Littoral sediment arsenic concentrations predict arsenic trophic transfer and human health risk in contaminated lakes

Abstract

Lake sediments store metal contaminants from historic pesticide and herbicide use and mining operations. Historical regional smelter operations in the Puget Sound lowlands have resulted in arsenic concentrations exceeding 200 μg As g-1 in urban lake sediments. Prior research has elucidated how sediment oxygen demand, warmer sediment temperatures, and alternating stratification and convective mixing in shallow lakes results in higher concentrations of arsenic in aquatic organisms when compared to deeper, seasonally stratified lakes with similar levels of arsenic pollution in profundal sediments. In this study we examine the trophic pathways for arsenic transfer through the aquatic food web of urban lakes in the Puget Sound lowlands, measuring C and N isotopes-to determine resource usage and trophic level-and total and inorganic arsenic in primary producers and primary and secondary consumers. Our results show higher levels of arsenic in periphyton than in other primary producers, and higher concentrations in snails than zooplankton or insect macroinvertebrates. In shallow lakes arsenic concentrations in littoral sediment are similar to deep profundal sediments due to arsenic remobilization, mixing, and redeposition, resulting in direct arsenic exposure to littoral benthic organisms such as periphyton and snails. The influence of littoral sediment on determining arsenic trophic transfer is evidenced by our results which show significant correlations between total arsenic in littoral sediment and total arsenic in periphyton, phytoplankton, zooplankton, snails, and fish across multiple lakes. We also found a consistent relationship between percent inorganic arsenic and trophic level (determined by δ15N) in lakes with different depths and mixing regimes. Cumulatively, these results combine to provide a strong empirical relationship between littoral sediment arsenic levels and inorganic arsenic in edible species that can be used to screen lakes for potential human health risk using an easy, inexpensive sampling and analysis method.

Fig 1. Map of study lakes and ASARCO smelter.

The shaded area represents the estimated deposition zone of As from the smelter’s plume [5]. Open data provided by the Washington State Department of Ecology (WA State Boundary, Tacoma Smelter Plume Footprint, DNR Hydrography—Water Bodies—Forest Practices Regulation; https://geo.wa.gov/search?collection=Dataset).

Fig 2. Biplot of δ¹³C versus δ ¹⁵N and total arsenic concentrations (μg g^-1) in organisms.

Fig 3. Mean percent inorganic arsenic compared to mean δ¹⁵N in organisms from Angle Lake and Lake Killarney.

Data labels indicate the Lake (A = Angle; K = Killarney) followed by organism type: F = sunfish; Z = zooplankton; S = B. chinensis; C = Chironomidae; M = macrophyte; Ph = phytoplankton; Pe = periphyton.

Fig 4

The relationships between total As in littoral sediment (μg As g^-1) and measured iAs (μg iAs g^-1) in (a) sunfish, (b) zooplankton, (c) snails, (d) phytoplankton, and (e) periphyton from Angle, Bonney, Killarney, and Steel Lakes. In panel (a), the dotted line represents the threshold for the concentration of iAs in fish required to exceed a 10⁻⁵ cancer risk at the 99^th percentile consumption rate.