Accumulation and Ecological Risk of Heavy Metals and Polycyclic Aromatic Hydrocarbons (PAHs) in Surface Sediments from Typical Estuaries in Hainan Island

Heavy metals and polycyclic aromatic hydrocarbons (PAHs) are the ecological research focus because of their teratogenicity, carcinogenicity, and mutagenicity. Hainan Island is China's first ecological civilization pilot area, and the continuous acceleration of urbanization will increase the pressure on environmental protection in the estuary area. The Changhua River, the Luodai River, and the Sanya River are important seagoing rivers in Hainan Island. At present, there is a lack of reports on heavy metals and polycyclic aromatic hydrocarbons in the sediments of the Changhua and Luodai Rivers, and there are differences in the related research results of the Sanya River.

To understand the characteristics, source, and ecological risk of heavy metals and PAHs in surface sediments from the estuary of the Changhua, Luodai, and Sanya Rivers in Hainan Island.

Sediment samples from the three estuaries were collected. Inductively coupled plasma-mass spectrometry/optical emission spectrometry (ICP-MS/OES) and atomic fluorescence spectrometry were used to determine the content of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn). Gas chromatography-mass spectrometry was used to determine the content of PAHs. Source apportionment was further explored based on the correlation analysis and composition of the contaminants, and the ecological risk evaluation was carried out with the potential ecological risk index (PERI) and sediment quality guidelines (SQGs).

The average contents of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the sediments of Changhua River were 3.24, 0.03, 7.03, 5.33, 0.007, 3.06, 16.9, and 14.1mg/kg, respectively. The corresponding values of these metals in Luodai River were 4.81, 0.02, 7.69, 4.56, 0.010, 3.29, 18.3, and 14.7mg/kg, and the corresponding values in Sanya River were 5.83, 0.05, 15.3, 8.28, 0.021, 4.91, 21.4, and 29.8mg/kg. Exception to As, the concentration of other heavy metals in the sediments were below or close to the Hainan soil baseline, showing little heavy metals accumulation effect. The contents of PAHs in the sediment range from 3.48 to 56.6μg/kg, from 8.72 to 56.8μg/kg, and from 6.41 to 573.9μg/kg for the Changhua, Luodai, and Sanya River, respectively. Compared with other regions, the sediment PAHs content in the study area was relatively low.

Arsenic in the estuarine sediments of the three rivers and Cd, Cu in the Sanya River are strongly influenced by anthropogenic factors, while the regional background mainly influences the remaining elements. PAHs originated mostly from the low-temperature combustion of biomass. The ecological risk evaluation demonstrates that the biotoxic effect of the heavy metals and PAHs is not obvious, mostly with low ecological risk. The present study on heavy metals and PAHs contamination in surface sediments of the three estuaries will provide a reference for future research.