Localization of polycyclic aromatic hydrocarbons and heavy metals in surface soil of Asia’s oldest oil and gas drilling site in Assam, north-east India: Implications for the bio-economy

The environmental influx of hazardous contaminants viz PAHs and HMs occurs due to oil and gas drilling, and processing of petroleum products in industrial facilities and refineries. This problem plagues crude oil drilling sites as PAHs are an essential component of and HMs coexist with crude oil. We analyzed the spatial distribution of 16 PAHs and 8 HMs in 10 contaminated sites of Assam, a state in India. These included Digboi, where crude oil was drilled in 1867 and the first oil well in Asia that was drilled. The Ʃ16 PAHs in soil were detected with a minimum of 13.48 and a maximum of 86.3 mgkg−1 and Ʃ 8 heavy metal concentrations in the soil ranged between 69.51 and 336.06 mgkg−1. A negative correlation was detected between the relative concentrations of PAHs and HMs. The results confirmed that the non-biodegradable nature of HMs made them stay in the soil for longer periods of time. In our study, we found that the levels of lead, copper, nickel, and chromium (total) in soil were 73.62, 11.86, 58.97 and 158.66 mgkg−1. The recovery percentage for PAHs and HMs were in the range of 67–97% and 90–95% respectively. Spatial distribution indices for Phenanthrene/Anthracene, Naphthalene/Acenapthhylene, Chyrsene/Benzo (g, h, i) perylene and Fluranthene/Pyrene) calculated for soil samples indicated that the spatial distribution of PAHs in soil is uneven which might be due to variations in contaminates disseminated in soil. Such regionalized concentration has serious implications on the bio-economy both in terms of health and economy, especially since the proximity of crude oil sites to paddy fields and/or tea plantations uniquely marks the landscape of upper Assam.

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