『Abstract
Tetracyclines (TCs) have been widely used as feed additives in
intensive livestock production, and are often detected in animal
manure and agricultural soils. Their fate in the environment,
e.g., adsorption, leaching and degradation, is influenced by soil
characteristics. This study evaluated the adsorption of tetracycline
(TC; H3L) on two soils as affected by phosphate
(P). Freundlich equations fit the adsorption data of TC on the
soils well with high correlation coefficients (0.994-0.999). Compared
with the control (without P addition), the Kf
values of TC after addition of 31 mg P l-1 decreased
from 9210 to 5700 on the Red soil (RS, Udic Ferrosols, with lower
pH and organic mater), and from 3730 to 2470 on the Wushan soil
(WS, Anthrosol, with higher pH and organic matter). Solution pH
strongly affected TC adsorption on the soils with and without
P. Addition of 31 mg P l-1 as orthophosphate increased
TC adsorption on the RS as pH<4 and then decreased with further
increasing pH. However, no significant influence of P on TC adsorption
was observed on the WS in a wide pH range. Phosphate is known
to convey negative charges to soil particle surface, which will
decrease the zeta potential of the soils, and consequently affect
TC adsorption on the soils. The adsorption model, in which species-specific
sorption coefficients (Kdi) were weighted
by pH-dependent fractions of each species, fits the experimental
data very well. The addition of P increased the sorption coefficients
of H3L+00 about 123% and 14.1%
on the RS and WS, respectively, while decreased the sorption coefficients
of H2L+-0 and HL+--.
Our results suggest that application of high rate of P fertilizer
may enhance TC leaching, especially from the soils with variable
charges.
Keywords: Antibiotic; Tetracycline; Phosphate; Adsorption; pH』
1. Introduction
2. Materials and methods
2.1. Soils and chemicals
2.2. Preliminary experiments to determine equilibrium time
2.3. Adsorption isotherms of TC on the soils as affected by P
2.4. Adsorption edge of TC with pH on the soils as affected by
P
2.5. Determination of zeta potential of the soils equilibrated
with TC and P
3. Results
3.1. Adsorption isotherms of TC on the soils as affected
by P
3.2. Adsorption edge of TC with pH on the soils as affected by
P
3.3. Predicting the adsorption coefficients of TC on the soils
4. Discussion
5. Conclusions
Acknowledgements
References