Pesticide Residues in Soil Invertebrates - Pesticides: Evaluation of Environmental Pollution - page 343

easily cultured in the laboratory. The lethal concentration to kill 50% of earthworms (LC 50 )
and no observed effect levels (NOELs) may then be measured. If the NOEL is greater than
the expected environmental concentration, then it is unlikely that the pesticide will have
appreciable effects under field conditions.
The effects of pesticides on earthworms depend on the type of pesticide and its rate
of application, earthworm species and age, and environmental conditions. Earthworm
metabolizes pesticides as well as concentrates them from soil. Aldrin, for example, is rap-
idly epoxidized to dieldrin by microsomal oxidases located in the intestine of earthworms.
Dieldrin is relatively stable in earthworms.
A single application of pesticides such as diazinon, isazophos, benomyl, carbaryl, and
bendiocarb in soil caused significant short-term reduction in earthworm numbers (Potter
et al. 1990). The most common action of agrochemicals on earthworms has been found to
be coiling of the body and longitudinal muscle contraction, after which the body becomes
rigid and sometimes swellings appear on the body surface. The swelling often bursts, cre-
ating bleeding sores. Pesticides such as propoxur, methidathion, endosulfan, triazophos,
carbofuran, terbufos, and methamidophos cause such symptoms.
Zoren et al. (1986) reported the teratogenic effect of benomyl, that is, posterior segment
regeneration of the earthworm, including an increased frequency of segmental groove
anomalies and a variety of monstrosities, including two tails. Anton et al. (1990) reported
the occurrence of various malformations due to the fungicide captan. Many carba-
mates have been reported to produce tumors and swellings along the earthworm's body
(Stenersen 1979a). Hans et al. (1990) reported that different chemicals produced different
symptoms in earthworms for chronic toxicity. For example, coiling and curling was caused
by aldrin, whereas lifting of the body and extrusion of coelomic fluid was caused by hep-
tachlor. Similarly, excretion of the mucus, glandular swelling, segmental construction
and white banding, and hyperactivity were caused by endosulfan, lindane, and imazalil,
respectively. Low dosages of phosphamidon caused hyperactivity of L. mauritii. Stenersen
(1979b) observed immobility and rigidity in all tested species of earthworm caused by
carbaryl and carbofuran.
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
annelid and some other invertebrate groups as well as sensitive fungi, have been used to
control earthworms on ornamental lawns and golf greens.
Studies carried out by Haque and Ebling (1983) by testing the toxicity of eight fungicides,
five herbicides, and ten insecticides showed that, despite the diverse chemical structure of
the compounds tested, there was species specificity in the earthworm toxicity response
to different pesticides. Behavioral disturbances of earthworms caused by the insecticides
were more severe than those caused by the herbicides or fungicides. There was also a dif-
ference in the sensitivity of worms of the same species to different pesticides.
Earthworms, Aporrectodea caliginosa , showed a 70%-80% inhibition of acetylcholine
esterase (Booth et al. 2000a) when exposed to 28 mg/g of chlorpyrifos in the soil. However,
there were no effects on the enzyme efficiency when exposed to recommended doses in
the field (O'Halloran et al. 1999). Chlorpyrifos added to soil was toxic to six species of
earthworms with 14-day no observed effect concentrations for survival of 46-875 mg/g
(Ma and Bodt 1993).
Many of these pesticides have drastic effects on the nervous system of the earthworms.
When earthworms were exposed to benomyl, they showed sublethal neurotoxic effects
(Drews et al. 1987; Drews and Callahan 1988).