Laurent Y. Alleman

Isotopic composition of silicon measured by multicollector plasma source mass spectrometry in dry plasma mode

Precise Si isotopic fractionation in silica (quartz), opal (diatomite, sponges) and standards have been determined employing a Nu Instruments Plasma multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) in dry plasma mode, using a Cetac Aridus desolvating nebulization system. Variations in sample 28Si/29Si ratios are expressed as δ29Si units, which represent deviations in ‰ from the same ratio of the NBS28 standard measured using the standard-sample bracketing technique. We measured Mg isotopes in dynamic mode for adequate correction of instrumental mass bias, applying the fractionation exponential law and external normalisation. The repeatability and the internal precision on the δ29Si measurements of a 1 ppm Si solution in diluted HF/HCl is better than ±0.1‰ (±2 σ). The accuracy has been assessed by cross analyses of an in-house standard with the laser fluorination-isotope ratio mass spectrometry (IRMS). The dry plasma methodology improves the sensitivity more than ten times compared to wet plasma MC-ICP-MS and hence is of great relevance regarding environmental, biogeochemical and geological sciences where Si isotopes open up a range of new studies.

Silicon Isotopic Fractionation in Lake Tanganyika and Its Main Tributaries

Silicon isotopic measurements in Lake Tanganyika were performed using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in dry plasma condition. Isotopic signatures are reported for dissolved ortho-silicic acid [Si(OH)4] collected during a 1-year-long surface waters survey in the southern basin along with several of the major tributaries. Deep-water Si isotopic profiles from a north-south transect cruise conducted in July 2002 are also described. The nutrient-like shape dissolved Si profiles and the isotopic disequilibrium between surface (δ29Si = 0.87±0.08 ‰) and deep waters (0.61 ± 0.05 ‰) suggest the occurrence of biological isotopic discrimination induced by diatoms biomineralisation in a fresh water system. Short-term surface water Si isotopic and diatom biomass variations obtained during the 1-year bi-weekly monitoring (2002–2003) in the south confirms this biological effect. Five epilimnion biogenic opal samples also were analyzed. Their signature (δ29Si of 0.28 ± 0.12‰) compared to those of surrounding waters are consistent with the diatom isotopic fractionation effect measured on marine tropical diatoms. This demonstrates the species and temperature independent character of the silicon isotope fractionations by diatoms. River signatures present variable dissolved Si concentrations which were positively correlated to δ29Si values in the range of previously published world river data. Because of its fast response to climate variability, nutrient dynamics, and limnological changes, δ29Si in siliceous organisms should be very useful in studying environmental changes and particularly the recent decline of diatom Si utilization in Lake Tanganyika.

Biomonitoring of indoor air genotoxic properties in ten schools using Scindapsus aureus

School is the most important indoor environment for children besides their home. Indoor air quality in school is a critical parameter that needs to be considered for childrens health. Atmospheric measurements provide concentrations of pollutants which are used for risk assessments. However, those data are limited to study complex interactions between pollutants, and the genotoxic potential of air pollution is still often misunderstood. The aim of this study was to assess the genotoxic potential of indoor air pollutants in ten schools in France. For this purpose, we have used the comet assay in Scindapsus aureus (pothos) which is a very common indoor plant. For all classrooms, data obtained with exposed plants were significantly higher than those obtained with control. This study shows that plants can be used in indoor environments as well as outdoor for air monitoring, and can participate in health risk assessment.

Quantification of trace metalloids and metals in airborne particles applying dynamic reaction cell inductively coupled plasma mass spectrometry.

Determination of trace contents of metals and metalloids, monitored in airborne particles for their adverse health and environmental impact or to discriminate pollutant particulate emission sources, requires very sensitive analytical methods. Dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS) has been applied to measure ultra-trace elements found in PM10 atmospheric particles in order to determine simultaneously, rapid and accurate concentrations for well known highly interfered isotopes (75As, 59Co, 52Cr, 53Cr, 58Ni, 60Ni, 78Se, 45Sc, and 51V). The challenge resides in the extremely low content of these elements encountered in PM10 particles, while thorough mineralization procedures in complex matrices are necessary to deal with refractory minerals. The potentially interfering polyatomic ions combining Ar, Cl, F, O, N, and C isotopes were significantly reduced by using NH3 as the reaction gas in the DRC, optimizing the reaction cell band pass and tuning of the gas flow rate. Standard Reference Material (NIST 1648) as well as real atmospheric samples were analyzed under the best defined conditions to validate and exemplify our methodology. The method detection limits are 450 ng/L for As, 13 ng/L for Co, 1210 ng/L for Cr, 780 ng/L for Ni, 47 ng/L for Se, 22 ng/L for Sc, and 26 ng/L for V. Based on real atmospheric sample measurements, DRC-ICP-MS associated with NH3 is confirmed as a cost effective technique to produce accurate results during routine working procedures for all these elements except Se.