Continuous monitoring of Folsomia candida (Insecta : Collembola) in a metal exposure test

Current recommended ecotoxicological tests with the parthenogenetic springt ail Folsomia candida using standard OECD soil do not allow for continuous m onitoring during the exposure period. Effects of chemicals cannot be determ ined until the end of the experiment (typically after 4 weeks), since the a nimals stay below the soil surface. In this study, F. candida were maintain ed on a plaster of Paris/graphite substrate for 7 weeks and were supplied w ith an aqueous suspension of yeast contaminated with Cd, Cu, Pb, and Zn as nitrate salts. Growth rate, time to first batch of eggs, quantity of food c onsumed, and the presence of graphite in the gut (a sign of avoidance of ye ast) were all affected by metal contaminated diets. The relative toxicities of Cd:Cu:Pb:Zn in the yeast were 1.0:1.07:12.0:4.3, respectively ton a wei ght basis) with Cd being the most toxic. Internal body concentrations incre ased, and the concentration factor (metal concentration in F. candida/metal concentration in yeast) decreased with increasing metal exposure. In gener al, metals are much less toxic when added to the food off. candida than whe n incorporated into soil in standard tests. It is suggested that Collembola have a greater tolerance of metals in the diet since they avoid contaminat ed food, and are able to excrete assimilated metals at moulting via exfolia tion of the midgut epithelium where the elements are retained as part of a storage-detoxification system. The methodology described in this article al lows effects on growth to be observed as early as 7 days after the beginnin g of the experiment. (C) 2001 Academic Press.