Complexation of arsenate with humic substance in water extract of compost.
The interactions of environmental toxicants with organic substances affect the speciation and dynamics, and subsequent toxicity, mobility, and fate of toxicants in the environment. For the purpose of understanding the complexation of As(V) with humic substances, arsenate-containing solutions with As concentrations from 1 to 8 mgl(-1) were prepared to react with the water extract of compost (WEC). All the reaction systems including the control were incubated for 48 h at 25 degrees C. The complexation of As(V) with humic substance was examined by dialysis and ion exchange techniques. From 30% to 51% of added As(V) reacted with organic substance in WEC to form an As-metal-organic complex. This was verified as a hydrophobic organic fraction after separation of As-metal-organic complex fraction from the hydrophilic fraction by XAD-8 resin. The complex substance was also identified as a humic substance by the method of proton binding formation function determination. This suggests that cations, such as Ca and Mg, and especially Fe, Al, and Mn act in cation bridging in the complexation of As(V) with humic substance. The role of metals in the complexation of As(V) with humic substance in terrestrial and especially aquatic environments thus merits close attention.
Residue Control Department, Taiwan Agricultural Chemicals and Toxic Substances Research Institute, Wufeng, Taichung County 413, Taiwan, ROC.
Haw-Tarn
HT
Lin
M C
MC
Wang
Gwo-Chen
GC
Li
D001149:Arsenates / Q000737:chemistry*; D006812:Humic Substances; D019216:Metals, Heavy / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D014867:Water / Q000737:chemistry; D014873:Water Pollutants / Q000032:analysis*
D001149:Arsenates; D006812:Humic Substances; D019216:Metals, Heavy; D012989:Soil Pollutants; D014873:Water Pollutants; D014867:Water; C025657:arsenic acid