Development of a test method for transformation of veterinary pharmaceuticals and biocides in anaerobic liquid manure

Abstract

Background: Spreading of manure on agricultural soils represents an important pathway by which veterinary medicinal and biocidal products enter the environment. To assess their environmental impact in the context of authorization processes, experimental testing of transformation of these compounds in manure is considered in regulatory guidance documents. However, there is no standardized experimental test method available so far. To fill this gap, an experimental test method was developed to examine transformation in liquid cattle and pig manure. Results: To account for manure specifics and for a possible influence of manure parameters on transformation rates, a comprehensive data acquisition and statistical analysis were performed. To address the variability of liquid manure of different type and origin, 30 manures were sampled and characterized. Thereof, three cattle and three pig manures were selected to perform anaerobic transformation studies with two radiolabeled veterinary medicinal active substances (14 C-salicylic acid and 14 C-paracetamol) and a confidential radiolabeled " 14 C-biocide B" serving as test compounds. Spatial and seasonal variability of manure parameters was quantified, and a sampling technique to obtain homogenous manure samples was developed. Transformation studies with six replicates per sampling point were conducted to examine the influence of test setup, of manure storage conditions, and of parameter variations between manure of the same species and of different species on half-lives, formation of extractable and non-extractable residues and mineralization rates. Finally, a test design was established that yields reproducible results for transformation studies in liquid cattle and pig manure under anaerobic conditions. Conclusions: Results give a reliable basis for an experimental test method to perform anaerobic transformation studies in liquid cattle and pig manure. The developed test method comprises detailed guidance on selection of sampling date and site, collection from manure tank, storage duration and temperature in the laboratory, duration of manure acclimation period, and the incubation system design. It proved to give reproducible results in a validation ring test performed in a follow-up project and is planned to be submitted as draft test guideline for approval by the OECD.

Assessing the influence of pig slurry pH on the degradation of selected antibiotic compounds

“…CFT, FLO, TYL and SMX were all observed to be impersistent within pig slurries at a pH of 7 and the DT 50 values were in-line with previous reports of degradation rates within pig slurries/manures and anaerobic digestion (Gilbertson et al, 1990;Hollis, 1991;Mohring et al, 2009;Chatterjee et al, 2013;Berendsen et al, 2018;Junker et al, 2020). Acid or alkaline treatments were observed to increase/decrease degradation rate constants.…”

“…Presently there is a lot of uncertainty regarding veterinary medicine degradation within manures due to differences in manure properties; despite the fact that a thorough understanding is critical for harmonisation of manure degradation studies (EMA, 2011;VICH, 2000;VICH, 2003). Variation exists between manure degradation studies, for example Blackwell et al (2005) reported a DT 50 of 79 d for oxytetracycline within pig slurries whereas Wang et al (2015) calculated a range of 9.05-9.65 d. When regulatory soil degradation studies are performed (e.g., OECD 307), the use of four soil types is usually required due to the known influence of soil properties on the degradation rate and route of organic compounds (OECD, 2002;Junker et al, 2020). Soil matrix properties can affect sorption, hydrolysis, microbial mineralization as well as the ionic strength and speciation of contaminants (pKa) via changes in pH (Sassman and Lee, 2005;ter Laak et al, 2006;Chatterjee et al, 2013;Jechalke et al, 2014;Mitchell et al, 2014;Junker et al, 2020).…”

“…Variation exists between manure degradation studies, for example Blackwell et al (2005) reported a DT 50 of 79 d for oxytetracycline within pig slurries whereas Wang et al (2015) calculated a range of 9.05-9.65 d. When regulatory soil degradation studies are performed (e.g., OECD 307), the use of four soil types is usually required due to the known influence of soil properties on the degradation rate and route of organic compounds (OECD, 2002;Junker et al, 2020). Soil matrix properties can affect sorption, hydrolysis, microbial mineralization as well as the ionic strength and speciation of contaminants (pKa) via changes in pH (Sassman and Lee, 2005;ter Laak et al, 2006;Chatterjee et al, 2013;Jechalke et al, 2014;Mitchell et al, 2014;Junker et al, 2020). Most regulatory manure degradation studies consider one animal manure per animal type, but we hypothesise varied manure properties such as pH to be of equal or greater importance to those of soils.…”

Sorption of selected antiparasitics in soils and sediments

“…This could be true for soils where agriculturally used biocides or disinfectants are spread with manure, potentially combined with antibiotics, antiparasitics, or other VMPs. Occurrence and transformation of biocides in manure and their fate in soils are only marginally investigated [ 77 , 78 ]. Moreover, biocide release into the environment could increase due to the SARS-CoV-2 pandemic [ 79 ].…”

Highlighting the gaps in hazard and risk assessment of unregulated Endocrine Active Substances in surface waters: retinoids as a European case study

“…In surface waters, wastewater treatment effluents are a constant contributor of anthropogenic bioactive compounds including retinoids [253]. To address transformation of pharmaceutically and cosmetically used retinoids, it is suggested that work being initiated at the OECD to develop a test guideline on anaerobic transformation of veterinary pharmaceuticals, organic compounds and biocides in liquid farmyard manure [302] could include retinoid-like monitoring endpoints. This would contribute to filling the assessment data gap of retinoid-like activity originating from farmyard manure and its fate in the environment.…”