Bioaccumulation Dynamics of Arsenate at the Base of Aquatic Food Webs

Abstract

Periphyton is an important food source at the base of freshwater ecosystems that tends to bioconcentrate trace elements making them trophically available. The potential for arsenic-a trace element of particular concern due to its widespread occurrence, toxicity, and carcinogenicity-to bioconcentrate in periphyton and thus be available to benthic grazers is less well characterized. To better understand arsenate bioaccumulation dynamics in lotic food webs, we used a radiotracer approach to characterize accumulation in periphyton and subsequent trophic transfer to benthic grazers. Periphyton bioconcentrated As between 3,200-9,700-fold (dry weight) over 8 days without reaching steady state, suggesting that periphyton is a major sink for arsenate. However, As-enriched periphyton as a food source for the mayfly Neocloeon triangulifer resulted in negligible As accumulation in a full lifecycle exposure. Additional studies estimate dietary assimilation efficiency in several primary consumers ranging from 22% in the mayfly N. triangulifer to 75% in the mayfly Isonychia sp. X-ray fluorescence mapping revealed that As was predominantly associated with iron oxides in periphyton. We speculate that As adsorption to Fe in periphyton may play a role in reducing dietary bioavailability. Together, these results suggest that trophic movement of As in lotic food webs is relatively low, though species differences in bioaccumulation patterns are important.

Periphyton and abiotic factors influencing arsenic speciation in aquatic environments

“…Static renewal not only maximizes potential As uptake, but also would tend to lower estimated enrichment factors because the average concentration in solution would be skewed upward by daily refreshed solutions compared with static exposures. These results reiterate the observation that periphyton is an important sink for As [16], as supported by observations from several field studies [13][14][15]. As with our earlier work, no apparent steady state was achieved; thus enrichment factors may be further underestimated.…”

“…Arsenic(V) accumulation by periphyton was consistent with previous observations [16]. Static renewal not only maximizes potential As uptake, but also would tend to lower estimated enrichment factors because the average concentration in solution would be skewed upward by daily refreshed solutions compared with static exposures.…”

“…Arsenic(V) accumulation in periphyton has been shown to be strongly influenced by pH [26]. Our previous work has shown similar correlations between As(V) and Fe distributions in periphyton [16], which may limit bioavailability and trophic transfer [34]. For example, As(V) has a strong binding affinity for Fe oxides [28], and there is evidence that As(V) is highly correlated with Fe content in both aquatic plants [29][30][31] and terrestrial plants [32], as well as in fungi [33].…”

“…Others have reported higher uptake of As(III) relative to As(V) in cyanobacteria [7], microalgae [6], and aquatic grasses [12]. Previous work suggests that periphyton biofilms strongly bioconcentrate As(V) from solution (as much as 9000-fold on a dry-wt basis without reaching steady state) [16]. Until recently, As accumulation dynamics in periphyton were unknown.…”

Metabolomics reveal physiological changes in mayfly larvae (Neocloeon triangulifer) at ecological upper thermal limits

“…Despite their ecological importance and use in monitoring programs, mayfly physiology remains poorly studied because relative few species are amenable to laboratory rearing. Neocloeon triangulifer is a parthenogenetic species that is emerging as a useful laboratory model (Weaver et al, 2015) for understanding responses to environmental stressors such as contaminants (Conley et al, 2009; Conley et al, 2011; Xie and Buchwalter, 2011; Kim et al, 2012; Conley et al, 2013; Kunz et al, 2013; Conley et al, 2014; Wesner et al, 2014; Lopez et al, 2016), salinity stress (Johnson et al, 2014; Soucek and Dickinson, 2015; Struewing et al, 2015) and temperature (Sweeney and Vannote, 1984). …”