VN April 2020

Vetnews | April 2020 11 The Toxicology Laboratory, Agricultural Research Council-Onderstepoort Veterinary Research (ARC-OVR) utilises gas chromatography-mass spectrometry (GC-MS) analysis to confirm the presence of pesticides in samples submitted for diagnostic purposes. As can be seen in Figure 1, terbufos was confirmed in the majority of poisonings ascribed to the cholinesterase inhibitors (organophosphorus and carbamate compounds) during the past two years. In 2018, terbufos was detected in half (50%) of all positive samples, which increased to 68% in 2019. Terbufos (Fig. 2), an organophosphorus compound that is applied to the soil at planting, is used as an insecticide and nematocide. Terbufos is highly toxic with an acute oral LD 50 of 1.6 mg/kg (male rats) and 5.4 mg/kg (female mice). Terbufos is commercially available in a free-flowing, solid granular formulation, thus it is easily subdivided, transferred to smaller containers and used in baits. For a number of years aldicarb was implicated in most of the malicious poisonings. When granules are seen in a bait sample or in stomach contents, it is often assumed to be aldicarb. However, aldicarb only contributed to 18% (in 2018) and 11% (in 2019) of all positive cases of poisoning caused by the cholinesterase inhibitors (Fig. 1). The company that marketed aldicarb, voluntarily withdrew Temik® from the market in 2012. A notice for the prohibition of import, export, possession, acquisition, sale, use and disposal of aldicarb has been published in the Government gazette in November 2013. Since then there is an increasing incidence of terbufos poisoning. Carbofuran was the third most identified compound in all samples submitted (Fig. 1). Carbofuran is also a highly toxic carbamate pesticide with acute oral LD 50 ’s of 8 mg/kg (rats) and 15 mg/kg (mice). Some granular formulations have a blue colour (Fig. 3). References: 1. Tomlin, CDS. 2009. ‘The pesticide manual’, 15th edn., British Crop Production Council, Hampshire. 2. Van Zyl, K. 2013. A guide to crop pest management in SA – A compendium of acaricides, insecticides, nematicides, molluscicides, avicides and rodenticides, AVCASA, Pretoria. v Terbufos - the most common cause of pesticide poisoning in animals in South Africa Christo Botha a,b and Heleen Coetser b a Department of Paraclinical Sciences, Faculty of Veterinary Science, Onderstepoort. b Toxicology Laboratory, Agricultural Research Council-Onderstepoort Veterinary Research. Figure 2: Greyish coloured terbufos granules. Figure 3: Blue-coloured carbofuran granules. Figure 1: The percentage of individual cholinesterase inhibitors identified during 2018 and 2019 in samples submitted to the Toxicology Laboratory, ARC-OVR.