| Concentrations of heavy metals in surface sediment collected from 18 stations of the Pearl River Estuary Pearl River estuary is one of the three largest estuaries in China with vital habitat supporting high biodiversity, many rare aquatic species and important aquaculture areas. In recent years, heavy metal pollution in the Pearl River estuary has increased, attributed primarily to human activities. In this investigation, the levels of six heavy metals (Cr, Cd, Cu, Pb, Zn, and Ni) were measured in surface sediments from the Pearl River estuary and the potential ecological risk was evaluated, based on the pollution index, geoaccumulation index (Igeo) and potential ecological risk index. The study provides a scientific basis for protecting the ecology of the Pearl River Estuary. Surface sediments were collected twice (January and April, 2015) at 18 stations (Z1-Z18), moving from north to south away from the shoreline of the Pearl River estuary. The average contents of Cr, Cd, Cu, Pb, Zn and Ni in the surface sediments of Pearl River estuary were 114.70, 0.80, 58.73, 80.01, 191.57 and 51.89 mg/kg, respectively, all exceeding the Class I standard for marine sediments (GB 18668-2002), but not the Class II criteria. The single-factor pollution index of the six metals followed the order: Cd > Pb > Zn > Ni > Cu > Cr. Cd pollution in the surface sediment was the most serious, with an average pollution index of 4.20 for all sampling stations and as high as 6 at stations Z3, Z5 and Z8. The pollution index of Cu was < 1 at Z4, Z12, Z15, Z16 and Z17, indicating slight Cu pollution, and it was moderate at other stations. Cr pollution in the surface sediments of the Pearl River estuary was moderate except at Z15. The pollution indices of Pb, Zn and Ni ranged from 1 to 3 across sites, indicating moderate pollution. The integrated pollution index for the 18 sampling stations ranged from 6.02 to 23.53, averaging 12.97. The highest integrated pollution index occurred at Z5 and the lowest at Z15. The index of geoaccumulation for Cr (＜0) indicates unpolluted sediment. The index of geoaccumulation for Pb, Zn, Cu, Cd and Ni all ranged from 0 to 1, indicating slightly polluted sediment. The index of geoaccumulation for Cd was the highest at Z1, Z10, Z11, Z13, Z14 and Z18, reflecting moderately polluted sediment. The range of the potential ecological hazard index for the sampling stations ranged from 25.79 to 386.02, with an average of 157.60, indicating that a moderate potential ecological risk is posed by heavy metals in the surface sediments of Pearl River estuary. The ecological risk in the northern (coastal) area was higher than the southern area and is clearly influenced by local discharges of industrial wastewater. The levels of the six heavy metals displayed similar distributions, declining from north to south and from west to east, with the highest levels primarily located at stations Z3, Z5, Z8 and Z11. Based on the three indices used in this study, the sediment in the study area is slightly to moderately polluted, but Cd pollution in the estuary is more serious and should receive attention. |
