Selenium Interactions with Algae: Chemical Processes at Biological Uptake Sites, Bioaccumulation, and Intracellular Metabolism

Abstract

Selenium (Se) uptake by primary producers is the most variable and important step in determining Se concentrations at higher trophic levels in aquatic food webs. We gathered data available about the Se bioaccumulation at the base of aquatic food webs and analyzed its relationship with Se concentrations in water. This important dataset was separated into lotic and lentic systems to provide a reliable model to estimate Se in primary producers from aqueous exposure. We observed that lentic systems had higher organic selenium and selenite concentrations than in lotic systems and selenate concentrations were higher in lotic environments. Selenium uptake by algae is mostly driven by Se concentrations, speciation and competition with other anions, and is as well influenced by pH. Based on Se species uptake by algae in the laboratory, we proposed an accurate mechanistic model of competition between sulfate and inorganic Se species at algal uptake sites. Intracellular Se transformations and incorporation into selenoproteins as well as the mechanisms through which Se can induce toxicity in algae has also been reviewed. We provided a new tool for risk assessment strategies to better predict accumulation in primary consumers and consequently to higher trophic levels, and we identified some research needs that could fill knowledge gaps.

Temporal Influences on Selenium Partitioning, Trophic Transfer, and Exposure in a Major U.S. River

“…Irrespective of time, green algae Se concentrations demonstrated an inverse relationship with corresponding dissolved Se levels (Figure S4d). This observation contrasts with the positive relationship between dissolved and particulate (broadly defined) Se concentrations reported in a recent synthesis of Se-impacted ecosystems; regardless, dissolved Se concentrations explained a similar low proportion of algal Se variability in this study as they did for the grouped particulates in the synthesis (38 vs 39%, respectively) . Taken together, these lines of evidence reinforce the consensus that dissolved Se concentrations are not consistently reflected by basal food web uptake patterns (i.e., exposure levels for subsequent trophic levels) and are therefore an insufficient basis for predicting Se concentrations in the Lower Gunnison River food web.…”

“…The first aim of this study was to assess temporal influences on Se partitioning to the LGRB food web and delivery to higher trophic levels. It is well established that Se is primarily bioaccumulated through the diet and that dietary exposure poses the dominant toxicological hazard. , Uptake into the food web following the release of Se to surface waters as inorganic selenate or selenite involves both Se partitioning to the particulate fraction and Se biotransformation by primary producers and herbivores to organoselenides which facilitate bioaccumulation and trophic transfer through food webs. ,, Selenium enrichment at the base of the food web involves the most substantial increase in Se concentrations among compartments with subsequent trophic transfers from primary producers and consumers being of a much lower magnitude (i.e., Se does not usually biomagnify along food chains) . Selenium partitioning is therefore considered an important indicator of potential exposure risk for higher trophic level animals. , Increases between dissolved and particulate compartmentsdefined broadly as including living and nonliving particulate fractionsare operationally defined with the partitioning coefficient ( k d ) and calculated as where C P is the Se concentration measured in the particulate fraction (μg g –1 dw) and C D is the dissolved concentration of Se in surface water (mg L –1 ).…”

“…This variability is documented in the wide range in TTF 1 values (1.1–5.7) observed along the studied reach of the lower Gunnison River mainstem which primarily reflects the 6.4-fold range in green algae concentrations (CV = 39%, Table S8). Complexity in Se partitioning to biotic particulate fractions is a function of dynamic kinetic processes and physiological factors including differing Se requirements among taxa and is a primary source of uncertainty in ecological risk assessments. , Because nonliving particulates are likely present to varying degrees in field collections of benthic algae and algal community structure is subject to a number of system-specific influences, considerable variation in algal Se speciation among and within Se-impaired systems and spatially within a given system is expected. We propose that ecosystem-scale models for dynamic systems like the LGRB will benefit from being based on Se concentrations in ecosystem compartments that demonstrate greater consistency in response to fluctuating Se exposure levels.…”

“…The processes of particulate Se adsorption and uptake are collectively referred to as environmental partitioning and are the major routes of Se entry to food webs . Selenium partitioning efficiency is therefore a principal mediator of the flux of hydrologically mobilized Se to aquatic food webs, governing exposure concentrations and attendant toxicity risks for upper trophic levels. − It is generally assumed that the potential for Se bioaccumulation is low in flowing waters, and especially during high-flow events, because short water residence times limit opportunities for dissolved Se partitioning to particulates . However, few studies have investigated how patterns in Se partitioning and trophic transfer (i.e., trophodynamics) through recipient food webs relate to the hydrodynamic timing of Se mobilization to rivers. , …”

Selenium Toxicity in Plants and Environment: Biogeochemistry and Remediation Possibilities

“…Selenium was also found to interact with other toxic metal/metalloid and accelerate the toxic effects [32]. Many plants efficiently take up Se and could be implemented to remove Se from the contaminated areas by several phytoremediation approaches such as phytoextraction, phytovolatilization, and rhizofiltration [33,34]. For instance, owing to the high level of accumulation, Brassica napus and B. juncea have been used for the Se phytoextraction [35].…”