Transformation of veterinary pharmaceuticals and biocides in liquid manure

Veterinary medicinal products administered to animals are excreted with urine and faeces. For animals housed in stables, the resulting manure is collected and stored before being spread onto agricultural land. Disinfection products used to sanitize stables are also transferred into the manure. Therefore, the spreading of manure is an important pathway of introducing veterinary medicines, biocides and their transformation products into the environment. As a consequence, the fate of veterinary medicines/biocides in manure is taken into account in the environmental risk assessment for these substances.

Although there is a need for guidance on the performance and evaluation of degradation studies with veterinary medicines/biocides in manure, a standardized and validated method is currently lacking. In 2011, the European Medicines Agency (EMA) adopted a guidance document on determining the fate of veterinary medicinal products in manure. This document is intended to provide guidance on the general conditions of studies on the transformation of veterinary medicines in manure, but is not an experimental protocol. Thus, further advice on experimental details is required to obtain reliable and sound results.

Against this background, an experimental test method and a draft guideline are currently under development within a research project funded by the German Federal Environment Agency that should, in the long run, lead to a guideline on transformation of substances in (liquid) manure. An international inter-laboratory comparison (pre-validation ring test) was performed in 2012/2013 to test the applicability of this draft test method (project report available here). Based on the resulting revised test method and a draft guideline a ring test was coordinated by ECT in 2013/2014. The anaerobic transformation of two ¹⁴C-labelled compounds (a veterinary pharmaceutical in pig manure and a biocide in cattle manure) was examined over an incubation period of 90 days by five institutions from Europe and North America. Besides a ¹⁴C mass balance, the following endpoints/parameters were determined, if possible: disappearance time (DT₅₀) of the parent compound, formation of transformation products, mineralisation (CO₂ and CH₄), extractable residues, and formation of non-extractable residues (NER). Based on the outcome of the ring test a revised draft guideline will be prepared.

German project title: Harmonisierung der Umweltexpositionsabschätzung für Tierarzneimittel und Biozide: Validierung eines OECD Prüfrichtlinienentwurfs zum Verhalten in Gülle