| Southeastern coast of Fujian province is one of thickly populated and fast economic developing district in China. After nearly three decades of economic reform and industrial development, a tremendous amount of waste was discharged to the coast, which resulted in serious environmental problems. Heavy metals are of considerable environmental concern due to their toxicity,wide sources, non-biodegradable properties and accumulative behaviors. Therefore, it is necessary to investigate the content, time-space distribution and speciation of heavy metals in coastal sediments where heavy metals accumulating. The result would make a great contribution to understand the heavy metal resources, pollution status and the effect to the ecosystem, and would have a great significance in protecting the marine environment and ensuring the sustainable development of marine economy.The spatial and temporal distribution, sources, speciation and bio-availability of ten heavy metals (Fe, V, Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb) were analyzed in the intertidal sediments collected from Quanzhou bay, an important estuary in southeast of Fujian province. Several assessment methods, which based on two different assessment systems (total content and sequential extraction), were applied to assess the pollution and potential ecological risk of heavy metals in the surface sediments. The main conclusions were summed up as follows.The average content order of heavy metals in the intertidal surface sediments from Quanzhou Bay was as following: Fe(38900 mg/kg)> Mn(1248 mg/kg)> Zn(238 mg/kg)> Cr(98.6 mg/kg)> Cu(82.5 mg/kg)> V(81.9 mg/kg)> Pb(74.0 mg/kg)> Ni(27.0 mg/kg)> Co(12.0 mg/kg)> Cd(1.17 mg/kg). The average contents of Pb,Cr,Cu,Zn,Cd and Mn in the intertidal surface sediments from Quanzhou Bay were higher than those in most of other domestic and overseas bays and estuaries, and were higher than the background values of Fujian coastal soil. Most of the studied heavy metals presented comparatively higher contents in the surface sediments of Jinjiang estuary and southern coast of Quanzhou Bay, whereas lower in the surface sediments of outside Quanzhou Bay because of the different impact of human activities. The results of multi-statistic analysis (including correlation analysis, principal component analysis and hierarch cluster analysis) showed that most of the studied heavy metals (except Fe and Mn) in the intertidal surface sediments of Quanzhou Bay mainly existed in fine grains, and combined tightly with organic matter other than sulfide and carbonate. Fe and Mn mainly came from the natural efflorescence and erosion of rock, and were influenced comparatively slightly by human activities. But most of other studied heavy metals had the same anthropogenic resources--industrial waste water, life sewage, solid waste, atmospheric settlement, and so on. The distribution of heavy metals in the core sediments showed that the highest polluted period was 1983~1995 on the whole. Since mid-1990s, the pollution degree of heavy metals presented appreciably light trend.The modified BCR-sequential extraction technique, assisted by microwave digestion, was used to determine the speciation (acid-soluble, reducible, oxidizable and residual fraction) of the studied heavy metals in the intertidal surface sediments from Quanzhou Bay. The results showed that Mn, Cd, Cu, Pb and Co mainly appeared in the extractable forms (the sum of the first three fractions), whereas Fe, V, Cr, Zn and Ni mainly appeared in the residual fraction, especially Fe and V presented more than 80% in the residual fraction. In the extractable forms, Mn, Cd and Zn presented comparatively higher percentages in the acid-soluble fraction, Cu, Pb and Co relatively higher in the reducible fraction, Cr and Ni relatively higher in the oxidizable fraction. Comparison of the sum of heavy metal contents in the four steps of BCR-sequential extraction procedure with the total digestion metal contents showed a good agreement for all elements,the recoveries for all metals ranged from 80% to 119%, indicating satisfactory accuracy and validation of the sequential extraction procedure. The mobility and bioavailability, based on the mean values of the relative abundance of the sums of the first three fractions, of the heavy metals in the surface sediments was in the following order: Mn (77.69%) >Cu (75.81%) > Pb (71.51%) > Cd (64.11%) > Co (53.97%) > Cr (49.13%)> Ni (48.92%) > Zn (46.55%) > V (18.34%) > Fe (18.07%). The extractable contents by 0.5 mol/L hydrochloric acid of most heavy metals (except Cr) accounted for the most of the extractable contents by BCR sequential procedure, and the extractable contents of most heavy metals (except V) by the two extracting methods presented significant positive correlation. But whether the comparatively simple one-step extracting method by dilute hydrochloric acid could be used instead of the relatively complex BCR sequential procedure to assess the bioavailability of heavy metals in sediments should be discussed further.Based on the total contents of heavy metals, five assessment methods were applied to assess the pollution degree and potential ecological risk of heavy metals in the intertidal surface sediments from Quanzhou Bay. The comparison of heavy metal contents from this study with that of Marine Sediment Quality (GB18668-2002) showed that the overall average contents of all studied heavy metals in the intertidal surface sediments from Quanzhou Bay met the secondary standard criteria but exceeded the recommended primary standard criteria. The results of geoaccumulation indices showed that Cd presented strong pollution, Cu presented moderate pollution, Cr, Mn, Zn, and Pb presented from low to moderate pollution, V, Co, Ni and Fe presented almost no pollution in most of the sites. According to the indices of potential ecological risk, the consequence of the average potential ecological risk index (Eir) for heavy metal was Cd > Cu > Pb > Ni > Co > Cr > Zn > Mn > V. On the whole, the comprehensive potential ecological risk index (RI) of the sediments presented very high degree. The potential ecological risk indices of the sediments for the different sampling area could be ranked in the following order: Jinjiang Estuary > Luoyang Estuary > Southern Coast of Quanzhou Bay > Outside Quanzhou Bay. According to the bio-effect concentration criteria, the average contents of Cr, Ni, Cu, Zn, Cd and Pb in the surface sediments of study area were all between the effects range low (ER-L) and the effects range media (ER-M), which indicating moderate negative bio-effect. According to the integrated response factors, the pollution indicator elements and their pollution contribution order were as follows Cd > Cu > Zn > Mn > Cr, and most sampling sites were polluted seriously by heavy metals.The result of the ratios of secondary phase and primary phase (RSP), based on the speciation analysis, showed that Cu, Mn, Cd and Pb were important pollution elements, and the pollution degree of heavy metals in the intertidal surface sediments from Luoyang Estuary was moderate whereas those in the other three study sub-areas were slight. Each of the above assessment methods has both strongpoint and shortcoming, and needs to be discussed and improved further. Therefore, several assessment methods should be combined to assess the pollution degree and potential ecological risk of heavy metals in sediments in order to ensure the rationality and scientificity of the assessment result.
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