1. Tasman Spirit oil Tanker in 2003
Evaluation of Marine Sediments Contamination by Polycyclic Aromatic Hydrocarbons (PAHs) along the Karachi Coast, Pakistan after Tasman Spirit Oil Spill
Sanober Kahkashana,c, Xinhong Wanga*, Chen Jianfangb ,Miaolei Yaa, Yizhi Caia, Monawwar Saleemc, Javed Aftabc
a State Key Laboratory of Marine Environmental Science, College of the Environment & Ecology, Xiamen University, Xiamen , China.
b Laboratory of Marine Ecosystem and Biogeochemistry, Second Institute of Oceanography, SOA, Hangzhou,310012, P. R. China
c National Institute of Oceanography, Clifton, Block-1,Karachi-75600, Pakistan.
ABSTRACT: In 27th July 2003, approximately 31,000 tons of Iranian light crude oil were affected the coast of Karachi. Ten years later, the aquatic pollution of the coastal area of the Karachi was evaluated by measuring the polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues (alkylated-PAHs) in marine surface sediment. A total of 24 surface sediment samples were collected at the spill sites, harbor, creek and offshore. The concentrations of PAHs (∑20 parent components) were in the range of to ng/g dw, the highest values being close to coastal urban areas (e.g. Karachi Harbor and Gizri Creek). Meanwhile, the concentrations of ∑alkylated PAHs in marine surface sediment were ng/g dw. The maximum components were fluorene (543.17ng/g dw), naphthalene (61.54ng/g dw), perylene (53.04 ng/g dw) and fluoranthene (50.91ng/g dw). The composition pattern of PAHs was dominated by the presence of three-rings (60.57% ±14.07%) and four-rings PAHs (13.65% ± 11.42%). The ratios of high molecular weight/low molecular weight (HMW/LMW), phenanthrene to anthracene (Phen/An), fluoranthene to pyrene (FL/Py) and benzo (a) anthracene to chrysene (BaA /Chry) showed that the main origin of PAHs in the sediments of the Karachi coast was originated largely from the high-temperature pyrolytic sources, whereas the petrogenic sources were more commonly responsible for PAH contamination in harbors and creeks. According to the numerical effect-based sediment quality guidelines of the USA, the current concentrations of PAHs in sediments of Karachi coast would be unlikely to cause adverse effects. The concentrations of 17 polycyclic aromatic hydrocarbons (PAHs), identified as priority pollutants by the USEPA, decreased relative to those reported for different parts of the world indicates a low to moderate level of PAH contamination in marine sediment of Karachi coast.
Introduction
An oil spill accident was recorded on July 27th 2003, a Pakistan National Shipping Corporation (PNSC) chartered Greek oil tanker, MT Tasman Spirit carrying 67,535 tons Iranian light crude oil for delivery to Pakistan Refinery Limited grounded at 1.5 nautical miles from shore adjacent to the approach channel of Karachi Harbor of Karachi city, Pakistan under unfavorable weather conditions. As a huge quantity about 31,000 tons of the oil spilled, due to rough sea conditions and high wind speed caused the biggest oil spill in Pakistan’s history. The worst oil impacted coastal areas were observed to be Clifton and DHA Beaches, Karachi Harbour and offshore area.
Karachi is situated in the south of the Pakistan at the coast of the Arabian Sea and coastal zone is about 167 km long. Karachi, the largest city, principal seaport, and the traditional business center of Pakistan
PAHs compositions
The PAHs’ composition pattern was dominated by the presence of three-ring (60.57% ±14.07) and four-ring PAHs (13.65% ± 11.42) (Fig.3).
Fig.3.The distribution pattern of 2–6-ring PAHs in surface sediments at different sampling stations
PAHs sources
Study area
The study area covers about 38.7 km of coastline extending from Paradise point to Ibrahim hyderi fish harbor(Fig.1)
Tasman Spirit oil Tanker in 2003
Fig.1. Location of sampling stations for surface sediment along Karachi coast (n=24)
Result and Discussion
Fig. 4. PAH cross plots for the calculated ratios
Molecular ratios showed (Fig.4) that the main origin of PAHs in the sediments of the Karachi coast was originated largely from the high-temperature pyrolytic sources, whereas the petrogenic sources was more commonly responsible for PAH contamination in harbors and creeks.
PAHs concentrations
The ∑ 20 P-PAH concentrations in sediments of the coast of Karachi ranged from to ng/g dw (Fig.2). The highest PAH levels were found in station S2 ( ng/g), which is close to Karachi harbour, outfall of Lyari river.The stations S19 and S20 which are less affected by human activities have shown the lowest concentrations of total PAHs.
Conclusion
The concentrations of ∑20 parent PAH ranged from to ng/g dw while the concentrations of ∑alkylated PAHs varied from ng/g dw.
The concentrations of ∑17 parent PAHs US EPA priority pollutants ( ng/g dw) in the current investigation decreased respect to concentration of ∑16PAHs ( ng/g dw) in 2006 after the Tasman spirit oil spill, which also indicated low to moderate level compared to other marine sediments from different parts of the world.
The possible source of PAHs in the majority of sediment samples at the Karachi coast is pyrogenic such as from incomplete and complete petroleum combustion from boats, ships, and vehicle engines. In other areas, the sources could be petrogenic such as from releasing of fuel oil from boats.
Concentrations did not exceed the SQG ERL (4022 ng/g), indicating the absence of acute biological effects
Fig.2.Total ∑20 P-PAHs concentration in sediment samples (ng/g dw) along Karachi coast
*Corresponding author.
Acknowledgements
The authors greatly thankful to colleagues of National Institute of Oceanography, Karachi, Pakistan and Second Institute of Oceanography, Hangzhou, China for support and assistant.