Seelen et al. 2023 — DOM thiol concentrations determine methylmercury bioavailability across aquatic continuum
This study measured dissolved organic matter (DOM) thiol concentrations alongside methylmercury (MeHg) and total mercury (tHg) in 20 aquatic sites spanning a terrestrial-to-marine continuum in the northeastern United States, and demonstrated that DOM thiol concentrations are the primary determinant of MeHg bioavailability to biota. Sites ranged from freshwater streams to coastal marine waters. The authors showed that thiols in DOM compete with biotic uptake sites for MeHg binding, and that sites with high thiol:MeHg ratios show markedly lower bioaccumulation of MeHg into food webs. This mechanism helps explain why MeHg bioaccumulation varies substantially across aquatic ecosystems even when total Hg concentrations are similar.
Key numbers
20 sampling sites. MeHg concentrations ranged from approximately 0.01 to 1.2 ng/L across sites. tHg ranged from approximately 0.3 to 8.5 ng/L. DOM thiol concentrations ranged from <1 to >100 nM. Thiol:MeHg molar ratio was a stronger predictor of MeHg bioaccumulation in the food web than MeHg concentration alone (R2 reported in source). All values water column, unfiltered and filtered fractions reported separately.
Methods (brief)
ICP-MS/CV-AFS for mercury speciation. DOM thiol analysis by DTNB and bimane derivatization assays. Sampling across 20 sites spanning rivers, estuaries, and coastal marine waters in northeastern USA. Bioaccumulation assessed through biotic samples at a subset of sites.
Implications
Certification: Mechanistic context for MeHg bioaccumulation in fish and seafood; relevant to understanding why MeHg varies by water body even with similar total Hg inputs. Courses: Key mechanistic insight for MeHg food-chain transfer module; DOM thiol competition is a critical lever. App: Not directly applicable to food matrix occurrence; relevant to background on MeHg bioaccumulation in seafood ingredients. Microbiome: MeHg bioavailability mechanisms are upstream of dietary exposure; relevant context for gut exposure modeling.