Petroleum hydrocarbon distribution in continental shelf region of southeast coast of India

In the surface sediment samples collected from 7 transects in the continental shelf region off Karaikkal, Parangipettai, Cuddalore-SIPCOT, Cheyyur, Chennai, Tammenapatanam and Singarayakonda in the southeast coast of India at the depths of 30m, 50m, 75m, 100m, 150m and 200m, the petroleum hydrocarbon (PHC) varied from 1.582 μg/g (Karaikkal 150m) to 4.065 μg/g (Cheyyur 75m). The correlation between PHC and organic carbon content was not significant. However PHC and mean particle diameter showed significant negative correlation (P<0.01). In Singarayakonda transect, the nature of the sediment was silty at all the depths (except 30m - coarse sand) and consequently the average concentrations of PHC and total organic carbon (TOC) (2.844 μg/g and 2.864 mg/g) were higher. This is attributed to the influence of rivers Krishna, Gundlakamma, Polleru and Uppuino which discharge more sediment besides agricultural runoff and urban sewage. The average concentration of PHC in Cheyyur, Cuddalore - SIPCOT and Parangipettai transects was 2.818, 2.332 and 2.324 μg/g respectively. It is attributed to the influence of rivers in these areas (Palar, Gaddillam, Uppanar, Vellar and Coleroon) besides Kalpakkam Atomic Power Station and industrial discharges from SIPCOT. In the Canonical Analysis of Principal Coordinates (CAP) plot, the first axis explained about 51.84% of the variability and the second 18.67 % (totally the first two axes explained 70.51% of the variability). The canonical correlation values of first 2 axes were 0.7497 and 0.5865 respectively. The PHC level observed in the present study was found to be lower than the levels reported from other coasts. As the coastal region in the study area continues to grow in all the dimensions economically, continuous monitoring of PHC is quite essential especially the three fractions pyrolytic, petrogenic and biogeneic fractions of PHC.