IMPORTANCE OF SALT IONS IN ECOTOXICOLOGICAL TESTS WITH SOIL ARTHROPODS

In soil ecotoxicological tests, the toxicity of metals is usually dete rmined by investigating the effects of metal salts without paying atte ntion to the influence of the anionic partner of the investigated meta l. In our studies, we evaluated the role of salt anions on the larval development of the hemiedaphic carabid Poecilus (Pterostichus) cupreus Linne 1758 and on the reproduction of the endogeic collembolan Folsom ia candida Willem. The experiment with P. cupreus was conducted in a s andy soil treated with CaCl2, CuCl2, CuSO4, and MgSO4 solutions. MgSO4 caused no observable effect. Both copper salts and the CaCl2 treatmen t caused a high mortality of P. cupreus larvae compared with the contr ol, and the toxic effect produced by copper could be clearly distingui shed from a chloride ion effect. Effects on the reproduction of F. can dida were investigated using a soil with variable total soil water con tent and a standard mixed salt solution, containing CaSO4, MgSO4, MgCl 2, KCl, and NaCl, applied at different concentrations. At higher salt concentrations, egg development was inhibited. Tests with single salt solutions showed that this was due to the inclusion of 43.5 mmol NaCl/ kg d.wt. soil in the mixed salt solution. CaCl2 tested separately at a concentration of 25.9 mmol/kg d.wt. soil also reduced egg survival. T he rate of collembolan reproduction differed with total soil water con tent, showing that tests with Collembola must be carried out in media with constant water content for results to be comparable. A comparison between a solution of salts and an elutriate of toxic waste containin g heavy metals and similar salt ions showed a clear combination of sal t effects and heavy metal effects. These studies indicate that chlorid e ions may interfere with the demonstration of toxic heavy metal effec ts. Consequently, when chloride salts are used to determine the toxici ty of metal cations, additional tests with comparable anion solutions of non-toxic cations are necessary, to clarify the results. (C) 1998 E lsevier Science B.V.