Quantification of carbon nanotubes in biological matrices for toxicology purposes

Despite numerous possible applications, the potential impact of Carbon Engineered Nanomaterials (CEN) on human health, particularly after exposure by inhalation, is still questioned. However, accurate quantification of CEN in the respiratory system is a recurring issue. In the context of toxicological evaluation, deposition and pulmonary biopersistence data are essential. Given this, a validated standard method for CEN quantification in lung tissue is thus of important need. The objective of this study was to develop a method effective enough to quantify CNT in the lungs of rats nose-only exposed to CEN aerosols at concentrations of 0.5 to 15 mg/m3 for 6 h/day, 5 days/week, over 4 weeks.<br/>
Based on the National Institute for Occupational Safety and Health 5040 method for atmospheric elemental and organic carbon analysis, as well as previous developments on biological matrices (e.g. Doudrick et al.), the proposed method involves a simple thermogravimetric analysis (TGA) of lyophilized samples, possibly preceded by chemical digestion of the tissues depending on the CEN nature.<br/>
Using 4 CEN (long and thick or short and thin carbon nanotubes or carbon black), the method was first validated in terms of selectivity, linearity, detection and quantification limits, bias, as well as within-preparation and between-preparation precisions. Calibration curves showed linearity in the range of 1 40 mg/g lyophilized lung. Limits of detection for the different CEN ranged from 6 to 18 g in 20 mg dry test sample. Within-preparation precision was on average below 20 and 10% for analyses with and without the digestion step, respectively, while corresponding between-preparation precision levels reached almost 20 and 15% respectively. <br/>
The method was then successfully applied in a toxicological study, for quantitative analysis of CEN contents in rat lung exposed by inhalation. Results obtained at different post exposure times (on Days 3, 30 or 180) illustrate the ability of the method to evaluate pulmonary clearance of the specific CEN as a function of time. This information is of particular importance as it enables the assessment of the biopersistence of certain materials, as well as the determination of the relationship between retained dose and health effects such as chronic inflammation, which may lead to granuloma, fibrosis or cancer.