Characteristics of Natural and Urban Soils - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 113

Table 2.3 Concentrations of antibiotics encountered in agricultural soils

Compounds and concentrations
found Author(s) Medium

gkg − 1 Thiele-Bruhn ( 2003 ) Agricultural soil Tetracyclines 450-900 μ

gkg − 1
Fluorquinolones 6-52

Macrolides 13-67 μ

gkg − 1 μ

gkg − 1 Thiele-Bruhn ( 2003 ) Soil fertilised with manure Tetracycline average 199 μ

gkg − 1 Chlortetracycline 7 μ

gkg − 1 Sulfadimidine 11 μ

Hamscher, Pawelzick,
Höper and Nau
( 2004 , 2005 )

Sandy soil fertilised with
liquid manure

Tetracyclines averages > 150 up to
300 gkg − 1

Sulfamethazine max. 11

μ

gkg − 1 μ

Beausse ( 2004 ) Sludge-treated soils, topsoil

0-2.5 cm

Ciprofloxacin and norfloxacin
residual 250 gkg − 1 ,

5 months after sludge disposal
respectively 450 and 350

− 300 μ

gkg − 1 μ

2.3.2 Adsorptive Behaviour and Specific Surface Areas

Soils have a major influence on the mobility of contaminants by virtue of their cation
and anion exchange capacity, specific adsorption (chemisorption) through the for-
mation of co-valent bonds between an element and the mineral surface, and solid
state diffusion by the penetration of an element into the pore spaces of a mineral's
structure (Dragun 2007 ).
In this section soils and geological materials are classified in terms of adsorptive
behaviour and specific surface areas.
The cation exchange capacity (CEC) of soils depends greatly on the content and
mineralogy of the clay fraction. Generally, younger and less weathered clays have
much greater specific CEC than older and more strongly weathered clays. Where
leaching can occur, weathering often results in a loss of silica from the soil. Thus,
the 2:1 layer type aluminosilicate minerals like smectite, vermiculite may be con-
sidered the less weathered clay minerals, with kaolinite being a highly weathered
clay, and illite occupying an intermediate position. Youthful soils on volcanic ash
deposits often have poorly crystallised clay minerals that have a high CEC. Gibbsite
(

γ

-AL(OH) 3 ) represents a highly weathered aluminium clay mineral. Along with the
loss of silica by weathering, other much less soluble soil minerals are formed and
concentrated in the soil, such as various iron, manganese, titanium and aluminium
oxides, hydroxides and oxyhydroxides (Table 2.4 ).
The anion exchange capacity (AEC) of mineral soils is dependent on the size
of the area along edges of clay minerals, where permanent positive charges exist,
and on the amount of oxides and hydroxides of aluminium, iron, and manganese,
which can generate both cation and anion exchange due to the adsorption of pro-
tons and hydroxyl ions, and hence on the pH of the soil (McBride 1994 ; Sposito
1989 ). Soils displaying both cation and anion exchange, depending on their pH, are
“variable-charge” soils. For example, adsorption of Cr(VI) by aluminium and