Evaluating pesticide ecotoxicity using a stimuli-response model in liposomes

Abstract

Pesticides are widely used around the home and in agriculture to control unwanted populations; however, they may also be toxic to non-targeted organisms. Because traditional methods of assessing pesticide toxicity are expensive, lengthy, and ethically questionable, we evaluated pesticide toxicities using stimuli-responses in liposomes. Pesticide ecotoxicity was evaluated using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes. Changes in membrane permeability were measured using calcein leakage assays as stimuli-responses in the presence of six pesticides (Chlorpyrifos-methyl, fluometuron, imidacloprid, pirimicarb, pyrethrin, and quizalofop-ethyl), for which the calcein release rate was analyzed using a first-order kinetics equation. The calcein release rate constants of the DPPC liposomes were used to classify the pesticides into lower and higher toxicity groups. In each group, the initial calcein release rate from the DPPC/DOPC liposomes mixed with 33 ​mol% DOPC correlated well with previously reported pesticide toxicities. The DOPC liposomes underwent lateral phase separation in a different manner between the two toxicity groups. Pesticides with lower toxicities were partitioned in the DPPC-enriched phase, disrupting the gel phase order through their hydrophobicity, whereas pesticides with higher toxicity were partitioned in the DOPC-enriched phase and stabilizing the liquid disordered phase owing to their hydrophobicity and molecular shape. The toxicity of each pesticide was well represented by an equation that combined the calcein release rate constant of the DPPC liposomes and the initial calcein release rate of the 33 ​mol% DOPC mixed liposomes. The findings indicate that stimuli-response assays using liposomes can be used to complement traditional ecotoxicity assessments.