Agriculture Reference
In-Depth Information
In most contaminated sites, a mixture of various contaminants will be present, so their
combined toxicity to earthworms must also be assessed. Posthuma et al. (1993) tested a number
of combinations of Cd, Zn, and Cu and observed both synergism and antagonism in earthworm
toxicity. Antagonistic responses to chemicals mean that just adding up toxicities of separately
tested metals can often overestimate the overall impact of the combined heavy metals under field
conditions.
Of the different soil factors affecting the toxicity of chemicals to earthworms (soil acidity,
pH, cation exchange capacity, percentage organic matter), pH plays the most important role. It
affects the health of different earthworm species directly and therefore their sensitivity to adverse
impacts. An example is the feeding rate and metabolic turnover of Pb uptake by earthworms
reported by Bengtsson and Rundgren (1992). It also influences the physicochemical binding and
the biological uptake processes of toxicants by earthworms, as shown by Marinussen and Van
der Zee (1997), and so indirectly influences the survival and functioning of various earthworm
species. In an extensive study, Janssen et al. (1997a,b) measured the chemical availability
and
biological concentration factor (BCF) of toxicants to earthworms in different field soil types for
four heavy metals (Cd, Zn, Pb, and Cu). They also measured a number of soil characteristics
and correlated both the chemical availability and the BCF to earthworms with these soil factors
by a multiple correlation analysis (Table 17.1). This impact of soil type on bioaccumulation in
combination with different background levels of toxicants in various soil types could result in a
metalloregion-specified derivation of environmental quality standards, as suggested by deGroot
et al. (2002).
Marinussen and Van der Zee (1997) discussed the importance of soil moisture to toxicity of
chemicals to earthworms. With increased soil moisture, the Cu content of the pore water decreased,
which illustrates that bioaccumulation of chemicals by earthworms has both physicochemical and
k
p
TABLE 17.1
Multiple Regression of Environmental
Availability
and Bioconcentration Factors
(BCFs) in the Earthworm
k
p
Eisenia fetida
of
Cadmium, Copper, Lead, and Zinc
a
Log
k
p
Cd
= 0.48*pH + 0.28
Cu
= 0.15*pH + 0.45*log Fe
−
0.71*log DOC + 1.33
ox
Pb
= 0.24*pH + 0.40*log Fe
+ 1.98
ox
Zn
= 0.61*pH
−
0.65
BCF
Cd
=
−
0.43*pH + 1.36*log clay
−
1.39*log OM + 3.19
Cu
=
−
0.65*log Fe
−
0.38*log clay + 1.38
ox
Pb
=
−
0.78*log clay
−
0.45*log Fe
+ 0.46
ox
Zn
=
−
0.39*pH
−
1.06*log Al
+ 0.73*log clay + 3.04
ox
a
Based on relation to various soil factors (arranged in decreasing
order of importance), according to the following general for-
mula: Log
k
, respectively, log BCF = a*pH(CaCl
) + b*log
p
2
OM + c*log clay +d*log Fe
+ e*log Al
+f* log DOC + g*log
ox
ox
I + h.
BCF = bioconcentration factor; OM = organic matter
Source: Janssen et al. 1997a,b.
