Feasibility of Rare Earth Element Determination in Low Concentration in Crude Oil: Direct Sampling Electrothermal Vaporization-Inductively Coupled Plasma Mass Spectrometry.

A comprehensive study was developed showing the feasibility of determination of rare earth elements (REE) in low concentration in crude oil by using direct sampling electrothermal vaporization system coupled to inductively coupled plasma mass spectrometry (ETV-ICP-MS). The effect of organic modifier on the REE signal was evaluated and the use of 6 mg of citric acid allowed calibration using aqueous reference solutions (selected pyrolysis and vaporization temperatures were 700 and 2200 °C, respectively). Because of the facility of REE in forming refractory compounds inside the graphite furnace during the heating step, the use of a modifier gas (Freon R-12, 3.0 mL min-1) was necessary to allow quantitative vaporization of these elements. A flow rate of 0.40 L min-1 was selected for both bypass and carrier gases. Under optimized conditions, the influence of sample mass was evaluated, and even using a relatively high mass of crude oil (up to 18 mg), accurate results were obtained. The accuracy was evaluated by the comparison of results by ETV-ICP-MS with those obtained by ICP-MS with ultrasonic nebulizer (USN) after high-pressure microwave-assisted wet digestion (MAWD) and microwave-induced combustion (MIC) and no statistical difference was observed between the results. The limits of quantification for REE by ETV-ICP-MS were lower (0.02-0.8 ng g-1) than those obtained by USN-ICP-MS after MAWD and MIC (0.6-5.1 ng g-1). Negligible blank values and relative standard deviations lower than 12% show the feasibility of the proposed ETV-ICP-MS method for routine analysis of crude oil.

Health risk assessment and soil and plant heavy metal and bromine contents in field plots after ten years of organic and mineral fertilization.

Heavy metals and bromine (Br) derived from organic and industrialized fertilizers can be absorbed, transported and accumulated into parts of plants ingested by humans. This study aimed to evaluate in an experiment conducted under no-tillage for 10 years, totaling 14 applications of pig slurry manure (PS), pig deep-litter (PL), dairy slurry (DS) and mineral fertilizer (MF), the heavy metal and Br contents in soil and in whether the grains produced by corn (Zea mays L.) and wheat (Triticum aestivum L.) under these conditions could result in risk to human health. The total contents of As, Cd, Pb, Cr, Ni, Cu, Zn and Br were analyzed in samples of fertilizers, waste, soil, shoots and grains of corn and wheat. Afterwards, enrichment factor (EF), accumulation factor (AF), health risk index (HRI), target hazard quotient (THQ) and target cancer risk (TCR) were determined. Mineral fertilizer exhibited the highest As and Cr content, while the highest levels of Cu and Zn were found in animal waste. The contents of As, Cd, Cr, Cu, Ni, Pb and Zn in soil were below the limits established by environmental regulatory agencies. However, a significant enrichment factor was found for Cu in soil with a history of PL application. Furthermore, high Zn contents were found in shoots and grains of corn and wheat, especially when the plants were grown in soil with organic waste application. Applications of organic waste and mineral fertilizer provided high HRI and THQ for Br and Zn, posing risks to human health. The intake of corn and wheat fertilized with pig slurry manure, swine deep bed, liquid cattle manure and industrialized mineral fertilizer did not present TCR.