Arsenic Analysis in the Petroleum Industry: A Review

The presence of arsenic in natural gas and liquid hydrocarbons is of great concern for oil companies. In addition to health risks due to its toxicity as well as environmental issues, arsenic is responsible for irreversible poisoning of catalysts and clogging of pipes via the accumulation of As-containing precipitates. To address these problems and to better design treatment units, robust methods for the analysis of arsenic and its compounds in oil streams are required. In addition, the use of feedstocks as a novel source of energy is becoming increasingly important. Most biomasses used as feedstocks are contaminated with arsenic. To avoid problems related to the presence of this element, it is therefore also necessary to have reliable methods for the analysis of arsenic and its compounds in these new fluids. This review outlines the sampling techniques, sample preparation methods, and arsenic analysis techniques developed during recent decades and commonly used in the oil industry and in the new feedstock energy domain.

Novel field-portable high-pressure adsorbent tube sampler prototype for the direct in situ preconcentration of trace compounds in gases at their working pressures: application to biomethane

In Europe, renewable energy gases such as biomethane are aimed at substituting natural gas provided their stringent compliance to natural gas quality standards stipulating maximal levels of several chemical trace compounds (TC). Preconcentration is generally required to detect TC and inasmuch as biomethane is compressed for injection in the natural gas grid, preconcentration is commonly either done by collecting the bulk pressurized gas in a high-pressure cylinder or by first depressurizing it to collect a bulk volume in e.g. a gas sampling bag. Such whole gas samples are then transported to the lab and transferred to a preconcentration unit, entailing contamination and TC loss risks. Therefore, here a novel handy field-portable device for the direct in situ high-pressure preconcentration of TC is presented, enabling to sample gases at pressures up to 200 bar_a through a self-assembled Tenax®TA + Carbopack™X multibed adsorbent tube. The effect of the gas sampling pressure on the preconcentration of TC on adsorbent tubes was evaluated using a synthetic gas mixture containing 41 halogenated volatile organic compounds each at 1 ppm_mol in N₂. At given normalized sampled volumes and in the pressure range 5–100 bar_a handled in French gas transport grids, the pressure had no influence on the preconcentration when the gas circulates through the adsorbent tubes and as long as the adsorbents are not saturated. Next, for the first time, a real biomethane stream was sampled using the novel direct high-pressure preconcentration method on Tenax®TA + Carbopack™X multibed adsorbent tubes, allowing to preconcentrate, in a single sampling run, a wide range of volatile organic TC. More than 26 distinct TC were detected, belonging to seven chemical families: alkenes, aromatics, alkanes (linear, cyclic and polycyclic), sulphur-compounds and terpenes, with linear alkanes (pentane, heptane, octane) and terpenes predominating. Semi-quantification indicated pentane, dimethylcyclopropane, hexane, heptane, octane, α-pinene and camphene are present at a ≤1 ppm_mol concentration threshold in the biomethane.

The circulating gas sampling pressure had no impact on the preconcentration of trace compounds on adsorbent tubes.

Arsenic: Various species with different effects on cytochrome P450 regulation in humans

Arsenic is well-recognized as one of the most hazardous elements which is characterized by its omnipresence throughout the environment in various chemical forms. From the simple inorganic arsenite (iAsIII) and arsenate (iAsV) molecules, a multitude of more complex organic species are biologically produced through a process of metabolic transformation with biomethylation being the core of this process. Because of their differential toxicity, speciation of arsenic-based compounds is necessary for assessing health risks posed by exposure to individual species or co-exposure to several species. In this regard, exposure assessment is another pivotal factor that includes identification of the potential sources as well as routes of exposure. Identification of arsenic impact on different physiological organ systems, through understanding its behavior in the human body that leads to homeostatic derangements, is the key for developing strategies to mitigate its toxicity. Metabolic machinery is one of the sophisticated body systems targeted by arsenic. The prominent role of cytochrome P450 enzymes (CYPs) in the metabolism of both endobiotics and xenobiotics necessitates paying a great deal of attention to the possible effects of arsenic compounds on this superfamily of enzymes. Here we highlight the toxicologically relevant arsenic species with a detailed description of the different environmental sources as well as the possible routes of human exposure to these species. We also summarize the reported findings of experimental investigations evaluating the influence of various arsenicals on different members of CYP superfamily using human-based models.

Coupling metabolisms of arsenic and iron with humic substances through microorganisms in paddy soil

Humic acid (HA) and fulvic acid (FA) are dominating humic substances (HS) in soil. In this study, the effects of HA and FA addition (0.2%-1.5%) on arsenic (As) mobility and microbial community composition in paddy soil were investigated. FA significantly increased the concentrations of As (12-fold), iron (Fe; 20-fold), manganese (Mn; 3-fold) and acetic acid (3-fold) in soil porewater, and also caused significant enrichment of Desulfitobacterium (41-fold). Furthermore, the FA addition significantly increased the relative abundance of Bathyarchaeota (4-fold), a microorganism that is suggested to be important for FA degradation. In contrast, HA slightly increased As (1.2-fold) in porewater, had little effect on Fe, Mn and acetic acid, and 1.5% HA addition significantly decreased As in porewater at day 14 (45%). Both HA and FA addition promoted As methylation. HA increased dimethylarsenate concentration and FA increased monomethylarsenate concentration in porewater. These results highlight the contrasting effects of different (HA vs. FA) organic substances on As fate in paddy soil and advance our understanding of the associations among As, Fe and organic substances through microorganisms in paddy soil.

Arsenic volatilization by Aspergillus sp. and Penicillium sp. isolated from rice rhizosphere as a promising eco-safe tool for arsenic mitigation

Arsenic (As) is a non-threshold human carcinogenic. This element can be volatilized either by nature or anthropogenic sources. In the present study, the analytical performance of an As volatile species trapping system was evaluated to assess the As volatilization promoted by Penicillium sp. and Aspergillus sp., both isolated from rice rhizosphere, and Aspergillus niger sp. considered as a reference. The study was conducted for 60 days (sampling of volatile As species from 1st to 30^th day and from 31st to 60^th day). The efficiency of As-volatilization was associated with the fungal growth. The highest As volatilization occurred from 31st to 60^th day. Penicillium sp., Aspergillus sp. and A. niger were capable of producing 57.8, 46.4, and 5.2% of volatile arsenic species, respectively. The speciation analysis has shown trimethylarsine (TMAs) as the main volatilized As-form, followed by mono- and dimethylarsine (MMAs and DMAs). The results are following the "Challenger pathway". Therefore, the tested fungi isolated from rice rhizosphere have shown promising properties concerning bio-volatilization with potential use for As-mitigation in paddy soils.

Biovolatilisation: a poorly studied pathway of the arsenic biogeochemical cycle

It has been known for over a hundred years that microorganisms can produce volatile arsenic (As) species, termed "arsines". However, this topic has received relatively little attention compared to As behaviour in soils and biotransformation through the trophic level in the marine and terrestrial environment. We believe this is due to long-standing misconceptions regarding volatile As stability and transport as well as an absence, until recently, of appropriate sampling methods. First and foremost, an attempt is made to unify arsines' designations, notations and formulas, taking into account all the different terms used in the literature. Then, the stability of As volatile species is discussed and new analytical developments are explored. Further, the special cases of diffuse low-level emissions (e.g. soil and sediment biovolatilisation), and point sources with high-level emissions (geothermal environments, landfills, and natural gas) are comprehensively reviewed. In each case, future possible areas of research and unknown mechanisms are identified and their importance towards the global As biogeochemical cycle is explored. This review gathers new information regarding mechanisms, stability, transport and sampling of the very elusive arsines and shows that more research should be conducted on this important process.

Toxicity of Methylated Bismuth Compounds Produced by Intestinal Microorganisms to Bacteroides thetaiotaomicron, a Member of the Physiological Intestinal Microbiota

Methanoarchaea have an outstanding capability to methylate numerous metal(loid)s therefore producing toxic and highly mobile derivatives. Here, we report that the production of methylated bismuth species by the methanoarchaeum Methanobrevibacter smithii, a common member of the human intestine, impairs the growth of members of the beneficial intestinal microbiota at low concentrations. The bacterium Bacteroides thetaiotaomicron, which is of great importance for the welfare of the host due to its versatile digestive abilities and its protective function for the intestine, is highly sensitive against methylated, but not against inorganic, bismuth species. The level of methylated bismuth species produced by the methanoarchaeum M. smithii in a coculture experiment causes a reduction of the maximum cell density of B. thetaiotaomicron. This observation suggests that the production of methylated organometal(loid) species in the human intestine, caused by the activity of methanoarchaea, may affect the health of the host. The impact of the species to reduce the number of the physiological intestinal microbiota brings an additional focus on the potentially harmful role of methanoarchaea in the intestine of a higher organism.

Atmospheric stability of arsine and methylarsines

Arsenic (As) occurs in a variety of different chemical forms, among them volatile (gaseous) species, usually referred to as arsine and methylarsines. Here we demonstrate that arsine and methylarsines are stable in air in concentrations at the μg/L gas level. We determined half-lives of approximately 8 h under daytime conditions (UV light) for all methylated arsines, while the same species were found to be considerably more stable in night-time (dark) conditions. Arsine (AsH₃) showed under both day and night-time conditions, considerably higher stabilities than methylated arsines. We show here that volatile As species seem stable enough to travel considerable distances in the atmosphere from a point source before converting into nonvolatile, oxidized compounds. Also, the degradation pathway leading to the conversion to nonvolatile compounds was investigated using computational chemistry. Arsine and methylarsines' reactions with the hydroxyl radical (•OH) as well as As-C and As-H bonds strengths in the species studied were modeled. Results showed that conversion could not be explained by H abstraction, nor by OH addition. Moreover, it was found that As-C and As-H bonds strengths are not the determining factor responsible for the decrease in stability with ascending methylation of the different volatile arsine species, as previously suggested.