Environmental Engineering Reference
In-Depth Information
Table 5
Concentrations of PAHs in runoff sediments (mg/kg)
Dibenzo-
thiophene
Anthr-
acene
Fluor-
anthene
Rivers
Sampling date
Indene
Azulene
pyrene
Mutale
Dec 01, 2005
72.5
469
877
313
2,350
4,620
Mutale
Dec 21, 2005
106
558
298
322
8,490
530
Nzhelele
Dec 21, 2005
166
ND
118
-
419
636
Nzhelele
Jan 10, 2006
176
ND
140
1,730
414
2,610
Mutshundudi
Dec 21, 2005
96.4
ND
2,530
18,200
5,170
4,180
Mutshundudi
Jan 10, 2006
123
ND
31,500
14,500
1,500
9,890
Dzindi
Jan 10, 2005
159
ND
341
6,740
15,100
17,800
Thohoyandou
Dec 01, 2005
67.5
ND
1,370
112
7,010
617
Thohoyandou
Dec 19, 2006
179
ND
2,700
16,400
12,700
3,280
University
Parking lot
Dec 19, 2005
124
ND
270
23,400
3,570
34,000
Probable sources of PAHs in the water and sediment samples might be contribu-
tions from traffic density coupled with the surface wash off of petroleum spillages
from gas stations and auto garages. Other sources might be from indiscriminate
refuse dumps and leakages from these dumps and from partially treated waste water
effluents from the town's water treatment plants which drains into the rivers. PAHs
which have anthropogenic origin are formed from either combustion of organic matter
or as a discharge of petroleum related materials. Petroleum derived residues contain
high levels of 2-3 ring PAH compounds, that is petrogenic, while high molecular
weight PAHs.are formed in high temperature combustion processes
[27]
. High levels
of pyrene and fluoranthene as shown relatively in this study were indicative of PAH
pollution from incomplete combustion, pyrolysis of fuel and oil burning (i.e., they
have pyrolytic origin)
[28]
. Most of the PAHs identified in this study are those usually
found in environmental samples some of which are carcinogenic
[29, 30]
.
Generally the values in this study were higher than those reported for some devel-
oped countries
[31]
. These elevated levels are probably due to indiscriminate dis-
posal of untreated industrial waste water into the environment, washout of spills
from auto garages, burning of fossil fuel and vegetation and exhausts from vehicles
which is common practice in the study area
[31]
. However, the levels of PAHs found
in the water samples are lower than the maximum allowable concentrations of 3
mg/L in water samples
[13]
. Thus the levels of PAHs in the water samples would not
pose any serious health threat to downstream users of water from the rivers.
Conclusion
Liquid/liquid extraction (LLE) and Soxhlet extraction (SE) methods have been
used to determine PAHs in water and sediment samples, respectfully. Levels in
surface runoff were higher than those in river water samples and levels in sediment
samples were higher than those in water samples. Generally levels of PAHs found
