Distribution and behaviour of polycyclic aromatic hydrocarbons in subtropical river estuary, Okinawa, Japan

ABSTRACT

Surface water samples were collected along the salinity gradient of Manko estuary in Okinawa, Japan, between January and November 2012, to examine spatial and temporal variability in the distribution, composition, behaviour, and sources of particulate polycyclic aromatic hydrocarbons (PAHs). Concentrations of total particulate PAHs ranged from 169.7 ng g⁻¹ at riverine station (N1) in November 2012 to 922 ng g⁻¹ at another riverine station (K3) in May 2012. Based on observed environmental behaviour, particularly relationships to organic matter, the PAHs appear divisible into two groups: group I (low molecular weight) PAHs were characterised by low particles affinity and strong correlations with a pool of autochthonous organic matter (e.g. high concentrations of polyunsaturated fatty acids), reflecting processes controlling their delivery to the estuary; and, in contrast, group II (high molecular weight) PAHs were characterised by high particles affinity and exhibited estuarine distribution primarily controlled by suspended solid load and inputs from terrigenous sources through river inflows. This relationship, coupled with isomer ratios indicative of combined mixed sources from petroleum and petroleum combustions, indicates that terrestrial run-off is the dominant mode of delivery of particulate PAHs in the estuary. The relationships between distinct groups of PAHs and lipid biomarkers demonstrated in this study suggest that very specific pools of particulate organic matter, as opposed to concentrations of particulate organic carbon alone, can be important in the transport and fate of hydrophobic contaminants.

KEYWORDS:

• Polycyclic aromatic hydrocarbon
• subtropical river estuary
• autochthonous organic matter
• Okinawa

Acknowledgements

I am grateful to Yumie Shiroma and other technical staff of the instrumental centre, University of the Ryukyus, for their dedicated and highly skilled assistance in the laboratory.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was partly funded by Schlumberger Foundation-Faculty for the future programme. Their support is highly appreciated.