Copper toxicity thresholds for earthworm <i>Dendrobaena veneta</i>: insights from a site with unique monometallic soil contamination

Ecotoxicological studies predominantly rely on artificially contaminated soils and fieldwork on contaminated soils remains scarce. This study focuses on the Kargaly site in the Orenburg region near the southern Urals, where a rare instance of monometallic soil pollution has occurred with copper (Cu). We established Cu toxicity thresholds for Dendrobaena veneta, a European nightcrawler, using soils collected along a Cu toxicity gradient (total Cu content of 121-10,200 mg kg-1) in a chernozem (Mollisol) agricultural field. Earthworm survival in the reproduction bioassay was an unreliable predictor of Cu toxicity. However, the number of juveniles in the reproduction bioassay and earthworm avoidance behavior were sensitive indicators of Cu toxicity. While total soil Cu strongly predicted earthworm responses, the effect of soluble (0.01 M CaCl2-extractable) Cu on earthworm responses was not statistically significant. Similarly, the Cu content in earthworm tissues was an unreliable predictor of Cu toxicity in D. veneta. The effect concentrations at 25% (EC25) and 50% (EC50) of total soil Cu for earthworms were 177 and 407 mg kg-1, respectively, for the reproduction bioassay, compared with 783 and 1,603 mg kg-1, for earthworm avoidance behavior. This study is among the few that estimate Cu toxicity thresholds for earthworms in real-world contaminated soils rather than artificially spiked ones. This is the first report of the Cu toxicity threshold for the genus Dendrobaena, highlighting the novelty of this study.