Distribution, risk assessment, and quantitative source apportionment of heavy metals in surface sediments from the shelf of the northern South China Sea.

The concentration of heavy metals (Cu, Pb, Zn, Cr, Co, and Ni) from 421 sediment samples from the shelf of the northern margin of the South China Sea (SNSCS) was analyzed. The heavy metal content and calculated potential ecological indicators (Eri < 40 and RI < 160) indicate that there is low potential ecological risk of heavy metal pollution in the SNSCS. The mean effects range-median quotient (M-ERM-Q) and hazard quotient (HQ) values of sediment toxicological characteristics indicate that heavy metals are a potential toxicological risk. The high-risk area is mainly distributed in the southwest of the nearshore SNSCS. The positive matrix factorization (PMF) analysis results showed that major contributors to heavy metal pollution were natural sources and anthropogenic activities in the SNSCS. The government should pay particular attention to the monitoring of heavy metals in the nearshore southwest of the SNSCS.

Distribution and source determination of rare earth elements in sediment collected from the continental shelf off Hainan Island, China.

Contents of rare earth elements (REEs), major elements, and the total organic carbon (TOC) were determined for 152 surface sediment samples collected from the continental shelf off Hainan Island (CSHI). From high to low, the average contents of REEs were as follows: Ce > La > Nd > Pr > Sm > Gd > Dy > Er > Yb > Eu > Ho > Tb > Tm > Tm. The LREEs in the south are more abundant than in the north, which is shown by the higher LREE/HREE values in south than in the north. This resulted higher values for the LREE/HREE ratio in the south than in the north. The mean enrichment factor (EF) could be arranged from highest to lowest as follows: Tm > Sm > Pr > Er > La > Lu > Ce > Tb > Eu > Nd > Yb > Gd > Ho > Dy. The EF indicates that pollution as a result of human activity was more serious in the southeast of the study area than in the north. The factors affecting the REE concentrations in this area include naturally occurring minerals and industrial pollution. Based on the spatial variation of upper continental crust (UCC)-normalized REE concentrations, the CSHI was classified into three geochemical provinces. The sediment of province I was controlled by the Red and Pearl rivers. The composition of the province II is mainly controlled by the Red River and the Pearl River, although some sediments have originated from the South China Sea Island. Province III sediments mainly originated from sources on Hainan Island.

The response of benthic foraminifera to heavy metals and grain sizes: A case study from Hainan Island, China.

Benthic foraminifera, heavy metals, and sediment grain sizes were studied in three bays of Hainan Island, and canonical correspondence analysis (CCA) and nonparametric regression were used to reveal the relationship between foraminifera and their environment. According to our survey, the three bays were moderately contaminated by Mo and As and uncontaminated to moderately contaminated by Pb, Zn, Cr, Sb, and Hg. The spatial pattern of heavy metals was comparable to sediment transport trends, indicating that their distribution was determined by sediment transport. Both living and dead foraminiferal assemblages were analyzed, and their compositions were similar, although the latter had a higher density and diversity. Based on the CCA method, species were divided into three groups, each of which responded differently to heavy metals and grain sizes. The response curves of individual species to heavy metals and grain sizes were obtained by using the Loess (locally weighted regression) method.

Change of coral carbon isotopic response to anthropogenic Suess effect since around 2000s.

The stable carbon isotope composition (δ13C) in coral skeletons can be used to reconstruct the evolution of the dissolved inorganic carbon (DIC) in surface seawater, and its long-term declining trend during the past 200 years (~1800-2000) reflects the effect of anthropogenic Suess effect on carbonate chemistry in surface oceans. The global atmospheric CO2 concentration still has been increasing since 2000, and the Suess effect is intensifying. Considering the coral's ability of resilience and acclimatization to external environmental stressors, the response of coral δ13C to Suess effect may change and needs to be re-evaluated. In this study, ten long coral δ13C time series synthesized from different oceans were used to re-evaluate the response of coral carbonate chemistry to Suess effect under the changing environments. These δ13C time series showed a long-term declining trend since 1960s, but the declining rates slowed in eight time series since around 2000s. Considering that the declining rates of the DIC-δ13C in surface seawater from the Hawaii Ocean Time-series Station and Bermuda Atlantic Time-series Station has not changed since 2000 compared with those during 1960-1999, the change in the coral δ13C trends at eight of ten locations may indicate that the response of coral δ13C to the anthropogenic Suess effect has changed since around 2000s. This change may have resulted from coral acclimatization to external environmental stressors. To adapt to acidifying oceans, coral may have the ability to regulate the source of DIC in extracellular calcifying fluid and/or the utilization way of DIC, therefore the response of coral δ13C to anthropogenic Suess effect will change accordingly.

The concentration distribution and biohazard assessment of heavy metal elements in surface sediments from the continental shelf of Hainan Island.

The level of heavy metals (Cr, Co, Ni, Cu, Zn, and Pb) and Al2O3 were quantified in 140 surface sediment samples from the continental shelf of Hainan Island (CSHI). The mean heavy metal concentration in the decreasing order was: Cr > Zn > Pb > Ni > Cu > Co. Although heavy metals were locally enriched in the CSHI, the overall pollution level was relatively low. The biohazard assessment results of the mean effects range-median quotient (M-ERM-Q) and hazard quotient (HQ) for a single metal element (Cu, Pb, Zn) in the surface sediments showed that the exposure to individual heavy metals posed a low health risk. However, the biohazard assessment of multiple metals was higher than the single metals. Particular attention should be paid to the potential biological hazard from Cr and Ni in the CSHI.

Bioaccumulation and changes of trace metals over the last two decades in marine organisms from Guangdong coastal regions, South China.

Trace metal (Cr, Ni, Cu, Zn, Cd and Pb) exposures, distribution and bioaccumulation were investigated in marine organisms from Guangdong coastal regions, South China. The results showed that all of the selected metals were observed in marine organisms with a predomination of Cu and Zn. The metal exposure levels exhibited obvious variations between species with the decreasing order of crab>shellfish>shrimp>fish. The higher metals enrichment seen in shellfish and crab species primarily attributed to their living habits and the higher sediment background values of trace metals. Endpoint bioaccumulation factor (BAFfd) was used to characterize the bioaccumulation potentials of marine organisms to trace metals, of which Cu and Zn were the most accumulated elements. The exposure of trace metals in the cultured organisms was far lower than those in wild marine organisms, which is probably due to the effect of growth dilution. Comparisons with previous studies demonstrated that the concentration profiles of most trace metals declined over the last one to two decades, except Cu, that increased indistinctively.

Distribution, source, and pollution assessment of heavy metals in Sanya offshore area, south Hainan Island of China.

Forty-four surface sediments from Sanya offshore area are analyzed for assessing heavy metals (Cu, Pb, Zn, Cr, Cd, Hg, and As) pollution. High metal values except for As are located in the southern areas which have fine-particle presence. However, high values of the metal As appear at a depth of 15-30 m in the Yazhou Bay. As and Pb show moderate contamination, and other metals show low contamination. The metals (except for As) are confirmed not to be enriched to slightly enriched, which are controlled by the grain size and mainly derived of the natural weathering products. The moderately severe to severe enrichment of As occurs in the Yazhou Bay and the nearshore area of the Sanya Bay. The reason is due in part to the excessive use of agricultural fertilizers. Further, it is also likely to be related to the high background value of As in the sea area.

Combined classification and source apportionment analysis for trace elements in western Philippine Sea sediments.

Trace elements have been widely used for classification (of variables and of samples) and source apportionment studies, but the comparison and combination of the two is uncommon in previous works. In this paper, the grouping of trace elements, clustering of samples, and source identification were merged for an integrated understanding of the origin and distribution of trace elements in western Philippine Sea sediments. The grouping and clustering studies were implemented by a nonlinear clustering method called a self-organizing map (SOM), and the source identification was accomplished by a nontraditional factor analysis method called positive matrix factorization (PMF). Through visualization and clustering techniques, the SOM simultaneously classified a database of 26 trace elements into four groups of trace elements and five clusters of samples. Each sample cluster occupies a certain geographic area and is characterized by high concentrations of trace elements that are classified within one or two groups. Five potential sources were identified by PMF, representing the land mass of Taiwan Island, anthropogenic emissions from Taiwan, nutrient exportation from the South China Sea, mineral attachment in the deep ocean, and biogenetic components and riverine inputs from the Luzon Islands. The spatial distributions of the sample clusters are comparable to the ranges of high contributions from the five sources distinguished by PMF. This conclusion was further supported by displaying the PMF outputs on the SOM plane. Furthermore, a corresponding relationship was observed between every factor profile and every trace element group. Our work tests the consistency of the classification (of the trace elements and of the samples) and source identification and improves the application of multiperspective methodology in environmental studies.