Agriculture Reference
In-Depth Information
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FIGURE 17.5
Organism/sediment ratios of
L. variegatus
3 weeks (+) and 21 months (
∆
) after mixing sediment
with tetrachlorodibenzo(para)dioxine (TCDD). (From Loonen, 1994.)
the development of tests of toxicity to earthworms at the physiological and biochemical level using
biomarkers. Moreover, these various effects (test end points) can have different impacts on the ultimate
survival of the earthworm or, when looking at the population level, on the intrinsic rate of population
increase or maintenance of the earthworm populations. Next, there are different earthworm ecotypes
(epigeic, endogeic, and anecic species), which exert different effects on the soil, so the impact of this
on the earthworm community must be assessed. When the input of earthworms to ecosystem processes
(turning over the soil, inÞuencing nutrient release, drainage and aeration processes) is included, the
assessment has to be at the ecosystem level as well. In a Ýnal scaling-up, it must be realized that
environmental impacts occur in a mosaic of different systems, which in practice means Ýelds with
different crops and pesticide treatments in agroecosystems.
Much effort has been put into the standardization of earthworm tests. The European Community
(Edwards 1983, 1984) OECD test using artiÝcial soil and
has proven
to be highly reproducible. By adding a small pellet of cow manure as food, the survival of the
earthworms improves greatly. The nutritive value of the peat, clay, and sand mixture of the artiÝcial
soil has proved to be rather low. An improved protocol setup has been developed (Van Gestel et
al. 1989) in which a more sensitive chronic end point (reproduction instead of survival) is used,
and a recovery period is introduced, which provides the opportunity to study the hatchability of
the cocoons produced. Taken together with cocoon production, this gives a potential prediction of
effects on population maintenance rates. Kula (1994) adapted the method for the assessment of
pesticide toxicity by applying the pesticide to the soil surface. Comparing the effect of surface
application of a compound with effects from mixing it through the total test soil mass produced
E. fetida
or
Eisenia andrei
reasonably similar results for the effects of benomyl
(
Table 17.2
)
.
The observation of earthworm behavioral responses to toxicants has received more attention
recently, although the Ýrst observation of active avoidance of copper-contaminated soil dates to the
1970s (Eijsackers 1981, 1989). Observations on such earthworm responses include pesticides
(diazinon, mecoprop, carbaryl, and potassium-fatty acid salts) (Bauer and Rmbke 1997; Slimak
1997; Reinecke and Reinecke 2002); brass powder-contaminated soil (Wentsel and Guelta 1988);
Þy ash (Ma and Eijsackers 1989); and harbor sludge (Ma et al. 1997). Capowiez et al. (2002)
studied earthworm behavior
using x-ray tomography and three-dimensional reconstruction.
In a number of studies, earthworms responded to much lower amounts of toxicants than they might
encounter in the Ýeld (Mather and Christensen 1998), which demonstrates the suitability of these
kinds of tests as early warning systems. Hence, toxicant avoidance should be incorporated as an
assessment end point in test procedures, as suggested by Yeardly et al. (1996).
in situ
