Abstract
The behavior of metals in surface water is complex and their partition coefficients can be impacted by many factors. Organic matter (OM) content in sediments, pH and salinity, are factors that may influence speciation and partitioning of metals. The difficulty in describing the impacts and relationships are that these processes are interconnected with no dominant associations among all. In this study, the partitioning of five metals (As, Cr, Cu, Ni and Zn) under different levels of salinity, pH, and OM content were investigated. A series of factorial design experiments are evaluated in which three levels of OM are tested each time against five levels each of salinity and pH; the design of experiments was generated by the statistical software program MiniTab16®. All metals tested showed a trend of increasing Kd with the increase of OM 0.36% to 4.32%. Higher Kd were the result of the increase in pH from 3-10.5 and lower Kd values resulted after an increase in salinity 0-3%. However, within that lower range of salinity, a positive linear correlation between Kd and salinity was observed which is attributed to potential formation of insoluble metal species with the increase of salinity. Multiple regression equations with the variables pH, OM and salinity were generated to predict Kd of each metal. The study showed no interaction between salinity/OM and pH/OM for all five metals.
Highlights
Metal pollution continues to be a complex problem, which plagues many of the world’s river systems, estuaries, and coastal embayments
A total of 102 isotherm runs were conducted in the randomized order as dictated by MiniTab16® software (Table 2)
analysis of variance (ANOVA) results in Table 6 determined that the pH/ Organic matter (OM) models showed significant differences in Kd values
Summary
Metal pollution continues to be a complex problem, which plagues many of the world’s river systems, estuaries, and coastal embayments. The mobility, fate and bioavailability of metals in surface water systems are directly related to their partitioning between suspended solids and water as well as the form of the metal itself and the other compounds within the environment. One percent of metal pollutants remain suspended within the water column; the residual metals settle on and are stored within the sediments, creating a sink [1]. High bottom shear stress often seen in fast flowing rivers or estuaries with large tidal currents can lead to a higher presence of metals in suspension. The metal partition coefficient Kd (L/kg) is the ratio of sorbed metal concentration on the solid phase m (mg/kg) to the dissolved metal concentration at equilibrium C (mg/L)
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