These authors exposed human Mono Mac 6 cells (monocytes) to two factors. The first was ultrafine carbon particles (UFP), which are products of combustion. The second factor was radiofrequency radiation (RFR), which was in 3 forms – continuous wave, or modulated at 217 Hz or modulated GSM-nonDTX. The RFR was at 1800 MHz, 2 W/kg SAR, for 60 minutes. The cells were exposed separately to the two factors, as well as combined, and were compared with incubator controls and with heat-treated samples.

The RFR had no effect on the release of free radicals of on Hsp70 levels. On the other hand UFP led to an increased release of free radicals. Co-exposure with RFR did not potentiate this effect. Heat treatment increased Hsp70 levels, whereas UFP, RFR or UFP+RFR did not.

The authors conclude that RFR exposure alone or in combination with UFP cannot influence stress-related responses.