Arsenobetaine formation in plankton: a review of studies at the base of the aquatic food chain

Abstract

Arsenobetaine is one of the major organoarsenic compounds found in aquatic organisms, including seafood and fish meant for human consumption. It has been widely studied over the last 50 years because of its non-toxic properties, and its origin is postulated to be at bottom of the aquatic food chains. The present review focuses on arsenobetaine formation in marine and freshwater plankton, comparing the arsenic compounds found in the different plankton organisms, and the methods used to assess arsenic speciation. The main findings indicate that in the marine environment, phytoplankton and micro-algae contain arsenosugars, with the first traces of arsenobetaine appearing in herbivorous zooplankton, and becoming a major arsenic compound in carnivorous zooplankton. Freshwater plankton contains less arsenobetaine than their marine relatives, with arsenosugars dominating. The possible role and formation pathways of arsenobetaine in plankton organisms are reviewed and the literature suggests that arsenobetaine in zooplankton comes from the degradation of ingested arsenosugars, and is selectively accumulated by the organism to serve as osmolyte. Several arsenic compounds such as arsenocholine, dimethylarsinoylacetate or dimethylarsinoylethanol that are intermediates of this pathway have been detected in plankton. The gaps in research on arsenobetaine in aquatic environments are also addressed: primarily most of the conclusions are drawn on culture-based experiments, and few data are present from the natural environment, especially for freshwater ecosystems. Moreover, more data on arsenic in different zooplankton species would be helpful to confirm the trends observed between herbivorous and carnivorous organisms.

Arsenic biotransformation by cyanobacteria from mining areas: evidences from culture experiments

“…3b). AsB is the main As excretion product in zooplankton and animals and is also produced by macroalgae (Caumette et al 2012). However, this As chemical species has not previously been detected in cyanobacteria.…”

Review of arsenic speciation, toxicity and metabolism in microalgae

“…Methylated arsenic species [MMA(V), DMA(V) and trimethylarsine (TMA)] are relatively minor or even below the detection limit (Karadjova et al 2008;Lai et al 1997;Levy et al 2005;Miyashita et al 2011). So far, there is no report about the existence of AB and AC in microalgae (Table 1) (Caumette et al 2012;Duncan et al 2013aDuncan et al , 2015. Some microalgae species, e.g., Chlorella, Spirulina and Dunaliella contain significant amount of valuable proteins, b-carotene, vitamins, and carotenoids etc., thus their nutritional value is highly recognized (Hosseini Tafreshi and Shariati 2009;Khan et al 2005;Merchant et al 2000;Raja et al 2007).…”

Assessment of pollution level using Mytilus galloprovincialis as a bioindicator species: The case of the Gulf of Trieste

“…Like other zwitterionic compounds, arsenobetaine has an osmolitic function in marine organisms, although its significance for marine biota is not yet entirely clear. The low phosphate found in seawater of the area might additionally enhance the uptake of otherwise low As and its metabolic transformation throughout the food chain (Caumette et al, 2006). In M. edulis, arsenobetaine levels increased when exposed to high salinity and decreased on exposure to low salinity (Clowes and Francesconi, 2004).…”

“…It seems that two pathways of As uptake exist; an efficient one via food and a less efficient one via water (Neff, 1997 and references therein). Eventually even minor local pollution can be reflected in elevated levels of several As compounds in algae, phytoplankton and organisms at higher trophic levels, especially if accompanied by low phosphate levels (Caumette et al, 2006), as is often the case in the Northern Adriatic (Degobbis et al, 2005). In this study, an integrated approach using the response of biomarkers, the isotopic composition of carbon and nitrogen (d 13 C and d 15 N), metal levels (Cu, Zn, As, Se, Cd and Pb) and As speciation in the soft tissues of M. galloprovincialis (sampled in 2009 and 2010 during two different seasons, at the end of winter and at the end of summer) was used to evaluate the pollution level of the marine environment in the Gulf of Trieste, in the north-eastern Adriatic.…”

“…As is taken up by phytoplankton and macro algae and is mainly converted into arsenosugars. Zooplankton and organisms feeding on phytoplankton and algae normally contain arsenobetaine (AsB) as the main As compound (Caumette et al, 2006), with lower amounts of trimethylarsine oxide (TMAO), dimethyl arsenic acid (DMA), inorganic As and arsenosugars. It seems that two pathways of As uptake exist; an efficient one via food and a less efficient one via water (Neff, 1997 and references therein).…”