Biotic and Abiotic Factors Influencing Arsenic Biogeochemistry and Toxicity in Fluvial Ecosystems: A Review

Abstract

This review is focused on the biogeochemistry of arsenic in freshwaters and, especially, on the key role that benthic microalgae and prokaryotic communities from biofilms play together in through speciation, distribution, and cycling. These microorganisms incorporate the dominant iAs (inorganic arsenic) form and may transform it to other arsenic forms through metabolic or detoxifying processes. These transformations have a big impact on the environmental behavior of arsenic because different chemical forms exhibit differences in mobility and toxicity. Moreover, exposure to toxicants may alter the physiology and structure of biofilms, leading to changes in ecosystem function and trophic relations. In this review we also explain how microorganisms (i.e., biofilms) can influence the effects of arsenic exposure on other key constituents of aquatic ecosystems such as fish. At the end, we present two real cases of fluvial systems with different origins of arsenic exposure (natural vs. anthropogenic) that have improved our comprehension of arsenic biogeochemistry and toxicity in freshwaters, the Pampean streams (Argentina) and the Anllóns River (Galicia, Spain). We finish with a briefly discussion of what we consider as future research needs on this topic. This work especially contributes to the general understanding of biofilms influencing arsenic biogeochemistry and highlights the strong impact of nutrient availability on arsenic toxicity for freshwater (micro) organisms.

Interactions with Arsenic: Mechanisms of Toxicity and Cellular Resistance in Eukaryotic Microorganisms

“…The redox potential of arsenic oxyanions is very relevant, in such a way that As(III) becomes stable in aqueous form under moderately reducing conditions (+300 mV at pH 4 to − 200 mV at pH 9), while As(V) is stable in oxidized aqueous solutions [21]. Additionally, As biotransformation by different physiological groups of microorganisms plays a significant role in the occurrence and behavior, as well as recycling of this metalloid in the aquatic environments [22,23]. In aquatic ecosystems, such as lakes, As(V) is the thermodynamically stable state in oxic conditions, while As(III) is predominant in reduced environments [24].…”

“…In general, at least in humans and many animals, the hierarchy in toxicity of inorganic and organic arsenicals is DMA(III), MMA(III) > As(III) > As(V) > DMA(V), MMA(V) >TMA. The major pentavalent products DMA(V) and TMA (as TMAO) are approximately 100-fold and a 1000-fold, respectively, less toxic than As(III) [10,23,[43][44][45]. Besides the chemical species and concentration, As toxicity is also related to bioavailability, and therefore with the rate at which it is metabolized and the degree of bioaccumulation in tissues and cells [44,46].…”

RISK ASSESSMENT OF TOXIC ELEMENTS (Pb, Cd, Hg, As) IN WATER, SEDIMENT AND IN THINLIP GREY MULLET (BOJANA RIVER)

“…It has established criteria maximum concentrations (CMC) and criteria continuous concentrations (CCC) for most inland surface waters. According to the US EPA, the CMC for acute arsenic exposure is 340 μg As/l, while the CCC for chronic arsenic exposure is 150 μg As/l (Barral Fraga, 2020).…”

“…Arsenic distribution between the water column and the sediment is controlled by several physico .chemical and biological processes, such as precipitation, solubilisation, adsorption, desorption, oxidation, reduction, incorporation in the crystal structure of minerals, and biological exchanges. Arsenic is ranked the first of all hazardous substances by the Agency for Toxic Substances and Disease Registry (Barral-Fraga, 2020). As is found in waters such as seawater, warm springs, groundwater, rivers, and lakes.…”

“…2): As>Pb>Cd=Hg. Arsenic levels in Pampean surface waters have been attributed to the hydrogeology of the streams, fed by an aquifer with high levels of arsenic (0.6 to 4.9 mg/l) originated from quaternary loess sediments (Barral Fraga, 2020). Geochemical investigations showed that most arsenic in the sediments of the Anllóns River is associated with lowmobility phases specifically as bound to Fe-oxide forms and in the residual phase.…”