Comparative toxicity of a zinc salt, zinc powder and zinc oxide to Eisenia fetida, Enchytraeus albidus and Folsomia candida Koen Lock * , Colin R. Janssen Department of Applied Ecology, Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, B-9000 Ghent, Belgium Received 3 February 2003; received in revised form 28 May 2003; accepted 12 June 2003 Abstract The pore water zinc concentration and the calcium chloride extracted zinc fraction are higher in the soils spiked with a zinc salt (ZnCl 2 ) compared to soils spiked with zinc oxide or zinc powder. Based on total zinc concentrations in the soil, the acute toxicity of zinc salt to the compost worm Eisenia fetida, the potworm Enchytraeus albidus and the springtail Folsomia candida was lower compared to zinc oxide and zinc powder. However, when expressed on the basis of pore water concentrations or calcium chloride extracted fractions, acute toxicity was higher for zinc salt, which indicated that dermal uptake via the pore water is not the only route of uptake. Chronic toxicity of zinc salt, zinc oxide and zinc powder was similar when based on total concentrations in the soil which again indicates that the pore water route of uptake is not the only route of exposure but that oral uptake is also important. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Exposure routes; Soil invertebrates; Terrestrial ecotoxicology; Toxicity data 1. Introduction Recently, a lot of toxicity data for soil invertebrates exposed to zinc salts became available (Lock and Jans- sen, 2001a). However, toxicity data for soil invertebrates exposed to other forms of zinc are almost lacking. Beyer and Anderson (1985) assessed the toxicity of zinc oxide to the woodlice Porcellio scaber and they found that soil litter spiked with 1600 mg Zn/kg dry wt soil litter caused significant negative effects. Unfortunately, only toxicity of zinc oxide was assessed in this soil litter, which makes comparison with zinc salt impossible. Different forms of zinc can have a different impact on the environment and therefore, the risk assessment of different forms of zinc should be handled separately. However, the risk of other forms of zinc besides zinc salts can not be assessed as long as toxicity data are lacking. In the present study, ecotoxicity of a zinc salt, zinc oxide and zinc powder were compared for the com- postworm Eisenia fetida, the potworm Enchytraeus al- bidus and the springtail Folsomia candida. To assess the route of uptake, toxicity was expressed on the basis of total concentration in the soil, pore water concentration and calcium chloride extracted fraction. 2. Materials and methods 2.1. Test organisms Enchytraeus albidus Henle 1847 (Annelida: Oligo- chaeta) is cultured in artificial soil (OECD, 1984) and Chemosphere 53 (2003) 851–856 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +32-9-264-37-10; fax: +32-9- 264-37-66. E-mail addresses: koen.lock@rug.ac.be, koen.lock@ugent. be (K. Lock). 0045-6535/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0045-6535(03)00593-9