Research Program Area: Health & Exposure
Topic Areas: Toxic Air Contaminants
Toxicological testing of particulate samples is an integral aspect of evaluating possible health effects associated with PM from new engine technology studies and source specific ambient PM. However, there are a multitude of possible standard operating procedures (SOPs) for sample preparation, each with inherent advantages and disadvantages. This is not surprising since all of these procedures require physical and chemical manipulation of the PM sample during isolation which can affect its inherent toxicological properties. The main objective of this study was to systematically investigate these different SOPs and evaluate which procedures can retain of the most toxicologically relevant chemical components of the sample for various toxicological assays while producing the fewest toxicological artifacts. To study the effect of sample preparation on the toxicity of diesel exhaust particles (DEP), six different sample preparation techniques were chosen for toxicological screening via a multi-point standard assay panel. The DEP samples studied include a NIST standard and filter samples collected from the exhaust stream of a dilution tunnel during a chassis dynamometer study. These samples were prepared using two whole particle and four selective (i.e. PM fractionation) extraction techniques. All sample extracts were toxicologically screened for ROS production via the acellular dithiothreitol (DTT) assay, cellular inflammation via the cyclooxygenase-2 and interleukin-8 expression measurements, PAH response via cytochrome P450 1A1 expression, and mutagenicity via the microsuspension Salmonella/microsome assay. Results demonstrated that: 1) selective extraction techniques consistently tend to enhance the effect of the more active DEP components by removing the less reactive matrix components that are included in whole particle techniques; 2) nonpolar compounds elicit the greatest responses across all assays except for ROS production, which is largest for the more polar DEP components; 3) strong evidence exists for composite interference or toxicological matrix effects, where the sum of responses to individual components is greater than the response to the composite of those components; and 4) although different sample preparation techniques appear to be equally repeatable across different assays, the techniques eliciting the most robust response are assay-specific and include cases where multiple techniques are equally effective. The regulatory and policy implications are the establishment of recommendations and guidelines for future ARB funded projects which require in vitro toxicological analysis of filter based sample media.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
Stay involved, sign up with CARB's Research Email Distribution List