On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals 1Department of Land, Air and Water Resources, University of California, Davis, 1 Shields Ave. Davis, CA 95616, USA
15 Oct 2012
2Agricultural and Environmental Chemistry Graduate Group, University of California, Davis, 1 Shields Ave. Davis, CA 95616, USA
Received: 21 Apr 2012 – Published in Atmos. Chem. Phys. Discuss.: 03 May 2012Abstract. 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.
Revised: 06 Sep 2012 – Accepted: 20 Sep 2012 – Published: 15 Oct 2012
Citation: Charrier, J. G. and Anastasio, C.: On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals, Atmos. Chem. Phys., 12, 9321-9333, doi:10.5194/acp-12-9321-2012, 2012.