On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals

Abstract

The rate of consumption of dithiothreitol (DTT) is increasingly used to measure the oxidative potential of particulate matter (PM), which has been linked to the adverse health effects of PM. While several quinones are known to be very reactive in the DTT assay, it is unclear what other chemical species might contribute to the loss of DTT in PM extracts. To address this question, we quantify the rate of DTT loss from individual redox-active species that are common in ambient particulate matter. While most past research has indicated that the DTT assay is not sensitive to metals, our results show that seven out of the ten transition metals tested do oxidize DTT, as do three out of the five quinones tested. While metals are less efficient at oxidizing DTT compared to the most reactive quinones, concentrations of soluble transition metals in fine particulate matter are generally much higher than those of quinones. The net result is that metals appear to dominate the DTT response for typical ambient PM2.5 samples. Based on particulate concentrations of quinones and soluble metals from the literature, and our measured DTT responses for these species, we estimate that for typical PM2.5 samples approximately 80 % of DTT loss is from transition metals (especially copper and manganese), while quinones account for approximately 20 %. We find a similar result for DTT loss measured in a small set of PM2.5 samples from the San Joaquin Valley of California. Because of the important contribution from metals, we also tested how the DTT assay is affected by EDTA, a chelator that is sometimes used in the assay. EDTA significantly suppresses the response from both metals and quinones; we therefore recommend that EDTA should not be included in the DTT assay.

In vitro Evaluation of Oxidative Stress Caused by Fine Particles (PM2.5) Exhausted from Heavy-Duty Vehicles Using Diesel/Biodiesel Blends under Real World Conditions

“…The metal content in these diesel/biodiesel exhausted particles seems to largely contribute to the ROS production and total oxidative potential measured by the DTT assay. This is also in accordance to the results reported by Shen and Anastasio, 47 Charrier and Anastasio 27 and Aust et al 48 They reported in these studies that transition metals may represent a major determinant of the toxicity of PM. Charrier and Anastasio 27 found a similar result for DTT loss measured in a small set of PM 2.5 samples.…”

“…This is also in accordance to the results reported by Shen and Anastasio, 47 Charrier and Anastasio 27 and Aust et al 48 They reported in these studies that transition metals may represent a major determinant of the toxicity of PM. Charrier and Anastasio 27 found a similar result for DTT loss measured in a small set of PM 2.5 samples. They estimated that for typical PM 2.5 samples approximately 80% of DTT loss is from transition metals, while quinones account for approximately 20%.…”

“…Other metals do not contribute at all for the DTT oxidation. 27 On the other hand, the DTT molecule itself may act as a soft Lewis' base and may coordinate to selected metals (e.g. Zn 42 Since in DTT assay we actually measure the remaining DTT after pre-established reaction times, this residual DTT would be virtually available to coordinate to any transition metal ion normally and generally present in appreciable quantities in any PM sample.…”

“…Oxidative stress is generally mediated by reactive oxygen species (ROS), such as hydroxyl radical (OH), hydrogen peroxide (HOOH), superoxide (O 2 -), organic hydroperoxides and other organic radical species. 1,6,16,[25][26][27][28] Although the actual mechanisms of how ROS damage cells are unknown, it is believed they trigger multiple biological signaling, which result in inflammation and other cellular distresses. 6,29,30 ROS may either be primarily transported on particles and/or be catalytically generated by other particle components through redox chemistry producing healthrelated issues.…”

An apportionment method for the Oxydative Potential to the atmospheric PM sources: application to a one-year study in Chamonix, France

“…This result disagrees with Fang et al (2016) as they found no activity for this source in the OP AA test. Such difference for the biomass burning source may be explained by the two extraction protocols (in water or in a SLF solution) or by the proximity of the biomass source 5 in Chamonix compared to the longer distance transport in Atlanta, that would change the chemistry of the source profile.…”