New guidelines to assess the environmental risk of veterinary medicines (VMs) have been proposed in the European Union. As in any risk assessment, exposure is a factor of critical importance. The predicted environmental concentration (PEC) in soil therefore is a pivotal decision parameter in the assessment procedures for VMs. As presently proposed, phases I and II of the assessment require a PEC at an appropriate level of refinement. Hence, it is necessary to calculate the PEC of VMs in a uniform way. The PEC for VMs depends on animal husbandry practices, on the use pattern of the product, on its kinetics in the treated animals and in soil, on physiological characteristics of these animals, and on the codes of good agricultural practices of excreta collecting, storage, and of fertilizing land. In this paper, basic calculations are presented to estimate the PEC from the concentration of residues in manure, the quantities of manure spread per unit land area, and the depth of incorporation into soil. Expanded calculations allow refinements for treatment of only part of the group of animals, metabolism, periods in house, transformation in manure or soil, and repeated application. Examples presented illustrate the dependence of the PEC on various parameters. The examples allow the examination of the regulatory framework of the phase I PEC and an alternative approach to judge the persistence during manure storage or the persistence in soil is proposed.
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Spaepen et al. (1997) studied this question.