Keywords: 
• BTEX /
• PAHs /
• Northern Bohai Sea /
• ecological risk assessment

Abstract: Occurrence of typical aromatic hydrocarbons near oil and gas areas and their surroundings in northern Bohai Sea was investigated in May 2015. Seawater samples collected in 32 sampling sites were analyzed with the concentration measurement of 7 benzene and its derivatives (BTEXs) and 17 polycyclic aromatic hydrocarbons (PAHs). A single and joint ecological risk assessment of studied chemicals was performed by risk quotient method and toxicity equivalent method. Our present results demonstrated that the total concentration of BTEXs ranged from 65.1 ng·L^-1 to 222.6 ng·L^-1 in the seawater of the study area, among which toluene was the highest one. Furthermore, their concentration in surface water was slightly lower than that in the bottom, and the average concentration of them near the oil and gas areas was lower than the surroundings, which was affected by land-based inputs. The total concentration of PAHs in the surface seawater ranged from 98.9 ng·L^-1 to 356.0 ng·L^-1, with an average value of 184.5 ng·L^-1. Compared with other regions, PAH pollution was generally at a medium level with the lower number ring ones as major components. The risk quotient method indicated that the PAHs in this area might mainly come from petroleum and its processed products. The risk quotient (RQ) of benzo(a)pyrene in the waters was higher than 0.1, showing a low risk, and the concentrations of the other three compounds were at an acceptable level. The joint ecological risk of the four aromatic hydrocarbons was low with the existence of some differences in different regions, which had potential adverse effects on the ecosystem. The offshore oil exploitation and terrestrial source inputs were important factors affecting the ecological risks of aromatic hydrocarbons in this sea.