Evaluation of Orthotrichum lyellii moss as a biomonitor of diesel exhaust

Exhaust from diesel combustion engines is an important contributor to urban air pollution and poses significant risk to human health. Diesel exhaust contains a chemical class known as nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) and is enriched in 1-nitropyrene (1-NP), which has the potential to serve as a marker of diesel exhaust. The isomeric nitro-PAHs 2-nitropyrene (2-NP) and 2-nitrofluoranthene (2-NFL) are secondary pollutants arising from photochemical oxidation of pyrene and fluoranthene, respectively. Like other important air toxics, there is not extensive monitoring of nitro-PAHs, leading to gaps in knowledge about relative exposures and urban hotspots. Epiphytic moss absorbs water, nutrients, and pollutants from the atmosphere and may hold potential as an effective biomonitor for nitro-PAHs. In this study we investigate the suitability of Orthotrichum lyellii as a biomonitor of diesel exhaust by analyzing samples of the moss for 1-NP, 2-NP, and 2-NFL in the Seattle, WA metropolitan area. Samples were collected from rural parks, urban parks, residential, and commercial/industrial areas (N = 22 locations) and exhibited increasing concentrations across these land types. Sampling and laboratory method performance varied by nitro-PAH, but was generally good. We observed moderate to moderately strong correlation between 1-NP and select geographic variables, including summer normalized difference vegetation index (NDVI) within 250 m (r = -0.88, R2 = 0.77), percent impervious surface within 50 m (r = 0.83, R2 = 0.70), percent high development land use within 500 m (r = 0.77, R2 = 0.60), and distance to nearest secondary and connecting road (r = -0.75, R2 = 0.56). The relationships between 2-NP and 2-NFL and the geographic variables were generally weaker. Our results suggest O. lyellii is a promising biomonitor of diesel exhaust, specifically for 1-NP. To our knowledge this pilot study is the first to evaluate using moss concentrations of nitro-PAHs as biomonitors of diesel exhaust.

Studying the influence of seasonal conditions and period of exposure on trace element concentrations in the moss-transplant Pylaisia polyantha

This study evaluates the effects of seasonal conditions and exposure periods on trace element concentrations in samples of the epiphytic moss Pylaisia ​​polyantha when transplanted into urban areas. This assessment was carried out in summer and winter at four sites differing in their level of technogenic trace element load. The contents of 25 trace elements (As, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, La, Lu, Mo, Nd, Rb, Sb, Sc, Sm, Sr, Tb, Th, U, Yb, and Zn) were determined using neutron-activation analysis, and it was shown that seasonal conditions do not affect vital activity in P. ​​polyantha graft moss. For most elements, the greatest increase in trace element concentration in P. ​​polyantha transplant moss was observed within one month. The high sensitivity of this epiphytic moss-transplant to the level of technogenic load has thus been demonstrated, and it may find utility in future research with similar objectives.

Effects of bark washing and epiphytic moss on 137Cs activity concentration in bark and stemflow in Japanese persimmon (Diospyros kaki Thunb.)

The effects of bark washing, and of epiphytic moss growing on the bark surfaces, on the ¹³⁷Cs activity concentrations in bark and stemflow samples were evaluated at two Japanese persimmon orchards located in Fukushima City and Date City, both approximately 60-65 km northwest of the Fukushima Dai-ichi nuclear power plant. The means of ¹³⁷Cs in stemflow captured by 1 g of sphagnum placed on the main trunks of washed and unwashed trees, and on sites with moss and with no moss growing on bark of the non-washed trees in Date City, were 0.37 Bq, 1.08Bq, 0.77 Bq and 0.52 Bq respectively. The ¹³⁷Cs was significantly lower in the washed bark and in the absence of moss at p = 0.00031 and p = 0.0443 by t-test respectively. The ¹³⁷Cs in directly-collected stemflow on the main trunks was significantly higher for the unwashed tree at 6.0 Bq L^-1 compared with the washed tree at 1.1 Bq L^-1 (p = 0.017 by Tukey's test). The extraction rate of dissolved ¹³⁷Cs with deionized water was 7.3% even after stirring for 40 h. These results indicate that the moss acts as reservoir of ¹³⁷Cs, and that bark-washing decontamination can reduce the additional ¹³⁷Cs supply from moss in subsequent years following the radioactive fallout.