[Acute toxicological effects of excessive Cu and Zn-containing in pig manure on earthworm]

Cu and Zn are popularly used as additives in animal feed in China, which could result in their excessive accumulation in manure to a toxic level, and thus, possibly threaten the environment when the manure is applied to farmland. In this paper, the acute and sub-acute lethal effects of pig manure with excessive Cu and Zn on earthworm were studied, and the results indicated that the concentration of Cu and Zn in pig manure had a significantly positive correlation with the mortality of earthworm, while a significantly negative correlation with earthworm growth rate. The individuals of earthworm had different tolerance to excessive Cu and Zn, with the threshold values causing death being 250 mg x kg(-1) and 400 mg x kg(-1) for Cu and Zn, respectively. The LD50 was 646.68 mg x kg(-1) for Cu, and 947.38 mg x kg(-1) for Zn. A strong synergistic effect was observed under the combined pollution of 250 mg x kg(-1) for Cu and 500 mg x kg(-1) for Zn, whereas antagonistic effect happened when 750 mg x kg(-1) for Cu was supplied, suggesting that the joint toxic effects of Cu and Zn on earthworm were closely correlated to their concentrations in pig manure.