Predicting biphasic responses in binary mixtures: Pelargonic acid versus glyphosate.

Area of Science:

• Environmental toxicology
• Plant science
• Chemical risk assessment

Background:

• Chemicals are often encountered as mixtures, necessitating an understanding of their combined effects.
• Hormesis, a dose-response phenomenon, complicates mixture toxicity predictions, especially at low exposure levels.
• Pelargonic acid and glyphosate are herbicides known to induce hormesis and exhibit interactions.

Purpose of the Study:

• To investigate mixture effects of pelargonic acid and glyphosate on lettuce root growth.
• To analyze mixture effects on both the dose-response relationship and the magnitude of hormesis.
• To evaluate the predictability of hormesis in herbicide mixtures.

Main Methods:

• Five in vitro experiments assessed lettuce root growth under varying pelargonic acid and glyphosate mixtures.
• Classical joint-action models, including concentration addition, were used to analyze dose-dependent effects.
• A linear reference model evaluated effects on hormetic magnitude (y_max).

Main Results:

• Mixture effects on the dose ranged from additive at low concentrations to strongly synergistic at high concentrations.
• Effects on hormetic magnitude (y_max) showed linear or non-linear trends depending on the mixture ratio.
• Synergism at the effective dose 50 (ED50) was linked to atypical y_max deviations, highlighting the importance of interaction at this point.

Conclusions:

• The study confirmed synergism in pelargonic acid and glyphosate mixtures, impacting hormetic magnitude.
• Predictability of hormesis in mixtures is feasible, with implications for risk assessment.
• Methodologies for incorporating hormesis into mixture-toxicity evaluations were advanced.