Agriculture Reference
In-Depth Information
Molnar (1997) reported that a number of the macronutrient metals (NaCl, KCl, CaCl
, MgCl
,
2
2
BaCl
, MnCl
, SnCl
, SrCl
, AlCl
, and Fe Cl
) reduced earthworm reproduction, and CoCl
, CuCl
,
2
2
2
2
3
3
2
2
and NiCl
proved to be acutely toxic to reproduction.
Studies of the susceptibility of different earthworm species to chemicals produced results that
are distinctly different. Neuhauser et al. (1986) claimed that the four species they tested showed
good correlations in relative toxicity. Haque and Ebing (1983) reported a significant relationship
between
2
for susceptibility to a series of pesticides. Heimbach (1985)
found, in general, a factor 2 to 3 difference in response when comparing
E. fetida
and
L. terrestris
E. fetida
and
L. terrestris
.
By contrast, Kula (1994) reported much greater differences between
E. fetida
and three other
earthworm species (
), ranging
from a factor of 4 to a factor of 80 in relative susceptibility. According to Kratz and Phhacker
(1994), two closely related species such as
A. caliginosa
,
Allolobophora chlorotica,
and
Allolobophora longa
Eisenia fetida fetida
and
Eisenia fetida andrei
have
distinctly different toxicity responses to carbendazim and phenmedipham.
Ma and Bodt (1993) tested the toxicity of chemicals to six earthworm species and suggested
a genus-related variation in toxicity to chlorpyrifos, with increasing susceptibility in the order
Eisenia
spp. These differences were not associated with
body weight, and it seems more likely that some physiological factor is involved. This conclusion
was supported by the observation of Stenersen et al. (1992) that the different sensitivities of the
closely related
spp. <
Aporrectodea
spp. <
Lumbricus
) to carbaryl was related
to the possession of a carbaryl-resistant enzyme by the first two species. For a more systematic
comparison, the results of four studies of various pesticides and a number of different earthworm
Eisenia
species
(E. fetida
,
E. andrei,
and
Eiseniella
veneta
species are plotted in a comparable way in
Figure 17.6
.
To this end, the LC
values are plotted on
50
) for that pesticide. In general,
E.
fetida
was always at the least sensitive end of the range, and the
Allolobophora
species was always
at the most sensitive end. But, there was no fixed sequence in sensitivity relationship between the
species. Hence, there is little basis for a taxonomically related sensitivity pattern, although it is
clear that
E. fetida
is usually the least-sensitive species and hence the least-suitable test species.
As was recommended at the Sheffield International Workshop on Earthworm Toxicity Testing
(Greig-Smith et al. 1992) and was confirmed later by Kula (1994), field-related doses should be
those used in tests and five times this dose. However, Springett and Gray (1992) showed that much
lower doses (20, 10, and 5% of field rate) can be toxic when applied regularly for a longer period
(100 days at 2-week intervals), which is in fact more relevant to the actual growing period of the
earthworm and agronomic practices.
The use of artificial soil as a substitute for natural soils has been scrutinized, and there are reports
indicating good correlations as well as only a limited correlation between them. With respect to both
heavy metals (Posthuma et al. 1993) and organic pesticides, the artificial soil test may overestimate as
well as underestimate the toxicity to earthworms in real soils. Lanno et al. (1997) observed a marked
influence of soil type, comparing three soil types, with respect to the impacts of benomyl, 2-chloroac-
etamide, diazinon, and pentachlorophenol on earthworms. Different toxicant availability may be a
governing factor because both organic matter and clay adsorb chemicals. Van Gestel and Van Straalen
(1994) stated that the organic matter content, in combination with soil sorption data, can provide a
good basis for a translation formula from artificial soil to real soil conditions.
the same scale irrespective of the absolute susceptibility (= LC
50
FIELD STUDIES
P
ESTICIDE
AND
H
EAVY
M
ETAL
T
OXICITY
S
TUDIES
The ultimate relevance of all toxicity testing lies in proper maintenance of the earthworm population,
as a key component of soil ecosystems, by turning over the soil continuously, thereby creating an
optimal soil condition, degrading organic matter, and working it into the soil. In agronomic systems,
