Biodegradation of arsenosugars in marine sediment

Abstract

In the marine environment, arsenic accumulates in seaweed and occurs mostly in the form of arsenoribofuranosides (often called arsenosugars). This study investigated the degradation pathways of arsenosugars from decaying seaweed in a mesocosm experiment. Brown seaweed (Laminaria digitata) was placed on top of a marine sediment soaked with seawater. Seawater and porewater samples from different depths were collected and analysed for arsenic species in order to identify the degradation products using high-performance liquid chomatography-inductively coupled plasma mass spectrometry. During the first 10 days most of the arsenic found in the seawater and the shallow sediment is in the form of the arsenosugars released from the seaweed. Dimethylarsenoylethanol (DMAE), dimethylarsinic acid (DMA(V)) and, later, monomethylarsonic acid (MMA(V)) and arsenite and arsenate were also formed. In the deeper anaerobic sediment, the arsenosugars disappear more quickly and DMAE is the main metabolite with 60-80% of the total arsenic for the first 60 days besides a constant DMA(V) contribution of 10-20% of total soluble arsenic. With the degradation of the soluble DMAE the solubility of arsenic decreases in the sediment. The final soluble degradation products (after 106 days) were arsenite, arsenate, MMA(V) and DMA(V). No arsenobetaine or arsenocholine were identified in the porewater.

Transformation of arsenic lipids in decomposing Ecklonia radiata

“…3 and Table S5). This rapid loss of arsenolipids was similar to that found for water-soluble arsenicals in decomposing algae as reported in our previous study (Duncan et al 2014a) and by others (Edmonds et al 1982;Pengprecha et al 2005;Navratilova et al 2011;Ojo and Onasanya 2013). By the latter stages of the experiment (days 45-60), almost all the AsPLs had degraded and only AsHC388 was detected in measurable concentrations (Fig.…”

Contribution of Arsenic Species in Unicellular Algae to the Cycling of Arsenic in Marine Ecosystems

“…DMAE has been detected in macro-algae in some studies; 97 however, often it is not present. 6−10,18−21,23−27,30,34,35,76,78,80,81,84−87,89,91,94−96 DMAE has, however, been widely detected in decomposing marine macro-algae [24][25][26][27]76,78,79 and has subsequently been designated a major arsenoriboside degradation product. As will be discussed further in the next section, one of the key limitations with existing research on the arsenic species produced by marine unicellular algae is that live and dead cells are difficult to separate.…”

“…Dimethylarsenoribosides, commonly known as arsenoribosides or arsenosugars, are the major arsenic species found in marine macro-algae. − The common arsenoribosides are differentiated by end groups containing glycerol (Gly-); phosphate (PO 4 -), sulfonate (SO 3 -), and sulfate (OSO 3 -) − (Figure ). Other arsenic species such as thio-arsenoribosides, thio-dimethylarsenoethanol (thio-DMAE), dimethylarsenoethanol (DMAE), dimethylarsenoacetate (DMAA), methylarsenate (MA), dimethylarsenate (DMA) (Figure ) and As­(V) have been associated with decomposing macro-algal tissue. − Arsenobetaine (AB) is the major arsenic species in almost all marine animals, typically accounting for more than 80% of the water-soluble arsenic content. ,,− Other arsenic species such as thio-arsenoribosides, thio-DMAE, DMAE, DMAA, tetramethylarsonium ion (TETRA), arsenocholine (AC), dimethylarsenopropionate (DMAP), and trimethylarsenopropionate (TMAP) (Figure ) are consistently found in marine animals, however, generally in low concentrations and proportions. ,,, …”

“…Many published studies describe total arsenic concentrations and arsenic species in higher marine organisms such as macro-algae, − ,− ,− seagrasses, ,,,, invertebrates, − ,,,,,,− and fish, ,,,,,,− with many of these investigating arsenic concentrations and species within food webs. − Unicellular algae (both pelagic and benthic) are integral components of marine food webs − but have been consistently overlooked with regard to their importance in marine arsenic cycling. In this context unicellular algae is the collective term given to single-celled photosynthetic organisms that occupy all aquatic ecosystems .…”

Effects of sample processing on arsenic speciation in marine macroalgae

“…Many are dedicated to examining new compounds and their behavior, transformations and metabolic pathways because algae are crucial organisms in arsenic biogeochemistry and furthermore many algae are selected for human consumption. [1][2][3][4][5] Studies and reviews have reported on the inuence of the storage, drying and powdering conditions on total arsenic and arsenic speciation in general or for particular compounds. [6][7][8][9] On the basis of these studies, it can be deduced that no common treatment is reliable and that handling and storage protocols should be established in function of the matrix composition, environmental conditions where the sample is collected (e.g.…”