There are various methods used in measurement of different physico-chemical parameters. pH, dissolved oxygen (DO), temperature, turbidity, flow rate, and conductivity parameters are measured using their respective individual probe meters. However, in this study LabQuest vernier instrument (Figure 2.2) was used to measure physico-chemical parameters. This instrument is designed in such a manner that probes of different physico-chemical parameters are connected to it. This method was used because of its advantages over individual meters. These include ability to measure four parameters at ago, easily portable, and a standalone device.
Figure 2.2: LabQuest Vernier device and its Probes
2.4 Polycyclic Aromatic Hydrocarbon in Water Bodies
Water plays an important role in sustaining life on earth for human, marine and aquatic ecologies. Specifically for man the pattern of human settlement throughout history has often been determined by its availability. Water is exposed to innumerous natural and/or anthropogenic influence in the form of pollutants including toxic metals such as lead, cadmium and chromium, persistent organic pollutants (POPs) such as polycyclic aromatic hydrocarbons (PAHs). Water pollution by PAHs has been determined for numerous rivers and seas of the world over time. A summary of some of these water bodies is given in table 2.2.
Table 2.2: Summary of Total Parent PAH Concentration (ng/L) in Surface Water from Various Sites in the World.
Location Range (ng/l) Mean ±standard deviation (ng/l) Source Aegean Sea(Eastern Mediterranean) 0.113 -0.489 0.216 Maldonado et al. (1999) Chesapeake Bay, USA
20 - 65.7 33.3 ±21.7) Gustafson and Dickhut (1997 Danube Estuary 0.183 -0.214 0.198±0.022 Maldonado et al.(1999) Seawater around
England and Wales
<1-24,821 1002±3342 Law et al. (1997) Seine River and
Estuary, France
4 - 36 20 ± 13 Fernandes et al. (1997) Surface water,
Northern Greece
184 - 856 465 ± 230 Manoli et al. (2000) Western Xiamen Sea,
China 106 - 945 355 ± 285 Zhou et al. (2000) Jiulong River Estuary, China 6960 -26,920 17,050 ± 5280 Maskaoui et al. (2002) Tonghui River, Beijing, China 192.9 - 2651 762.3 ±7 77.4 Zhang et al. (2004) Surface waters in Hangzhou, China 989–9663 3717 ± 2294 Chen et al. (2004) Mississippi river, USA 62.9–144.7 114.9 ± 17.2 Zhang et al. (2007)
York river, USA 2.09–122.85 Countway et al.(2003)
Daliao River watershed, china
946.1-13448.5 Guo et al. (2007)
Daya Bay, China 4228 – 29 325 Zhou and Maskaoui, 2003
In the United States of America a number of studies with regard to PAHs pollution are reported. Rhea and co-workers reported on levels of PAHs in water, sediment and snow from Lakes in Grand Teton National Park, Wyoming where concentrations of total PAHs in water, sediment and snow were 320 ng/L, 480 ng/g and 600 ng/L, respectively (Rhea
et al., 2005). Most of the water and snow samples contained primarily naphthalene and Phenanthrene attributed to anthropogenic activities. The concentrations of phenanthrene, fluoranthene, pyrene and benzo[a]pyrene in surface waters of the York River, VA Estuary and of Mesohaline region of Chesapeake Bay were found to range between 2.09 ng/L to 122.85ng/L (Gustafson and Dickhut, 1997; Countyway et al., 2003). The findings
indicated that there was little or no threat to fish, wildlife or humans based on the concentration of PAHs (Countyway et al., 2003). Water from the Mississippi river had three- and four-ring PAHs constituting the bulk of the total PAHs although the concentration range and composition were found comparable to those in several water bodies in the United States (Zhang et al., 2006).
In Germany, PAHs in water and sediment of the Baltic Sea showed that during autumn, the concentrations of total PAHs ranged from 0.001 to 4.8 ng/L and that two and three ring aromatics like naphthalene, acenaphthene and phenanthrene was more predominated than the those of the higher molecular weight five and six ring compounds which remained below 0.1 ng/L. The concentration of PAHs in spring was lower than during autumn and the lowest concentrations were measured in the summer. This was attributed to the fact that during the winter period, low sea water temperatures limit the microbial degradation of the PAHs. Further, the photo-oxidation of these compounds which is correlated to light intensity is also lower in autumn. On the other hand, during the spring plankton bloom, a high amount of detrital material is produced that might effectively scavenge the PAHs and transfer them to the sea floor. The conclusion made was that long-term exposure to low concentrations of PAHs found in the water samples can result to sub-lethal effects for aquatic organisms (Witt, 1995). Similarly, water from River Lo`dz` in Poland had mean concentration levels ranging from 0 to 18 ng/L for benzo(a)pyrene in water and in drinking water it was ranging from 10 to 20 ng/L although these levels were lower than 200 ng/L as recommended by WHO. The levels were generally high during the rainy summer and in autumn-winter which correlated with extensive rainfall and snowfall (Kabzinski et al., 2002).
In china extensive studies on PAHs pollution have been carried out with PAHs levels attributed to increasingly intense urban and industrial development and hence likely related to urban runoff, sewage outfalls and wastewater discharges. In Tonghui River, total PAHs concentrations in water varied from 192.5 ng/L to 2651 ng/L. High concentrations of 2610 ng/L and 1230 ng/L were found at the outlet of sewage and at the end of Wenyu River, which combines Tonghui River before merging with Beiyun River. In addition, there are many industries to the east of Beijing near the study area. Many of these industries were discharging black smokes, which could be potential atmospheric sources for PAHs in the area. The levels of PAHs in surface waters were relatively high although lower than those with known problems and that analysis of the possible sources of PAHs suggests heavy fuel combustion dominated PAH origin. Further investigation on levels of PAHs in suspended particle matter, atmosphere and biota were recommended (Maskaoui et al., 2002; Zhang et al., 2003).
In other water bodies in China, high levels have been reported. Levels of PAHs in water, suspended particulate matter and sediment from Daliao River watershed, China ranged from 946.1 to 13,448.5 ng/L in surface water. Concentrations were found to be very high near petroleum and chemical factories (Guo et al., 2006). Levels of PAH were also detected in the watershed and linked to sewage discharges, urban runoffs and wastewater from industrial area discharges. In terms of individual PAH in surface water, many of the PAHs compounds were present at concentrations in excess of 1000 ng/L, suggesting that the water in the area was heavily contaminated by PAHs. The concentration gradually decreased along the river due to the dilution of river water. The levels of PAHs were relatively higher in water and suspended particulate matter and lower in sediments in
comparison with those reported for other rivers and marine systems around the world. Further from this study it was found out that 4-6 rings PAHs predominated in the water, sediments and suspended particulate matter (Guo et al., 2006).
Next, in Daya Bay, China on distribution of PAHs in water and surface sediments revealed the levels of the total concentration of PAHs varying from 4228 to 29325 ng/L in water and from 115 to 1134 ng/g dry weight in sediments. The high concentration was found near Aotou port with intense urban and industrial development. This obviously could be related to urban runoffs, sewage discharges and intense shipping activities which were observed during the sampling. High concentrations (>11000 ng/L) were also found at Stations 7, 9, 10 and 13 which were close to an important oil terminal used for national and international trade, so any high concentrations there are potentially derived in part at least from the operation of oil loading and unloading there. In addition, there were many boats and a few ships travelling in the bay during sampling, many of them were discharging black smokes throughout their movement and hence there are many nonpoint sources of PAHs in the bay, contributing to the wide variations of PAH concentrations detected. Many of the PAH compounds were present at concentrations in excess of 1000 ng/L, suggesting that the water in the area was also heavily contaminated with PAHs. In comparison to many other marine systems studied, the PAH levels in Daya Bay waters were relatively high, and at six sites they were sufficiently high (more than 10 mg/L) to cause acute toxicity (Zhou and Maskaoui, 2003).
Chen et al. (2004) study on the distributions of PAHs in surface waters, sediments and soils of Hangzhou city, China reported total concentrations of 10 PAHs in water ranging
from 0.989 ug/L to 9.663 ug/L, with a mean concentration of 3.717 ug/L. The composition pattern of PAHs in water by ring size showed that three-ring PAHs (fluorene, phenanthrene, and anthracene) were the most abundant in all water samples. Four-Ring PAHs (fluoranthene, pyrene, benzo(a)anthracene, and chrysene) were more abundant in some water samples. Five-ring PAHs (benzo(a)pyrene, benzo(k)fluoranthene and benzo(a)pyrene concentrations were the lowest in all water samples and not detected in some water samples. Hangzhou section was heavily polluted by PAHs released from industrial wastewater in the past and now PAHs in sediment may serve as sources of PAHs in surface water. PAHs in Qiantang River were contributed from soil runoff. Municipal road runoff was mostly contributed to West Lake PAHs.
Finally, in the Jiulong River Estuary and Western Xiamen Sea, China Maskaoui et al.(2002) reported total PAH concentrations in water ranged from 6.96 ug/L at Station 12 to 26.9 ug/L, with a mean concentration of 17.0 ug/L. The highest concentration was observed at Station 1, which is situated just outside the bay. As a result of high PAH concentrations in water and pore water, it is likely that they may have caused mortality to certain exposed organisms. With increasingly intense urban and industrial development around Jiulong River and Western Xiamen Sea, the amount of PAHs detected there were also related to urban runoffs, sewage outfalls and wastewater discharges. The levels of PAHs in water were relatively high in comparison to other estuaries and bays. Contamination was dominated by high molecular weight compounds, particularly 5-ring PAHs. The PAH distribution profile in the study area indicated inputs from both point and diffuse sources, as the levels were high throughout the sampling sites.
In Africa, various studies have explored the pollution of the environment by PAHs. Essumang et al. (2009) reported average concentration of PAHs in the water ranging from 0.000 of many of the PAHs to 0.552 μg/L. Concentrations ranging from below detection level to 14.587 μg/L were also recorded at the Oblogo solid waste dump and its environ. The results of this study demonstrated that there were elevated levels of PAHs in the water samples of the Densu River, Chemu, Korle and Kpeshi Lagoons. These concentrations may have resulted from the combustion of the solid waste with the presence of domestic refuse and discarded solid materials such as those from commercial, industrial and agricultural operations. The higher concentration of some PAHs in the diluted leach with rain water shows how the atmosphere has been polluted through anthropogenic sources. All the concentrations detected in the leach diluted with rain water and downstream of river Densu were above the WHO’s limit of 0.05 μg/L. In analyzing PAH associations and their possible origins, correlation results revealed that Fluoranthene (containing 3 fused aromatic rings) showed inverse correlation with Naphthalene (at 0.01 level) containing 2 fused aromatic rings. It is speculated that some fraction of these compounds could be from the biodegradation of Fluoranthene (FL) by natural occurring population of water microorganisms since Fluoranthene is a PAH consisting of naphthalene and a benzene unit connected by a four- membered ring. Results revealed that people living around the Oblogo solid waste disposal site, who swim and bath in the downstream of river Densu would be exposed to PAHs and may be at risk of their harmful effects.
Levels of PAHs in selected water bodies in the Niger Delta, Nigeria varied from as low as 1.95 ug/L for relatively clean stream with practically no crude oil activity to 10.9 ug/L
for the most polluted stream (Anyakora and Coker, 2006). These levels were relatively high in that environment exceeding the WHO recommended maximum value for safety (50 ng/L). This suggests significant risk of cancer to the people of this environment. High molecular mass PAHs such as benzo(ghi)perylene, dibenz(a,h)anthracene and indeno(1, 2, 3-cd)pyrene were mostly absent confirming low water solubility of these compounds and carcinogenic PAHs were general lower in concentration than the non carcinogenic ones. The study pointed out that considering the limited water solubility of PAHs, it is expected that significantly higher concentrations will be detected in other lipid rich samples of that environment.
A similar study in Niger Delta in Ekpan Creek demonstrated that the total PAHs concentration was averaged at 0.1761 mg/L in water of Ekpan Creek was high compared to 0.002 mg/L and 0.003 mg/L recommended guidelines for fresh water. Contrary to reports in other creeks of the Warri River, the percentage composition of the 2, 3 - ring, low molecular weight PAHs in water of Ekpan creek was calculated to be about 63.4%, essentially higher than the percentage composition of the high molecular weight PAHs. This relative abundance of low molecular weight PAHs (LPAHs) indicated that the PAHs were from petrogenic origin such as oil leakages or inadvertent oil spills. Composition of PAHs in surface water was found to be largely different from that of the sediment of Ekpan Creek of the Warri River. While the origin of PAHs in the surface water was determined to be petrogenic because phenanthrene, anthracene, fluoranthene, pyrene, chrysene and benzo(a)anthracene were not detected, that of the sediment were from pyrogenic sources. There could have been unprecedented phenomena during the periods of sampling campaigns such as accidental oil or fuel leakages from barges or
transportation media along the water course which could possibly have played a major role in this sharp variation in source distinction between surface water and sediment of the aquatic system (Okoro, 2007).
In south Africa, Sibiya (2012) reported the levels of PAHs in water which ranged from 1.8 to 615.7 ng/L for liquid samples, where naphthalene, acenaphthene and phenanthrene were the most dominant. On comparing PAHs levels with those reported in the literature it was found that Western Cape was the most polluted province with acenaphthene and naphthalene being dominant. In Gauteng, naphthalene, acenaphthene and naphthalene were the most dominant and in Limpopo, fluoranthene and pyrene were dominant. These differences were attributed to the diverse sources of PAHs in each region. The correlation of liquid samples for the individual PAHs showed a positive correlation for naphthalene/pyrene (R2 =0.9798) and fluoranthene/pyrene (R2 = 0.7296). In South Johannesburg area (Jukskei River), its only fluoranthene/phenanthrene which showed a positive correlation (R2 = 0.8526). These positive correlations suggested similar source of
PAHs but generally results indicated that PAHs were from various sources.