Effects of a herbicide formulation, Tordon 75D®, and its individual components on the oxidative functions of mitochondria

Abstract

This investigation evaluates the toxicity of a herbicide formulation, as well as testing its active and other components (other components comprise all components of Tordon 75D® excluding the active components: i.e. the solvents, triisopropanolamine and diethyleneglycol monoethyl ether, a silicone defoamer and a proprietary surfactant, polyglycol 26-2). The results showed that Tordon 75D® (a mixture of the triisopropanolamine salts of 2,4-dichlorophenoxy acetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram) and its other components) impaired the oxidative functions of submitochondrial particles (SMPs). The effective concentrations that caused 50% inhibition of SMP activity (EC 50s) for Tordon 75D® were in the low micromolar range for 2,4-D and picloram in the presence of the other components, while in the absence of the other components exposure to 136 times higher concentrations of the triisopropanolamine forms of 2,4-D and picloram administered as a mixture were required to inhibit the oxidative functions of SMPs. Tordon 75D® also significantly decreased the respiratory control ratio of intact rat liver mitochondria. The results show that the toxic effects of Tordon 75D® on SMPs (at the EC 50) and intact rat liver mitochondria were not due to any additive or synergistic actions of a mixture of its active and other components, but rather were caused solely by the proprietary surfactant. Since mitochondria are responsible for over 90% of the energy production in all eukaryotic organisms, the use of the SMP assay provides a convenient in vitro assay for evaluating cellular toxicity and can be regarded as an informative screening assay when designing chemical products which contain mixtures of chemicals.