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Sorption of the Antibiotic Tetracycline to Humic-Mineral Complexes

^a Univ. of Wisconsin-Madison, Madison, WI 53706, present address, Dep. of Crop Sciences, Michigan State Univ., East Lansing, MI
^b Dep. of Biological Systems Engineering, Environmental Chemistry and Technology Program, 460 Henry Mall, Univ. of Wisconsin-Madison, Madison, WI 53706

View larger version (21K): [in this window] [in a new window]   Fig. 1. (a) Structure and (b) pH-dependent speciation of tetracycline (TC).

View larger version (8K): [in this window] [in a new window]   Fig. 2. Interaction of Elliott soil humic acid (ESHA) with hydrous Al oxide (HAO) as a function of pH (ionic strength = 0.01 mol L–1 NaCl; dissolved organic C [DOC] = 48 mg C L–1; equilibration time = 72 h). qe represents the amount of ESHA sorbed to HAO. Mean values and ranges for qe are included (if not shown, range values are within the symbols).

View larger version (14K): [in this window] [in a new window]   Fig. 3. Isotherms for tetracycline sorption to (a) hydrous Al oxide (HAO), (b) Elliott soil humic acid (ESHA) and (c) ESHA-HAO complexes at two different ionic strength (I) values (pH = 6.2 ± 0.1). Ce denotes the equilibrium tetracycline concentration, qe represents the amount of tetracycline sorbed, and foc indicates the organic carbon content for ESHA loading to HAO. Mean values and ranges for qe and Ce are included (range values if not shown are within the symbols). Model estimates based on a simple additive relationship for the binary ESHA-tetracycline and HAO-tetracycline systems are included in Fig. 3c.

View larger version (23K): [in this window] [in a new window]   Fig. 4. Isotherms for Elliott soil humic acid (ESHA) sorption and desorption to hydrous Al oxide (HAO) (pH = 6.2 ± 0.1; ionic strength = 0.01 mol L–1 NaCl; equilibration time = 72 h). Ce denotes the equilibrium ESHA concentration, Ca is the equilibrium ESHA concentration after the sorption experiment, and qe represents the amount of ESHA sorbed to HAO. Mean values and ranges for qe and Ce are included (range values if not shown are within the symbols).

View larger version (16K): [in this window] [in a new window]   Fig. 5. Surface charge (zeta potential) characteristics of hydrous Al oxide (HAO) and concomitant release of soluble Al as a function of increasing Elliott soil humic acid (ESHA) loading (pH = 6.2 ± 0.1; ionic strength = 0.01 mol L–1 NaCl; equilibration time = 72 h). qe is the amount of ESHA sorbed to HAO. Mean values and ranges for qe, zeta potential, and soluble Al are included (range values if not shown are within the symbols).

View larger version (14K): [in this window] [in a new window]   Fig. 6. Release of soluble Al as a function of increasing tetracycline sorption onto hydrous Al oxide (HAO) and Elliott soil humic acid (ESHA)-HAO complexes (pH = 6.2 ± 0.1; ionic strength = 0.01 mol L–1 NaCl; equilibration time = 24 h). qe represents the amount of tetracycline sorbed. Mean values and ranges for qe and total soluble Al are included (range values if not shown are within the symbols).