ECOTOXICOLOGICAL EFFECTS OF THE ANTI-EPILEPTIC DRUG LAMOTRIGINE ON ZOOPLANKTON COMMUNITIES

Abstract

Pharmaceuticals are essential in modern medicine, to ensure physical and mental health. However, after consumption, these chemicals are discharged into the environment through wastewater treatment plants and pose risks to non-target organisms. Knowledge on the chemical occurrence and exposure pathways are essential to produce reliable risk assessments and set guidelines for policies on chemical production and usage. In this framework, the anti-epileptic drug lamotrigine is an example of a knowledge gap, as more data is needed to infer conclusions on the risk it poses on the environment. Lamotrigine is, in fact, detected in freshwater environments, but no data is publicly available on its occurrence in marine environments. Furthermore, ecotoxicological data on this substance is scarce, often not well documented and from sources without peer reviews, such as, safety data sheets from chemical manufacturers. This thesis wants to increase the knowledge on the ecotoxicological effects of lamotrigine on natural zooplankton communities, with a focus on copepod communities. These organisms are keystone species for the marine environment, influencing biogeochemical processes and the biological food web – by being primary consumers, and at the basis of secondary consumers’ diet. Studies on communities are also more ecologically relevant compared to single-species tests. Through several experiments, I analysed lamotrigine toxicity across different life stages of copepods by assessing functional sublethal endpoints (feeding rate, egg production rate, egg hatching, nauplii development into copepodites), lethal endpoints (nauplii and copepodites mortality), and structural endpoints (community composition shifts). After refining the chemical range to test, I was able to conclude that lamotrigine toxicity to marine zooplankton has a non-monotonous trend, with the highest adverse effect observed at a concentration of 1 μg L-1. However, statistical significance was rarely met likely due to the high natural variation that characterize natural communities. The results of my thesis highlights the complexity of assessing pharmaceutical toxic effects on marine zooplankton, and the difficulty in explaining non-monotonous responses when only little data are available. This thesis underlines the need for more environmental occurrence data in the marine environment, to assess if lamotrigine can represent a risk giving the ecotoxicity data I obtained. In addition, to have a comprehensive risk assessment, I suggest that different species and/or communities should be tested to have a clearer understanding of lamotrigine ecotoxicity