Approved Abstracts

DO MICROPLASTICS AFFECT MICROBIAL-MEDIATED DETOXIFICATION OF MERCURY IN AQUATIC ECOSYSTEMS?



Author(s): NEUSA FIGUEIREDO; LAURA SILVA; SARA PEREIRA; CRISTINA CARVALHO; VASCO BRANCO; PAULA SOBRAL; MARTA MARTINS;
Presenter: LAURA TIÊ ZANCHI DA SILVA

Aquatic ecosystems may be widely impacted by a high number of pollutants, including heavy metals, such mercury (Hg) and plastic debris, mainly microplastics (MP), i.e., fragment with lower than 5 mm in diameter1. These pollutants tend to accumulate in the sediment2, where they can exert toxic effects to the wildlife and even to humans (e.g. bioaccumulation and biomagnification of methylmercury)1. In addition, MPs may act as a vector of mercury to organisms1. On the other hand, it is well known that bacteria play a key role in the biogeochemical cycle of Hg2-3 in aquatic systems and, at the same time, they can develop biofilms on MPs surface, contributing for the formation of the plastisphere. In this sense, the present work aims at disclosing the interaction effects of MP on the microbial-mediated mercury detoxification processes. Mercury-resistant microbial communities and pure colonies were isolated from sediment and water samples of two Hg-contaminated areas of Tagus estuary (a highly contaminated area – Barreiro, and a moderated contaminated area – Rosário, Portugal) and the effect of MP polystyrene (MP-PS) (40 mg/L) were assessed (i) on microbial growth of the isolated community, and (ii) on Hg detoxification processes mediated by the Hg - resistant microbial communities at 24, 72 and 120 h of incubation. After these periods of incubation, MP-PS were collected for microscope and FTIR analysis, and the supernatant was collected for pH measurement and total Hg quantification, as well as to evaluate the acute toxicity of the leachate. The results showed that the presence of MP-PS affected the bacterial growth and the Hg- detoxification process. The microbial community of Tagus estuary contributed for the Hg detoxification, by removing ≥ 50% of the initial Hg2+. However, when MP-PS were present, ≈ 50% of Hg was adsorbed to these plastics, decreasing Hg’s bioavailability for microbiological detoxification. These results show that the presence of MP-PS interferes with the biological transformation of Hg in aquatic systems, leading to the persistence of such toxic element in these systems by hindering the natural bioremediation processes.
Financial support: This work was supported by the Plastisphere project (PT-IL/0001/2019) and the Marine and Environmental Sciences Centre —MARE (UIDB/04292/2020; UIDP/04292/2020), both financed by national funds from Fundação para a Ciência e Tecnologia (FCT; www.fct.pt). Vasco Branco is financed by national funds via FCT, I.P. through Norma Transitória -DL57/2016/CP1376/CT002. Marta Martins is financed through FCT, I.P., under the Scien-tific Employment Stimulus—Institutional Call (CEECINST/00102/2018).

References:
1. Barboza, L.G.A. et al. (2018). Aquat. Toxicol. 195:49—57. DOI: 10.1016/j.aquatox.2017.12.008.
2. Figueiredo, N. et al. (2016). Ecotoxicol. Environ. Saf. 124:60–67. DOI:10.1016/j.ecoenv.2015.10.001.
3. Figueiredo, N. et al. (2014). J. Toxicol. Environ. Health, 77:14-16, 959-971. DOI: 10.1080/15287394.2014.911136.


Keywords: Mercury; Microplastic; Microbial detoxification

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