Monitoring of heavy metal concentrations in home outdoor air using moss bags

One monitoring station is insufficient to characterize the high spatial variation of traffic-related heavy metals within cities. We tested moss bags (Hylocomium splendens), deployed in a dense network, for the monitoring of metals in outdoor air and characterized metals’ long-term spatial distribution and its determinants in Girona, Spain. Mosses were exposed outside 23 homes for two months; NO2 was monitored for comparison. Metals were not highly correlated with NO2 and showed higher spatial variation than NO2. Regression models explained 61–85% of Cu, Cr, Mo, Pb, Sb, Sn, and Zn and 72% of NO2 variability. Metals were strongly associated with the number of bus lines in the nearest street. Heavy metals are an alternative traffic-marker to NO2 given their toxicological relevance, stronger association with local traffic and higher spatial variability. Monitoring heavy metals with mosses is appealing, particularly for long-term exposure assessment, as mosses can remain on site many months without maintenance.

Research highlights
► Moss bags can be used to measure the metal’s long-term spatial distribution within cities.
► Heavy metals in mosses are not highly correlated with ambient NO2 concentrations.
► Heavy metals show higher spatial variation and association with traffic than NO2.
► Bus lines in the nearest street explain 75–85% of Mo, Cr, Sb, Sn and Cu variability.
► Moss bags are useful for long-term at home exposure assessment in epidemiological studies.