Trace metals in Texas rivers: A trace metal speciation study.

摘要

An ion-exchange preconcentration technique was used to determine concentrations of different fractions of trace metals in Texas rivers. Three dissolved metal fractions (labile, organic and inert), total dissolved metal concentrations, total recoverable and particulate metal concentrations were measured and compared to environmental conditions. Samples were collected three times in 1997--1998 from multiple locations in Texas rivers of varying characteristics.;The two eastern Texas river basins (Sabine and Neches) are characterized by heavy vegetation, which results in water with high dissolved organic carbon (DOC) and low pH. Effects from human activities on these rivers are small. However, dissolved concentrations were generally high for metals solubilized by low pH, such as Al, Fe and Mn. Vanadium showed the reverse trend with lower dissolved concentration in the Sabine and Neches Rivers. Trace metals that form organic complexes (Al, Co, Cu, Fe, Ni and Pb) were found to vary with DOC. Environmental conditions in the central Texas rivers (Trinity, Brazos and Colorado) were highly variable, because they flow through different physiographic regions owing to their longer lengths. Anthropogenic effects on these central Texas rivers, and on the San Antonio River, were obvious. However, the presence of artificial physical barriers (lakes and reservoirs) provide sinks for trace metals in these rivers.;This study found that several factors are important to trace metal partitioning in Texas rivers. Ethylenediaminetetraacetic acid (EDTA) and phosphate in river water were found to extract trace metals (Cd, Co, Cu, Ni, Pb and Zn) from suspended particulate matter (SPM) and sediments, elevating dissolved and labile fractions of these metals. This effect sometimes lowered the distribution coefficient between dissolved and particulate metals (Kd) by 1--2 orders of magnitude relative to areas without elevated EDTA and phosphate concentrations. DOC, SPM, pH and salt content also affected trace metal partitioning among the labile, organic and particulate metal fractions, but their effects were less than that from EDTA and phosphate.