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Arsenic and mercury distribution in an aquatic food chain: importance of femtoplankton and picoplankton filtration fractions

350 210 Stroud Water Research Center

Alowaifeer, A.M., S. Clingenpeel, J. Kan, P.E. Bigelow, M. Yoshinaga, B. Bothner, and T.R. McDermott. 2022. Environmental Toxicology and Chemistry, early online access.

https://doi.org/10.1002/etc.5516

Abstract

As and Hg were examined in the Yellowstone Lake food chain, focusing on two lake locations separated by ~20 km and that differed in lake floor hydrothermal vent activity. Sampling spanned from femtoplankton to the main fish species, Yellowstone Cutthroat Trout and the apex predator Lake Trout. Hg bioaccumulated in muscle and liver of both trout species, biomagnifying with age, whereas As decreased in older fish, which indicates differential exposure routes for these metal(oid)s. Hg and As concentrations were higher in all food chain filter fractions (0.1, 0.8, 3.0 μm filters) at the vent associated Inflated Plain site, illustrating the impact of localized hydrothermal inputs. Femtoplankton and picoplankton size biomass (0.1 and 0.8 μm filters) accounted for 30-70% of total Hg or As at both locations. By contrast, only ~ 4% of As and <1% of Hg were found in the 0.1 μm filtrate, indicating that comparatively little As or Hg actually exists as ionic forms or intercalated with humic compounds, a frequent assumption in fresh and marine waters. 18S rRNA gene sequencing of DNA derived from the 0.1, 0.8 and 3.0 μm filters showed significant eukaryote biomass in these fractions, providing a novel view of the femtoplankton and picoplankton size biomass, and assists in explaining why these fractions may contain such significant Hg and As. These results infer that femtoplankton and picoplankton metal(loid) loads represent aquatic food chain entry points that need to be accounted for, and important for better understanding Hg and As biochemistry in aquatic systems.