In situ DGT Measurement of Bioavailable Metals in River Sediments

in International Symposium (poster summary), 國際研討會(摘要海報發表)
標題In situ DGT Measurement of Bioavailable Metals in River Sediments
AuthorsChang-Ling Miaw, 繆昌琳, Chi-Ying Hsieh 謝季吟, L.F. Lin 林立芳, & Shih M. Liang 梁仕旻
出版日期Oct 18 2017 12:0

Sediments are complex, within which many processes (physical/chemical interactions, acid volatile sulfide (AVS) interaction, and biological) occur that affect contaminant bioavailability. A combination of chemical assessment and biological toxicity testing was conducted to predict the toxicity of metals in sediments or pore water. Equilibrium partitioning models using AVS were applied simultaneously with extracted metals analyses to evaluate the bioavailability of sediment metals that exhibit toxic effects in the Niuchou (N1~N5) and Wuluo (W1~W5) Rivers in southern Taiwan.
In this study, the basic physico-chemical properties of sediments showed that those in the Niuchou River were mainly sand while in the Wuluo River they consisted of a higher proportion of silt. Total organic carbon ranged from 0.35% to 6.42%, with the lowest found at site N2 and the highest at station W5. The degree of contamination, based on different sediment quality indicators (Taiwan sediment quality guideline, threshold effect levels (TEL) / probable effects levels (PEL), and consensus-based sediment quality guidelines (CBSQGs)), indicated that Wuluo sediments exceeded guideline upper limits more often than in the Niuchou River. Site W4 in the Wuluo River exceeded three guideline values and three indicators (ΣSEM / AVS > 9, ΣSEM – AVS > 2 μmol/g, and ΣSEM - AVS / foc > 130 μmol/g) exerted the highest toxicities, and therefore had the greatest adverse impacts on aquatic life. The lowest impacts from metals were at sites N5, W2, and W3, as all three indicators did not exceed their thresholds. Our results showed that diffusion gradient thin films (DGT) under a 96-hr in situ field exposure were significantly correlated with adsorption mass in laboratory tests. A combination of the sequence extraction technique and risk assessment code calculation (RAC) showed that the risk in the Wuluo River was in the range of 62.5% (W2) ~ 87.5% (W3) and that the highest risks were from Mn and Pb. The risk for the Niuchou River was between 62.5% ~ 75%, with higher risk values being found for Mn and Zn. The potential ecological risk index showed that serious sediment contamination in the Wuluo River was from either single or multiple sediment indicators and the highest risk was at site W4.
In addition, whole-sediment acute toxicity tests using Hyalella azteca showed the highest survival rates at sites N1 and W2 while there were no survivors at sites N3, N4, W3, and W4. Our results showed that survival in porewater toxicity tests at sites N1 and N4 were 100% but less than 20% at sites W1, W4, and W5. The differences in survival between whole-sediment and porewater for N4 sediment were presumably caused by insoluble contaminants. Survival in toxic porewaters and DGT metal concentrations were better correlated than other extraction processes (total concentration of sediment, acid-diluted) for predicting bioavailability. The present findings support that these monitoring tools are comparable in the field for providing time-integrated assessments of metals and their bioavailabilities.

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