

Duration:

18 h

Initial conc. measured:

500 mg/kg soil d.w.

Sample No.:

#3

Duration:

18 h

Initial conc. measured:

550 mg/kg soil d.w.

Sample No.:

#4

Duration:

18 h

Initial conc. measured:

600 mg/kg soil d.w.

Sample No.:

#5

Duration:

18 h

Initial conc. measured:

650 mg/kg soil d.w.

Sample No.:

#6

Duration:

18 h

Initial conc. measured:

100 mg/kg soil d.w.

Sample No.:

#7

Duration:

18 h

Initial conc. measured:

500 mg/kg soil d.w.

Sample No.:

#8

Duration:

18 h

Initial conc. measured:

550 mg/kg soil d.w.

Sample No.:

#9

Duration:

18 h

Initial conc. measured:

600 mg/kg soil d.w.

Sample No.:

#10

Duration:

18 h

Initial conc. measured:

650 mg/kg soil d.w.

Type:

Koc

Value:

>= 48.89 - <= 143.6

Type:

log Koc

Value:

>= 1.69 - <= 2.16

Adsorption and desorption constants:

The mean values from 7 determinations performed with CTC were:

Sorption partition coefficients (Kp)
2.140±0.478 for the silt loam and 48.9±16.16 for the sandy loam

Sorption Coefficients (Koc)
143.6±32.11 for the silt loam and 48.9±16.16 for the sandy loam, while the weighted mean Koc value for both soils was calculated being 115.2

Recovery of test material:

CTC showed an average extraction efficienty of 65±11.6% in the Captina silt loam and 58±4.7% in the McLaurin sandy loam.

Concentration of test substance at end of adsorption equilibration period:

no data

Transformation products:

not measured

Validity criteria fulfilled:

not applicable

Executive summary:

Most CTC released to soil is expected to volatilize rapidly due to its high vapour pressure. A fraction of CTC remaining in the soil may adsorb to the soil organic matter. Nevertheless, CTC is expected to be moderately mobile in most soils, depending on the organic carbon content. The composition of the soil organic matter and the water content of the soil may also affect adsorption.

Walton et al. (1992) studied the adsorption of CTC from solution onto two soils, a silt loam (1.49% organic carbon) and a sandy loam (0.66% organic carbon). The soil was shaken with several concentrations of CTC (100, 500, 550, 600, and 650 mg/kg soil) in a mixture together with 15 further volatile and semi-volatile substances in a Zero Headspace Extractor (for reduction of volatilisation losses) for 18 h. The K_ocmeans from 7 determinations were 143.6±32.11 for the silt loam and 48.9±16.16 for the sandy loam, while the weighted mean K_ocvalue for both soils was calculated being 115.2. The sorption was independent from the concentrations used. This implicates that soil sorption from non-ionic organic compounds from water on soil sorption is a non-competitive process under the conditions tested and the found values for CTC are considered valid and comparable to ones from single component tests.

Description of key information

Based on data available on CTC, the substance is considered as highly mobile in soils according to McCall et al. (1980) (Koc <150 L/kg).

Constituent values (Koc):

Carbon tetrachloride (CTC): 115.2 L/kg

Key value for chemical safety assessment

Koc at 20 °C:

115.2

Additional information

No experimental study was conducted on the multiconstituent substance (Flux1). Instead, a constituent-based, Weight-of-Evidence approach, was performed.

The three major constituents were targeted, representing ca 95% of a typical composition (carbon tetrachloride(CAS n° 56-23-5), 1,2-Dichloroethane (CAS n°107 -06 -2) and chloroform (CAS n° 67-66 -3)). Numerous published data were available, and a single consensus value was selected for each, from a reliable source.

No average key value was derived for the multiconstituent substance: as the Risk Assessment is conducted per constituent, individual values are the key data.

Carbon tetrachloride (Walton et al. 1992; K2):

The K_ocmeans from 7 determinations were 143.6±32.11 L/kg for the silt loam and 48.9±16.16 L/kg for the sandy loam, while the weighted mean K_ocvalue for both soils was calculated being 115.2 L/kg.

Carbon tetrachloride is considered as highly mobile according to McCall et al. (1980) (Koc<150 L/kg).