Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton

Zhike Li; Zhengyu Wu; Shao Bo; Jie Chi; Xiaoyu Cui; Wei He; Xiaomei Cui; Yiwen Liu; Yingxin Zhao; Yindong Tong

doi:10.1016/j.chemosphere.2024.142104

Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton

Chemosphere. 2024 Apr 21:358:142104. doi: 10.1016/j.chemosphere.2024.142104. Online ahead of print.

Authors

Zhike Li¹, Zhengyu Wu², Shao Bo², Jie Chi², Xiaoyu Cui², Wei He³, Xiaomei Cui⁴, Yiwen Liu², Yingxin Zhao², Yindong Tong⁵

Affiliations

¹ School of Environmental Science and Engineering, Tianjin University, Tianjin, 300072, China; School of Resources and Environment, Southwest University of Science and Technology, Mianyang, 621000, China.
² School of Environmental Science and Engineering, Tianjin University, Tianjin, 300072, China.
³ School of Water Resources and Environment, China University of Geosciences, Beijing, 100083, China.
⁴ Key Laboratory of Biodiversity and Eco-Environmental Protection of the Qinghai-Tibetan Plateau (Ministry of Education), School of Ecology and Environment, Tibet University, Lhasa, 850000, China.
⁵ School of Environmental Science and Engineering, Tianjin University, Tianjin, 300072, China; Key Laboratory of Biodiversity and Eco-Environmental Protection of the Qinghai-Tibetan Plateau (Ministry of Education), School of Ecology and Environment, Tibet University, Lhasa, 850000, China. Electronic address: yindongtong@tju.edu.cn.

PMID: 38653399
DOI: 10.1016/j.chemosphere.2024.142104

Abstract

Uptake of methylmercury (MeHg), a potent neurotoxin, by phytoplankton is a major concern due to its role as the primary pathway for MeHg entry into aquatic food webs, thereby posing a significant risk to human health. While it is widely believed that the MeHg uptake by plankton is negatively correlated with the concentrations of dissolved organic matter (DOM) in the water, ongoing debates continue regarding the specific components of DOM that exerts the dominant influence on this process. In this study, we employed a widely-used resin fractionation approach to separate and classify DOM derived from algae (AOM) and natural rivers (NOM) into distinct components: strongly hydrophobic, weakly hydrophobic, and hydrophilic fractions. We conduct a comparative analysis of different DOM components using a combination of spectroscopy and mass spectrometry techniques, aiming to identify their impact on MeHg uptake by Microcystis elabens, a prevalent alga in freshwater environments. We found that the hydrophobic components had exhibited more pronounced spectral characteristics associated with the protein structures while protein-like compounds between hydrophobic and hydrophilic components displayed significant variations in both distributions and the values of m/z (mass-to-charge ratio) of the molecules. Regardless of DOM sources, the low-proportion hydrophobic components usually dominated inhibition of MeHg uptake by Microcystis elabens. Results inferred from the correlation analysis suggest that the uptake of MeHg by the phytoplankton was most strongly and negatively correlated with the presence of protein-like components. Our findings underscore the importance of considering the diverse impacts of different DOM fractions on inhibition of phytoplankton MeHg uptake. This information should be considered in future assessments and modeling endeavors aimed at understanding and predicting risks associated with aquatic Hg contamination.

Keywords: Dissolved organic matter; Hydrophobic and hydrophilic components; MeHg uptake by phytoplankton; Resin fractionation; Spectral and mass spectrometry analyses.