SUBLETHAL EFFECTS OF ALUMINUM ON EARTHWORMS IN ACID SOIL - THE USEFULNESS OF DENDRODRILUS-RUBIDUS (SAV.) IN A LABORATORY TEST SYSTEM

Soil acidification is often associated with increased mobility and ava ilability of certain metal ions naturally occurring or unintentionally transported to the soil. One potentially toxic metal in soil solution under acid conditions is aluminium. The impact of the combination of increased aluminium concentrations and soil acidity was studied in the laboratory using as a test organism the earthworm Dendrodrilus rubidu s (Sav.), a common species in temperate forest ecosystems. By adding A l-chloride to an experimental soil (mixed mull, sand, cattle dung) a s eries of soils with gradually increasing aluminium concentration was c reated. The treatment led to lowered soil pH. To distinguish the impac t of aluminium from that of lowered pH, a parallel pH-series was produ ced. Experimental soil and field-collected, just matured D. rubidus we re added to test chambers. Survival of the P-generation, its activity, production of cocoons and loss of weight in differently treated soils were followed over four months (the approximate length of the reprodu ctive period of the species). Hatching success, survival and growth of the F-generation were determined. Lowered soil pH more than the metal affected most test parameters, 'juvenile growth' being the exception. Newly hatched specimens hardly grew in soils with increased Al-concen trations; even at low Al-concentrations (10 and 25 mg Al kg(-1) soil) their growth was affected negatively. At higher concentrations the juv eniles decreased in size over the experimental period and died. Other, more ecologically realistic, test species than Eisenia fetida and E. andrei are needed in soil risk assessment, since Eisenia is never foun d in temperate forest ecosystems, the soils of which are exposed to ac idification. D. rubidus is a potential candidate, but has an obvious d rawback: its reproductive mode is not fully understood. Some further c onsiderations concerning its usefulness in a test system (test substra te, length of test period, number of specimens per chamber, hatching o f cocoons etc.) are presented.