A new assessment method of heavy metal pollution in tidal flat sediments using color indexes

Environmental monitoring methods for environmental protection of tidal flats is an important topic in wetland research. To search for a rapid assessment method of soil heavy metal contamination, in this work a color index system (L^*, a^*, b^*) was designed to evaluate the concentration of heavy metals (Cu, Cr, Pb, Zn, Mn, Fe ) in the sediments of Chongming Dongtan. The results indicated a strong correlation between the color indexes and heavy metal contents in sediments, which implies that the content of heavy metals in sediments can potentially be quantitatively deduced from the sediment color indexes. Regression models between the color indexes and the heavy metal concentrations were established and tested. In the low, middle and high beach sediments of Chongming Dongtan, there were significant negative correlations between Cu, Pb, Zn and L^*, with the highest correlation coefficient of Cu being -0.97, of Pb being -0.88 and of Zn being -0.98; there were significant positive correlations between Cu, Pb, Zn and a^*, but there were significant negative correlations between Cr and a^*. This work shows that when the heavy metal content in the estuary is stable, the color indexes can be rapid, efficient and useful proxies for detailed, large-scaled surveys or monitoring of heavy metal pollution in tidal flat sediments.