Oil exploration activities: assessment of hazardous impacts on 'Golden silk' cultivation

Aliphatic-aromatic hydrocarbons and heavy metals (Cd, Cu, Co, Cr, Ni, Pb and Zn) were estimated in soil and leaf samples of Machilus bombycina (host plant of Antheraea assama silkworm) plantation along with atmospheric benzene, toluene and xylene (BTX) concentration near the oil exploration region of upper Assam, India, during the pre-monsoon and post-monsoon periods in six different sites. The results revealed higher aliphatic-aromatic hydrocarbons (ranging from 26.55 to 59.42 mg kg^-1) and heavy metal contaminations in all the six soil sampling sites during the pre-monsoon period while the trend was the opposite for the plant leaves. Polyaromatic hydrocarbons (9.85 mg kg^-1) were found in one soil sampling site near an abandoned oil well. The lead concentration in the soil showed values from 14.36 ± 1.5 to 96.5 ± 5.6 mg kg^-1 and found to be higher than the WHO limit in most of the samples. The aliphatic-aromatic hydrocarbon m-xylene was also found in M. bombycina plant leaves which could be traced due to crude oil. Cd and Pb concentrations in leave samples were found to be higher than the maximum allowable limit of 0.3 and 5.3 mg kg^-1, respectively. Principal component analysis of hydrocarbons in soil and leaves showed different clusters during the pre-monsoon and post-monsoon periods. The crude protein and total carbohydrate contents in the leaves were lower than those of uncontaminated samples which are an indication of a major disturbance to overall growth of plants. BTX concentration was found in the range of 119-198 μg m^-3 which indicates that atmospheric contamination in the studied area is causing the death of A. assama larvae.