Ra Enrichment Research Articles

Short communication: In vivo deposition of [1-13C]vaccenic acid and the product of its Δ9-desaturation, [1-13C]rumenic acid, in the body tissues of lactating goats fed oils

This study was conducted in lactating goats with the aim of measuring the deposition of trans-11 18:1 (vaccenic acid, VA) and the product of its Δ9-desaturation, cis-9, trans-11 18:2 (rumenic acid, RA), in the major tissues that are involved in lipid metabolism in the lactating ruminant (i.e., mammary secretory tissue, liver, and omental and perirenal adipose tissues) and examining its potential link with variations in the expression of genes encoding Δ9-desaturase [stearoyl-CoA desaturases 1 and 5 (SCD1 and SCD5)]. Eight lactating goats were fed a diet supplemented with sunflower oil (n=4) or sunflower oil plus fish oil and additional starch (n=4), based on the hypothesis that these dietary treatments could affect Δ9-desaturase gene expression in specific tissues. A chemical tracer, 1.5g of [1-13C]VA as nonesterified fatty acid, was delivered by jugular injection. Goats were slaughtered 4 d later, and tissue samples were collected for the measurement of [13C]VA and [13C]RA enrichment and SCD1 and SCD5 expression. The addition of fish oil and additional starch to a diet containing sunflower oil was associated with several changes in [13C]VA and [13C]RA enrichment. These results support previous studies suggesting that mammary secretory tissue is the primary site of Δ9-desaturation in lactating goats. In adipose tissues, the [13C]VA + [13C]RA enrichment was consistent with a net uptake of circulating fatty acids to reconstitute body reserves at the end of the lactation cycle. The putative uptake of [13C]RA synthesized by other tissues precludes any conclusion from being drawn regarding potential Δ9-desaturation in the liver of goats, despite the detection of SCD1 and SCD5 mRNA in this tissue. Finally, no significant effect of dietary treatment was observed for SCD1 or SCD5 mRNA abundance in the mammary secretory tissue or other body tissues.

Tannins as feed additives to modulate ruminal biohydrogenation: Effects on animal performance, milk fatty acid composition and ruminal fermentation in dairy ewes fed a diet containing sunflower oil

In vitro studies have suggested that feeding tannins to ruminants can favourably alter ruminal biohydrogenation of dietary linoleic acid, enhancing accumulation of trans-11 18:1 (VA, vaccenic acid) in the rumen and thereby the content of some human health promoting fatty acids, such as VA and cis-9 trans-11 18:2 (rumenic acid, RA), in dairy or meat products. However, reports on impacts of these phenolic compounds on milk fatty acid (FA) profile are very limited and inconsistent. Therefore, fourteen Assaf ewes in mid lactation were used to examine effects of addition of a mixture (1:1, w/w) of two commercial oenological extracts of quebracho condensed tannins (CT) and chestnut hydrolysable tannins (HT) to a diet containing sunflower oil (SO) on animal performance, milk yield and composition, and ruminal fermentation. All sheep received a total mixed ration based on alfalfa hay and a concentrate (400:600), supplemented with 20 g of SO/kg dry matter (DM) plus 0 (Control; n = 7) or 10 (TAN; n = 7) g of tannins/kg DM. Milk production and composition was analyzed on days 0, 3, 6, 9, 12, 15, 18, 21, 24 and 27 on treatments, and milk FA profile on days 0, 3, 6, 12, 18 and 27. Neither DM intake nor milk, or its component, yield was affected by TAN treatment. Similarly, addition of the extract of tannins to a SO containing ration did not alter concentrations of the major FA classes in milk ( i.e., saturates, monounsaturates, and polyunsaturates), had very limited effects on the proportion of particular FA, and was not able to enhance milk VA and RA enrichment above that achieved with SO supplementation. Temporal changes in milk FA composition were characterized by an increase in unsaturated FA with 18 carbons, mainly cis and trans 18:1, and a concomitant reduction in most short and medium chain saturates (6:0 to 12:0 and 16:0; P<0.05) attributable to the presence of SO in the diet. Addition of tannins did not affect ruminal fermentation parameters ( i.e., pH, lactate, ammonia, and total volatile fatty acid concentrations) measured after 28 days. Reasons for the lack of effects of either type (quebracho CT and chestnut HT) or amount of tannins in the diet are discussed.

The 226Ra enrichment in oceanic basalts: Evidence for melt‐cumulate diffusive interaction processes within the oceanic lithosphere

U‐Th decay chains in young volcanic rocks have become a unique geochemical tool with the potential to constrain the physical processes involved in the generation and transport of magmas. Among the different isotopes of the decay series, the measured disequilibrium between 226Ra and 230Th isotopes in basaltic melts has been a crucial player in the interpretation of the U‐series data as a whole. However, the key assumption proposed in all previous models, that the origin of 226Ra‐230Th disequilibrium in oceanic basalts is only produced during mantle melting processes, has remained largely unchallenged. Here we present an alternative process for the origin of the 226Ra‐230Th disequilibrium in oceanic basalts. We argue that diffusive interaction of magmas with cumulates formed in the oceanic crust beneath mid ocean ridges or oceanic islands may be responsible for the observed 226Ra‐230Th disequilibrium in oceanic basalts. Hence the inferences drawn from (226Ra)/(230Th) activity ratios about mantle melting and melt transport processes beneath mid‐ocean ridges and ocean islands are at best equivocal.

Ra isotopes and Rn in brines and ground waters of the Jordan-Dead Sea Rift Valley: enrichment, retardation, and mixing

Thirty-six springs and wells from the Dead Sea Rift Valley were periodically sampled and analyzed. The latter included full chemical analyses, 222Rn and 226Ra (by α-counting emanometry), as well as 228Ra/ 226Ra and 224Ra/ 228Ra activity ratios (γ spectrometry). Sampling stretched over almost 2 yr. Several hundred Rn-Ra analyses and close to a hundred isotopic ratios were measured. Most waters in the Rift Valley have both elevated Ra (several to 750 dpm/L) and Rn (a few hundred to almost 60,000 dpm/L) content. In practically all samples 222Rn activity considerably exceeds that of its parent 226Ra. The Ra content is the result of all Dead Sea Rift Valley waters being mixtures of fresh water with saline brines. Ra is efficiently extracted from surrounding rocks into the brine end member. 228Ra/ 226Ra ratios are exceptionally low −0.07 to 0.9, mostly less than 0.2. This apparently reflects the U over Th enrichment in the source rocks that contribute the Ra. Ra enrichment (both 228Ra and 226Ra) is locally correlated throughout the Rift Valley with water salinity. This correlation can be used to constrain the age of the brine-freshwater mixing process. In one of the hydrologic subsystems studied (the Fuliya block), the mixing of the shallow ground water must have occurred in less than 200 to 300 yr ago, probably before no more than some 30 yr. High radon activities in surface waters along the Dead Sea Rift Valley result from the formation of radium-enriched linings on the aquifer rock surface. The mixing of the radium-extracting brines with fresh water leads to continual adsorption of radium as water salinity decreases. The unique combination of fast upward flow and continual mixing in the Dead Sea Rift Valley accounts for a constant replenishment of radium in the waters. This causes a gradual buildup of a radium lining on the aquifer walls until eventually a steady-state surface activity is established.

Crustal Origin for Peralkaline Rhyolites from Kenya: Evidence from U-Series Disequilibria and Th-Isotopes

The Olkaria complex is a recent, peralkaline rhyolite field in the Kenya Rift Valley close to the axial region of the Kenya Dome. U–Th disequilibrium was measured by α-spectrometry in whole rocks and mineral separates from seven geographically and compositionally distinct groups (centres) of rhyolites. Forty-three whole-rock samples show variable Th/U ratios (2.8–6.2) and a large range of (238U/232Th) ratios (0.5–1.1); 79% of the rhyolites show U excess. Rocks from some centres plot entirely to the left or right of the equiline, whereas some centres straddle it. Internal isochrons give U–Th ages of between 14.6+2.2−2.1 and 36.2+2.6−2.6 ka (2σ) respectively for the Gorge Farm centre and 50.5+7.9−7.3ka for the Broad Acres centre. These ages, interpreted as phenocryst crystallization ages, are older than eruption ages by 103–104 yr. The youngest centre displays (226Ra/230Th) > 1, indicating that Ra–Th fractionation has taken place <8000 yr bp. There is a positive correlation between (226Ra/230Th) and (238U/230Th) ratios for rocks of the youngest centre, indicating that the Ra enrichment and the U enrichment probably occurred during the same event. Closed-system fractionation of observed mineral phases cannot alone explain the U-series disequilibria although it may have contributed to other compositional features of the rhyolites. The degree of U enrichment is related to major and trace element variations in the rhyolites as a whole, in that there is a correlation with peralkalinity and thus with incompatible trace element abundances, in particular Nb, Rb and Zr. There is a good correlation between (238U/230Th) and pre-eruptive F contents but not pre-eruptive H2O contents, consistent with previous suggestions that the rhyolites formed by halogen-fluxed melting of the crust. Compositional variations between groups of rhyolites are related to heterogeneity of the crustal source rocks, degree of partial melting(and thus residual mineralogy) and the composition and abundance of metasomatic fluids.

Th isotope and U-series studies of subduction-related volcanic rocks

The activities of 6–7 radionuclides measured by alpha spectrometry are reported for 35 samples of recent volcanic rocks from 24 volcanoes in 9 arcs. These include continental margins (Cascades, Alaska, Costa Rica), island arcs (the Sunda, Banda, and Sangihe arcs of Indonesia, Marianas, Japan, Aleutians, Antilles, Tonga), and a backarc basin (Lau Basin). Enrichment of 238U over 230Th is more common (over 2 5 of the samples) and greater (up to 59%) in these subduction-related volcanics than in those from other tectonic environments. 230Th 232Th ratios also extend to higher values, both in absolute numbers and relative to other isotope ratios. Enrichment of 210Po and 226Ra over 230Th is widespread and is more common and greater in island arcs than continental margins. The level of Po or Ra enrichment (50–300% in island arcs, 10–50% at continental margins) is similar to that in ocean island and ridge basalts and decreases with differentiation. The differences in Th-U systematics between subduction-related and other volcanic rocks are attributed to variations in the process of melt extraction, changes in bulk partition coefficients within the mantle wedge, or preferential addition of U from subducted lithosphere. Ra enrichments are attributed to partial melting processes which are similar to those at ocean ridges. Smaller excesses at continental margins are attributed either to slower ascent or to differences in the process of melt formation beneath continents.

U [sbnd]Th [sbnd]Ra radioactive disequilibria and magmatic processes

This paper presents the available data on U Th Ra disequilibria in recent volcanic rocks, and their significance to the understanding of magmatic processes. It is shown that 238U 230Th and 226Ra 230Th disequilibria are particularly useful in the study of mantle sources, their recent modifications, the transfer time of the magmas towards the surface and magma dynamics in active volcanoes. The Th Sr isotopic correlation is confirmed by new results on MORB and OIB. These magmas must have short (< 10 4 years) transfer times. In contrast with MORB and OIB data, which have activity ratios ( 238U/ 230Th) < 1, many subduction zone volcanoes display activity ratios ( 238U/ 230Th) > 1, together with 226Ra enrichments over 230Th. The latter are largest in continental ultrapotassic and related rocks. This suggests that fluids play an important role in magma genesis processes in subduction zones, before (metasomatism) and/or during partial melting. In the absence of fluids, the enrichment pattern is Ra⋍Th>U, and in a “wet” environment Ra > U > Th. The study of ( 230Th/ 232Th) 0 initial ratios through the volcanic history of a single volcano confirms that basaltic volcanoes on oceanic islands, such as Piton de la Fournaise (Reunion), Mauna Kea (Hawaii), Marion (Prince Edward hot spot have short magma transfer times (< 10 4 years). Other volcanoes, like Etna, located in continental crust areas, appear to have longer transfer times (> 10 5 years). From the few available results on Ra Th disequilibria, it seems that the time of magma transfer in the volcanoes studied so far is always longer than 100 years. Work in progress on Etna shows that Ra enrichment is a characteristic of the whole historic period and a deep-seated phenomenon.

Short-lived radioactive disequilibria and magma dynamics in Etna volcano

The interest of radioactive disequilibria for the study of magmatic processes has long been recognised1. The use of 230Th-238U disequilibria has been growing in recent years2–4; but, since the pioneering work by Capaldi et al.5, very few studies have been concerned with a systematic use of short-lived isotopes of the radioactive series (for example, 226Ra, 210Pb, 210Po in the 228U series, and 228Ra, 228Th in the 228Th series). Here we present new precise results on the short-lived disequilibria in some recent lavas from Etna volcano. Our data show that a Ra enrichment took place in the Etna magma between 100 and 8,000 yr ago. Moreover, there is a clear correlation between (226Ra/230Th) activity ratios and the degree of differentiation of the magma, as indicated by its Th content. This correlation is interpreted as the result of mixing of a differentiated magma and a deep basic magma with a high (226Ra/230Th) ratio. The Ra and U enrichments relative to Th in recent volcanics could be a consequence of fluid-transfers in the mantle sources or in crustal magma reservoirs.