Cardiac Toxicity of Nicotine and Its Synergistic Effect with Caffeine: The Daphnia pulex Model

Purpose: Nicotine and caffeine are among the most frequently self-administered licit psychoactive drugs in Taiwan. This study investigated whether Daphnia pulex could be used to investigate the effects of nicotine and caffeine on the heart and to establish Daphnia as a model for investigating the role of toxins. Methods: The toxic effects of pure nicotine and caffeine were measured and compared with the EC50 value of the mixed drugs using D. pulex acute toxicity test, chronic toxicity test, measurement of heart rate, and mixed toxicity test. Results: The heart rate fluctuated within the first 14 days, and then it dropped dramatically on the 15(superscript th) day and hit the lowest point at experiment termination. It can be concluded that heart of water fleas may respond to low concentrations of chemicals until the 15(superscript th) day. With a Mixture Toxicity Index of 2.6, we found that combined caffeine and nicotine had a synergistic effect. Conclusion: The impact of chemicals on D. pulex can be displayed with better clarity by incorporating heart rate analysis. The water fl ea can be studied as an indicator of the presence off environmental toxicants.