Appendix D - Dossier (PDF) - Tera

date: 20–JUL–2005
3. Environmental Fate and Pathways Substance ID: 71–43–2
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Type: volatility
Media: water – air
Method: other: calculated
Year: 1996
Method: Calculation of volatilisation of benzene from flowing river
water as a function of depth and flow velocity of river and
temperature of river water at a low wind velocity (0.25
m/s): the transfer rate of benzene across the water/air
interface is determined by the Henry’s law constant and the
mass transfer coefficients within the liquid and gas phases
respectively.
In case of volatilisation from water the initial
concentration in air is assumed c = 0.
Result: Winter (water temperature: 5°C, wind velocity: 0.25 m/s)
Half–life of benzene (in days) at water flow velocities of
0.032 m/s 0.316 m/s 3.16 m/s
Depth of river (m)
10 m 68.2 21.8 7.13
3.2 m 12.2 3.93 1.32
1 m 2.18 0.713 0.249
0.3 m 0.393 0.132 0.049
0.1 m 0.071 0.025 0.010
Summer (water temperature: 25°C, wind velocity: 0.25 m/s)
Half–life of benzene (in days) at water flow velocities of
0.032 m/s 0.316 m/s 3.16 m/s
Depth of river (m)
10 m 42.3 13.5 4.39
3.2 m 7.55 2.42 0.803
1 m 1.35 0.439 0.150
0.3 m 0.242 0.080 0.029
0.1 m 0.044 0.015 0.006
For a river with a depth of 3.2 m, the half–life distance at
low wind velocities (0.25 m/s) varies from 20.6 km or 33.3
km (25°C or 5°C, flow velocity 0.032 m/s) to 220 km or 359
km (25°C or 5°C, flow velocity 3.16 m/s).
For a stream with a depth of 0.32 m, the half–life distance
at low wind velocities (0.25 m/s) varies from 0.66 km or
1.05 km (25°C or 5°C, flow velocity 0.032 m/s) to 7.9 km or
13.4 km (25°C or 5°C, flow velocity 3.16 m/s).
So, the half–life distance of benzene is most strongly
influenced by the depth of the flowing surface water and
least strongly by the change in temperature (here: 5°C and
25°C).
The calculation method appears to be valid and gives results
very relevant for estimating the spreading of benzene
pollution in rivers under different environmental
conditions.
Source: German Rapporteur
Test condition: No data
Test substance: No data
Reliability: (2) valid with restrictions
Flag: Risk Assessment
16–MAR–2004 (868)
Appendix D: Benzene SIDS Dossier
– 189/957 –