The role of laboratory terrestrial model ecosystems in the testing of potentially harmful substances

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Abstract
A classification of terrestrial model ecosystems (TMEs) was introduced which is based upon the physical properties of intactness of the physical medium and openness to the atmosphere. This gave rise to four types of system, namely open and closed intact systems and open and closed homogeneous' systems. These systems have different capabilities with respect to fate and effect end-points with various substances. The large closed TMEs are generally very complex, require a high degree of operator skill, expensive and therefore not replicable. Whilst these can provide estimates of losses due to volatility, they are not useful for determining effect end-points because of low replicability; high replicability being necessary because of natural variation in organism response. Open systems, especially those having intact soil-cores, are usually smaller, less complex and therefore more replicable. These have provided useful information on integrative functional effect end-points, but can only produce mass balances with non-volatile substances. Homogenization of the medium has also helped elucidate ecotoxicological effects by increasing replicability, but may introduce artifacts because of the disruption to soil organisms.