Liposome-mediated delivery of challenging chemicals to aid environmental assessment of Bioaccumulative (B) and Toxic (T) properties

Mafalda Castro,Dennis Lindqvist

doi:10.1038/s41598-020-66694-3

Abstract

Standard aquatic toxicity tests of chemicals are often limited by the chemicals’ water solubility. Liposomes have been widely used in the pharmaceutical industry to overcome poor pharmacokinetics and biodistribution. In this work, liposomes were synthesized and used in an ecotoxicological context, as a tool to assure stable dosing of technically challenging chemicals to zooplankton. Three chemicals with distinctly different characteristics were successfully incorporated into the liposomes: Tetrabromobisphenol A (TBBPA, log Kow 5.9, pKa1 7.5, pKa2 8.5), chlorinated paraffin CP-52 (log Kow 8–12) and perfluorooctanoic acid (PFOA, pKa 2.8). The size, production yield and stability over time was similar for all blank and chemical-loaded liposomes, except for when the liposomes were loaded with 10 or 100 mg g−1 PFOA. PFOA increased the size and decreased the production yield and stability of the liposomes. Daphnia magna were exposed to blank and chemical-loaded liposomes in 48 hour incubation experiments. A dose-dependent increase in body burden in D. magna and increased immobilization (LD50 = 7.6 ng CPs per individual) was observed. This confirms not only the ingestion of the liposomes but also the successful internalization of chemicals. This study shows that liposomes can be a reliable alternative to aid the study of aquatic toxicity of challenging chemicals.

Highlights

Standard aquatic toxicity tests (e.g., OECD guidelines for the testing of chemicals) are valuable tools that help to decrease uncertainty and increase reproducibility of results
The production yield varied between 89 and 126% of the control when tetrabromobisphenol A (TBBPA) and CPs were incorporated into the liposomes (Supplementary Table S1)
CPs proved highly suitable for incorporation in liposomes with a high incorporation potential, high recoveries, and even a slightly higher production yield of liposomes compared to the control

Summary

Introduction

Standard aquatic toxicity tests (e.g., OECD guidelines for the testing of chemicals) are valuable tools that help to decrease uncertainty and increase reproducibility of results. The most commonly used aquatic toxicity testing guidelines, both in regulatory and scientific contexts, have been published by the Organisation for Economic Co-operation and Development (OECD) These guidelines were originally developed for readily water-soluble and stable chemicals, and it has been historically difficult to accommodate these tests for the whole range of chemicals in the marketplace[3]. The water solubility of tetrabromobisphenol A (TBBPA) varies from 0.17 mg L−1 at pH 3 (100% neutral form) to 30.5 mg L−1 at pH 8 (when double negatively charged)[12] Amphiphilic chemicals such as per- and polyfluoroalkyl substances (PFAS) are of particular complexity due to their simultaneous hydrophobicity and lipophobicity. The hypothesis of this study was that liposomes could be used as a tool for the delivery of highly hydrophobic, ionic, and amphiphilic chemicals to D. magna, and could be established as a means to aid the aquatic toxicity testing of challenging chemicals. We used three model chemicals: i) tetrabromobisphenol A (pH sensitive speciation), ii) perfluorooctanoic acid (amphiphilic chemical), and iii) chlorinated paraffins (highly hydrophobic chemicals)

Methods

Results

Conclusion