Arsenobetaine in Seawater: Depth Profiles from Selected Sites in the North Atlantic

Arsenic occurs in marine waters, typically at concentrations of 1–2 μg As kg^–1, primarily as the inorganic species arsenate. Marine animals, however, contain extremely high levels of arsenic (typically 2000–20 000 μg As kg^–1 wet mass), most of which is present as arsenobetaine, an organic form of arsenic that has never been found in seawater. We report a method based on ion-exchange preconcentration and HPLC/mass spectrometry to measure arsenobetaine in seawater, and apply the method to samples of seawater collected at various depths from seven sites in the North Atlantic. Arsenobetaine was detected in most samples at levels ranging from 0.5 to 10 ng As kg^–1, and was found at depths down to 4900 m. Furthermore, we report the presence of 15 additional organoarsenicals in seawater, 14 of which had never been detected in marine waters. The arsenobetaine depth profile was related, albeit weakly, to that of chlorophyll; this relationship probably reflects arsenobetaine’s release to water from marine animals associated with the euphotic zone rather than its direct biosynthesis by primary producers. Future application of the new method for seawater analysis will shed new light on the biogeochemical cycle of marine arsenic

Quantifying Inorganic Arsenic and Other Water-Soluble Arsenic Species in Human Milk by HPLC/ICPMS

Because the toxicity of arsenic depends on its chemical form, risk assessments of arsenic exposure must consider the type of arsenic compound, and hence they require sensitive and robust methods for their determination. Furthermore, the assessment should include studies on the most vulnerable people within a population, such as newborns and infants, and thus there is a need to quantify arsenic species in human milk. Herein we report a method for the determination of arsenic species at low concentrations in human milk by HPLC/ICPMS. Comparison of single and triple quadrupole mass analysers showed comparable performance, although the triple quadrupole instrument more efficiently overcame the problem of ArCl⁺ interference, from the natural chloride present in milk, without the need for gradient elution HPLC conditions. The method incorporates a protein precipitation step with trifluoroacetic acid followed by addition of dichloromethane or dibromomethane to remove the lipids. The aqueous phase was subjected to anion-exchange and cation-exchange/mixed mode chromatography with aqueous ammonium bicarbonate and pyridine buffer solutions as mobile phases, respectively. For method validation, a human milk sample was spiked with defined amounts of dimethylarsinate, arsenobetaine, and arsenate. The method showed good recoveries (99–103%) with detection limits (in milk) in the range of 10 ng As kg^–1. The method was further tested by analyzing two Norwegian human milk samples where arsenobetaine, dimethylarsinate, and a currently unknown As species were found, but iAs was not detected

Photoinduced Reactivity of the Soft Hydrotris(6-<i>tert</i>-butyl-3-thiopyridazinyl)borate Scorpionate Ligand in Sodium, Potassium, and Thallium Salts

The soft scorpionate ligand hydrotris­(6-<i>tert</i>-butyl-3-thiopyridazinyl)­borate (<b>Tn</b>) was found to exhibit pronounced photoreactivity. Full elucidation of this process revealed the formation of 6-<i>tert</i>-butylpyridazine-3-thione (<b>PnH</b>) and 4,5-dihydro-6-<i>tert</i>-butylpyridazine-3-thione (<b>H</b>_<b>2</b><b>PnH</b>). Under exclusion of light, no solvolytic reactions occur, allowing the development of high-yield preparation protocols for the sodium, potassium, and thallium salts and improving the yield for their derived copper boratrane complex. The photoreactivity is relevant for all future studies with electron-deficient scorpionate ligands

Quantification of Arsenolipids in the Certified Reference Material NMIJ 7405‑a (Hijiki) using HPLC/Mass Spectrometry after Chemical Derivatization

Arsenic-containing lipids (arsenolipids) are novel natural products recently shown to be widespread in marine animals and algae. Research interest in these arsenic compounds lies in their possible role in the membrane chemistry of organisms and, because they occur in many popular seafoods, their human metabolism and toxicology. Progress has been restricted, however, by the lack of standard arsenolipids and of a quantitative method for their analysis. We report that the certified reference material CRM 7405-a (Hijiki) is a rich source of arsenolipids, and we describe a method based on HPLC-ICPMS/ESMS to quantitatively measure seven of the major arsenolipids present. Sample preparation involved extraction with DCM/methanol, a cleanup step with silica, and conversion of the (oxo)­arsenolipids originally present to thio analogues by brief treatment with H₂S. Compared to their oxo analogues, the thioarsenolipids showed much sharper peaks on reversed-phase HPLC, which facilitated their resolution and quantification. The compounds were determined by HPLC-ICPMS and HPLC-ESMS, which provided both arsenic-selective detection and high resolution molecular mass detection of the arsenolipids. In this way, the concentrations of two arsenic-containing hydrocarbons and five arsenosugar phospholipids are reported in the CRM Hijiki. This material may serve as a convenient source of characterized arsenolipids to delineate the presence of these compounds in seafoods and to facilitate research in a new era of arsenic biochemistry

Arsenolipids Detected in the Milk of Nursing Mothers

Arsenic-containing lipids (arsenolipids), common constituents of fish, are currently being studied with regard to human health because of recent research that showed that some of the compounds are highly toxic to human cells and that they have the potential to cross the blood–brain barrier. As part of a study of the role of early exposure to environmental toxicants, we determined the arsenic content of milk from nursing mothers. Although the original intention of the study was to focus on inorganic arsenic, we discovered in an initial testing of 10 samples that a significant portion of the arsenic in the milk was lipid-soluble. We then investigated in detail this lipid-soluble arsenic in five of the samples by purifying the major compounds and using high-performance liquid chromatography coupled to both elemental and molecular mass spectrometry to identify them as arsenic hydrocarbons and arsenic fatty acids. This study is the first to report the presence of arsenolipids in human milk. The concentrations of arsenolipids in the milk were low (combined total of approximately 0.5 μg of As/kg) compared to the current recommended maximum for arsenic in water (10 μg/L), but of potential concern when one considers the possibility of the lipids crossing the blood–brain barrier and the critical stage of brain development in the newborn child

Arsenic Methyltransferase is Involved in Arsenosugar Biosynthesis by Providing DMA

Arsenic is an ubiquitous toxic element in the environment, and organisms have evolved different arsenic detoxification strategies. Studies on arsenic biotransformation mechanisms have mainly focused on arsenate (As­(V)) reduction, arsenite (As­(III)) oxidation, and arsenic methylation; little is known, however, about the pathway for the biosynthesis of arsenosugars, which are significant arsenic transformation products. Here, the involvement of As­(III) <i>S</i>-Adenosylmethionine methyltransferase (ArsM) in arsenosugar synthesis is demonstrated for the first time. <i>Synechocystis</i> sp. PCC 6803 incubated with As­(III) or monomethylarsonic acid (MMA­(V)) produced dimethylarsinic acid (DMA­(V)) and arsenosugars, as determined by high performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC/ICPMS). Arsenosugars were also detected in the cells when they were exposed to DMA­(V). A mutant strain <i>Synechocystis</i> Δ<i>arsM</i> was constructed by disrupting <i>arsM</i> in <i>Synechocystis</i> sp. PCC 6803. Methylation of arsenic species was not observed in the mutant strain after exposure to arsenite or MMA­(V); when <i>Synechocystis</i> Δ<i>arsM</i> was incubated with DMA­(V), arsenosugars were detected in the cells. These results suggest that ArsM is a required enzyme for the methylation of inorganic arsenicals, but not required for the synthesis of arsenosugars from DMA, and that DMA is the precursor of arsenosugar biosynthesis. The findings will stimulate more studies on the biosynthesis of complex organoarsenicals, and lead to a better understanding of the bioavailability and function of the organoarsenicals in biological systems