Acute toxicity of local anesthetics used for humans and other animals in the larvae of marine crustacean, red-clawed crab Chiromantes haematocheir.

Local anesthetics such as lidocaine have been used in humans and other animals to perform surgical procedures, therapeutics, and experiments. Lidocaine discarded into the environment through industrial waste, human and animal excretion, and household waste has been detected in the aquatic environment. For example, lidocaine in rivers, lakes, and influent and effluent water has been detected at wastewater treatment plants (7 ng/L-2.06 μg/L), suggesting that this chemical substance influences aquatic animals. However, the toxic effects of lidocaine on marine organisms have not been investigated. This study examined the acute toxicity of local anesthetics (lidocaine and dibucaine) on the marine zoea larvae of red-clawed crabs, which feature a life cycle in which adults live on land and larvae live in the sea. Survival analysis of zoea larvae revealed that dibucaine was more toxic than lidocaine. The 50% effective concentrations (EC₅₀s) for lidocaine and dibucaine were 1.64 × 10^-3 and 4.63 × 10^-5 M, respectively, after 24 hr of exposure. Next, RNA sequencing was performed using the EC₅₀ of each drug. Both local anesthetics were highly toxic to the kidneys, in addition to their effects on the heart, nerves, and liver. These local anesthetics were also found to affect melatonin metabolism and possibly decrease melatonin levels in zoea larvae. To the best of our knowledge, no prior study conducted a comprehensive analysis of the effects of local anesthetics on aquatic larvae, illustrating the need to focus on the toxicity of these drugs in aquatic animals.