Earthworm responses to metal contamination : tools for soil quality assessment

Abstract

Tuomas Lukkari tutki väitöstyössään kuinka haitta-aineet, esimerkkinä metallit, vaikuttavat ympäristöömme ja sen eliöihin. Lukkari selvitti lieroista mitattavien muuttujien avulla, kuinka haitallisia metallit ovat ja miten haitallisuutta olisi hyvä arvioida. Lierot ovat monien maaekosysteemien avaineliöryhmiä ja altistuvat maahan päätyville haitallisille aineille sekä ravinnon että suoraan ihokontaktin kautta. Useimpien haitta-aineiden pitoisuudet ovat mitattavissa lierojen kehosta, mikä antaa tietoa todellisesta altistuksesta ja aineiden kertymistaipumuksesta.

Responses of earthworms to soil metal contamination were studied in field and laboratory experiments. In the field, earthworm communities and metal bioavailability to earthworms along contamination gradients were surveyed in three areas located close to metal industry in Finland. In the laboratory, toxicity tests and experiments using field soil simultaneously contaminated with Cu and Zn, and with different earthworm species and populations with different exposure histories were established to determine species- and population-specificity in responses to metals. In two of the three field areas studied, soil metal concentrations close to the emission source were high enough to induce clear harmful effects on earthworm total number, biomass, and diversity. In the laboratory experiments, earthworms avoided contaminated soils with metal concentrations lower than those needed to induce biochemical responses. Increasing soil metal concentration reduced earthworm activity, interfering with reproduction and decreasing biomass, and finally caused mortality. Aporrectodea tuberculata, the species used in most of the experiments, tolerated higher metal concentrations in the field soil than in the standardised artificial soil. A species used in standardised tests, Eisenia fetida, appeared to be more tolerant of metals and to regulate metal body burdens more strictly than A. tuberculata. Ecologically different species avoided metal contaminated soils differently, partly clarifying species-specific differences found in the field. Earthworms of a population with long-term exposure to metal contamination seemed to tolerate higher metal concentrations than a population without earlier exposure. In addition, earthworms seemed to reduce the mobility and bioavailability of metals in the soil. When interpreted with care, earthworm data shows the effects of metal contamination and other soil conditions. Results of this study emphasise that it is important to consider ecological characteristics and possible tolerance of the species, and even those of the population, used in ecotoxicological tests and field surveys. In summary, the inclusion of earthworm responses to support soil chemical analyses is highly recommended when potential harmfulness of anthropogenic substances and soils are estimated in risk assessment procedures.