Toxicological study using single-cell ICP-MS

Abstract

Algae have been widely used as models in environmental assessment of the toxic effects of heavy metals. The essential metals, e.g., Mg, of the cells are useful indicator of the health state of the cells. We have used single-cell inductively coupled plasma - mass spectrometry (SC-ICP-MS) for direct quantification of the metal contents of individual biological cells [1]. An advantage of SC-ICP-MS is that the method provides information on the distribution of metal contents of the cell population, whilst conventional bulk analysis gives the average contents only. The distribution of the spike intensity of algal cells can be used to characterize the growth and health conditions of the cell population. The peak maximum (Pm) of the distribution is proportional to the average of the metal contents. The range and symmetry of the distribution are indicators of cell heterogeneity. Changes in the shape of the distribution are a good indicator of cell viability under environmental stress. In this study, Chlorella vulgaris, an unicellular green alga, was used as a model cell for toxicological studies of chromate. Cell cultures in the log phase of growth were exposed to the toxic metal ions at environmental relevant concentration (100 - 1000 ppb). The concentration is of similar order of magnitude of the maximum contaminant level of heavy metals. The growth of the cells was directly characterized by measurement of the SC-ICP-MS spike intensity of Mg of the cells and the number of the intensity spikes at regular time intervals. The uptake and accumulation of Cr was determined from the SC-ICP-MS intensity of Cr. The Mg ICP-MS intensity distribution is log-normal for the control algal culture but the distribution becomes asymmetrical for the chromate-treated population. The Mg-intensity distribution correlates well with the size distribution of cells which was directly determined using optical microscopy. The stimulatory or inhibitory effects by chromate are evaluated by comparing the Mg intensity distribution of the control and the chromate-treated populations. The Mg-intensity distribution of the algal cells are also correlated to the Cr-intensity distribution. SC-ICP-MS provides useful information concerning cell-to-cell variations for toxicological studies and environmental assessments. Financial support from the General Research Fund of the University Grants Committee of Hong Kong (Project No. 17300414) and the Committee on Research and Conference Grants of the University of Hong Kong is acknowledged. References 1. Ho K.S. and Chan W.T., J. Anal. At. Spectrom., 2010, 25, 1114-1122. 2. Tsang C.N., Ho K.S., Sun H. and Chan W.T., J. Am. Chem. Soc., 2011, 133, 7355-7357.