Assessment of cadmium contamination in the sediments of Changjiang （Yangtze） River by reflectance spectroscopy

• Published in: Chinese journal of geochemistry 2006, Vol.25 (B08), p.226-226
• Main Author: Xueqi XIA Jun CHEN Hongrui MA Junfeng JI
• Format: Article
• Language: English
• Subjects: 反射光谱法; 水体污染; 沉积物; 环境污染
• ISSN: 1000-9426; 1993-0364

A recent multi-purpose geochemical mapping program revealed cadmium （Cd） anomaly along the entire Changjiang River Basin. The sediments of the Changjiang River and the related soil are shown to have Cd concentrations several times higher than the background value. In this study, we investigated the relationship between Cd concentration and the spectral reflectance of the sediments within the visible-near-infrared （VNIR） region （0.4-2.5 μm） and explored the feasibility of predicting the Cd concentration in the Changjiang sediments using measurements of Reflectance Spectroscopy. Based upon the measurements from 70 sediment samples collected in the lower reaches of the Changjiang, we found a significant correlation between sediment Cd concentration and the first derivative values of the reflectance spectra between 450-720 nm （approximately within the visible spectral region）, and the results showed that the Cd concentration in the Changjiang sediments can be predicted by a power equation： y=133.25×power （x, 1.759） （R2=0.666）, wherey is Cd concentration and x the first derivative value of reflectance at 694 nm. This observation agrees with the spectral characteristics of Fe oxides and clay minerals in the 450-720 nm range, and the high slopes （first derivative values） of goethite and hematite at 694 nm. The prediction of Cd concentration by spectral data depends on the inter-correlation of Fe oxide and Cd. Fe oxides have strong scavenging efficiency for heavy metals and also an absorbent for heavy metals. This hypothesis is further supported by the sequential extraction procedure of the sediments based on the BCR protocol, which indicates that about 40% of extractable Cd in the sediments is reducible and bound to Fe and Mn oxides, and another 40% is in the exchangeable, water and acid soluble state, in which a large part may be absorbed by Fe oxides; only 20% was bound to organic matter and extracted by H202. Moreover, Cd in reducible state is highly correlated with total sediment Cd concentration. Reflectance spectroscopy provided a nondestructive, less expensive, and fast method for the prediction of sediment Cd concentrations.