COMBINED EFFECTS OF COPPER, DESICCATION, AND FROST ON THE VIABILITY OF EARTHWORM COCOONS

The effects of heavy metal pollution on earthworms have been extensive ly studied, but no studies have examined how earthworms react if they are simultaneously exposed to metal pollution and climatic stress. Thi s question has been addressed in a laboratory study where cocoons of A porrectodea caliginosa and Dendrobaena octaedra were initially exposed to copper in aqueous solutions of copper chloride and thereafter expo sed to realistic degrees of either desiccation or frost. Earthworm emb ryos absorbed copper in amounts (up to approx. 200 mg/kg dry tissue we ight) comparable to concentrations found in various tissues of earthwo rms from metal-polluted soils. Desiccation and copper exposure in comb ination had synergistic effects on survival rates for both species. Fo r example, at full saturation, the NOEC (the highest tested concentrat ion with no statistically significant effect) for copper of A. caligin osa was 12 mg/L, whereas at 97% relative humidity it was only 6 mg/L. Frost and copper exposure in combination also showed synergistic effec ts in some experiments. No cocoons of A. caliginosa exposed to 20 mg c opper/L were viable after exposure to -3 degrees C but at 0 degrees C viability was as high as 95%. The same tendency was seen in D. octaedr a but not as clearly as in A. caliginosa. A change of the environmenta l conditions (moisture. temperature) to increasing severity caused a s hift in the statistically derived NOEC toward lon er critical values o f copper. The involvement of combination effects in ecotoxicological t ests could therefore improve risk assessment of soil-polluting compoun ds.