Heavy metal concentrations in caterpillars fed with waste-grown vegetables

Our previous experiments showed that flowering Chinese cabbage (Brassica parachinensis) and Chinese radish (Rhaphanus sativus) var. longipinnatus grown in soil amended with sewage sludge and animal manure accumulated Pb, Cu, Zn and Mn. In this experiment, caterpillars of the common white butterfly (Pieris canidia) were fed with the waste-grown vegetables. Caterpillars fed with sewage sludge-grown vegetables had a lower body weight and a higher level of heavy metals than those fed with animal manure-grown vegetables (average fresh body weights of caterpillars fed with waste-grown leaves of Chinese radish were 75, 122, 186 and 196 mg for activated sludge, digested sludge, chicken manure and pig manure, respectively). Those fed with flowering Chinese cabbage accumulated a higher level of heavy metals than those fed with Chinese radish (Pb, 6·7-fold, Cu, 6·0-fold, Zn, 6·8-fold and Mn, 5·7-fold in treatments with activated sludge). As a whole, the accumulation of heavy metals in the caterpillars, in descending order, was from vegetables manured with activated sludge, digested sludge, chicken manure and pig manure.

Caterpillars, even though ingesting an enormous amount of the leaves, accumulated a lower level of Pb, Cu and Zn than that found in the vegetables. The route of elimination was not verified but it was suggested that the egestion of faeces might play an important role.