Conventional plastics have become a major environmental concern due to their persistence and accumulation in marine ecosystems. The development of potential degradable polymers (PBP), such as polyhydroxyalkanoates (PHAs) and polylactic acid (PLA), has gained attention as an alternative to mitigate plastic pollution, since they have the potential to biodegrade under certain conditions, and their production is increasing as replacement of conventional polyolefins. This study aimed to assess and compare the toxicity of leachates of pre-compounding PBP (PLA and the PHA, polyhydroxybutyrate-covalerate (PHBv)) and polypropylene (PP) on five marine planktonic species. A battery of standard bioassays using bacteria, microalgae, sea urchin embryos, mussel embryos and copepod nauplii was conducted to assess the toxicity of leachates from those polymers. Additionally, the presence of chemical additives in the leachates was also verified through GC–MS and LC-HRMS analysis. Results showed that PHBv leachates exhibited higher toxicity compared to other polymers, with the microalgae Rhodomonas salina, being the most sensitive species to the tested leachates. On the other hand, PP and PLA generally displayed minimal to no toxicity in the studied species. Estimated species sensitivity distribution curves (SSD) show that PHBv leachates can be 10 times more hazardous to marine plankton than PP or PLA leachates, as demonstrated by the calculated Hazardous Concentration for 5 % of species (HC5). Qualitative chemical analysis supports the toxicological results, with 80 % of compounds being identified in PHBv leachates of which 2,4,6-trichlorophenol is worth mentioning due to the deleterious effects to aquatic biota described in literature. These findings underscore the fact that whereas environmental persistence can be targeted using PBP, the issue of chemical safety remains unsolved by some alternatives, such as PHBv. Gaining a comprehensive understanding of the toxicity profiles of PBP materials through a priori toxicological risk assessment is vital for their responsible application as alternatives to conventional plastics., Agencia Estatal de Investigación | Ref. PID2020-120479GA-I00, Agencia Estatal de Investigación | Ref. PCI2020-112110, Ministerio de Universidades | Ref. FPU19/02280, Fundação para a Ciência e a Tecnologia | Ref. C2020/65, Agencia Estatal de Investigación | Ref. RYC2018-025770-I, Universidade de Vigo/CISUG

Conventional plastics have become a major environmental concern due to their persistence and accumulation in marine ecosystems. The development of potential degradable polymers (PBP), such as polyhydroxyalkanoates (PHAs) and polylactic acid (PLA), has gained attention as an alternative to mitigate plastic pollution, since they have the potential to biodegrade under certain conditions, and their production is increasing as replacement of conventional polyolefins. This study aimed to assess and compare the toxicity of leachates of pre-compounding PBP (PLA and the PHA, polyhydroxybutyrate-covalerate (PHBv)) and polypropylene (PP) on five marine planktonic species. A battery of standard bioassays using bacteria, microalgae, sea urchin embryos, mussel embryos and copepod nauplii was conducted to assess the toxicity of leachates from those polymers. Additionally, the presence of chemical additives in the leachates was also verified through GC–MS and LC-HRMS analysis. Results showed that PHBv leachates exhibited higher toxicity compared to other polymers, with the microalgae Rhodomonas salina, being the most sensitive species to the tested leachates. On the other hand, PP and PLA generally displayed minimal to no toxicity in the studied species. Estimated species sensitivity distribution curves (SSD) show that PHBv leachates can be 10 times more hazardous to marine plankton than PP or PLA leachates, as demonstrated by the calculated Hazardous Concentration for 5 % of species (HC5). Qualitative chemical analysis supports the toxicological results, with 80 % of compounds being identified in PHBv leachates of which 2,4,6-trichlorophenol is worth mentioning due to the deleterious effects to aquatic biota described in literature. These findings underscore the fact that whereas environmental persistence can be targeted using PBP, the issue of chemical safety remains unsolved by some alternatives, such as PHBv. Gaining a comprehensive understanding of the toxicity profiles of PBP materials through a priori toxicological risk assessment is vital for their responsible application as alternatives to conventional plastics., This research was funded by the Ministry of Science and Innovation—Spanish Agency of Research through the RisBioPlas Project (AEI: 10.13039/501100011033) to RB, the MICROPLEACH project (PID2020-120479 GA-I00) to RA, the Joint Programming Initiative, Healthy and Productive Seas and Oceans, JPI Oceans-Spanish National Research funding Agency through the RESPONSE Project, (PCI2020-112110). S.L.I. was supported by the Ministry of Universities of Spain (FPU grant reference FPU19/02280). This study was also supported by the ULPGC- FPCT (subcontract DTU-ULPGC, C2020/65) and a Ramon y Cajal Program grant (RYC2018-025770-I) to RA. Universidade de Vigo/CISUG provides funding for open access charges., Peer reviewed

14 pages, 6 figures, supplementary data https://doi.org/10.1093/ismejo/wraf195.-- Data availability: The raw data used in this study are publicly available at Figshare (https://doi.org/10.6084/m9.figshare.29891216); the code is available from the corresponding author upon request., Millions of tons of plastic enter the ocean annually, yet the effects of their leachates on the microbial loop are poorly understood. This study investigates how dissolved organic carbon released from field-collected plastics and a bioplastic influences the growth of the protozoan Oxyrrhis marina and its associated bacterial community. Plastics increased dissolved organic carbon concentrations in seawater by 5 to 34-fold, stimulating O. marina growth by up to an order of magnitude compared with the control. After exposure to conventional beach plastic leachates and bioplastic leachates, O. marina exhibited growth rates up to 0.3 and 0.4 d⁠, respectively, even in the absence of microalgal prey. We estimated that each gram of microplastics could lead to daily assimilation of up to 0.7 g of carbon per gram of protozoan, indicating that plastic-derived carbon enhances heterotrophic metabolism in the microbial loop through osmotrophy. Given that autotrophic prokaryotes are negatively impacted by plastic leachates and that plastic pollution is expected to triple in the coming decades, plastic leaching could alter the balance between microbial primary production and heterotrophy in the ocean, This study was funded by the Spanish Ministry of Science and Innovation and the National Agency of Research through the MICROPLEACH project (Agencia Estatal de Investigación, PID2020-120479 GA-I00/AEI/10.13039/501100011033) to R.A. It was also supported by a ”Juan de la Cierva” grant from the Spanish Ministry of Science and Innovation to J.L.D.-C. and a ”Ramón y Cajal” grant from the Spanish Ministry of Science (RYC2018-025770-I) to R.A. C.R.C. was also supported by a ”Ramón y Cajal” grant from the Spanish Ministry of Science (RYC2020-029555-I) and acknowledges the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S), Peer reviewed

This repository contains the datasets that underpin the analyses and figures in the ISME Journal article 'Plastic leachates promote protozoan growth' by Jessy Le Du-Carree, Cristina Romera-Castillo, and Rodrigo Almeda, published 2025 (DOI: [DOI or accession link]). The files are:
Bacteria_concentrations.xlsx — Bacterial abundance/concentration measurements.
CDOM_FDOM.xlsx — Chromophoric and fluorescent dissolved organic matter (CDOM/FDOM), and dissolved organic carbon (DOC) data.
Cell_concentration-size_oxyrrhis.xlsx — Oxyrrhis marina cell concentrations and size metrics.
EEMs.xlsx — Excitation–Emission Matrix (EEM) fluorescence data.
These datasets are shared to ensure transparency and reproducibility and constitute the complete data used in the published manuscript. Please cite the ISME Journal article above when reusing any portion of these data, This study was funded by the Spanish Ministry of Science and Innovation and the National Agency of Research through the MICROPLEACH project (Agencia Estatal de Investigación, PID2020-120479 GA-I00/AEI/10.13039/501100011033) to RA. It was also supported by a “Juan de la Cierva” grant from the Spanish Ministry of Science and Innovation to JLD and a “Ramón y Cajal” grant from the Spanish Ministry of Science (RYC2018-025770-I) to RA. CRC was also supported by a “Ramón y Cajal” grant from the Spanish Ministry of Science (RYC2020-029555-I) and acknowledges the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S). We sincerely thank Torkel Nielsen (DTU Aqua, Denmark) for providing the Rhodomonas and Oxyrrhis cultures, and Alex Campillo (CSIC, Barcelona, Spain) for his valuable assistance with the bacterial analysis, Peer reviewed