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

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 (EC50s) 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 EC50) 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.