Isotope Tracer Method Research Articles

Experimental study on oxy-fuel combustion behavior of lignite char and carbon transfer mechanism with isotopic tracing method

In this work, the conventional combustion in O2/Ar and O2/CO2 atmospheres at temperatures of 700–1000 °C and isotopic tracing experiments at 700–800 °C were conducted respectively in a micro fluidized bed reactor to clarify the conversion characteristics of lignite char and influence mechanism of elevated CO2 concentrations. The isotopic method employing C18O18O provides an intuitive insight into the CO2 gasification behavior by tracking the evolution of the 18O atom throughout the oxy-fuel combustion. The results reveal that char conversion rate significantly reduces when the atmosphere is switched from O2/Ar to O2/CO2 at low temperature range (e.g. 700–800 °C), primarily caused by thermo-physical properties of CO2. However, at higher temperature range (e.g. 950–1000 °C), the C-O2 reaction is limited by the external O2 diffusion and the C-CO2 reaction contributes to the carbon consumption, resulting in a higher combustion rate, especially at O2-deficient conditions. The presence of the atomic 18O in the product C18O16O originating from C18O18O confirms that CO2 is indeed involved in the whole oxy-fuel combustion process and the overall reaction could be described as C + C18O18O+16O16O → 2C18O16O. Besides, total contributions to carbon conversion by the C-CO2 reaction decrease as O2 concentrations and particle sizes increasing.

Phosphorus deficiency induced by aluminum in a marine nitrogen-fixing cyanobacterium Crocosphaera watsonii WH0003

Large amounts of aluminum (Al) enter the ocean through atmospheric dust deposition and river runoffs. However, few studies have reported the effects of Al on marine phytoplankton, especially nitrogen-fixing cyanobacteria. By using the isotope tracer method and quantitative reverse transcription PCR (RT-qPCR), we examined the physiological effect of Al (0.2, 2 and 20μM) on the unicellular marine nitrogen-fixing cyanobacterium Crocosphaera watsonii in Aquil* medium. We show that Al has an inhibitory physiological effect on C.watsonii, including changes in growth rate, nitrogen fixation rate, carbon fixation rate, cell size, fast rise chlorophyll fluorescence kinetics, cellular photosynthetic pigment and C/N/P content, the same as that of the phosphorus deficient treatment. The ratio of cellular elements C:N:P showed that phosphorus was deficient in the cell of C.watsonii after Al treatment (2 and 20μM). In addition, Al stimulated the expression of phosphorus-related genes pstS, phoH, phoU, ppK and ppX in C.watsonii. All these results suggest that Al-treated C.watsonii is phosphorus-limited, and that the phosphorus deficiency induced by Al may be one mechanism behind aluminum's toxicity.

Activity, Abundance, and Community Composition of Anaerobic Ammonia–Oxidizing (Anammox) Bacteria in Sediment Cores of the Pearl River Estuary

Anaerobic ammonium oxidation (anammox) is an important pathway for the removal of fixed nitrogen from aquatic and terrestrial ecosystems. Previous studies on anammox were focused on the surface sediments in estuaries, but the activity and community composition of anammox bacteria in the estuarine subsurface sediments remained unknown. In this study, we used high-throughput sequencing of 16S rRNA gene combined with 15N isotope tracing method to investigate the activity, diversity, and spatio-temporal distribution of anammox bacteria in sediment cores of the Pearl River Estuary (PRE). Our results indicated that anammox in the subsurface sediments has significant potential activity, contributing to approximately 17.49% of the total microbial nitrogen loss. A variety of anammox bacteria, including Candidatus Scalindua, Ca. Brocadia, Ca. Jettenia, and Ca. Kuenenia, were all detected in the subsurface sediments. Moreover, the anammox bacterial community had a significant specific geographic distribution but no obvious difference along the sediment depth. Multiple environmental factors including salinity, and NH4+ and NO3− contents, synergistically shaped the diversity and distribution of anammox bacteria in PRE sediments.

Nitrogen interception and fate in vegetated ditches using the isotope tracer method: A simulation study in northern China

During periods of heavy precipitation, farmland drainage ditches are the main routes for farmland nitrogen flowing into surface waters in northern China. Vegetated ditches can be engineered to mitigate N loss from agricultural runoff. We used a simulation study to evaluate the interception of nitrogen in a ditch without vegetation and three vegetated ditches. The 15N stable isotope tracer method was used to analyze the fate of ditch intercepting farmland runoff nitrogen. The three vegetated ditches were planted with Lolium perenne L., Bromus inermis Leyss. and Elytrigia repens (L.) Nevski. The results showed that the interception rates of nitrogen in the three vegetated ditches were higher than in the ditch without vegetation. The L. perenne ditch had the lowest interception rates of nitrogen among the three vegetated ditches. The interception of nitrogen by the three vegetated ditches was primarily achieved by the capture of nitrogen runoff in the soil ditch bed, which allowed water infiltration. Nitrogen retained in the ditch bed soil of the ditch without vegetation was enriched in the 0–10 cm soil layer from surface mainly. However, in the three vegetated ditches, it was transported to the 50 cm soil layer. All of the nitrogen retained in the vegetated ditches was absorbed by the L. Perenne and E. repens, and the interception of nitrogen was affected by plant species and growth stage in the vegetated ditch.

A method for Si isotope tracer kinetics experiments: Using Q-ICP-MS to obtain 29Si/28Si ratios in aqueous solutions

Here we show that silicon isotope tracer kinetics experiments can be economically conducted with measurements of 29Si/28Si ratios in the experimental aqueous solutions using Quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) with sufficient precision. Although the isotope tracer method promises orders of magnitude improved detection sensitivity of reactions, its application has been hampered by the limited availability of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for Si isotope analysis. However, in Si isotope tracer kinetics experiments, dissolution rates are often derived from isotope fractional abundance increments by as much as 0.5 unit (equivalent to 50%) and the method essentially relies on the difference in isotope ratios over a period of time, which render uncertainties in < ±0.01 fraction (or ±1%) in Si isotope abundances tolerable. Laboratory-measured silicate dissolution rates typically carry uncertainties of more than ±25% and with even poorer intra- and inter-laboratory replications. These special situations of kinetics experiments circumvent the conventional concerns of using Q-ICP-MS to measure isotope ratios.To test this hypothesis, we conducted two experiments. The first used Q-ICP-MS to measure a set of mixing solutions or reference solutions with known isotope compositions. The results show that the difference is an average of ±0.009 in f29. A second test used both MC-ICP-MS and Q-ICP-MS to measure the 29Si/28Si ratios in experimental solutions of albite dissolution. Ten albite dissolution experiments were conducted at 50°C and pH 8.8. Student t-test showed that the rates calculated from the two analytical data sets have no statistically significant differences at the 95% confidence level. These results demonstrate that the Q-ICP-MS measurements of 29Si/28Si ratios produced tolerable uncertainties for determining silicate dissolution rates. However, the cost is significantly reduced and more significantly, the reduced wait time makes isotope tracer experiments more feasible. Silicate minerals make up 90% of the Earth’s crust. The kinetics of silicate-water reactions is of paramount significance to many society’s mega-environmental enterprises. This method to conduct Si isotope tracer experiments, as well as the possibility to use this approach for other non-traditional stable isotopes, will have significant impact on geochemical kinetics studies.

Hungry for your alanine: when liver depends on muscle proteolysis.

Fasting requires complex endocrine and metabolic interorgan crosstalk, which involves shifting from glucose to fatty acid oxidation, derived from adipose tissue lipolysis, in order to preserve glucose for the brain. The glucose-alanine (Cahill) cycle is critical for regenerating glucose. In this issue of JCI, Petersen et al. report on their use of an innovative stable isotope tracer method to show that skeletal muscle-derived alanine becomes rate controlling for hepatic mitochondrial oxidation and, in turn, for glucose production during prolonged fasting. These results provide new insight into skeletal muscle-liver metabolic crosstalk during the fed-to-fasting transition in humans.

Unidirectional kaolinite dissolution rates at near-equilibrium and near-neutral pH conditions

Kaolinite dissolution rates at ambient temperature and pH 7.1–8.5 were measured with the isotope tracer method. A rare Si isotope 29Si was introduced to the experimental solutions, which reacted with Georgia kaolinite (KGa-1b) composed of mostly 28Si. Reaction rates were tracked by 29Si/28Si ratios of reacted solutions. The 16 batch experiments were designed with a grid of solutions that ranged from near saturation to supersaturation with respect to kaolinite. An average dissolution rate (unidirectional) of 5.4 ± 1.6 × 10−14 mol (kaol) s−1 m−2 consistently fitted the 29Si/28Si ratios for all 16 experiments, indicating the dissolution rates were independent of pH in near-neutral pH waters and independent from the levels of departure from equilibrium. In other words, it appears that the dissolution reaction mechanisms do not change across from the kaolinite-undersaturated to kaolinite-supersaturated solutions near-equilibrium.The near-equilibrium kaolinite dissolution rates in this study are a new type of rates—unidirectional rates (from the isotope tracer method), which differ from all near-equilibrium kaolinite dissolution rates in the literature that are based upon Si or Al concentrations and are net rates (dissolution minus precipitation rates). Kaolinite dissolution was non-stoichiometric in all experiments. The Si and Al concentrations were sometimes systematic but more often erratic, resulting from the precipitation of AlSi secondary phases. The experimental solutions were grossly supersaturated with respect to gibbsite, allophanes, and imogolites. This confirms our hypothesis that the scatter and conflicts of near-equilibrium data are caused by unaccounted-for secondary phase precipitation, but the isotope tracer method successfully circumvents this experimental pitfall. Most natural waters are supersaturated with clays and are near-neutral pH. Our experimental rates are more applicable to the studies of natural waters than the majority rates available in the literature, which have mostly been measured at far-from-equilibrium, acidic pH, and high temperatures.

Editorial introductions

Editorial introductions

Measuring rhizosphere effects of two tree species in a temperate forest: A comprehensive method comparison

Abstract: Rhizosphere effects have been increasingly recognized to play an important role in soil biogeochemical cycling. However, various methods were adopted to sample rhizosphere vs. bulk soils and to measure rhizosphere effects. Here we provide a comprehensive comparison of three commonly used methods to measure rhizosphere effects of two tree species (Larix principis-rupprechtii and Pinus sylvestris var. mongolica) in a temperate forest. Specifically, we used two root chamber methods with non-native C4 soil and native C3 soil (C4 and C3 soil chamber) and the adhering soil method (C3 soil natural). The rhizosphere effects ranged from negative to neutral and positive, and varied greatly among methods and variables, but not between species. Generally, the two root chamber methods showed negative or neutral rhizosphere effects, while the adhering soil method often indicated positive or neutral rhizosphere effects. For example, rhizosphere effects of Larix and Pinus on soil carbon mineralization (Cmin, based on 30-day lab incubation of sieved soils) ranged from −25% to 17% for the two chamber methods, while from 13% to 87% for the C3 soil natural method. However, the non-destructive isotopic tracing method using the C4 soil chambers (by trapping CO2 from the intact root-soil system) showed the highest rhizosphere effects on Cmin (162% for Larix and 42% for Pinus). Such differences in rhizosphere effects among methods could be due to a few factors, including different degrees of soil drying by root water uptake, different definitions of rhizosphere, and different levels of perturbation of the root-soil system during sampling and measurement. Further, we found positive correlations in rhizosphere effects between soil properties and microbial biomass and enzyme activities across three methods and two species, but rhizosphere effects on Cmin were only positively correlated with rhizosphere effects on soil total nitrogen. Taken together, we suggest researchers to use both root chamber and adhering soil method together, better control soil moisture and incubation time for root chamber method, and quantify root traits in relation to rhizosphere effects for both methods to deepen our understanding of rhizosphere effects of woody plants in future work.

Analysis of water conductivity and water gushing source of collapse column in changcun mine

Based on the water conductivity of Lu’an coal mine collapse column and the analysis of the causes of water inrush of Lu’an coal mine collapse column, the water inrush source of collapse column in Changcun Mine was comprehensively analyzed by stable isotope tracing method. It was found that the groundwater runoff conditions and geological structure condition of collapse column seriously affected the water inrush of collapse column. It is determined that the water inrush source of N2-7 collapse column in Changcun coal mine is the same as the Upper Sandstone water source, that is, the infiltration supply of atmospheric precipitation, but has no direct connection with the aquifer of Ordovician limestone., which provides a relatively reliable method for the water inrush source identification of collapse column.

Spatial-Temporal Pattern of Sulfate-Dependent Anaerobic Methane Oxidation in an Intertidal Zone of the East China Sea.

Methane is a primary greenhouse gas which is responsible for global warming. The sulfate-dependent anaerobic methane oxidation (S-AOM) process catalyzed by anaerobic methanotrophic (ANME) archaea and sulfate-reducing bacteria (SRB) is a vital link connecting the global carbon and sulfur cycles, and it is considered to be the overriding methane sink in marine ecosystem. However, there have been few studies regarding the role of S-AOM process and the distribution of ANME archaea in intertidal ecosystem. The intertidal zone is a buffer zone between sea and land and plays an important role in global geochemical cycle. In the present study, the abundance, potential methane oxidation rate, and community structure of ANME archaea in the intertidal zone were studied by quantitative PCR, stable isotope tracing method and high-throughput sequencing. The results showed that the potential S-AOM activity ranged from 0 to 0.77 nmol 13CO2 g-1 (dry sediment) day-1 The copy number of 16S rRNA gene of ANME archaea reached 106 ∼ 107 copies g-1 (dry sediment). The average contribution of S-AOM to total anaerobic methane oxidation was up to 34.5%, while denitrifying anaerobic methane oxidation accounted for the rest, which implied that S-AOM process was an essential methane sink that cannot be overlooked in intertidal ecosystem. The simulated column experiments also indicated that ANME archaea were sensitive to oxygen and preferred anaerobic environmental conditions. This study will help us gain a better understanding of the global carbon-sulfur cycle and greenhouse gas emission reduction and introduce a new perspective into the enrichment of ANME archaea.IMPORTANCE The sulfate-dependent anaerobic methane oxidation (S-AOM) process catalyzed by anaerobic methanotrophic (ANME) archaea and sulfate-reducing bacteria (SRB) is a vital link connecting the global carbon and sulfur cycles. We conducted a research into the spatial-temporal pattern of S-AOM process and the distribution of ANME archaea in coastal sediments collected from the intertidal zone. The results implied that S-AOM process was a methane sink that cannot be overlooked in the intertidal ecosystem. We also found that ANME archaea were sensitive to oxygen and preferred anaerobic environmental conditions. This study will help us gain a better understanding of the global carbon-sulfur cycle and greenhouse gas emission reduction and introduce a new perspective into the enrichment of ANME archaea.

Biochar amendment and Calamagrostis angustifolia planting affect sources and production pathways of N2O in agricultural ditch systems.

Nitrous oxide (N2O) from agricultural ditches is a non-negligible source of anthropogenic greenhouse gas (GHG) emissions, but few studies have addressed this topic in depth. On the other hand, although there are numerous reports that biochar application can affect N2O emissions from soil, the understanding of the process and source of changes is still incomplete. To examine the effect of biochar and Calamagrostis angustifolia on N2O emissions, we conducted experiments with constructed ditches where corn stalk biochar (pyrolysis temperature of 450 °C) was applied at a rate of 16.77 Mg ha-1 and C. angustifolia was planted. The sources (native sediment versus exogenous inorganic N) and production pathways (nitrification versus denitrification) of N2O emissions were discriminated using the 15N isotope tracer method. We observed that biochar application reduced the cumulative total N-N2O emissions from the native sediment by 10.8-18.7% and reduced the cumulative 15N-N2O emissions from the exogenous 15N-labelled inorganic N by 25.7-68.6%; C. angustifolia planting reduced these cumulative N2O emissions by 48.8-53.3% and 93.3-92.4%, respectively. The results showed that biochar stimulated nitrification and nitrification-derived 15N-N2O emissions, but reduced denitrification-derived 15N-N2O emissions in bare sediment microcosms; C. angustifolia effectively reduced both nitrification-derived and denitrification-derived 15N-N2O emissions. Therefore, we concluded that the effect of biochar application on N2O emissions may depend on its dominant N2O production pathway and biochar application plus C. angustifolia planting could be beneficial for the mitigation of N2O emissions in agricultural ditch systems.

Denitrifying Anaerobic Methane Oxidation: A Previously Overlooked Methane Sink in Intertidal Zone.

The intertidal zone is an open ecosystem rich in organic matter and plays an important role in global biogeochemical cycles. It was previously considered that methane was mainly removed by sulfate-dependent anaerobic methane oxidation (sulfate-AOM) process in marine ecosystems while other anaerobic methane oxidation processes were ignored. Recent researches have demonstrated that denitrifying anaerobic methane oxidation (DAMO), consisting of nitrite-dependent anaerobic methane oxidation (nitrite-AOM) and nitrate-dependent anaerobic methane oxidation (nitrate-AOM), can also oxidize methane. In this work, the community structure, quantity and potential methane oxidizing rate of DAMO archaea and bacteria in the intertidal zone were studied by high-throughput sequencing, qPCR and stable isotope tracing method. The results showed that nitrate-AOM and nitrite-AOM were both active in the intertidal zone and showed approximate methane oxidation rates. The copy number of 16S rRNA gene of DAMO archaea and DAMO bacteria were 104 ∼ 105 copies g-1 (dry sediment), whereas NC10 bacteria were slightly higher. The contribution rate of DAMO process to total anaerobic methane removal in the intertidal zone reached 65.6% ∼ 100%, which indicates that DAMO process is an important methane sink in intertidal ecosystem. Laboratory incubations also indicated that DAMO archaea were more sensitive to oxygen and preferred a more anoxic environment. These results help us draw a more complete picture of methane and nitrogen cycles in natural habitats.

Ileal digestibility of intrinsically labeled hen's egg and meat protein determined with the dual stable isotope tracer method in Indian adults

ABSTRACTBackgroundProtein quality assessment through the Digestible Indispensable Amino Acid Score requires accurate measurements of true ileal protein and amino acid digestibility, for which a dual isotope technique was recently developed. However, the ileal digestibility of indispensable amino acids (IAA) in humans from high-quality proteins is not well known.ObjectiveThe aim of this study was to intrinsically label hen's egg and meat protein by the use of uniformly 2H-labeled amino acids, and to measure their true ileal indispensable amino acid (IAA) digestibility via the dual isotope method in humans.Design 2H-labeled lyophilized boiled egg white protein, whole boiled egg, and cooked meat were obtained from layer hens (BV-300) administered a uniformly 2H-labeled amino acid mix orally for 35 d with their daily feed. The ileal IAA digestibility of these proteins was determined with reference to digestibility of previously characterized [U-13C]spirulina in a dual tracer method in healthy Indian subjects whose intestinal health was measured by the plasma kynurenine-to-tryptophan (KT) ratio.ResultsAll subjects had normal KT ratios. The mean ± SD true ileal IAA digestibility of 2H-labeled egg white protein, whole boiled egg, and cooked meat was 86.3% ± 4.6%, 89.4% ± 4.5%, and 92.0% ± 2.8%, respectively. Leucine digestibility correlated with the KT ratio (r = −0.772; P = 0.009).ConclusionsUniformly 2H-labeled hen's egg and meat protein can be used to measure ileal IAA digestibility by the dual isotope tracer approach in humans. The mean IAA digestibility values for these high-quality proteins in the healthy Indians studied were similar to values obtained in earlier human and animal experiments. Leucine digestibility in these meal matrices correlated with the KT ratio, but this aspect needs further evaluation. This trial was registered at the Clinical Trials Registry of India (http://ctri.nic.in) as CTRI/2018/03/012265.

Simultaneous uptake of Cd from sediment, water and diet in a demersal marine goby Mugilogobius chulae.

The embryonic state of our knowledge regarding the simultaneous uptake of trace metals via multiple routes in aquatic organisms makes it difficult to accurately assess the bioaccumulation and risk of metals. This study used cadmium (Cd) and a demersal marine fish (the yellowstripe goby) as a model system to determine tissue-specific uptake of Cd under conditions of simultaneous exposure to Cd from water, sediment and diet. A triple stable isotope tracing method was used in which each exposure route was spiked by a different stable isotope (110Cd, 111Cd and 113Cd). The results revealed that the fish took up waterborne and sedimentary Cd via gills and gastrointestinal tract (GT), and that of dietary Cd was via the GT. The gills absorbed Cd predominantly from water (77.2-89.4%) whilst the GT absorbed Cd mainly from diet (81.3-98.7%). In the muscle and carcass, the Cd uptake was mainly from the diet (47.1-80.4%) and water (22.8-51.6%). Our study demonstrated that when aquatic animals were subject to simultaneous exposure through multiple uptake routes, the uptake and relative importance of each route for metal accumulation was highly tissue-specific and more complex than a single route of metal exposure.

Carbon-13 stable isotope analysis reveals the existence but insignificance of ruminal methanogenic pathway from acetate in a batch culture system

A series of in vitro batch culture incubations were conducted to investigate the extent of carboxyl group and methyl group in acetate converted to CH4 using a stable isotopic tracer method. Ground lucerne hay was incubated as a substrate with buffered ruminal fluid, and 13C labeled CH313COONa or 13CH3COONa was supplied into the incubation bottles at a dose of 0, 15, 35 or 55 mM. Increasing CH313COONa or 13CH3COONa supplementation linearly increased (P < 0.05) absolute 13CH4 and 13CO2 production (mL/bottle) at all the time points measured. Yet, the conversion rates (CR) of 13CH4 and 13CO2 produced from labeled CH313COONa or 13CH3COONa were very low. For instance, the relative 13CH4 CR (%) was ranged from 0.0028-0.14% with incubation time extended to 48 h, and the relative 13CO2 CR (%) was ranged from 0.054 to 1.3%. Moreover, acetate supplementation linearly increased (P < 0.01) the concentration of butyrate, 16S rRNA gene copies of protozoa, total methanogens, Methanosphaera stadtmanae, Methanobrevibacter smithii and Methanosarcina barkeri. In summary, our study indicates existence of methanogenesis from acetate, but such pathway of methanogenesis makes little contribution to the total CH4 production through in vitro ruminal fermentation.

Hydrologic implications of the isotopic kinetic fractionation of open-water evaporation

The kinetic fractionation of open-water evaporation against the stable water isotope H218O is an important mechanism underlying many hydrologic studies that use 18O as an isotopic tracer. A recent in-situ measurement of the isotopic water vapor flux over a lake indicates that the kinetic effect is much weaker (kinetic factor 6.2‰) than assumed previously (kinetic factor 14.2‰) by lake isotopic budget studies. This study investigates the implications of the weak kinetic effect for studies of deuterium excess-humidity relationships, regional moisture recycling, and global evapotranspiration partitioning. The results indicate that the low kinetic factor is consistent with the deuterium excess-humidity relationships observed over open oceans. The moisture recycling rate in the Great Lakes region derived from the isotopic tracer method with the low kinetic factor is a much better agreement with those from atmospheric modeling studies than if the default kinetic factor of 14.2‰ is used. The ratio of transpiration to evapotranspiration at global scale decreases from 84±9% (with the default kinetic factor) to 76±19% (with the low kinetic factor), the latter of which is in slightly better agreement with other non-isotopic partitioning results.

Editorial introductions

Editorial introductions

A kinetic study on char oxidation in mixtures of O2, CO2 and H2O

Flue gas is usually recycled to a boiler during oxy-fuel combustion. Elevated levels of CO2 and steam in the recycled flue gas may affect coal combustion. To investigate the effect of H2O and CO2 on char oxidation, two kinds of Chinese coals, including YQ anthracite and SH lignite, were combusted in the mixtures of O2, CO2 and H2O atmosphere. The char conversion rates in different atmospheres were measured at the temperature of 1273 K. Further, H218O isotopic tracing method was adopted to clarify the reaction path of H2O. The results show that the shrinking core model is applicable to predict both combustion and gasification reactions in TGA. For both YQ and SH chars, char-O2 reaction is independent but char overall oxidation rate is promoted by the increase of H2O partial pressure. The active sites for char-O2 and char-H2O reactions are partly independent and partly at the same active sites for YQ anthracite, but they share common active sites for SH lignite. Char-H2O reaction is inhibited by char-O2 reaction but the 18O in H2O is still transferred to CO2 even in oxygen-rich atmosphere. The possible reaction may be C + H218O + 16O2 = C16O18O + H216O. However, CO2 has little influence on YQ char oxidation, but it has a slight promotion on SH char oxidation in low oxygen atmosphere at 1273 K. Also, the active sites for char-O2 and char-CO2 reactions are partly independent and partly at the same active sites for SH lignite, though the active site for char-CO2 reactions is few. Finally, a reaction kinetic model is purposed to predict char consumption rate in the mixtures of O2, CO2 and H2O.

Biokinetic Modeling of Cd Bioaccumulation from Water, Diet and Sediment in a Marine Benthic Goby: A Triple Stable Isotope Tracing Technique.

Aquatic animals are often simultaneously exposed to metals through multiple routes in the natural environment. This study explored a triple stable isotope tracing method to quantify simultaneous cadmium (Cd) uptake biokinetics by yellow stripe goby from water (traced by 110Cd), sediment (traced by 111Cd), and diet (traced by 113Cd) when the fish were exposed to Cd for 24 h. The simultaneous uptake of Cd from multiple routes during 4 weeks was then predicted by the modified biokinetic model. The results demonstrated that the uptake rate constant of waterborne 110Cd, sediment-associated 111Cd, and dietary 113Cd was 3.1 L kg-1 d-1, 2.2 × 10-4 g g-1 d-1, and 3.3 × 10-3 g g-1 d-1 in the fish. Sedimentary Cd was less bioavailable than the waterborne and dietary Cd; however, sediment could become the predominant Cd source of the total Cd bioaccumulation when the partition coefficient of Cd between sediment and seawater ( Kd) is larger than 6 × 104 L kg-1. The simultaneous uptake of Cd from the three routes could be successfully predicted by the modified model. The model revealed that the Cd bioaccumulation generally increased with the increase of ambient Cd concentration in all the three routes. Overall, our findings demonstrated that the multiple stable isotopes tracing method and the modified biokinetic model have a wide generality and applicability for predicting Cd bioaccumulation under multiple routes of metal exposure scenario and may have application to other metals.