Multiphase distribution and migration characteristics of heavy metals in typical sandy intertidal zones: insights from solid-liquid partitioning

Abstract With the increase of development and utilization of coastal tidal flats, the desertification of intertidal zone is becoming more and more serious, which will inevitably lead to changes in the distribution and migration of heavy metals. This study reported the multiphase distribution and solid-liquid partitioning of Cr, Ni, Cu, Zn, Pb and Cd in typical sandy intertidal zones and predicted the migration of heavy metals with stepwise multiple linear regression. The distribution of heavy metals in surface water was comparable with that in pore water, while the content of heavy metals in suspended solids was obviously greater than that in sediments. Compared to non-sandy sediments, the bioavailability state of heavy metals extracted from sandy sediments by diethylene triamine penta-acetic acid was much smaller. The mean partitioning coefficient values (Kd) ranged from 21.56 to 166.18, which were 10–40 times lower than those of organic-rich sediments and 100–750 times lower than those of mineral soils. The dynamics in solid clay, SOC and ORP greatly affected the variations of Kd values. Clay had a significant positive correlation with bioavailability but did not have a significant correlation with logKd, indicating that the adsorption capacity of heavy metals in the intertidal zone is not the only factor controlling heavy metal migration. Stepwise multiple linear regression analysis confirmed that the prediction equations of heavy metals are composed of multiple physicochemical factors. All predicted and tested values were of the same order of magnitude, with R2 values ranging from 0.8223 to 0.9775. Although our data focus on a single species of sandy intertidal zone, characterizing the Kd value and its relationship with site-specific factors provides different tools for assessing the probability of heavy metal contamination and migration in sandy intertidal zones.