Pesticide Residues in Soil Invertebrates - Pesticides: Evaluation of Environmental Pollution - page 346

was shown to actively avoid copper-contaminated soil (Salminen and Haimi 2001). Copper
oxychloride has recently been shown to reduce populations of the earthworm, Aporrectodea
caliginosa, in field trials six months following the application of the fungicide (Maboeta
et al. 2003). Elevated copper concentrations have been shown to reduce beneficial mycor-
rhizal associations (Liao et al. 2003), reduce microbial activity and function (Bogomolov
et al. 1996), and impact a range of mesofauna (Böckl et al. 1998). Direct tests have shown that
concentrations of copper in the soil ranging between 100 and 150 ppm are in most cases suf-
ficient to produce a consistent decrease in earthworm numbers. Thus, it is worrisome that
higher concentrations of copper are found in the soil in many orchards around the world.
Potter et al. (1990) found that a single application of the fungicide benomyl or the insec-
ticides ethoprop, carbaryl, or bendiocarb at labeled rates reduced earthworm populations
in turfgrass by 60%-90%, with significant effects lasting for 20 weeks. Other insecticides
including diazinon and chlorpyrifos caused less severe, but significant earthworm mor-
tality in some tests (Potter et al. 1990). Similarly, Choo and Baker (1998) reported that the
nematicide fenamiphos and the insecticide endosulfan reduced the growth and inhibited
the reproduction of the earthworm Aporrectodea trapezoides (Lumbricidae) when applied at
recommended rates to an Australian pasture soil. The nematicide carbofuran is also well
documented as having an adverse effect on earthworm growth and activity (Parmelee
et al. 1990; Reddy 1999).
Fungicides are generally highly toxic to earthworms, especially copper and zinc resi-
dues from copper sulfate and carbamates, respectively. Soil fumigants, nematicides, and
fungicides such as D-D mixture (dichloropropane:dichloropropene), metham-sodium,
and methyl bromide are highly toxic to earthworms. The majority of fumigants and con-
tact nematicides are toxic to earthworms as well (Edwards and Bohlen 1992). Carbamate
fungicides such as benomyl and carbendazim are also highly toxic to earthworms. For
example, it has been reported that about 1.8 kg/ha per year of benomyl may destroy all
the Lumbricus terrestris and most of the Allolobophora spp. present in an apple orchard in
England (Brown 1978).
One group of fungicides—the benzimidazoles—is highly toxic to earthworms, and
studies have shown reductions of the activity in soils to which compounds such as car-
bendazim have been applied. These fungicides, which inhibit microtubule assembly in
annelids and some other invertebrate groups as well as sensitive fungi, have been used to
control earthworms on ornamental lawns and golf greens.
12.3.4 Effect of Pesticides on Soil Nematode Communities
Nematodes are the most abundant metazoans on the Earth and also the most abundant
invertebrates in the soil ecosystem where they perform many ecological functions. and
particularly bacterivorous nematodes play an important role in the nutrient cycling (Wood
1988). They interact closely with other soil organisms and their activity affects primary
production, decomposition, energy flows, and nutrient cycling, especially nitrogen cycle
(Sohlenius 1980; Freckman and Baldwin 1990). Soil nematodes belong to microfauna liv-
ing in the pore-water of soil top layer, where they can be exposed substantially to the soil
contaminants that are usually accumulated here. The thin cuticle covering their body is
water-permeable, which makes them very sensitive to the uptake of the dissolved frac-
tion of contaminants. After exposure and effects of toxicants, the ability of nematodes to
play their ecological roles may be impaired with possible deleterious effects at the eco-
system level. In ecological studies, change in nematode community structure is used as a
sensitive marker of environmental stress as well as of pollution (Yeates 2003). Nematodes