TRACE METAL SPECIATION IN TEXAS RIVERS
The Sabine and Neches Rivers flow through forests and wetlands in east Texas and have high dissolved organic carbon (DOC) concentrations compared to other Texas Rivers. In their waters, a large fraction of metals such as Cu and Fe were organically complexed. However, for some metals organic complexation was inhibited by the low pH from high organic acid concentrations. In that case, total dissolved Fe, Mn and Al concentrations were strongly dependant on pH values, and a large portion of Fe and Al were associated with organic complexes or colloidal material.
High concentrations of ethylediaminetetraacetic acid (EDTA) and phosphate, which form strong complexes with some metals, were found in high population density sections of the San Antonio and Trinity Rivers. Distribution coefficients between particulate and dissolved metals and EDTA (or phosphate) concentrations showed an inverse relationship, suggesting that EDTA and phosphate are capable of extracting metals from suspended particulate matter (SPM) and bottom sediments. This process elevated total dissolved Cd, Co, Cu, Ni, Pb and Zn concentrations in these river sections. The EDTA and phosphate complexes are not retained by either Chelex-100 or AG MP-1 resin and are thus classified as an inert fraction. The inert fraction was small in most samples but was as high as 95% of total dissolved metal concentrations in a few San Antonio River samples.