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

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.

Human health risk from consumption of aquatic species in arsenic-contaminated shallow urban lakes.

Arsenic (As) causes cancer and non-cancer health effects in humans. Previous research revealed As concentrations over 200 µg g-1 in lake sediments in the south-central Puget Sound region affected by the former ASARCO copper smelter in Ruston, WA, and significant bioaccumulation of As in plankton in shallow lakes. Enhanced uptake occurs during summertime stratification and near-bottom anoxia when As is mobilized from sediments. Periodic mixing events in shallow lakes allow dissolved As to mix into oxygenated waters and littoral zones where biota reside. We quantify As concentrations and associated health risks in human-consumed tissues of sunfish [pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus)], crayfish [signal (Pacifastacus leniusculus) and red swamp (Procambarus clarkii)], and snails [Chinese mystery (Bellamya chinensis)] from lakes representing a gradient of As contamination and differing mixing regimes. In three shallow lakes with a range of arsenic in profundal sediments (20 to 206 µg As g-1), mean arsenic concentrations ranged from 2.9 to 46.4 µg g-1 in snails, 2.6 to 13.9 µg g-1 in crayfish, and 0.07 to 0.61 µg g-1 in sunfish. Comparatively, organisms in the deep, contaminated lake (208 µg g-1 in profundal sediments) averaged 11.8 µg g-1 in snails and 0.06 µg g-1 in sunfish. Using inorganic As concentrations, we calculated that consuming aquatic species from the most As-contaminated shallow lake resulted in 4-10 times greater health risks compared to the deep lake with the same arsenic concentrations in profundal sediments. We show that dynamics in shallow, polymictic lakes can result in greater As bioavailability compared to deeper, seasonally stratified lakes. Arsenic in oxygenated waters and littoral sediments was more indicative of exposure to aquatic species than profundal sediments, and therefore we recommend that sampling methods focus on these shallow zones to better indicate the potential for uptake into organisms and human health risk.

Arsenic and lead distribution and mobility in lake sediments in the south-central Puget Sound watershed: the long-term impact of a metal smelter in Ruston, Washington, USA.

The American Smelting and Refining Company (ASARCO) smelter in Ruston, Washington, contaminated the south-central Puget Sound region with heavy metals, including arsenic and lead. Arsenic and lead distribution in surface sediments of 26 lakes is significantly correlated with atmospheric model predictions of contaminant deposition spatially, with concentrations reaching 208 mg/kg As and 1,375 mg/kg Pb. The temporal distribution of these metals in sediment cores is consistent with the years of operation of the ASARCO smelter. In several lakes arsenic and lead levels are highest at the surface, suggesting ongoing inputs or redistribution of contaminants. Moreover, this study finds that arsenic is highly mobile in these urban lakes, with maximum dissolved arsenic concentrations proportional to surface sediment levels and reaching almost 90 µg/L As. With 83% of the lakes in the deposition zone having surface sediments exceeding published "probable effects concentrations" for arsenic and lead, this study provides evidence for possible ongoing environmental health concerns.

Metal stress and decreased tree growth in response to biosolids application in greenhouse seedlings and in situ Douglas-fir stands.

To assess physiological impacts of biosolids on trees, metal contaminants and phytochelatins were measured in Douglas-fir stands amended with biosolids in 1982. A subsequent greenhouse study compared these same soils to soils amended with fresh wastewater treatment plant biosolids. Biosolids-amended field soils had significantly higher organic matter, lower pH, and elevated metals even after 25 years. In the field study, no beneficial growth effects were detected in biosolids-amended stands and in the greenhouse study both fresh and historic biosolids amendments resulted in lower seedling growth rates. Phytochelatins - bioindicators of intracellular metal stress - were elevated in foliage of biosolids-amended stands, and significantly higher in roots of seedlings grown with fresh biosolids. These results demonstrate that biosolids amendments have short- and long-term negative effects that may counteract the expected tree growth benefits.

Long-term fate of a pulse arsenic input to a eutrophic lake.

The long-term fate of a 30-year-old pulse arsenic input to a eutrophic lake was studied to determine if As has become effectively trapped in sediments or remains in active exchange with the water column. Legacy As was readily mobilized from sediments of Spy Pond (Arlington, MA), a eutrophic kettle-hole lake that was treated with 1000s kg As in the 1960s to manage excessive aquatic macrophyte growth. Arsenic was mobilized from hypolimnetic sediments during bottom-water anoxia in spring, summer, and fall, and As accumulated to maximum concentrations of 2100 nM. Mobilization of As from epilimnetic sediments was the largest source of As to the water column on a mass basis (145 mol), despite the fact that the epilimnion remains oxic year-round. Sediment cores revealed that surficial sediments contained As at 30-50 times background levels and suggested that there is contemporary As loading to hypolimnetic sediments (590 mol y(-1)). Mass balance estimates indicate that <5% of the contemporary As load comes from external inputs and that the remainder can be explained by mobilization and redistribution of legacy As, both through the water column and by vertical migration of dissolved As within sediments. These findings demonstrate that, decades after As inputs cease, As in contaminated sediments may remain labile and be mobilized to both anoxic and oxic water columns and accumulate to levels near the sediment surface and in the water column that may pose ongoing risks to ecological health.

Biomonitoring for metal contamination near two Superfund sites in Woburn, Massachusetts, using phytochelatins.

Characterizing the spatial extent of groundwater metal contamination traditionally requires installing sampling wells, an expensive and time-consuming process in urban areas. Moreover, extrapolating biotic effects from metal concentrations alone is problematic, making ecological risk assessment difficult. Our study is the first to examine the use of phytochelatin measurements in tree leaves for delimiting biological metal stress in shallow, metal-contaminated groundwater systems. Three tree species (Rhamnus frangula, Acer platanoides, and Betula populifolia) growing above the shallow groundwater aquifer of the Aberjona River watershed in Woburn, Massachusetts, display a pattern of phytochelatin production consistent with known sources of metal contamination and groundwater flow direction near the Industri-Plex Superfund site. Results also suggest the existence of a second area of contaminated groundwater and elevated metal stress near the Wells G&H Superfund site downstream, in agreement with a recent EPA ecological risk assessment. Possible contamination pathways at this site are discussed.