Μg Cl Research Articles

1379-P: Combination of FGF21 and ß3-Adrenergic Treatment in Obese Mice

An induction of lipolysis by β3-adrenergic agonist CL316,243 (CL) increases plasma free fatty acid (FFA) level resulting later in ectopic lipid accumulation in liver. The peak of FFA stimulates insulin secretion and causes acute drop of blood glucose (BG) in chow-fed mice. This glucose-lowering effect is attenuated in insulin-resistant dietary obese (DIO) mice. Fibroblast growth factor 21 (FGF21) treatment increases insulin sensitivity while inhibiting lipolysis. Both FGF21 and CL induce uncoupling protein 1 (UCP1) in brown adipose tissue, increasing capacity for combustion of glucose. Thus, the FGF21 treatment has a potential to modulate the glucoregulatory action of CL. Here we aim to characterize the effect of the CL+FGF21 combination and to investigate the role of UCP1 in this effect. DIO C57Bl/6 mice were housed at 30 °C in order to minimize basal adrenergic tone. Animals were treated 2x daily with 65 μg FGF21 or its vehicle for 8 days. This treatment lowered insulin (increased insulin sensitivity) . Subsequently, the mice were injected with 35 μg CL or with saline. CL increased FFA and insulin in control mice, but did not affect BG (probably because of impaired insulin sensitivity) . The day after CL injection, 4-fold rise in ectopic lipid content in liver was observed in comparison to saline-treated group. In FGF21-treated mice, the CL-induced rise of NEFA and insulin was only transient, but sufficient to cause a drop of BG. The hepatic lipid accumulation after CL was completely preveted by FGF21. The same experimental set-up was repeated in DIO UCP1+/+ and -/- mice. Although the BG-lowering effect of the CL+FGF21combination was observed in both genotypes, the effect was significantly stronger in UCP1+/+. Thus, FGF21 sensitizes DIO mice to the BG-lowering effect of adrenergic stimulation while it prevents ectopic lipid accummulation. The drop of BG is observed even in the absence of UCP1, but UCP1 activity is required to reach the maximal BG-lowering effect of the combination. Disclosure P.Zouhar: None. Funding Czech Science Foundation (19-05356Y)

Diversity, Abundance, and Ecological Roles of Planktonic Fungi in Marine Environments.

Fungi are considered terrestrial and oceans are a “fungal desert”. However, with the considerable progress made over past decades, fungi have emerged as morphologically, phylogenetically, and functionally diverse components of the marine water column. Although their communities are influenced by a plethora of environmental factors, the most influential include salinity, temperature, nutrients, and dissolved oxygen, suggesting that fungi respond to local environmental gradients. The biomass carbon of planktonic fungi exhibits spatiotemporal dynamics and can reach up to 1 μg CL−1 of seawater, rivaling bacteria on some occasions, which suggests their active and important role in the water column. In the nutrient-rich coastal water column, there is increasing evidence for their contribution to biogeochemical cycling and food web dynamics on account of their saprotrophic, parasitic, hyper-parasitic, and pathogenic attributes. Conversely, relatively little is known about their function in the open-ocean water column. Interestingly, methodological advances in sequencing and omics approach, the standardization of sequence data analysis tools, and integration of data through network analyses are enhancing our current understanding of the ecological roles of these multifarious and enigmatic members of the marine water column. This review summarizes the current knowledge of the diversity and abundance of planktonic fungi in the world’s oceans and provides an integrated and holistic view of their ecological roles.

Development towards stable chlorine isotope measurements of astromaterials using the modified Middleton source of an accelerator mass spectrometer

The volatile element Cl can be lost during the formation and evolution of planetary bodies, leading to fractionation of its two stable isotopes 35Cl and 37Cl. Chlorine isotope variations (reported as δ37Cl in parts per thousand (‰) relative to Standard Mean Ocean Chloride, SMOC) are documented to exceed 80‰ between different lunar rock samples and have been variably interpreted as the fingerprint of degassing during accretion, magma ocean, or volcanic portions of lunar history. The large intersample and intrasample variations observed by both bulk isotope ratio mass spectrometry (IRMS) and in-situ secondary ion mass spectrometry (SIMS) methods are difficult to interpret in part because of a paucity of bulk Cl isotope measurements. This lack of high-precision bulk data is due to the relative rarity of IRMS laboratories capable of making these high precision measurements on small samples of precious planetary materials such as those returned by human or robotic exploration. Here we present a new method for performing high precision δ37Cl measurements using the modified Middleton ion source of an existing accelerator mass spectrometer. For samples with as little as 1 μg Cl–the equivalent of 2–4 mm3 of a typical lunar rock sample–the average cathode accuracy is ∼1‰. Cathode reproducibility is typically ∼1‰ (2σ) for samples with at least 10 μg of Cl, increasing to ∼3–6‰ for aliquots with ∼1–2 μg Cl, similar to published SIMS results and sufficient to study astromaterials from the Moon, Mars, or 4 Vesta, which have tens of ‰ observed variations.

Evaluating the efficacy of Atriplex spp. in the phytoextraction of road salt (NaCl) from contaminated soil

Soil and freshwater salinization are growing issues worldwide. Road salt, primarily sodium chloride (NaCl), is a significant contributor to this issue in North America. In this study, the ability of three native Canadian halophytes (Atriplex patula, Atriplex hortensis, and Atriplex canescans) to remove Na+ and Cl− from contaminated soil was investigated. Field and greenhouse studies determined plant survivability in roadside areas, as well as Na+ and Cl− extraction levels. The Atriplex spp. accumulated 18–55 mg Na+ g−1 dry weight (DW) and 41–64 mg Cl− g−1 DW when grown for a two-month period in soil spiked with NaCl to simulate a very highly contaminated roadside. Using A. patula, it would theoretically take 6 growing seasons to remove all salt from an area contaminated with 1540 μg Cl− g−1, while A. hortensis and A. canescens would take 19 and 9 years, respectively. Salt content in shoot components (seeds, stem, leaves) was determined to provide further insight on phytoextraction processes. In all three Atriplex species, the leaves had the highest Cl− concentration, followed by the seeds (bracteoles included), with the lowest concentrations found in the stem. These novel findings provide important information for road salt remediation and indicate that using Atriplex spp. may be a viable way in which to reduce the environmental impact of road salting.

HPLC-ICPMS/MS shows a significant advantage over HPLC-ICPMS for the determination of perchlorate in ground, tap, and river water

Perchlorate is an environmental contaminant that originates from anthropogenic as well as natural sources. The health effects of perchlorate with respect to the thyroid function are well known. The capabilities of the inductively coupled plasma mass spectrometry (ICPMS) has been recently expanded by coupling with tandem mass spectrometry. The advantages of HPLC-ICPMS/MS has not yet been thoroughly assessed for chlorine speciation analysis. We report a rapid and simple method for perchlorate determination in ground, tap, and river water and we show that the ICPMS/MS offers as a chromatographic detector at least 10-fold improvement in the detection limit relative to single quadrupole ICPMS. The achieved limit of detection was 0.3 μg Cl L−1 perchlorate and could be yet improved by simple freeze-drying (down to ca. 50 ng Cl L−1, based on the river water matrix), which is comparable with HPLC-ESIMS/MS, with the advantage of eliminating the need for the 18O-perchlorate isotopically labeled internal standard. The method was validated in the various water matrices in terms of recovery at levels 5.0–250 μg Cl L−1 (±10%), repeatability (RSD<5%), and linearity (r2 = 0.9999), and revealed the presence of trace levels in the Mur river water (0.33 ± 0.04 μg Cl L−1). Carbon was found to significantly decrease signal response for chlorine, and we shed light on the general effects of carbonate on chlorine speciation in hard water analysis.

Degradation and DBP formations from pyrimidines and purines bases during sequential or simultaneous use of UV and chlorine

Purine and pyrimidines are present an important pool of dissolved organic nitrogen in aqueous medias and also precursors of disinfection byproducts. The degradation kinetics of cytosine and adenine—model pyrimidine and purine compounds—were investigated along with their transformation pathways leading to the formation of disinfection byproducts during two typical multi-barrier disinfection processes: UV irradiation and UV/chlorine pretreatment followed by post-chlorination. UV irradiation followed by post-chlorination enhanced the degradation of cytosine and adenine (by 17.1 and 26.1%, respectively), but it also generated more byproduct precursors compared to chlorination alone. The presence of reactive species in the UV/chlorine treatment greatly enhanced cytosine and adenine degradation (by 61.8 and 123.0%) but generated even more disinfection byproducts. Compared to 24 h chlorination, the concentrations of byproducts increased by up to 361.6% for cytosine and 85.1% for adenine with longer UV/chlorine treatment (from 2 to 30 min). Thirty minutes of combined UV/chlorine treatment decreased the total organic chlorine produced from cytosine by 34.4% (from 233.8 to 153.3 μg Cl L−1) but it increased byproduct generation by 68.3% compared with 24 h of simple chlorination. The TOCl from adenine increased by 50.0% (from 9.2 to 18.4 μg Cl L−1) but byproduct generation was 11.0% less after 30 min of UV/chlorine pretreatment followed by 24 h of chlorination. The intermediates generated were analyzed in detail and multiple transformation pathways leading to byproduct formation are proposed.

Removal of Adsorbable Organic Halides from Water Containing Bromide Ions by Conventional and Advanced Oxidation

ABSTRACTThe article focuses on an assessment of adsorbable organic halides degradation during the process of conventional ozonation and advanced oxidation as far as the water containing bromides is concerned. The amount of AOX in the water examined varied from 59 to 105 μg Cl−/L, and the bromides concentration exceeded 200 μg Br−/L. The effects obtained by O3 and O3/UV methods were compared with the results achieved for the water which underwent only UV irradiation. The analysis of presented research results shows that out of the examined oxidation methods, in water of pH 6.8–9.5 and temperature of approximately 287 K, the highest degree of AOX decomposition, was achieved by UV irradiation of water, which was previously subjected to ozonation. However, when the ozone dose reached ≥ 0.3 mg O3/mg C in an alkaline environment, bromates were formed in amounts exceeding the maximum contaminant level in both processes.

Online measurements of low-volatile organic chlorine for dioxin monitoring at municipal waste incinerators

In this study, an automatic sampling device and an analysis device have been developed for the measurement of low-volatile organic chlorine (LVOCl) in flue gas. The concentrations of dioxins (polychlorinated dibenzo- p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls) have been estimated by online measurements of LVOCl at a municipal solid waste incinerator (MSWI) using these devices. The LVOCl concentration at the outlet of the selective catalyst reactor (SCR) of the MSWI increased momentarily up to 95 μg Cl m −3 during the startup period of the MSWI; subsequently, it gradually decreased to less than 1.0 μg Cl m −3 after 50 h from the start of waste feeding. The concentration of toxic equivalent quantity (TEQ)-Dioxins at the SCR outlet had a linear positive relationship with the LVOCl concentrations. Moreover, the level of TEQ-Dioxins concentration can be estimated by using this relationship with LVOCl. From our results, since the LVOCl concentrations in a flue gas can thus be automatically analyzed every hour by online measurements, the operators of an MSWI would be able to monitor approximate TEQ-Dioxin emissions on a daily basis.

When a habitat freezes solid: microorganisms over-winter within the ice column of a coastal Antarctic lake

A major impediment to understanding the biology of microorganisms inhabiting Antarctic environments is the logistical constraint of conducting field work primarily during the summer season. However, organisms that persist throughout the year encounter severe environmental changes between seasons. In an attempt to bridge this gap, we collected ice core samples from Pony Lake in early November 2004 when the lake was frozen solid to its base, providing an archive for the biological and chemical processes that occurred during winter freezeup. The ice contained bacteria and virus-like particles, while flagellated algae and ciliates over-wintered in the form of inactive cysts and spores. Both bacteria and algae were metabolically active in the ice core melt water. Bacterial production ranged from 1.8 to 37.9 μg CL(-1) day(-1). Upon encountering favorable growth conditions in the melt water, primary production ranged from 51 to 931 μg CL(-1) day(-1). Because of the strong H(2) S odor and the presence of closely related anaerobic organisms assigned to Pony Lake bacterial 16S rRNA gene clones, we hypothesize that the microbial assemblage was strongly affected by oxygen gradients, which ultimately restricted the majority of phylotypes to distinct strata within the ice column. This study provides evidence that the microbial community over-winters in the ice column of Pony Lake and returns to a highly active metabolic state when spring melt is initiated.

Helminth Cysteine Proteases Inhibit TRIF-dependent Activation of Macrophages via Degradation of TLR3

Helminth pathogens prepare a Th2 type immunological environment in their hosts to ensure their longevity. They achieve this by secreting molecules that not only actively drive type 2 responses but also suppress type 1 responses. Here, we show that the major cysteine proteases secreted from the helminth pathogens Fasciola hepatica (FheCL1) and Schistosoma mansoni (SmCB1) protect mice from the lethal effects of lipopolysaccharide by preventing the release of inflammatory mediators, nitric oxide, interleukin-6, tumor necrosis factor alpha, and interleukin-12, from macrophages. The proteases specifically block the MyD88-independent TRIF-dependent signaling pathway of Toll-like receptor (TLR)4 and TLR3. Microscopical and flow cytometric studies, however, show that alteration of macrophage function by cysteine protease is not mediated by cleavage of components of the TLR4 complex on the cell surface but occurs by degradation of TLR3 within the endosome. This is the first study to describe a parasite molecule that degrades this receptor and pinpoints a novel mechanism by which helminth parasites modulate the innate immune responses of their hosts to suppress the development of Th1 responses.

Microbiological performance of a water treatment unit designed for household use in developing countries

Interventions to improve water quality, particularly when deployed at the household level, are an effective means of preventing endemic diarrhoeal disease, a leading cause of mortality and morbidity. Following a national survey indicating widespread faecal contamination of drinking water in Indian cities, a point-of-use water treatment unit was developed, which combines filtration and disinfection, does not require power or water pressure and has an operating cost of Rs. 0.25 (US$0.0057) per litre. We assessed the microbiological performance of the unit in the laboratory over the full 1500 l design life of the unit's consumable components. Geometric mean reductions for the units were more than 6 logs (99.9999%) for bacteria, more than 7 logs (99.99999%) for viruses and more than 3 logs (99.9%) for the test surrogate for protozoan cysts. Geometric mean reductions exceeded levels established for microbial water purifiers. The product water was free of detectable chlorine. If these results are validated in field trials, the deployment of the unit on a wide scale among vulnerable populations may make an important contribution to public health efforts to control intractable waterborne diseases.

Filtering activity of Spongia officinalis var. adriatica (Schmidt) (Porifera, Demospongiae) on bacterioplankton: Implications for bioremediation of polluted seawater

A study on the filtering activity has been carried out on reared specimens of the demosponge Spongia officinalis var. adriatica coming from an off-shore farm displaced off the Apulian coast (Ionian Sea). The experience was carried out under laboratory conditions, by using natural seawater collected from the sponge environment. The study demonstrates a high efficiency of the sponge in removing bacteria. Bacterial concentration significantly decreases in presence of the sponge, with a marked drop after 2h from the start of the experience. The maximum clearance rate was 210mlh−1g−1 DW at 60min. Retention efficiency reached the highest value of 61% at 120min. The bacterial density removed by the S. officinalis filtering activity was 12.3±1.8×104 cellsml−1 corresponding to a biomass of about 11.7±1.4μg Cl−1. The sponge fed preferentially large- and medium-size bacteria, whereas the small ones are fed after the removal of the largest size categories. The results obtained suggest that S. offcinalis is a suitable species for marine environmental bioremediation.

Microbial ammonium cycling in the Mississippi River plume during the drought spring of 2000

Microbial potential uptake and regeneration rates of ammonium (NH 4 + ) were studied along a salinity gradient (salinities 0.2-34.4) in the Mississippi River plume during an extreme drought in spring 2000. Chlorophyll concentrations up to 30 μg L -1 were highest in the low- and mid-salinity regions (salinities 8.5-28.2) and comparable to records of other years but extended over smaller areas than during periods of normal river flow. Bacterial biomass (5.1-28.3 μg CL -1 ) was at the low end of the range observed in normal flow years, decreased with distance from the river mouth and did not peak with chlorophyll. Heterotrophic mncflagellate abundance (1.4-4.0 μg CL -1 ) did not reflect phytoplankton and bacterial spatial distribution but peaked at 9.2 μg C L -1 at salinity 8.5. Microbial NH 4 + regeneration rates were estimated by 15 NH 4 + isotope dilution experiments for the whole microbial community, under light and dark conditions, and for the <2 μm bacterium-dominated size fraction. Microbial. NH 4 + regeneration rates (0.018-0.124 μmol N L -1 h -1 ) were low relative to previous reports and peaked at salinity 28. Total NH 4 + regeneration rates were higher than those in the <2 μm size fraction at only four stations, suggesting that bacterial mineralization was a significant component of NH 4 + recycling in some parts of the river plume. Higher AH 4 + regeneration in whole-water samples versus <2 μm fractions provided evidence for microbial grazing in regions where chlorophyll and regeneration rates peaked and at two full-salinity stations.

Production and food web interactions of Arctic freshwater plankton and responses to increased DOC

A gradient of dissolved organic carbon (DOC) was added to enclosures in a high Arctic lake (Svalbard, 79° N). The aim was to simulate the effect of increased concentrations of DOC that will be a predicted effect of increased temperature and precipitation. The study aimed to provide information on the overall effects of such increased levels of DOC on the pelagic food-web, as well as the increased attenuation of UV-radiation (UV-R) caused by increased DOC. The biomass development of phytoplankton, heterotrophic bacteria and ciliates from 15. July (shortly after ice-off) to 8. August revealed a consistent pattern across all enclosures. Initial phytoplankton biomass decreased from maxima around 600μg Cl -1 towards 50μg Cl -1 by the end of July. Similarly, ciliate biomass decreased from ∼100 to 5 μg Cl -1 , while heterotrophic bacteria decreased from initially 280μg Cl -1 to biomasses near 100μg Cl -1 . Over the same period, zooplankton biomass (almost a monoculture of Daphnia tenebrosa) increased from <40 to some 170μg Cl -1 . These patterns were reflected also in decreasing absolute production of bacteria and phytoplankton, while production:biomass ratio remained fairly constant. In general, the study demonstrated a very dynamic system over the brief ice-free season, where Daphnia grazing had a strong impact on the unicellular biota. Additions of DOC initially stimulated planktonic production, yet this effect was soon overruled by Daphnia grazing. This stimulating effect could be a result both of increased UV-R attenuation and some growth stimulating effect. Since no corresponding stimulating effect was observed in the bag shielded with Mylar filter to screen off UV-B, the latter cause seems most likely.

A closed system digestion and purification procedure for the accurate assay of chlorine in fossil fuels

This paper describes a robust and quantitative method to separate, purify, and assay the amount of chlorine in fossil fuels using isotope dilution mass spectrometry. The digestion/extraction process uses Carius tubes containing the fossil fuel samples in the presence of HNO3, AgNO3 and a 37Cl spike. The closed system oxidation permits complete equilibration of the sample and spike Cl. The evolved chlorine is trapped as AgCl within the Carius tube, and can then be separated and cleaned. The purified AgCl is also amenable to isotopic analysis by solid or gas source isotope ratio mass spectrometry. For isotope dilution mass spectrometry, the chlorine can be readily measured in a thermal ionization mass spectrometer in a negative ion mode as 37Cl/35Cl ratios with an approximate detection limit (LOD) of 0.3 μg Cl and a precision of 0.2%, relative. This technique may also be used to produce samples suitable for high precision measurements of chlorine isotopic variations in fossil fuels and chlorinated hydrocarbons.

The supremacy of invertebrate predators over fish - factors behind the unconventional seasonal dynamics of cladocerans in Lake Hiidenvesi

In the eutrophic Lake Hiidenvesi (30.3 km 2 ), the early summer biomass maximum of cladoceran zooplankton is missing and the highest biomass is found unusually in mid summer. The contribution of the phantom midge Chaoborus flavicans to the unconventional seasonal dynamics of cladocerans was studied. The seasonal development of the C. flavicans population and the zooplankton community was studied together with food consumption by chaoborids and the most common vertebrate predator, smelt. The population density of Chaoborus peaked in June and collapsed in mid summer. Thereafter, another peak occurred at the end of August. The maximum density of chaoborids in the water column varied between 5,500 and 8.700 inc./m 2 . In early summer, the most common food items of Chaoborus were bosminids while later in summer the share of daphnids increased. Food consumption by the Chaoborus population peaked at 26-46 μg Cl -1 d -1 in June and clearly exceeded the production rate of cladocerans. Cladoceran consumption by smelt population reached its maximum, 1.13 μg Cl -1 d -1 , in early July. Cladocerans showed a 20-40 μg C/l biomass peak in July-August, coincidently with the minimum density of chaoborids. When predation pressure decreased, the mean size of cladocerans increased at 10-15 m, the depth occupied by chaoborids during daytime. The results suggest that in early summer the high predation pressure prevents cladocerans from reaching a sufficient body length to defend them against Chaoborus and that the timing of the cladoceran biomass peak is determined by the relaxation of chaoborid predation.

UV-light induced mineralization of organic matter bound chlorine in Lake Bjän, Sweden––a laboratory study

Surface water and aqueous solutions of isolated organic matter from a humic rich lake in southern Sweden were exposed to artificial UV radiation to investigate the UV light induced influence on organic matter bound chlorine in natural systems. It was found that the photodegradation of organic matter bound chlorine was more pronounced than the photodegradation of organic carbon. After 120 h of irradiation of the isolated organic matter, only 35% of the initial organochlorine was still in the solution compared to about 70% of the dissolved organic carbon (DOC). A similar result was obtained for unfractionated surface water. Furthermore, our results indicate that the loss of organic chlorine was mainly due to a mineralization of organic chlorine into chloride ions. The total decrease of organic chlorine after 120 h was 32 μg Cl org l −1, of which the major part disappeared in the initial irradiation phase. A similar increase was observed in the chloride concentration (34 μg Cl − l −1).

Particulate organic matter dynamics in a river floodplain system: impact of hydrological connectivity

The retention efficiency of a specific reach is one key factor controlling the dynamics of particulate organic matter (POM) in running waters. Floodplains enhance the retention of riverine POM, thereby altering its structure and diagenetic state, and constitute a substantial autochthonous source. Hydrological connectivity between the river and its floodplains determines the impact of floodplains for the POM dynamics of the entire river. The elemental and isotopic (δ 13 C, δ 15 N) composition and microbial utilisation of POM was investigated in relation to hydrological connectivity in the Danube River and two floodplain segments, one of which was isolated, the other dynamically connected. The latter had been subjected to river restoration measures. An increased integration in the riverine network was the effect of the restoration. Within both floodplains, isolated, disconnected and connected conditions were distinguished depending on the location of inflow areas and the riverine water level. Hydrological connectivity, expressed as water age, significantly influenced the quantity and composition of POM in the dynamic floodplain. Carbon isotopic composition of POM clearly separated riverine and connected conditions from those disconnected and isolated, the latter representing autochthonous material mainly derived from plankton. At disconnection, the maximum contribution of phytoplankton to POC was determined (54.5 % ± 28.8 SE), which also supported the highest bacterial productivity (4.61μg Cl -1 h -1 ± 0.55 SE). Connected conditions were characterised by relatively enriched, allochthonous POM (δ 13 C: -23.27‰ ± 0.98 SE). In the isolated floodplain, high standing stocks of aquatic macrophytes developed which act as 'sinks' of carbon for the river. Restoration efforts like the Danube restoration project, which increase hydrological connectivity, enhance the importance of autochthonous POM and its further transformation by re-establishing dynamically connected floodplains in regulated, temperate large rivers.

Species-Specific Productivity of Cryptomonas ovata (Cryptophyceae) in the Pal'tang Reservoir, Korea

ABSTRACT Population dynamics and primary productivity of Cryptomonas ovata were investigated in a riverine zone of Pal'tang Reservoir from April through November in 1997. Standing crops of C. ovata ranged from 0.4 to 52 % of total phytoplankton cell number. Its productivity varied from 2.8 to 137.9 μg Cl−1 hr−1 (ca. 1 to 74 % of total productivity) and contributed ca. 28 % of total phytoplankton productivity on an annual basis. Species-specific productivity (SSP) of C. ovata fluctuated between 14.6 and 81.5 pg C cell−1 hr−1 and its seasonal trend was not clear. Volume-specific SSP (SSP/cell volume) of C. ovata was significantly higher in summer, which suggests high growth rate potential at higher temperatures (23–27 °C). However, the C. ovata population reached its maximam density in spring.

Study of the electrothermal atomization of selenium (IV) in transversely-heated graphite atomizers in the presence of nickel compounds as chemical modifiers

The electrothermal atomization of selenium, in transversely-heated graphite atomizers, was studied with regard to the effect of the addition of nickel nitrate and nickel chloride as chemical modifiers. Particular importance was given to the behavior of the analyte in aqueous standards and in sodium chloride containing solutions, after thermal reduction of the modifiers prior to the injection of the analyte solution into the atomizer. Thermal reduction of either nickel compound brings about an enhancement in the sensitivity of selenium measurements, as compared to those obtained by the injection of both the analyte and the modifier together into the atomizer. Additionally, thermal reduction of the modifiers permits the presence of chloride, as sodium chloride, to be tolerated in amounts as high as 500 μg Cl − with sensitivity losses lower than 10%.