Accumulation of heavy metals and trace elements in fluvial sediments received effluents from traditional and semiconductor industries

Abstract

Metal accumulation in sediments threatens adjacent ecosystems due to the potential of metal mobilization and the subsequent uptake into food webs. Here, contents of heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) and trace elements (Ga, In, Mo, and Se) were determined for river waters and bed sediments that received sewage discharged from traditional and semiconductor industries. We used principal component analysis (PCA) to determine the metal distribution in relation to environmental factors such as pH, EC, and organic matter (OM) contents in the river basin. While water PCA categorized discharged metals into three groups that implied potential origins of contamination, sediment PCA only indicated a correlation between metal accumulation and OM contents. Such discrepancy in metal distribution between river water and bed sediment highlighted the significance of physical-chemical properties of sediment, especially OM, in metal retention. Moreover, we used Se XANES as an example to test the species transformation during metal transportation from effluent outlets to bed sediments and found a portion of Se inventory shifted from less soluble elemental Se to the high soluble and toxic selenite and selenate. The consideration of environmental factors is required to develop pollution managements and assess environmental risks for bed sediments.

Figure 1. Sampling sites for river waters, sediments, or discharged sewage effluents in the Fazih and the Wu River basin.

Water and sediment samples were collected from 12 sampling sites scattered in the Fazih River (F1–F6) and the Wu River (W1–W6). The sewage effluents were discharged from hospitals (S1 and S2), the Taichung Industrial Park (S3), the Taichung Precision Machinery Innovation Technology Park (S4), and the Central Taiwan Science Park (S5). The map was generated using ArcGIS 10.0 software.

Figure 2. Environmental factors of water. (a) pH, (b) ORP, and sediments (c) EC, (d) amorphous Fe, (e) amorphous Al, and (f) TOC for the sampling sites.

The pH, ORP, and EC data were collected from water samples. Amount of amorphous Fe, Al, and TOC were derived from sediment samples.

Figure 3. Metals contents for river waters sampled from the Fazih (F1~F6) and the Wu (W1~W6) River, and the sewage sampled from effluent outlets (S1–S5).

Dash lines are values of the Criterion Continuous Concentration (CCC) established by the USEPA. Currently there is no CCC available for Ga, In, and Mo.

Figure 4. Metals contents of sediments sampled from the Fazih (F1~F6) and the Wu (W1~W6) River.

Dash lines are values of the probable effect level (PEL) established by the Canadian Council of Ministers of Environment (CCME). Currently there is no PEL available for Ni, Ga, In, Mo, and Se.

Figure 5. Ecological risk indices (RI) for sediments sampled from the Fazih (F1~F6) and the Wu (W1~W6) River.

The RI values of 150, 300, and 600 are the boundaries to determine the potential ecological risk.

Figure 6. Plots of the PCA based on metal concentrations and environmental factors in (a) water and (b) sediment samples.

Figure 7. Selenium K-edge XANES spectra (dashed lines) and results of linear combination fitting (solid lines) for sediments collected in the Fazih (F2, F3, and F6) and the Wu (W4 and W5) River as well as suspension solids collected from the effluent outlet of S5.